Efficiency of PULS Power Supplies
Maximilian Hülsebusch l Marketing Communications Specialist
For a power supply, it is essential to achieve a high level of efficiency throughout the entire load range. It helps users minimize system costs and increase system availability, irrespective of the area of application, industrial branch or region. Anyone, who attaches importance to the efficiency, reliability and longevity of his machines and who wishes to save money, should be familiar with the efficiency of his power supply.
One important factor for the reduction of system costs is to allow as little heat as possible to form inside the cabinet. Heat puts a strain on the lifetime of essential elements. This means that a high level of effort is required for cooling. However, the higher the efficiency of a power supply, the lower the no-load losses in the form of heat.
The following description of an experi-mental setup, which was implemented by the PULS Application Support team, shows clearly how much the cabinet temperature depends on the efficiency of the power supply.
Test setup: Heat generation in the cabinet
Three DIN-rail power supplies of the device class 240W 24V / 10A are opera-ted under identical conditions (load: 8A / input voltage: 230VAC) and in identical boxes (volume = 3.15l). The initial tempe-rature in all boxes is 21.5°C (±0.3°C). The ambient temperature is 20.6°C (±0.1°C). In the middle box, you can see the PULS DIMENSION CP10.241, which has an efficiency of 95.2%. The competitor device (left) A has an efficiency of 88.5%. Power supply B (right) reaches at least 91%, ac-cording to the manufacturer‘s datasheet information.
These three devices run for four hours without interruption. The thermometer at the CP10.241 in the middle box, which has the thermally most unfavourable position due to the heat emitted from the right and the left, shows a temperature increase to 40.5°C. The temperature in the box of the left competitor rises to 56.8°C. On the right a temperature in-crease to 48.3°C is measured. (see image 1 and 2) This means that an efficiency difference of 6.7% or 4.2% makes a tem-perature difference of 16.3°C or 7.8°C.
(see diagram 1)
A High Level of Efficiency Ensures System Availability
These are important findings when considering what harmful effect high temperatures can have on the lifetime of the power supply and other essential elements in the cabinet, which can put at risk the availability of the entire system. In power supplies, the electrolytic capacitors are subject to the greatest wear and therefore determine the lifetime. The following formula applies to these temperature-sensitive components: any increase in the operating temperature by 10°C reduces the electrolytic capacitors‘ lifetime by factor 2. This becomes evident in the clearly decreasing capacity of the electrolytic capacitors. This loss of capacity does not necessarily result in an immediate failure of the power supply but it impairs the availability of the system. For instance, this can also be felt in the device‘s control behaviour, performance and output values or in case of power failures.
Electrolytic capacitors should therefore not be exposed to overly high ambient temperatures. This rule should be taken into consideration right from the beginning, when designing the devices. For this reason, PULS designs its switch-mode power supplies based on the principle
of „Cool Design“. Temperature-sensitive components are positioned at the coolest spots within the device and their temperature is controlled perfectly by means of convective air flow. Our Cool Design clearly focuses on customer benefit, since the combination of thermal and electrical layout always presents a great challenge to the designers.
However, even the other essential cabinet elements profit from this effort. If the waste heat is
lower, they age significantly slower. If a cooling system is used, less
energy is required and this saves on costs.
PULS is convinced that the minimum service life specification of a power supply is fundamentally important information for the user. Since 2005, the company has therefore been providing corresponding specifications in their datasheets for all products of the DIMENSION product family. The family standard that applies to DIMENSION is a lifetime of at least 50,000 hours at an ambient temperature of 40°C under full load. The CP10.241 achieves a minimum lifetime of 120,000 hours under these conditions.
High Level of Efficiency Enables Higher Packing Density
Efficiency even influences the dimensions of convection-cooled power supplies. The devices require less volume to dissipate the heat loss into the environment. Thanks to their high level of efficiency, the housing volume of the CP10 power sup-plies could be reduced to just 0.57 liters and a width of 39mm. The narrow design saves space on the DIN-rail and enables higher packing density within the cabinet, thus reducing operational costs.
High level of efficiency saves energy costs Efficiency can potentially also help save on electricity costs. Due to international competition, companies must face strong cost-related pressure. This pushes buyers into acquiring system components that are as cheap as possible. However, when it comes to power supplies, it is wrong to focus on the purchase price only. Cheap power supplies do not achieve efficiency levels higher than 92%. The additional costs arising from the purchase of energy-efficient power supplies are balanced off by lower energy costs.
The following short calculation example demonstrates this. A user requires a power supply of the device class 240W with 24V / 10A for his system. The electricity rate is about €0.153/kWh (Federal Association of the German Energy and Water Industry, 2014 average industrial electricity). A machine runs 21 hours a day and 300 days a year. We can choose between the three power supplies from the experimental setup.
When transferred to electricity costs, this means: Due to its losses (under full load), the resulting annual electricity costs for CP10.241 amount to €11.66. Power supply A costs €30.07 per year and power supply B €22.84 per year. (see diagram 2)
If the user opts for the CP10, he saves operational costs of €18.41 or € 11.18 per year, thanks to the higher level of efficiency of 6.7% or 4.2%. If one extends this to a lifetime of 10 years, the amount that can be saved on operational costs is €184.10 or €111.80. If the user also uses a cooling system, these savings can be multiplied by 2 because less energy is required for cooling the system.
Efficiency = 88,5%, Losses under full load = 31,2W
Efficiency = 91,0%, Losses under full load = 23,7W
Efficiency = 95,2%, Losses under full load = 12,1W
Power supply A:
Power supply B:
It is Worth Asking and Comparing?
It is important to compare the efficiency rates of different power supply service providers, however, in practice this is easier said than done. Instead of binding efficiency values, many manufacturers only specify potential maximum values (up to x % efficiency) in their datasheets. This is a best-case statement and actually just means that this value is not exceeded. For instance, power losses at different mains voltages, loads or ambient conditions are not mentioned to the user. When it comes to measuring efficiency, there are no binding standards for manufacturers. PULS sees a great need for information and catching up with technologies. This is why the company provides clear and binding information on the efficiency of all its products. PULS also informs about its measurement methods to make them transparent and theoretically reproducible for everyone – provided that the necessary equipment, such as a power analyser, is available.