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I've been thinking about efficiency factors, I've read that they are more efficient at higher loads? I was wondering why this is...

On the one hand at higher loads (maybe lifting a heavier mass) the rotation rate is reduced so this reduces energy losses due to friction? (so goes with the increased efficiency idea)

but to lift heavier loads wouldn't you need a higher current? (so more I^2R heat losses in the winding (so this reduces efficency?)

also at low rotation speed less back emf? (less energy losses due to eddy currents?)

Have I got the basic ideas correct here? Would appreciate input.

This also got me thinking about efficiency of a motor if you were lifting a constant load but reducing voltage (assuming the voltage was enough to lift the load), I would predict that efficiency would drop with increasing voltage due to ...

1) increased rotation speed and therefore friction losses

2) increase back emf/eddy current losses

Is this correct also? am I missing anything meaningful?

Regards,

Glenn.