"Bob Swinney" wrote in message
news:BBR2b.205710$Oz4.54331@rwcrnsc54...
Gary sez:

"Why do you think you can count the same resistance twice? The current
only
goes through it once, regardless of whether it is being used as a motor or
a
generator."

He is not counting anything twice. Go back and read the post carefully.
You can rely on anything that Jim says as gospel.

Bob Swinney

Ah, I read it carefully, and I read it the same way that Gary does. It isn't
entirely clear why "Operated at the same speed as a generator, 80% of the
original motor input power is available as generated output," unless he's
talking about armature resistance losses. There are other losses but that
seems to be the subject. Then he counts armature resistance losses again,
no?

Ed Huntress




"Gary Coffman" wrote in message
...
On Tue, 26 Aug 2003 23:57:15 +0100, wrote:
On Tue, 26 Aug 2003 07:12:47 -0700, Eric R Snow
wrote:
If a motor is used as a generator will it put out about the same
wattage as it consumes when used as a motor?
Thanks,
Eric

Only if it's 100% efficient. The simplest case to look at is a low
speed permanent magnet DC motor where the armature resistance is the
major loss component.
With an 80% efficient motor, 20% of the input power is lost in
armature resistance. Operated at the same speed as a generator, 80% of
the original motor input power is available as generated output.
However it now has to travel through the armature resistance before it
reaches the output terminals and this loses a further 20% of the
available power.
For the same internal heating, an 80% efficient machine used at
the same speed as a generator will deliver about 0.8 x 0.8 = 64% of
its rated motor input power.


Gary