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RE: Electric motor power ?

To: Neil Sherry <sherry@invention-machine.co.uk>,
Subject: RE: Electric motor power ?
From: Randall Young <ryoung@NAVCOMTECH.COM>
Date: Mon, 23 Jul 2001 09:38:03 -0700
Neil Sherry wrote :
>
> Ideally horsepower for electric and petrol motors should be equivalent  -
> although BHP is actual power at the shaft (this will be a
> maximum, elsewhere
> in the rev. range there will be less) and that motor power will be
> electrical input (output will be around 20% lower).

At least in the US, electric motors are rated by output at the shaft.
However, particularly in the case of DC motors, this is a 'continuous'
rating limited largely by heat buildup, it may be possible (depending on
motor design) to get much more power for a limited time (like accelerating a
car from standstill).

In general, electric cars make do with much less raw horsepower on tap than
gasoline powered cars do, simply because it isn't practical to stuff a 100hp
electric motor in one (or to feed it the roughly 100 kilowatts it would
consume at full power).  DC motors will typically also deliver full power
over a much wider range than a gasoline engine, and are further enhanced by
not needing as much in the way of gearboxes and differentials (which waste
power).

Randall

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