Quote:
Originally Posted by Roadam
Any electrical engineers out there?
I just want to know if I am thinking right. As I think that permanent magnet alternator running at high rpm would induce high voltage. (Induced voltage is proportional to the speed that magnetic flux changes. )
Loses are mainly heat which rises with square of a current running trough the windings. So at high voltage and low current, loses would be smaller compared to power produced.
Although it would be a waste of a big alternator, running it at high speed and low power would be energy efficient. I think.
To be more specific, I recently saw an alternator which can produce 1900W at 425V at 500rpm. I digged its efficiency at 85%. So its internal resistance is probably about 17 Ohms. If I would set the current so that it would produce only 500W at the same voltage and speed, the efficiency would be about 95%. But I am not sure how much of that 15% original losses come from bearings.
Anyone care to comment?
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85% efficiency is very good for a small generator. The published ratings, in this case 1900W at 425V and 500 RPM is probably the "sweet spot" on the curves for the particular generator, which is why the manufacturer publishes those numbers. You'd have to look at the performance curves to be sure, but if you tried to increase or decrease rpms, or mess with the operational voltage, you will almost certainly lose efficiency.
As far as producing lower amperage output to increase efficiency, you could easily have the generator produce less amperage, but the efficiency would only go up very slightly. As you noted base inefficiencies like bearing loss,flux leakage, and other things are always there. No matter what you did, I would not expect you to get efficiencies above 85%.
