I am building a DC permanent-magnet generator with the magnets in the rotor. The stator coils are my unique winding. The overall efficiency of the generator is measured with a digital torque meter on the input shaft, and checking electrical output on the other, for an efficiency rating of around 95%. To be able to compare this to off-the-shelf generators, I need to know how the efficiency rating for an excited-coil generator is derived. I was told their ratings were only on the coil and not the entire unit. Does anyone have this answer?
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\$\begingroup\$ Question and title are two different things. Question : Efficiency can be derived the same way, adding the power consumed in the field coil to the losses. Title : for a car alternator, I've seen figures like 40W for that loss, and a typical alternator might be about 50A (600W). \$\endgroup\$– user16324Commented May 7, 2020 at 19:46
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\$\begingroup\$ Some of them must be tested with torque and speed input measurement and electrical output measurement. Others may be determined with output measurement and some combination of loss determination methods including simulation, calculation and tests. The only way to know somewhat certainly would be to get a certified test report from the manufacturer or by one and test it yourself. \$\endgroup\$– user80875Commented May 7, 2020 at 19:52
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\$\begingroup\$ The "I was told" sentence makes no sense, but it doesn't really matter what you were told. \$\endgroup\$– user80875Commented May 7, 2020 at 19:55
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\$\begingroup\$ I think the old guy at my work increases the input power by the field winding power. He said it's not quite accurate though but I forget why. \$\endgroup\$– DKNguyenCommented May 11, 2020 at 16:29
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