Design Article
Making motors more energy efficient
Steven Strasser, Power Efficiency Corporation
6/2/2010 1:13 AM EDT
In the meantime, there is an alternative strategy. Electric motors, such as those in our homes, consume over 25% of the electricity in the U.S. and many operate inefficiently. By dedicating ourselves to maximizing energy efficiency, we can significantly cut the costs of operating the standard electric appliances we all use as well as reducing the amount of energy they consume.
Consider the operation of the single-phase motors that are found in residential and small commercial appliances such as refrigerators, clothes washers and dryers, air conditioning units, pumps, and fans. Such motors are designed to run most efficiently at high loads, usually at least 70% of their full-rated load. Yet in real-world applications, motors often operate at less than 40% of full load for extended periods of time. Future models of these appliances could be made to run more efficiently with the use of a single-phase motor efficiency controller. In addition, existing lines of appliances can be fitted to enhance their efficiency as well.
How does an efficiency controller work? Consider a washing machine: more energy is required when the appliance is filled with many clothes and less when there are just a few items to wash. Yet most washing machines consume more electricity than they need when they are lightly loaded, wasting energy. By contrast, an efficiency controller will provide precisely the right amount of power to the washing machine to meet the demands of its motor at any given time. High-speed response circuits continuously monitor the current and voltage and adjust these accordingly, so that the motor maintains its rated speed and torque under variable loads. More specifically, when the voltage and current sine waves diverge greatly (i.e., when the phase lag increases), the motor is lightly loaded and operating inefficiently. The efficiency controller detects this and reduces the current and voltage appropriately. Conversely, when the load on the motor increases, the device registers this fact and increases the power to the motor so it doesn't stall.
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bcvd
6/3/2010 11:43 AM EDT
This sounds like it uses similar technology as a VFD (drive) except that the frequency is maintained at the original 60Hz. Many high efficiency appliances now use brushless DC motors that require drives that incorportate similar feedback circuitry. Is this intended to be a lower cost alternative? Also, is the controller 3rd party certified? There are concerns about the single fault failure mode of the semiconductor circuitry and software (firmware). IEC/UL/CSA 60730 documents include requirements to address safety concerns.
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mac_droz
6/4/2010 10:15 AM EDT
We all should save energy, but how much will you save? How often do you use washing machine? Me? 2 to 3 washes a week and the heater is the most energy consuming part of it. I'd rather get a washing machine that is going to last for 10 years than the super efficient one. You can't cheat on heating :)
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twk
6/7/2010 3:56 PM EDT
Thus far the product implementations I have experienced have really missed the mark. I see a HVAC unit with a fan motor that saves energy but they replace a $39 motor with a $700 motor to get the savings. As the consumer that both buys the system and operates it the actual payback is negative. They have to get the total life cycle cost to improve before I can even be interested. It is also real life that the reliability gains touted due to thermal improvement are far overcome by the reliability degredation by adding a bunch of electronics.
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