Contact us

+ 49 89 9278 0

Email

Request your online meeting

Do you need support with selecting the best power supply for your application? Our team is looking forward to answer your question.

Request your meeting

More electric drives, less pneumatics: What does this mean for the power supply?

The shift from pneumatic to electric drives is a well-known development in the industry. However, in recent years, this topic has gained significant momentum. This is due to the continuously increasing cost pressure and the ever-stricter requirements for CO2 reductions. In both areas, the advantages of electric solutions prevail. This blog article illustrates, using the example of OEMs in the automotive industry, how smart industrial power supplies support the transition from pneumatic to electric drives.

Electric and pneumatic drives each have their advantages and disadvantages.

Pneumatic drives are inexpensive to purchase, easy to operate, offer high overload resistance, and are robust against environmental conditions such as temperature fluctuations and increased dust exposure. However, pneumatic drives require a central, continuous compressed air generation, which involves significant effort. It is necessary to distribute and maintain a consistent pressure throughout the entire factory. If there is a loss of compressed air due to a leak in the system, it must be quickly identified and repaired, which entails high maintenance efforts.

Especially in applications with many switching cycles, the high energy losses due to poor efficiency are significant during operation. Even in modern compressed air systems, the majority of energy is lost as waste heat. Additionally, the compressed air system must always be ready for use and therefore in operation, which results in high energy consumption. This leads to generally high operating costs and CO2 emissions.

Electric drives combined with servo motors offer better energy efficiency and enable high speed and precision. Thanks to integrated microprocessors, most electric components have a bigger range of functions and allow access to application data in connection with a central monitoring system. Operating costs are generally lower, and the CO2 footprint can be sustainably reduced. Additionally, electricity can be easily distributed in the factory – almost without losses. The ability to convert and store electricity is another advantage. New technologies, such as wireless energy transmission, also come into play. Electric solutions are also significantly quieter, which reduces noise pollution for the workforce.

However, electric drives are more expensive to purchase. Additionally, the systems are more complex compared to pneumatic solutions and may require retrofitting existing equipment.

OEMs are generally cautious about changes to proven systems. But the economic, political, and social pressure regarding energy efficiency is prompting more and more manufacturers to opt for the purely electric route. Therefore, new industrial plants often omit the installation of a pneumatic system right from the start. As is often the case, the automotive industry and its suppliers are taking a pioneering role in this regard. The numerous projects to switch from pneumatics to electricity that PULS has accompanied in this segment had one thing in common: the right power supply system is crucial for success.

Decentralised power supply of conveyor systems

In the automotive industry, everything from large body parts and heavy engines to components from the small parts warehouse is transported via kilometer-long conveyor belts and driverless transport systems. In the BMW plant in Regensburg, Germany the assembly lines alone have a total length of 5.5 km.

When the stoppers, diverters, as well as lifting and rotating units in conveyor systems are converted from pneumatic to electric drives, a decentralised and protected power supply is ideally suited. In order to realise this, space-saving and powerful power supplies with sufficient power reserves are needed directly in the field. Long, loss-prone supply lines are eliminated, and flexibility is increased.

PULS has developed the product category ‘Field Power Supplies’ for this purpose, which consists of 360 W and 600 W power supplies with high protection classes IP54, IP65 and IP67, as well as many different connector options.

Additional features, such as up to four integrated current-limited outputs, ensure the safety of electrical consumers. With these eFuses integrated into the power supply, it is possible to realise selective power distribution, protection, and monitoring outside the control cabinet.

The Field Power Supplies are very robust both mechanically and electrically, and resistant to harsh environmental conditions such as moisture, dust exposure, and vibrations.

Field mounted power supply solution from PULS

Sufficient power reserves for dynamic motion sequences

For cobots, smaller robots, and decentralised applications in the automotive industry, electric drives have also become the first choice.

A reason for that is also the significant technological advances in electric motors. In recent years, these have contributed to making electric drives a real alternative to pneumatics. The motors generate a lot of power with small dimensions and weight. However, the rapid movements that electric motors enable, for example in robotic applications, require power supplies that can not only handle higher loads in the short term but also process the resulting regenerative energy.

Many PULS power supplies have generous power reserves, known as BonusPower. Numerous DIN rail power supplies from the proven DIMENSION product family provide up to 150 % power for 4 seconds. The FIEPOS field power supplies also achieve 200 % power for 5 seconds thanks to BonusPower. Upcoming product families for DIN rail mounting, currently in development, will even surpass these values in terms of peak performance and dynamics.

Thanks to the generous power reserves, oversizing of the power supply is unnecessary, resulting in cost and space savings.

Wireless charging of autonomous guided vehicles and mobile robots

Loss-prone pneumatic drives are becoming increasingly rare in autonomous guided vehicles (AGVs) and industrial trucks. Instead, manufacturers are also relying on electric solutions here, which are better suited for mobile applications. However, for efficient power supply and battery charging during operation, an appropriate charging infrastructure is needed in the factories first.

Several leading automotive manufacturers are already using the innovative wireless charging technology from the PULS Business Unit Wiferion for charging AGVs and cobots.

Wiferion’s contactless charging technology allows these vehicles to remain continuously in operation without disruptive charging breaks or manual interventions. Wireless charging offers significant advantages over conventional charging systems, such as the elimination of mechanical wear or the risk of tripping hazards from cables or contact strips.

With Wiferion’s etaLINK and CW systems, AGVs and mobile robots can be efficiently and autonomously charged during their normal work cycle, such as during short stops at stations. The elimination of long downtimes for energy intake increases the fleet availability significantly. The energy transfer takes place directly via charging pads, which allow for high positioning tolerance and start the charging process in less than a second.

With the established 3 kW and the new 1 kW systems, Wiferion technology is currently leading in the market. The maintenance-free solutions enable a significant increase in fleet efficiency and operational safety – ideal for 24/7 continuous use in demanding environments such as the automotive and logistics industries.

1

Reliable and efficient IP20 DIN rail power supplies for applications inside the control cabinet.

2

Wireless charging solutions for AGVs and CoBots.

3

Field Power Supplies with IP54, IP65 and IP67 for on-machine mounting in decentralised applications.

Increasing system availability through application data

Every minute of system downtime is extremely costly. OEMs in the automotive industry therefore try to minimise the so-called downtime of machines and conveyor systems to an absolute minimum.

With pneumatic drives, there is a risk of a leak in the compressed air system that must first be located. Electric drives are easier to manage in terms of control and preventive maintenance.

PULS offers power supplies with various communication interfaces, including IO-Link, EtherCAT, and power supplies with integrated displays. This allows for easy and quick access to application data and power supply functions.

Based on the power supply data, machine builders and operators can further optimise their machines in terms of efficiency and productivity. EtherCAT (e.g., CP10.241-ETC or CP20.241-ETC) is ideal for monitoring, logging, and remote control of complex systems thanks to real-time data transmission.

Power supply data is particularly advantageous within real-time control loops. Operators can control drives or other energy-intensive consumers optimally to keep the dynamic power demand within the capabilities of the power supply system. This optimal utilisation of the power supplies enable improved system efficiency. In particular, the power supplies, together with other system components, enable automated responses to handle unplanned operating conditions that previously often led to downtime or even damage.

Power supplies with communication overview

For example, the power supply provides precise measurements of the output current – that is, the load current. Using these finely sampled values, it is possible to recognise and describe digital load profiles.

Based on the information about the output current, the operator can determine whether a load, such as an electric motor, changes over a longer period. This change can be an indication of wear. In the case of worn profiles, a sine wave would be recognisable in the load profile. Computer-aided data analysis helps to detect and report this anomaly early. This way, it is easy to replace the wearing component before a failure and system downtime occur.

Increasing efficiency in 24/7 operation and reducing CO2

The decision for an electric drive is only one factor that positively impacts efficiency and the CO2 balance. Power supplies with high efficiency also support this process. The higher the efficiency of a power supply, the lower the power losses and thus the energy waste. PULS now achieves efficiencies of over 96 % with its power supplies.

An example calculation illustrates the importance of this value. With an efficiency of 96.4 % (e.g., with the SP960.241-S), losses of 3.6 % occur. For the corresponding power supply with 960 W output power, the power loss is thus 34.5 W, which is dissipated as heat to the environment.

A thought experiment shows the significance of each percentage point in efficiency. If we reduce the efficiency to 92 %, we see increased losses of 76.8 W, more than double.

Applying this to the total number of power supplies in a factory and considering the additional cooling, it significantly impacts the CO2 balance. The higher the efficiency of a power supply, the lower the energy waste and thus the CO2 emissions.

Summary: Efficient transition from pneumatic to electric drives

Increasing cost pressure and stricter CO2 reduction requirements drive the shift from pneumatic to electric drives in the industry. Electric drives offer better energy efficiency and lower operating costs, although they are more expensive and complex to purchase. Especially in the automotive industry, it is evident that decentralised power supply with powerful power supplies increases flexibility and minimises energy losses. PULS supports the transition from pneumatic to electric drives with suitable industrial power supply solutions. This not only contributes to reducing the CO2 footprint but also makes financial sense for companies.

What is the meaning of the IP ratings for power supplies?

The IP rating indicates to what extent an electrical device is protected against the penetration of foreign objects and moisture. In this blog post, you can find out which IP codes there are, what the differences are between them and what you need to pay attention to when choosing a power supply.

Environmental influences such as dust or moisture can prevent the electrical components in a power supply from functioning correctly. In addition, the interior of the power supply may need to be protected from penetration by foreign objects, such as tools, screws and wires, and from accidental contact by the user. It is important to pay attention to the IP code (international protection code), particularly when power supplies are installed outside a cabinet. The power supply can only be used safely and costly downtime can only be avoided if the IP rating is suitable for the conditions.

What IP codes are there?

The IP code generally consist of the abbreviation IP (international protection or sometimes ingress protection) and two digits (for example, IP20, IP54, IP67 etc.).

The first digit identifies the protection against accidental contact and the penetration of foreign objects, like sand and dust into the device. The second digit indicates the protection against water and moisture.

In the case of industrial power supplies, DIN EN 60529 is the relevant standard for determining the IP rating. The ISO 20653:2013 standard is also frequently used for road vehicles. However, it only applies to electrical components in vehicles that need additional protection against pressure washing, for example with a steam cleaner.

In the context of power supplies, IP codes are occasionally confused with protection classes. While IP codes relate to the penetration of foreign objects and water and to accidental contact, the IEC protection (or appliance) classes determine the structure and insulation of power supplies with the aim of protecting users from electric shocks.

The following table gives an overview of the meaning of the numbers of the different IP ratings:

Foreign objects
o No protection
1 Protected against solid foreign objects with a diameter ≥ 50 mm (e.g. a hand)
2 Protected against solid foreign objects with a diameter ≥ 12 mm (e.g. a finger)
3 Protected against solid foreign objects with a diameter ≥ 2.5 mm (e.g. a tool)
4 Protected against solid foreign objects with a diameter ≥ 1 mm (e.g. wires)
5 Complete protection against contact and dust
6 Complete protection against contact and fully dust-tight
Water
o No protection
1 Protected against vertically dripping water
2 Protected against vertically dripping water when the enclosure is tilted (up to 15°)
3 Protected against water falling as a spray at an angle up to 60° from the vertical on both sides
4 Protected against water splashing from any direction
5 Protected against water jets from any direction
6 Protected against powerful water jets from any direction
7 Protected against temporary immersion
8 Protected against continuous immersion
9 Protected against high-pressure, high-temperature water jets

Which IP ratings are frequently applied to industrial power supplies?

The IP rating required depends on the installation site and the environmental conditions in each case. Power supply manufacturers that supply products to their customers ex stock generally only offer products with selected IP ratings that have become industry standards. The following table gives an overview of the most common IP ratings for industrial power supplies.

IP rating  Foreign objects Water Application
IP20 2 Protected against solid foreign objects with a diameter ≥ 12 mm (e.g. a finger) 0 No protection Use in a protected environment such as a cabinet
IP54 5 Complete protection against contact and dust 4 Protected against water splashing from any direction Use in a decentralised location outside a cabinet
IP65 6 Complete protection against contact and fully dust-tight 5 Protected against water jets from any direction
IP67 6 Complete protection against contact and fully dust-tight 7 Protected against temporary immersion

If different combinations of protection against contact and moisture are needed in special cases, customer-specific power supplies are often the ideal solution.

What do codes such as IPX4 and IP6X mean?

Electronic devices are often tested in relation to only one of the two codes for foreign objects and water.

The “X” indicates that the product has not been subjected to the corresponding tests for this code. Therefore, this is not a variable that can simply be replaced by any of the values from the table of IP ratings.

A power supply with the code IP6X offers full protection against contact and is dust-tight, but has not been tested for water penetration. In a similar way, a power supply with the code IPX4 has undergone the necessary tests for water splashing, but has not been evaluated for the penetration of foreign objects.

Which IP ratings does PULS offer for its power supplies?

PULS offers a variety of power supplies with the IP ratings described above. The products can be divided into two categories:

IP rating Application Product families
IP20 Use in a protected environment such as a cabinet DIMENSION

PIANO

MiniLine

IP54 Use in a decentralised location outside a cabinet FIEPOS
IP65
IP67

In the light of the increasing trend for decentralisation, the IP rating of industrial power supplies now plays a more important role than it did a few years ago. The DC supply is very often installed directly on the machines, outside the protective cabinet. To ensure the safety of employees and the correct functioning of the power supply, IP54 is required as a minimum across all system components (e.g. SPS, HMI, sensors etc.).

For these applications, PULS has developed the field power supplies in the  FIEPOS product family.

Die dezentralen FIEPOS Schaltnetzteile mit hoher Schutzart IP54, IP65 oder IP67 wurden für den flexiblen Einsatz direkt im Feld entwickelt.

Figure 1: The decentralised FIEPOS switch-mode power supplies with a high IP rating – IP54, IP65 or IP67 – have been developed for flexible use directly in the field.

Summary

The IP rating describes how well a device is protected against accidental contact, foreign objects and liquids. The majority of IP codes consist of two digits. The first digit represents the protection against accidental contact and foreign objects, while the second digit indicates the protection against water and moisture. The higher the numbers, the greater the protection. Industrial power supplies that are used inside a cabinet normally have the rating IP20. Power supplies installed outside a protected environment should have a higher rating, e.g. IP54 or IP67.

Analysing backfeeding events with the help of power supply data

Backfeeding is a physical process that is highly desirable in many applications, such as electric vehicles, for the purpose of energy recovery. However, in an industrial setting, backfeeding can be a problem and lead to costly system downtimes if the power supply units fail. In this blog article you will learn how power supply data can help you to identify those backfeeding events and take measures.

Resistance to backfeeding: why is it important for power supplies?

Rotating machine components, such as drum motors, store kinetic energy which they feed back during braking in the form of voltage to the output of the power supply. On its output side, the power supply can absorb a certain amount of this energy in its output capacitors. At the same time, the output voltage increases accordingly.

The resistance to backfeeding events describes the maximum voltage allowed at the output of the power supply. If this figure is exceeded, the power supply will switch off and the system or machine will shut down.

However, even plant operators are often not aware of the backfeeding figures in real operating conditions. There is a lack of specific data concerning the frequency and the maximum values.

A detailed real-life load profile is helpful when choosing a suitable power supply during the planning phase and when analysing faults in the operating phase. The question is: how can this data be obtained?

The power supply as a data source

The power supply manufacturer PULS has developed the FIEPOS family  of power supplies for decentralised use and has integrated the option of application analysis.The power supply functions like a sensor. It records a variety of application-related parameters (for example, voltage, current, temperature) and makes them available in real-time.

As the decentralised power supply is on the field level, PULS logically uses an IO-Link interface for communicating these data. Therefore, the FIEPOS power supplies function as reliable data sources and make the perfect complement to the existing condition monitoring systems. The following practical example clearly demonstrates the value that these data can add.

Application analysis with the help of the power supply

A manufacturer of intralogistics solutions planned to replace its existing 24 V power supply with a different decentralised solution. The power supply that was currently in use was constantly causing system shutdowns and it had not been possible to identify the cause.

PULS advised the company about the available solutions and made available a sample of the three-phase 360 W FPT300 power supply. With the support of application specialists from PULS, the customer evaluated the initial data after putting the power supply into operation.

The aim was to investigate three different processes:

  1. The parallel operation of the running motors without braking.
  2. The parallel operation of running and braking motors.
  3. The serious case of all the motors stopping abruptly at the same time, for example in the event of an emergency stop.

In all three situations, the output voltage and the current were measured and analysed over a specific period.

Analysis of the load profile in normal operation

Figure 1: Load profile in normal operation

As expected, in situation 1, where the motors were running, there were no noticeable problems (see Figure 1). However, the first load profile for the plant in normal operation was determined, which can help with identifying the correct size of the power supply.

Analysis of the load profile for parallel operation of running and braking motors

Figure 2: Load profile for parallel operation of running and braking motors

In situation 2, the parallel operation of running and braking motors was analysed. In almost all cases, the energy from the braking motors resulting from backfeeding was directly absorbed by the running motors. Only one brief occurrence of a slightly increased output voltage and a negative current spike was observed, which did not present a problem for the power supplies (see Figure 2, marked in red).

Analysis of the load profile for an emergency stop situation

Figure 3: Load profile for an emergency stop situation

Situation 3 was more critical. All the drum motors stopped simultaneously and caused a rapid drop in current and an increase in voltage to 31 V (see Figure 3).

The data analysis showed that this situation led to the system shutdowns that were mentioned initially. The capacity of the output capacitors in the previous power supplies was not sufficient in this case. As a result, the power supplies shut down.

The FIEPOS power supplies are very electrically robust. The highest permitted output voltage during a backfeeding event is 35 V/4.3 J for the FPT300. The output capacity is 18,000 µF.

As a result, the worst figure of 31 V in this example presented no problem for the power supply. As soon as the voltage fell again, the FIEPOS power supply automatically continued working in normal mode. However, it is worth mentioning here that the motor control centres from different manufacturers shut down for self-protection at a voltage of around 32 V.

The detailed inspection by the technical specialists at PULS before the customer made their purchase decision gave the customer the confidence that they were opting for a reliable, future-proof solution.

Decentralised solutions for intralogistics

Alongside its extensive IP20 portfolio, PULS is expanding its range of power supplies in protection classes IP54 and IP65/IP67 for decentralised use outside the cabinet. For system developers that means greater flexibility when planning a plant and more space in the system, together with time and cost savings.

The FIEPOS product family is based on single-phase and three-phase 360 W or 600 W field power supplies. The majority of the systems also function at 200 percent for 5 seconds. This makes them ideal for starting high-current loads and prevents the need for expensive, oversized power supplies. Over the next few months, additional performance classes will be added to the FIEPOS portfolio.

The power supplies are available with a variety of connector configurations, including M12-L/-T/-A, 7/8” and Han Q series. The power supplies from the FIEPOS eFused range have up to four current-limited outputs. These systems allow for selective current distribution, protection and monitoring in the field.

Summary

A reliable and versatile power supply is an essential feature of end-to-end decentralization in intralogistics systems

However, for this goal to become reality, power supply manufacturers must collect as much practical data as possible from the field of intralogistics to be able to offer appropriate solutions. The key is to gather and evaluate real application data.

PULS plays a leading role as an innovator in application analysis on the basis of power supply data. A global team of application engineers advises customers and users on overcoming their technical challenges. The team members can answer questions about complex application situations and identify the best solutions.

The findings from these data are also essential for the development of the decentralised power supply solutions of the future.

Efficient power supplies – An investment in the future

In the search for a suitable power supply, the costs play a major role, alongside the technical requirements. The focus is often on the initial purchase price, while other potential costs that may be incurred during the operation of the power supply are not taken into consideration. In this blog post, we demonstrate why the decision to purchase a high-quality power supply is a profitable investment for your company, by taking a close look at all the costs involved.

How do I find the right power supply?

Let’s assume for a moment that you have to select a power supply for a new project and the choice is between a  CP20.241  and a power supply from another manufacturer. You already know that from a technical perspective both products are suitable for your purpose.

You have access to the device data in Figure 1 and the application data in Figure 2. Figure 1 shows that both power supplies produce the same power. The efficiency of the CP20.241 from PULS is 1.6 percent higher, which results in power losses that are 8.5 W lower. Figure 2 shows the relevant data for the operation of the plant.

 

Comparison of the power supplies’ basic data

Figure 1: Device data

Specifications based on the application data

Figure 2: Application data

 

Alongside the data from Figures 1 and 2, you also know that the purchase price of the CP20.241 is €20 more than the power supply from supplier A, which is less efficient.

You are a project buyer and you need to keep track of the project costs, so you are tending towards choosing the device with the lower purchase price.

But before you make the decision, you remember that the company has a new CFO who is currently evaluating the profitability of all the projects and who is focusing in particular on projects that are profitable in the long term. You try seeing things through the CFO’s eyes and, alongside the purchase price, you want to check the potential running costs and include them in your decision-making process.

You take a detailed look at the data and, in particular, the differences between the two devices. On the basis of the existing data, you immediately notice the power losses, which are linked to possible savings or additional costs when it comes to the electricity bill. You examine these data more closely.

Your aim is to avoid losses as far as possible. Using the power loss figures and the application data from Figure 2, you calculate the potential energy savings over one year of operation, if you choose the more efficient power supplies:

With a more efficient power supply, this is how much energy you can save per year.

Figure 3: Calculation of the energy savings per year

It emerges that the 100 power supplies you need could give you additional savings of 5355 kWh/year if their efficiency level is 95.6 percent instead of 94 percent. You calculate the potential cost savings on the basis of an electricity price of €0.11/kWh, which will remain the same for the next ten years. You discover that you can make savings of up to €589 per year over the entire operating period:

A lower energy consumption also results in lower electricity costs.

Figure 4: Electricity cost savings per year

Note on electricity costs

Electricity costs fluctuate considerably over time and vary from one region to another. This means that it is not possible to generalise. In the European Union, for example, in the first half of 2022 industrial customers were paying on average €0.18/kWh (Electricity price statistics – Statistics explained (europa.eu)). In our example, we have used a low, fixed electricity cost of €0.11/kWh and disregarded future general and inflationary price increases during the operating period. Of course, higher electricity costs also result in significantly higher savings.

Purchasing a power supply: an investment decision?

You now have the following figures available when you consider the power supplies with 95.6 percent efficiency:

  • Initial investment: additional costs of: 100 items x €20 = €2000
  • Annual saving on electricity costs of: €589

As you have already realised, your new CFO thinks in terms of cash flows, which affect the liquidity and the value of the company. You know that an investment is profitable in the long term if you get a positive figure when you add together the initial investment and all the future cash flows. You can work out the number of years of operation that it will take for an investment to pay for itself.

You calculate the impact that the decision about the 10-year runtime will have on the costs and savings. If you choose the 100 power supplies with 95.6 percent efficiency, the cash flows are as follows:

You can also work out the break-even point, which is the time when the expenses correspond to the savings.

Calculation of the break-even point
Figure 5: Calculation of the break-even point

You discover that the savings are so considerable by the fourth year that they fully compensate for the higher initial investment. With a runtime of ten years, further savings are possible. In this example, up to €3890 can be saved if future savings are taken into consideration alongside the investment costs before the purchase decision.

Linear savings not including the net present value (NPV).

Figure 6: Savings not including the net present value (NPV)

You are very surprised by the results and you realise that focusing only on the purchase price is too simplistic and does not form an adequate basis for decision-making.

In a brief meeting, your CFO gives you the feedback that simply comparing initial investments and future cash flows can be helpful in coming to a quick, straightforward assessment of which investment is better. However, this approach is too simple to provide a reliable basis for decision-making. Your CFO explains that, wherever possible, you should also take into the consideration the change in the value of the future cash flows.

The CFO as the decision-maker on investments?

Following your meeting with the CFO, you receive an e-mail with the following information:

Dear John,
Thank you very much for the information you gave me. I think you need to extend your calculation to take into account the value of the money over time. In periods of high inflation, it is clear that future cash flows are worth less than payments made today. For example, €100 today is worth more than €100 in two years. To take these changes in value into consideration, you must discount all the future cash flows to their current value in your investment calculation. To make a decision about an investment, you need to calculate the net present value, which discounts and adds together all the current and future cash flows. This allows you to decide on an investment on the basis of realistic figures.
I have attached a detailed explanation of net present value.
Best regards
Susanne

What is net present value?

Net present value is one of the most important figures for assessing the value and the cost-effectiveness of an investment. A positive NPV means that an investment is worthwhile and will generate profits in the future.

The relevant factors in the calculation are the initial investment and all the future cash flows (inflows and outflows of funds). It is important to take into consideration the present value. Earlier cash flows have a higher value than later ones. The initial investment is then added to the discounted incoming and outgoing payments in the operating years. Alongside the payment flows, an interest rate must be included in the discount. This covers possible loan interest, the inflation rate and a risk mark-up and is normally decided on by each individual company or for each individual project.

The NPV is calculated as follows:

Formula for calculating the net present value (NPV)

Figure 7: Formula for calculating the NPV

You are very pleased to have had the input from the CFO and you try out the new calculation. To take into account inflation and loan interest, you use a fictitious interest rate of 5 percent. The result is as follows:

Net present value (NPV) taking into account inflation and loan interest.

Possible savings taking into account the NPV

Figure 6: Savings not including the net present value (NPV)

You realise that the future cash flows discounted against the current value are much lower than in the previous calculation. However, it is clear that using this approach the investment will also start to pay for itself in the fourth year and that additional savings of more than €2500 are possible over ten years of operation.

You have now completely rejected your original idea of choosing the cheaper option with the lower level of efficiency. Despite the higher initial investment, you opt for the more efficient power supplies, which means that your company is making an investment that is profitable in the long term.

Efficient power supplies increase sustainability

It is obvious that alongside the financial considerations, the efficient power supplies also contribute to increased sustainability. In our example, in addition to the financial benefit over the 10-year operating period, there is also a reduction in CO2 emissions of around 19.6 tonnes (5355 kWh/year x 10 years x 0.366 kg CO2/kWh). Would you like to find out more about this? Then take a look at our blog post “How do efficient power supplies contribute to CO2reduction?

This explains how highly efficient power supplies can make a valuable contribution to more climate-friendly and sustainable industrial production by reducing energy wastage and therefore also CO2 emissions.

Summary

This simple example makes it clear that from a financial perspective the choice of a power supply should not be based solely on the initial purchase price. A calculation of this kind is too simplistic and, in many cases, will result in significantly higher costs in the future.

Our sales specialists will be happy to advise you on your choice of power supply. They will also help with investment calculations and take your specific cost factors and regional requirements into consideration. You are welcome to contact us.

What does the MTBF (Mean Time Between Failures) tell you?

MTBF is the measure for the reliability of a device or system component. In this blog article you will learn what exactly is meant by MTBF, why it is an important quality indicator for power supplies and how it differs from service lifetime.

The term MTBF appears in the data sheets of various technical system components and often causes confusion. This is mainly due to the different calculation methods and the risk of confusion with the service lifetime of a device. At PULS, many R&D specialists deal with both parameters on a daily basis. With this knowledge, we bring a little light into the darkness in this blog article.

What is MTBF?

The term MTBF is the abbreviation for “Mean Time Between Failures“. The value is considered a measure of the reliability of electronic devices, assemblies or systems.

Users thus receive an expected value for how often a device fails on a statistical average. Of course, most manufacturers try to keep the number of failures as low as possible; however, it is inevitable that a technical device will fail with a certain probability. Knowledge of this value is particularly important for the maintenance of equipment.

How is the MTBF calculated?

The MTBF is the reciprocal of the failure rate λ (lambda). The failure rate λ in turn indicates how many failures are statistically to be expected when operating a certain number of units over a certain period of time. Due to the specification in 1/hour, λ is a very small number.

The MTBF, on the other hand, is specified in hours and is thus easier to use in practice, which is why this value has become accepted as a common indicator of reliability.

The correlation between failure rate and MTBF becomes clear with a calculation example.

In a factory, 1,000 identical units are installed and operated for 2,000 hours. This results in a total of 2 million operation hours.If 4 units fail during this period of time, then the following calculation for the failure rate λ applies:

Calculation of the failure rate λ.

For the MTBF as the reciprocal of the failure rate, the following formula applies:

The MTBF is the reciprocal of the failure rate.

It is important to note that both the failure rate and the MTBF relate to statistical failures. These apply from the first hour of operation.

How to visualise the MTBF?

The best-known graphical visualisation of the MTBF is the so-called bathtub curve (see Figure 1).

Early failures (see phase A) are not taken into account in the MTBF, as the manufacturer should exclude them from being delivered to customers thanks to internal quality testing.

During the operational phase (see phase B), higher temperatures in particular can accelerate the processes that ultimately lead to failure. The thermal stress to which the components are exposed in such a case increases the failure rate. Therefore, system developers and maintenance specialists are primarily concerned with low temperatures in the application in order to keep the failure rate as low as possible.

By the way, wear effects (see phase C) are not included in the MTBF, as only the phase of the service lifetime is considered in which no age-related failures may occur.

The bathtub curve is a graphical visualisation of the MTBF.

Figure 1: The bathtub curve is a graphical visualisation of the MTBF.

How is the failure rate λ determined in practice?

The failure rate λ can be determined in different ways. Depending on which way is chosen, the results will differ. Users must therefore always refer to the specification and the underlying operating conditions for the determination of the failure rate or the MTBF values stated in the product data sheet.

Using the example of a DIN rail power supply we look at two different approaches for the calculation.

The quickest and simplest method to determine λ is the so-called “Parts Count”. Here, only the individual components in the power supply unit are counted and multiplied by an average failure rate. The result is then evaluated as the failure rate of the entire power supply unit. However, this method is inaccurate.

A much more complex alternative is to determine the failure rate for each individual component. For this purpose, the electrical load is calculated for each component and the thermal stress is determined by measurements. Based on these values, the failure rate for the component is determined via software. This procedure is common for PULS.

Various standards can be applied for the calculation of the failure rate. The MIL Handbook 217F is frequently used for the calculation on a global level. However, the failure rates determined on the basis of MIL are rather to be assessed as conservative. The values based on the calculation method of the Siemens standard SN 29500 according to IEC 61709 are more realistic.

The sum of the individual component failure rates finally results in the total failure rate λ of the power supply unit. Next the MTBF of the power supply unit can be calculated, as described above.

Good to know!

MTBF values are worthless without naming the underlying standard and the operating conditions. In particular, the load conditions and the prevailing ambient temperatures are decisive. When comparing products from different manufacturers, special attention must be paid to these values and, if necessary, enquiries must be made.

PULS provides all information relevant to the MTBF in its product data sheets.

What is the difference between MTBF and service lifetime?

The data sheet information on service lifetime is not about statistical failures during the operating time. The service lifetime indicates the time after which the components become unusable due to wear.

In a power supply unit, special attention must be paid to the electrolytic capacitors. These components are considered to be life-determining, as they lose capacity over time due to the diffusion of electrolytes.

The electrolytic capacitor manufacturers specify an end of life in their data sheets. At this point, important parameters such as capacitance and internal resistance deviate from the initial value by a certain amount.

Electrolytic capacitors react particularly sensitively to high ambient temperatures. Every 10 °C increase in temperature shortens the service lifetime of the electrolytic capacitors by a factor of 2 and thus has a direct influence on the service lifetime of the power supply unit.

Why are the MTBF and service lifetime of a power supply important?

Industrial power supplies should be reliable from the first minute of operation and at the same time secure the power supply of a system for many years. Therefore, both MTBF and service lifetime are important quality indicators of a power supply unit and should be at a high level.

At PULS, the reliability and service lifetime of its power supplies have always had a very high priority. The corresponding values for MTBF and service lifetime are described in detail in the data sheets of the devices and specified precisely for various operating conditions.

These reliable values make it easier for customers and users to plan and realise complex systems that are often made up of hundreds of system components.

At the same time, reliable and durable power supplies are also good for our planet. Because the power supply units need to be replaced less often, resources are conserved and less electronic waste is produced.

How can the availability of a system be increased?

For plant operators, the primary goal is to ensure maximum availability of machines and systems. This requires a reliable power supply throughout the entire lifetime of the system. Therefore, it is important that the applied power supplies are reliable, safe and durable. Within a power supply system, however, the power supply unit is often just one component among many. DC UPS, fuses and redundancy or buffer modules are also included. Such a holistic power supply system must be planned conscientiously. Find out more about what you should pay attention to in the blog article.

With the right system approach in the background, users no longer have to worry about the availability of their system. Ideally, they already deal with feasible solutions in the planning phase so that a system failure cannot occur in the first place.

What does system availability mean?

The system availability indicates the relationship between the planned operating time and the actual operating time. The higher this value, the more reliably the system operates. The availability of a system or machine therefore has a direct influence on the productivity and effectiveness of the company, which is why it must be ensured under all circumstances. As a manufacturer of industrial power supplies, PULS focuses on the DC supply, within the application. The power supplies are the interface between the power grid and the internal systems. The quality of the mains voltage is therefore an essential factor in the all-encompassing consideration of a solution. System designers should take this into account as early as the planning phase of a system.

The risk of poor power grid quality

PULS operates three of its own factories in Germany, China and the Czech Republic for the production of its products. System availability is also a top priority here, but is heavily dependent on the local quality of the grid voltage. This is particularly clear from the example of the PULS factory in the Czech Republic. Statistically, Czech companies are affected by 0.6 network failures in average per month. The European average of 0.3 network failures per month is just below this, which sounds very low at first. However, this value indicates that, statistically speaking, a production facility in Europe is affected by a power outage every three months.

In Europe, the stability of the grid voltage is generally very high, which is unfortunately rarely the case in other parts of the world. The power grid in the eastern part of Asia and the Pacific region already fails 4.8 times a month on average. In the USA, too, just under a quarter of the companies surveyed are affected by a power outage at least once a month.

If the mains voltage is of poor quality, it potentially causes damage to production machinery and economic losses. For large manufacturing sites, this quickly means costs in the millions. An important aspect here is also the issue of safety. A system must remain permanently safe in the event of a fault and must not pose any danger to users.

This makes it all the more important to integrate a suitable overall system for a reliable power supply. Appropriate protective measures, which can be realised for example by uninterruptible power supplies (DC-UPS) and battery systems, provide a remedy.

A safe overall system is crucial for a reliable power supply.
Graphic 1: A safe overall system is crucial for a reliable power supply.

The power supply unit as a component of a power supply system

The heart of any application is the power supply unit. For the customer, a CP10.248 was selected in the current example (see graphic). This is a single-phase 24 V power supply unit with 10 A. The special feature of this variant is the integrated display, via which the user and service technician can keep an eye on all relevant information about the status of the application as well as the quality of the mains voltage.

The power supply has a real-time mode that displays, for example, the current value of the input and output voltage, output current, operating time and the current temperature of the power electronics.

In addition to real-time data, the power supply also provides an overview of recorded data. For example, users can view the minimum and maximum values of input voltage or device temperature at any time (see graphic 2, C2).

The power supply unit also detects transients on the input side and reliably counts them. In the event of a fault, the device triggers an alarm (see graphic 2, C1) and informs the user of the status. Since this enables the situation to be analysed quickly, downtimes can be minimised.

The integrated display allows users to see the quality of the mains voltage at any time.

Graphic 2: The integrated display allows users to see the quality of the mains voltage at any time.

Another means of increasing system availability is the use of a redundant power supply system. Two identical power supplies are connected to a PULS MOSFET redundancy module (e.g. YR20.242 ) for this purpose. By connecting the two power supplies in parallel on the output side, 1+1 redundancy is created. This means that in case of failure of one power supply, the full load is immediately transferred to the functioning power supply. The MOSFET redundancy module decouples the two power supplies in the circuit. Consequently, each power supply unit must be able to handle the load to be applied in the application on its own in the event of a fault.

A 1+N redundancy system, which can also be realised with PULS power supply units and redundancy modules, also allows load distribution over several power supply units in the event of a fault. Even if several power supplies fail at the same time, the load can be covered without system failure. A redundant power supply system increases the availability of the system enormously.

Load protection by electronic circuit breakers

If several different loads are connected to one power supply unit, it makes sense to use an electronic circuit breaker. In the above example, the customer uses an electronic circuit breaker with 8 channels, of the PISA-B type.

The device transfers the current equally to the different channels and allows different tripping characteristics. Channels 1 and 2 are optimised for loads with large capacitances. The output currents and the threshold values for the tripping behavior are displayed individually for each channel via an LED matrix on the front of the device.

The electronic circuit breaker can also be locked with a PIN code to prevent tampering and thus increase safety. If a channel is overloaded, the electronic circuit breaker triggers an alarm and informs the user. In this way, the user always has an overview of the system status, even from a distance. Via a relay input, it is also possible to reactivate switched-off channels remotely. This increases the availability of the system and reduces downtimes.

 

The electronic circuit breaker distributes the current equally to the eight different channels.

Graphic 3: The electronic circuit breaker distributes the current equally to eight different channels.

For safety-critical loads, a DC UPS is recommended

The quality and reliability of the mains voltage plays an important role in the design of a system. An uninterruptible power supply (UPS) is particularly recommended in applications with safety-relevant loads, such as systems for plant safety (e.g. light barriers, emergency stop switches, etc.), emergency lighting or pumps in municipal water treatment.

Mains failures and similar fault situations can be bridged in this way in conjunction with a battery. The buffer time depends on the selected battery size and the load. Depending on requirements, it is suitable for a short or longer buffer time. If the longest possible buffer time is required until a repair is carried out, a larger battery is needed. Small batteries, which have correspondingly shorter buffer times, are sufficient to shut down machines and bring them to a safe state.

Mains failures can be bridged with a DC-UPS in combination with a battery.

Graphic 4: Mains failures can be bridged with a DC-UPS in combination with a battery.

Critical loads and applications can be optimally protected depending on the objective and with sufficient local grid quality. In our customer example mentioned above, the DC UPS and the battery are connected between the respective load and the electronic circuit breaker. The customer chose a UB10.241 with the UZK12.261 a lead-acid battery module with 25 Ah, for the mentioned device combination. With an already aged battery and 10 A load, this results in a buffer time of at least 40 minutes. In the existing example, this bridges the expected failures and increases the availability of the system. Continuous operation is thus ensured.

The availability of a system determines production costs

An all-round reliable power supply system – consisting of high-quality power supply units, redundancy and buffer modules is a wise investment. The system can permanently reduce production costs during the operating phase and even pays for itself before the first failure.

This is because downtime costs include more than the lost profit due to a lower production output. Other additional costs, some obvious and some hidden, are almost impossible to prevent. For example, there may be increased personnel costs, due to the deployment of qualified service teams or the extra work required of the overall staff, to make up for the production downtime. Even smaller factories can quickly be affected by downtime costs of up to tens of thousands of euros.

Some basic components can only be kept in the machine for a short time, depending on the industry. If spare parts are not readily available, the costs of disposing of the raw materials or products and, if necessary, cleaning the machine are added to the costs of lost production. This is the case, for example, in the chemical and pharmaceutical industries or in food processing machinery.

One solution to reduce such downtime costs is to keep all spare parts immediately available in stock. Another option is to rely on a permanently available and reliable power supply system. Overall, the latter is more cost-effective.

This can be illustrated with the help of a small rough calculation. Even in the first few minutes of a failure, which are required for the detection of the fault alone, the additional costs for an improved, constantly reliable DC power supply are exceeded by the direct failure costs.

The additional costs for a constantly reliable DC power supply are lower than the direct failure costs.

Graphic 5: The additional costs for a constantly reliable DC power supply are lower than the direct failure costs.

Does a systems approach make more sense than stand-alone devices?

To increase the availability of a system, the focus should not only be on an individual power supply unit, but on the holistic power supply system, which is made up of safety-relevant components. This system solution pays off for the user in every phase of the system’s life and prevents high downtime costs.

Which system solution is right for you depends on your application and objectives. To find a suitable solution for your system, you are welcome to consult our experts.

Simply contact our team of experienced application engineers.

Parallel connection and redundancy of power supplies – What is the difference?

You are in need of a higher total power for your system or machine, or want to ensure a reliable power supply? Common solutions include the parallel connection or establishing a redundant power supply system. In this blog post, you will learn more about the definition, the differences and the correct use of both system types.

Maximizing utilization vs. minimizing downtime

By connecting two or more power supply units of the same type in parallel, they share the supply of a system or machine. Collectively supplying power thus enables a higher total power.

A redundant power supply system, on the other hand, increases the reliability of the system or machine. Here, additional power supply units are installed in the machine or system as a reserve. In case one of the units fails, the remaining power supply units maintain the system operation. Redundancy modules protect against back feeding into a possibly short-circuited power supply output.

More total power – How does a parallel connection work?

By using power supplies in parallel, the load current required by the system or machine is supplied jointly by several power supply units.

What types of parallel connection are there for power supplies?

In general, you can classify power supplies, that can be connected in parallel into two groups: power supplies with and without load sharing.

In the case of power supplies without load sharing, it is not possible to ensure a balanced current distribution. This can lead to overload and overheating of a power supply, which can develop into a failure of the device.

Power supply units with load sharing, on the other hand, ensure a balanced current distribution. This prevents one or more devices from being overloaded. A distinction can be made here between active and passive load sharing.

In active load sharing, connected control circuits ensure exact synchronization of the output voltages among the power supplies. However, this is very complex and susceptible to interference.

Simple parallel connection of two power supplies

Figure 1: Structure of a simple parallel connection

 

If a 100% balanced distribution is not fundamental, passive load sharing can be used. Here, the output voltages are set to be as congruent as possible.
As the output current increases (from no-load voltage to full load), the output voltage is reduced (inclined characteristic curve). If one power supply unit falls below the output voltage of the other, the other unit participates in the current supply (see figure 2).

Example of a passive paralleling with inclined characteristic curve

Figure 2: Passive parallel circuit with inclined characteristic curve

 

The more congruent the power supplies are set, the more balanced is the current distribution – for example, in a 40 to 60 % ratio. However, a totally balanced 50:50 distribution will not be achieved here.
Passive load sharing is reliable and inexpensive. For many systems and machines, this mode of operation is absolutely sufficient. PULS, therefore, specializes in passive load sharing for most power supply units with paralleling functionality.

How do I set up a parallel connection correctly?

To achieve a balanced load between the power supply units connected in parallel, the output voltages must be set as precisely as possible to the same value. Each power supply manufacturer designs its output circuit differently. Therefore, it is recommended to use identical power supply units of the same brand. This enables reliable adjustments and prevents unforeseen problems during operation.

Higher availability – What is a redundant power supply system?

In a redundant power supply system, more power supplies are used than are actually required to supply the load. The units share the total load among themselves (= paralleling). If one of them fails, the total load is carried by the remaining power supply units. Should the defective power supply unit have a short circuit in the process, a redundancy module protects it from being fed back into the short circuit.

This reliable power supply thus ensures the high availability of the machine or system. Redundant power supply systems are used especially when a power supply failure is intolerable.
One application is in the automotive industry, where the cost of a production shutdown far exceeds the cost of setting up a redundant power supply system from the beginning. Another example is the food industry: Due to hygiene regulations, systems that have come to a standstill must be completely cleaned before they can be put back into operation. This maintenance is time-consuming and cost-intensive and can be prevented by a redundancy system.

What types of redundancy are there?

There are several redundant systems to choose from. Some of the most commonly used include the 1+1 and N+1 redundancy.

1+1 redundancy

1+1 redundancy

The 1+1 redundancy requires three components: two identical power supply units and one redundancy module.

The power supplies share the load current among themselves. If one of the two fails, the other takes over 100 % of the load to be supplied. For a 10 A load current, two 10 A power supply units are needed.

You could set up this 1+1 redundancy system with two CP10.241 power supply units and one YR20.242 redundancy module.

N+1 redundancy

N+1 redundancy

With a N+1 redundancy, one power supply is installed as a reserve in addition to the required power supply units (N = number).

For a total load of 60 A, for example, three 20 A power supply units are required. In this case, however, four 20 A units share the load (at 15 A each). If one fails, the three remaining power supplies can still provide the total load.

You could set up this N+1 redundancy system with four CP20.241 power supply units and two YR40.241 redundancy modules.

In a redundant power supply system you must also pay attention to the rules of parallel connection, mentioned before.

With the N+1 redundancy, you should only use power supply units which are allowed to be used in parallel. As for the 1+1 redundancy, the total load can be supplied by a single unit, which is why a single unit is never overloaded. For this reason, power supply units that are not explicitly marked as parallel-capable can also be used for the 1+1 redundancy.

What should you pay attention to when using redundancy?

For the redundant power supply system to serve its purpose, each power supply should be connected to a different AC source. This prevents a total failure in the event of a fault on the input side. However, this separate AC supply is often difficult to implement in the control cabinet.

A redundant system should also provide a means of monitoring the power supply units. In the event of a fault, an external signal sends an alarm to the PLC which informs the maintenance team. The technician can then quickly replace the faulty power supply unit without any downtime. This seamless monitoring of the units enables smooth maintenance work.

Conclusion

A parallel connection of power supplies is primarily used to increase the total power. Here, power supply units jointly provide the load required to operate a machine or system.

A redundant power supply system focuses on the reliability of the power supply. In this case, several power supply units jointly supply a machine or system with power as well. In contrast to parallel connection, the total load in a redundant system can be provided without interruption even, if one power supply unit fails. To achieve this, more power supply units are used than are actually required for the load current. Redundancy modules protect against backfeeding into a possibly short-circuited power supply output. This solution is used when downtime must be prevented.

Please do not hesitate to contact our team of PULS Application Engineers (PAC) for further information. Please use the contact form or get in touch with your contact person directly.

What does daisy chaining mean for power supplies?

The colloquial term daisy chaining has established itself as a description for the direct connection of technical devices in series. In this blog article, you will learn what you should consider if you want to operate several power supplies in a daisy chain.

Daisy chaining refers to a wiring scheme in which several devices, such as power supplies, are connected directly in parallel. This type of wiring is also referred to as “looping through”. The English term “Daisy Chaining” is used colloquially, since the structure is vaguely reminiscent of a daisy chain. The principle can be used both to achieve a higher total current and to transmit analog signals or digital data.

If the wiring of a power supply system is planned according to this principle, it is not wired in a star configuration. Instead, the current is looped through to the load in a linear or ring-shaped manner on one line.

Is daisy chaining recommended for power supplies?

Before setting up a power supply system using the daisy chain method, it is essential to check the data sheet for the relevant type of power supply. Some power supplies do not allow direct connection of outputs. If this warning is ignored, there is a safety risk. It can lead to overloaded circuits and even fire hazard.

What does daisy chaining mean for power supplies?
Graphic 1: With daisy chaining, the power supply outputs are directly connected to each other. It is important to have a look at the data sheet beforehand.

If a power supply is suitable for daisy chaining the outputs, particular attention must be paid to the specification of the connection terminals. The decisive factor here is the load on the terminals: The maximum specified current of the terminal must not be exceeded, even with the last power supply in the series. PULS specifies the corresponding current values in the product data sheets. For example, a maximum current of 25 A is permissible for the 240 W power supply CP10.241 (24 V, 10 A). (See graphic 1) If more than three power supplies are connected in parallel, a fuse or circuit breaker must be integrated for each power supply output. Alternatively, a diode or a redundancy module can be used. This protective measure increases the safety of the parallel connection.

Incidentally, devices with output terminals, which feature two positive poles and three negative poles, are best suited for daisy chaining. Most PULS power supplies are equipped with these terminals as standard.

As you can see, daisy chaining should only be used with caution on power supplies and by qualified staff. But what if this method is not allowed for the selected power supply according to the data sheet? Or, if it is theoretically allowed, but the required current should be higher than the specified current which is allowed for the connection terminals?

What is the alternative to daisy chaining?

A reliable alternative to daisy chaining is the usage of distribution terminals in the control cabinet. In this case, the outputs of the power supplies and the input of the load are connected to the distribution terminals. (See graphic 2) The total current is thus no longer limited by the maximum current allowed for the power supply terminals and can be higher.

Solution with distribution terminals as an alternative to daisy chaining.
Graphic 2: The use of distribution terminals enables a higher total current.

Conclusion

Daisy chaining of power supplies is a common practice in industrial applications. To increase the total current, the outputs of several power supplies as well as the load can be connected directly to each other. The decisive factor here is the information on the maximum permissible current that may flow through the connection terminals of the power supply units. These values can be found in the respective data sheet. However, not all power supplies are suitable or approved for daisy chaining. Therefore, this wiring method should always be carried out only by qualified staff on the basis of the data sheet information.

How to correctly measure the efficiency of a power supply!

Manufacturers’ data sheets often only give blanket information on efficiency and power losses of their power supplies at different mains voltages or loads. Therefore, it is advisable for users to measure the efficiency of a power supply themselves. In this blog article, you will learn what you should pay attention to.

Multimeter, wattmeter or power analyzer – which is the (measurement) tool of choice?

There are a number of measuring instruments which are used for the determination of efficiency. Nevertheless, the measurement tolerances and the capabilities of measuring instruments in measuring various signals (AC or DC) vary considerably.

Multimeters:

Accurate multimeters do a great job measuring the voltage and current of purely DC inputs and outputs. The voltage can be measured with high precision directly at the input and output of the power supply. Many multimeters also have built-in ability to measure current, but this is usually too inaccurate (inaccuracy of 1 % or more) or it does not have sufficient measuring range (usually limited to 10 A). Instead, the current should be measured by highprecision shunt resistors with 0.01 % tolerance. However the non-synchronous detection of values can be problematic because it leads to errors if fluctuating conditions are present.

Watt meters:

Watt meters are used for measuring AC signals and follow the right principle. The instantaneous values of current and voltage are multiplied and a mean value is calculated from these products – this corresponds to the physical definition of performance. However, most simple watt meters have a high measurement inaccuracy (around 1 %). Moreover, frequently changing input or output currents (AC input, varying output load) cause additional measuring errors. Fluctuating values are thus difficult to interpret. Generally, only high-precision watt meters should be used when measuring efficiency.

Data loggers:

Data loggers are even better for DC measurements. They consist of a single, usually highly accurate meter, which is used several times by multiplexing. In the same measuring range, the errors even cancel off each other and all values can be promptly recorded and evaluated quickly with a spreadsheet.

Power analyser:

PULS uses power analysers to measure the efficiency of its power supplies. (See image 1) The advantages of this are the high basic accuracy of 0.02 %, the correct measuring of active power, the simultaneous and thus synchronous measuring of input and output, and the direct display of power losses and efficiency. The downside of this method of measuring is the high purchase price involved. Nevertheless, the power analyser is the tool of choice for the accurate determination of efficiency.

The efficiency of PULS' switched-mode power supplies is measured with ultra-modern power analysers.

Image 1: The efficiency of PULS’ switched-mode power supplies is measured with ultra-modern power analysers.

Tip:

However, AC input power cannot be measured with multimeters or data loggers. It is a common mistake to assume that it is sufficient to measure the true RMS of the current and voltage and to multiply the two values to determine the input power. This calculation, however, determines the apparent power and not the real power which is crucial for the power losses. The measurement of AC input power, even with True RMS multimeters, thus gives incorrect measurements and is an absolute no-go!

Avoiding mistakes in the measurement setup

A precise and expensive power analyser may however not provide accurate results if mistakes were made during the measurement setup.

Correct wiring:

All power losses that do not come from the device under test are not allowed to be included in the measurement! This is the main principle, when it comes to correct wiring in the measurement setup. Because every cable and every contact resistance causes additional power losses that may distort the measurement results. A proper four-pole measurement (Kelvin measurement) must have separate cables for the measurement of current and voltage. (See image 2)

Voltage source:

Simple DC voltage supplies are sufficient for switch-mode power supplies with DC-input. For AC measurements, it is important to know that the internal resistance of the voltage source influences the measurement through the curve shape of the mains sine. In a 240 W power supply without PFC, a difference of 0.4 % was measured between the soft power from an isolating regulating transformer and the hard power from an electronic AC source. This gives the most reproducible values and is therefore preferable.

The correct cabling of a power supply is decisive.

Image 2: It is decisive to do the wiring correctly. A proper four-pole measurement (Kelvin measurement) with separate cables for the measurement of current and voltage is a must.

EMC interferences:

Unshielded power supplies in the prototype stage can interfere with meters and/or can cause loads to fluctuate. You should not accept any signals with HF interference from meters. Additional filters, mostly inductors in the input lines, prevent these problems. In addition you should not allow power losses to flow into the measurement. There should be no problems with clean, radio interference- suppressed power supplies.

Loads:

Besides the power source, the used load must also be stable and reproducible. The loads from power resistors are problematic because they do not draw a constant current. However, electronic loads represent a defined and reproducible load of the device under test and even fluctuating transition resistances do not alter the current.

Taking environmental conditions into consideration

In respect to environmental conditions, temperature plays a decisive role, because the power losses from a power supply are temperature dependent. The temperature of the components in a power supply is a crucial factor. The component temperature is the sum of ambient temperature and self-heating.

Temperature:

The various components in the power supply react differently to temperature. In some essential elements, an increase in temperature results in a reduction of power losses. But in other components the losses increase. The NTCs used for limiting the input inrush current have a strong influence. Power supplies with such components have less power losses during the startup phase and in higher ambient temperatures (negative temperature coefficient), but at higher temperatures the increase of power loss is outweighed again by other essential elements. (See diagram 2)

Devices with active input inrush current limiter show a more stable temperature behaviour. Here there is only a small increase inpower loss from temperature. For all efficiency measurements, the startup time and the ambient temperature should be documented so that the results remain traceable.

Diagram 2: Due to the NTC, efficiency is highly dependent on time and temperature.

Diagram 3: The active input inrush current limiter without NTC gives an efficiency that is less time and temperature dependent.

Altitude and air pressure:

Since cooling is done by air, the air pressure has an influence on self-heating. PULS has calculated how much additional heat is generated by components at a high altitude: by approx. + 10 °C at an altitude of 2,000 m above sea level and approx. + 20 °C at 4,000 m. Humidity plays only a very minor role and can be neglected.

Sample distributions:

Each component has tolerances and therefore not every device is the same. But to find genuine errors, PULS measures power losses very closely even during production – although not quite as accurate as in the laboratory. A mean value of 95.27 % with a deviation of ±0.15 % was measured on a production batch of 200 devices of the type CP10 . (See diagram 4)

More information on the topic of efficiency and how it affects the efficiency of power supplies can be found here. (link)

Diagram 4: In the PULS production, an efficiency mean value of 95.27 % with a deviation of ±0.15 % was measured on a production batch of 200 devices of the type CP10

Conclusion

The correct efficiency measurement of switched-mode power supplies is complex. But it is worth questioning the manufacturer’s data sheet information and measuring it yourself if necessary. PULS has been dealing with the exact measurement of the efficiency of its products for decades and is available to advise its customers on all questions. We have even set up our own team of experienced application engineers to provide application advice.

How do medical power supplies help protect patients and hospital staff?

In medical technology, the protection of patients and hospital staff has top priority. For this reason, medical power supplies are subject to strict requirements regarding safety, reliability and EMC. In this blog article you will find out how medical technology can benefit from the experience gained in machine building and system engineering.

Power supplies have to convert voltage as safely and efficiently as possible, while ensuring smooth operation over many years and in the tightest of spaces. Although this is a principle that applies to medical technology and to machine building alike, it is the industrial engineering segments where standard power supplies that meet these requirements are much more widespread. In turn, this means that medical equipment manufacturers are often dependent on customised rack or panel-mount power supplies.

Medical applications in hospital technology, building technology, laboratory technology and imaging diagnostics in particular stand to benefit from high industrial standards and rapid availability when it comes to power supplies. With its medical power supplies that have machine building in their DNA, PULS bridges the gap between the two fields of application.

Protection against electric shock 

In addition to basic safety, EN 60601-1 primarily focuses on the functional safety of medical equipment. In the case of power supplies, this means protecting patients and operators from electric shocks in everyday hospital life – both during normal operation and in the event of a fault.

The highest protection level is 2 MOPP (Means of Patient Protection), which is intended to ensure the safety of the patient as someone who may be in a weakened state. In the power supply, this is ensured by appropriately sized clearance and creepage distances, thicker insulation between the primary and secondary circuits, and compliance with the stipulated leakage currents.

We have modified our PULS CP series of industrial power supplies in a way that ensures they fulfil the medical specifications for 2 MOPP. This offers manufacturers the flexibility and safety to use the power supplies with the ending “-M1” nearby patients without a second thought.

Protection against electromagnetic interference

Medical equipment also has to produce high levels of electromagnetic immunity to external radiation, such as mobile radio signals, but at the same time it must not interfere with the technology in its vicinity. This means that it is subject to clear regulations for electromagnetic emissions. Electromagnetic compatibility, or EMC for short, is a collective representation of the interference immunity and emissions that an item of equipment demonstrates. The limit values for medical technology are specified in IEC 60601-1-2 (Edition 4).

These specifications repeatedly present manufacturers of medical power supplies with technical challenges. Due to high-frequency noise, output ripple and noise voltage, many switch-mode power supplies cause electromagnetic interference both on the lines and through radiation.

Our development engineers reduce interference within the circuit design itself as much as possible, allowing its industrial power supplies to achieve excellent EMC values. For our medical power supplies, we have once again gone one better, ensuring successful medical EMC testing according to IEC 60601-1-2 (e.g. EN 55011 Class B for radiated interference emissions).

Protection against device failures

Reliability and durability are often key considerations in the process of selecting system components in machine building and system engineering. Many machines are designed to continue operating for years or even decades – and the same is true of medical technology. In the medical field, however, reliability takes on another dimension: to maintain patients’ health and help them recover, reliable systems are crucial.

This is an aspect that we also bear in mind when developing our medical power supplies. The focus is on maximising the minimum service life and the MTBF (Mean Time Between Failures). We provide in-depth specifications for both values and publishes this information in the datasheets for each power supply.

The key to ensuring excellent reliability and a long service life is achieving an high efficiency. The higher the efficiency, the lower the power losses and, as a result, the less heat is generated inside the power supply. This is important because a 10°C temperature increase in the power supply halves the service life of electrolytic capacitors. Although losses of this kind do not necessarily entail an immediate failure of the power supply, they do compromise the service life of the power supply as a whole.

Calculation example: When it comes to efficiency, every percentage point counts

With our medical power supplies, we achieve efficiency rates of 94.3 % to 95.2 % depending on the performance class. A calculation example illustrates the importance of this rate: if efficiency is 95.2 % (as it is in the case of the CP10.241-M1, 24 V, 10 A), losses amount to 4.8 %. With 240 W output power, the no-load losses between input and output are 12.1 W, dissipated to the environment by way of heat (see diagram 1).

To understand the importance of every efficiency percentage point, it is essential to draw a comparison with a power supply whose efficiency amounts to just 91 %: while this 4.2 % difference might not sound significant, it results in almost double the no-load losses at 23.7 W.

In a test setup, PULS ran both units in identical boxes (with a volume of 3.15 l) and under identical conditions (load: 8 A / input voltage: 230 VAC) for four hours. After this time, the temperature difference was already 7.8 °C. It is not just the power supply itself that is affected by this higher temperature: the surrounding system components also suffer.

The higher the efficiency of a power supply, the less energy is wasted and the CO2 emissions decrease.

Graphic 1: Efficiency of the medical power supply CP10.241-M1.

Apart from the service life, the MTBF also worsens as a result of high temperatures. The MTBF describes how many failures can be expected as a statistical average when operating a certain number of units over a specific period of time.

A simple example illustrates this: if the MTBF value is 1,000,000 hours, for example, this means that statistically one unit will fail every 1000 hours if 1000 units are installed. Early failures are not included in this calculation because manufacturers exclude them as part of quality assurance. The effects of wear do not play a role in the calculation of the MTBF either, as no age-related failures occur during the use phase (see diagram 2).

We make sure that both our medical power supplies and our industrial power supplies have a high MTBF (for example, at 24 V, 5 A and 40 °C, the CP5.241-M demonstrates an MTBF of 867,000 hours according to MTBF standard SN 29500). The units are therefore extremely reliable and have a very low failure rate.

MTBF - bathtub curve

Figure 2: The phase of random failures (phase B) is decisive for the MTBF.

Protection against noise pollution

Highly efficient power supplies offer another advantage in that they allow for passive convection cooling, something that has become the standard for power supplies in machine building and system engineering. Given that less heat is generated in the power supply overall, it can be dissipated from the unit via a cooling air flow and the aluminium housing. This means that the units do not require fans to remove the warm air – a feature that works across the entire power range.

This aspect is particularly attractive in medical technology. Fans inevitably generate noise and this can be perceived as annoying, especially if the equipment is near the patient. As a mechanical component, fans are also more frequently affected by failures.

By contrast, power supplies with convection cooling operate silently in the background, promoting a healing environment for patients and enabling maintenance-free operation.

New opportunities for developers of healthcare technology

Medical power supplies from PULS

Graphic 3: PULS offers medical power supplies for three different power classes 120W (24V, 5A), 240W (24V, 10A) and 480W (24V, 20A).

Given the high standards of hygiene that hospitals and laboratories have to meet, medical equipment designs avoid corners and edges wherever possible. This makes units easier to clean and disinfect – but at the same time, a rounded design substantially reduces the space available for electronics. Power supplies that are as compact as possible suit this scenario and are opening up new possibilities in medical design.

Thanks to the high efficiency levels of its power supplies, PULS is able to create designs that are highly compact and yet still comply with all the required protective measures for the patient environment. Most medical power supplies are larger than their industrial counterparts due to the additional insulation measures they require, such as larger clearance and creepage distances. For its medical power supplies, however, our PULS developers have succeeded in using housings that are identical to those used in standard power supplies for machine building and system engineering.

This makes it possible to accommodate 240 W in a housing measuring only 39 x 124 x 117 mm (width x height x depth). As a result, medical technology is also reaping the benefits that the progressive miniaturisation of system components is bringing in machine building.

Another industry feature that is gaining a foothold in an increasing number of sectors is the DIN rail. The most important arguments in favour of assembling system components on a DIN rail are quick installation and maximum flexibility, which enables a modular system structure. This means that individual components from different manufacturers can be combined to create a customised system that makes it possible to achieve the efficiency, performance and price levels required for the application. Another advantage of DIN rail assembly is that it allows users to mount power supplies from different performance classes on a single mounting system – something that also makes it easier to retrofit or replace components.

Summary

Manufacturers of medical devices tend to use open frame power supplies: most power supplies with medical approval available on the market are based on this design. With the M1 units in the CP series, PULS is taking a different approach. Based on our successful industrial power supplies, we are developing an expanding medical technology portfolio with solutions currently available for three different power classes: 120W (24V, 5A) ,240W (24V, 10A) and 480W (24V, 20A).

Our developers are driven by a mission to combine the efficiency and reliability found in machine building and system engineering with the safety standards that the medical sector demands. The result is secure, durable and compact medical power supplies that benefit system developers, users and patients alike.