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Understanding the advantages of utilizing high efficiency power supplies - Electronic Products & TechnologyElectronic Products & Technology

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Efficiency is one of the most important functions that every control system engineer/designer must consider when choosing a power supply that suits their application requirements. When using a power source, energy flows through the product, but 100% of the energy cannot be used. The difference between available energy and lost energy is dissipated as heat. Heat is the number one enemy in switchboards, because it degrades power supplies and other surrounding electrical equipment.

Let's compare two power supplies; one has an efficiency of 92% and the other has an efficiency of 96%. The 92% efficiency unit is very good, so what is the point of reaching 96%? Using these numbers, one might think that the difference is only 4% (96%-92% = 4%). Taking a 100-watt power supply as an example, a power supply with an efficiency of 92% loses 8.7 watts, and a power supply with an efficiency of 96% loses 4.2 watts. This is more than 100% less heat loss than the 96% efficient power supply.

Let us look at a real example using two 480 watt power supplies. The efficiency rating of manufacturer A is 95.6%, and the efficiency rating of manufacturer B is 93.1%. The apparent difference is 2.5%. It's not a big deal, right? The following table illustrates the actual differences between these two power supply units.

Based on 50 hours of operation per week and $0.13 per kilowatt.

Heat is the number one enemy of power supply, because electrolytic capacitors are used in all switch-mode power supply designs, and the degradation rate of electrolytic capacitors will be higher in high temperature environments. Usually, much more sensitive electronic components are present in the chassis, which are affected by heat, such as PLCs, industrial computers, communication equipment and HMI. Heat will fundamentally change the reliability and lifespan of the power supply, and in many cases will force you to increase the size of the cabinet, install some form of cooling and/or reduce the rating of the equipment to compensate for the high heat loss. The general rule of thumb issued by capacitor manufacturers is that for every 10°C increase in temperature, the capacitor/power supply life will be reduced by 50%. Since capacitors are very sensitive to heat, a good power supply design will also thermally isolate the capacitor from heating elements such as transformers and bridge rectifiers. As shown in the figure below, the big blue circle (1) at the bottom and the three smaller blue circles (2, 3, 4) at the top right are electrolytic capacitors. These capacitors should be placed in a naturally cool location (bottom), or separated by air channels to protect them from stagnant heat, thereby prolonging their service life and reliability. More importantly, the reduced heat will extend the life of all products, significantly reduce replacement costs, and lower the total cost of ownership.

Therefore, choosing a power supply with the highest efficiency and good thermal design can mean the difference between a highly reliable control system and a system that will eventually cause problems.

Another area that designers should carefully consider is the amount of energy loss required to operate the load. If we review the same example of two 480 watt power supplies, but this time from an energy point of view, you will be surprised by the results. The power supply with an efficiency of 93.1% evaluated by the manufacturer B has an energy loss of 35.6W. According to a simple calculation, it loses 1.78KW during a 50-hour working period of a week. Compared with manufacturer A's 95.6% high-efficiency power supply, the loss during the same period is only 1.1kW. Using an average kW cost of US$0.13 per kWh, manufacturer B’s lower effective power supply would waste approximately US$12.03 per year, while manufacturer A’s would cost US$7.47 per year, multiplied by the number of power supplies used in the facility to save costs. It is of great significance in the entire life cycle of the control system.

Let us look at three examples of 240 watt power supplies of different brands. If we calculate the energy loss and 10-year lifetime of a facility with 50 power sources and an ambient temperature of 40°C, we can see the real cost difference. According to the data from the manufacturer of the electrolytic capacitor used in the power supply, the loss of manufacturer A is 14.5W and the lifetime is 57,000 hours. Manufacturer B has a loss of 18.8W and a life of 18,000 hours, and manufacturer C has a loss of 17.6W and a life of 34,000 hours. The following table shows the true cost of ownership for each power supply brand.

Based on 24/7 operation and $0.13 per kilowatt.

This data shows many significant effects of choosing the right manufacturer to provide efficient power supplies. The main benefits for customers are:

Best practices when determining which brand to choose include maintaining the highest full-load and part-load efficiency, recorded electrolytic capacitor life (not only calculated MTBF), accurate and detailed data sheets, and the lowest total cost of ownership.

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