Don Foreman wrote: (clip) I respect both contributors, agree with Gary here
(clip)
^^^^^^^^^^^^^^
I respect everybody, but I agree with Gary also. Look at it this way. Say,
you have this 80% efficient motor running, and drawing 1 kw. Then 800 watts
of power will appear at the output shaft, and 200 watts will be lost as heat
in the electrical and maehanical losses of the motor. It is the motor's
ability to dissipate heat that determines the motor rating. If you load it
more, it will develop more power, but overheat.

Now, let's say we couple this motor to the shaft of an identical motor,
hooked up as a generator. It is receiving 800 watts of power as input on
the shaft, and, being 80% efficient, it will put out 640 watts of power, and
throwing off 160 watts as heat. In this cnfiguration, you to count the
losses twice, because you are running two machines in series.

But that wasn't the question. The question was, can the motor, run as a
generator, develop about the same power? Note that the second unit is only
dissipating 160 watts of heat, so it is not being run at capacity. If you
had the power available from some other source (windmill, waterwheel, gas
engine...whatever) you could boost the load until the heat losses reached
the design limit of 200 watts, and you would be running the motor as a
generator at the same power it is rated for as a motor.

So, you may count the losses twice only if you are running two units. And
you CAN load to the same power level, regardless of which way the power is
flowing.