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In a push to improve the use of our resources, there are a number of industry and governmental initiatives with the goal of providing products and services in environmentally friendly ways. One of the techniques in the electronics and computer industry that can show almost immediate benefit is to improve the electrical efficiency of the power system. Every electronic system has to have a source of electrical power. Typically the power is derived from the AC mains or from banks of batteries. In almost every case, there is a need for an electronic converter that will take in this raw electrical power and convert it to a well-regulated, low voltage DC level that can be used to power the electronics. The efficiency of this electrical conversion process is defined as the ratio of the output power to the input power. The output power is measured in watts, and can be calculated as the product of output voltage times output current in Amps. The input power is also measured in watts, and is also the product of input voltage times input current. If the input is provided from an AC (50 or 60 Hz) mains, the modern power converter will include a processor that will correct the input current so as to be a sine wave, in phase with the input voltage wave. This process is called power factor correction, and ideally provides a sine wave of current that is 99% pure sine wave.
To understand the impact of efficiency, it is useful to look at an example. Figure 1 below shows a chart that gives the input power(Pin) and the output power (Pout) at different output current (Iout) levels for a high efficiency power converter. The efficiency is calculated by dividing output power by input power and listing the result as a percentage. We can also compute the internal power by subtracting the output power from the input power. This is the power that gets dissipated inside the power converter, and is undesirable. This power is wasted in the power converter. It heats up the converter and serves no useful function. Ideally this number would be as low as possible.
There are several interesting features shown on the chart. If we make a graph of internal power versus the load current, it will look like Figure 2. It shows that even with no output current, there is some internal loss inside the power converter. This is generally the power needed to run the cooling fans and provide power for the internal circuits in the converter. Then, as the load is increased there is a gradual increase in the internal loss until we reach, in this case, a level of about 10 amps, and then the internal loss goes up on a steeper curve. This effect is due to the resistive losses in the input and output sections of the converter, and they come to dominate the internal losses as the load increases. The two conclusions that may be drawn from this data is, first, there is a loss at even no-load, which is encountered when the electronics goes into a ‘sleep’ or ‘hibernate’ mode. If even less dissipation is required in this mode, it is possible to inhibit the power supply and turn off the fans and selected circuitry. Secondly, at lower load levels, there is a load range where the internal loss does not increase very much. If indeed the expected loads will be only at low levels, the electronic systems designer should consider re-sizing the power supply or evaluating what the best trade-off would be in terms of providing redundancy in the power systems. There is an ‘overhead’ energy cost associated with redundancy and this should be balanced against the added system reliability advantage that comes with power redundancy.
The chart presented in Figure 1 is taken from measured data on a new, high-efficiency, AC/DC power supply that is optimized for higher efficiency. To understand the cost benefit of this higher efficiency, refer to Figure 3. In this chart, we compare the difference in internal power between the high efficiency converter and a standard one with an efficiency of 80%. The difference between these two converters is shown as the line on the chart with a diamond-shape marker. It represents how much more power is wasted in the less efficient converter at different levels of output loading.
As an example, at a output loading of 30 amps, which corresponds to an output power level of 1632 watts at 54.4volts, there is approximately 268 additional watts of power dissipated in the less efficient converter. If this is powering a constantly on, 24 x 7 piece of equipment, what would be the cost of this wasted power? Electrical energy is costed in terms of a certain cost per Kilowatt-hour. Although cost per Kilowatt-hour vary around the world, let’s take a look at annual cost using a typical cost of $0.10/KW-hr.. In one year there will be a total of 268watts x 24 hr/day x 365 day/year x 1Kwatt/1000 watt = 2348 Kw-hrs/year of wasted power. Cost of this wasted power is 2348 x $0.10 = $234.80 per system per year.
Many users will find that the high efficiency power supply is a good choice, especially when powering critical electronic and computer applications. Although the original equipment manufacturer generally does not incur the operating costs associated with these types of applications, it is a useful feature that will make the efficient system attractive to the OEM’s customers. In addition to the reduced operating costs, the less electrical power that is wasted will show up in reduced cooling requirements for the end customer. Many datacenters, computer/server farms, and Telco equipment are loaded with electronic gear and the cost to cool the hardware is one additional operating cost that goes down when the power conversion efficiency goes up.
To understand the impact of efficiency, it is useful to look at an example. Figure 1 below shows a chart that gives the input power(Pin) and the output power (Pout) at different output current (Iout) levels for a high efficiency power converter. The efficiency is calculated by dividing output power by input power and listing the result as a percentage. We can also compute the internal power by subtracting the output power from the input power. This is the power that gets dissipated inside the power converter, and is undesirable. This power is wasted in the power converter. It heats up the converter and serves no useful function. Ideally this number would be as low as possible.
There are several interesting features shown on the chart. If we make a graph of internal power versus the load current, it will look like Figure 2. It shows that even with no output current, there is some internal loss inside the power converter. This is generally the power needed to run the cooling fans and provide power for the internal circuits in the converter. Then, as the load is increased there is a gradual increase in the internal loss until we reach, in this case, a level of about 10 amps, and then the internal loss goes up on a steeper curve. This effect is due to the resistive losses in the input and output sections of the converter, and they come to dominate the internal losses as the load increases. The two conclusions that may be drawn from this data is, first, there is a loss at even no-load, which is encountered when the electronics goes into a ‘sleep’ or ‘hibernate’ mode. If even less dissipation is required in this mode, it is possible to inhibit the power supply and turn off the fans and selected circuitry. Secondly, at lower load levels, there is a load range where the internal loss does not increase very much. If indeed the expected loads will be only at low levels, the electronic systems designer should consider re-sizing the power supply or evaluating what the best trade-off would be in terms of providing redundancy in the power systems. There is an ‘overhead’ energy cost associated with redundancy and this should be balanced against the added system reliability advantage that comes with power redundancy.
The chart presented in Figure 1 is taken from measured data on a new, high-efficiency, AC/DC power supply that is optimized for higher efficiency. To understand the cost benefit of this higher efficiency, refer to Figure 3. In this chart, we compare the difference in internal power between the high efficiency converter and a standard one with an efficiency of 80%. The difference between these two converters is shown as the line on the chart with a diamond-shape marker. It represents how much more power is wasted in the less efficient converter at different levels of output loading.
As an example, at a output loading of 30 amps, which corresponds to an output power level of 1632 watts at 54.4volts, there is approximately 268 additional watts of power dissipated in the less efficient converter. If this is powering a constantly on, 24 x 7 piece of equipment, what would be the cost of this wasted power? Electrical energy is costed in terms of a certain cost per Kilowatt-hour. Although cost per Kilowatt-hour vary around the world, let’s take a look at annual cost using a typical cost of $0.10/KW-hr.. In one year there will be a total of 268watts x 24 hr/day x 365 day/year x 1Kwatt/1000 watt = 2348 Kw-hrs/year of wasted power. Cost of this wasted power is 2348 x $0.10 = $234.80 per system per year.
Many users will find that the high efficiency power supply is a good choice, especially when powering critical electronic and computer applications. Although the original equipment manufacturer generally does not incur the operating costs associated with these types of applications, it is a useful feature that will make the efficient system attractive to the OEM’s customers. In addition to the reduced operating costs, the less electrical power that is wasted will show up in reduced cooling requirements for the end customer. Many datacenters, computer/server farms, and Telco equipment are loaded with electronic gear and the cost to cool the hardware is one additional operating cost that goes down when the power conversion efficiency goes up.
This blog was written by Vance Burns, Director of Product Development for UNIPOWER.
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