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Subject: TWL: RE: Alternator efficiency
From: Arild Jensen (elnav@XXX.XXX)
Date: Sat Jan 25 2003 - 20:43:44 EST
Rob wrote:
-----Original Message-----
>From Balmar's data, significant losses apparently occur generating dc
amperage via alternators. For one, heat losses are enough to make high
output
alternators too hot too touch, even with fan cooling...add to that belt
friction and other lossess and maybe it's understandable.
REPLY
Please keep in mind that the Balmar data is a guideline for the non
technical customer who is simply looking for a "rule of thumb"
The 25 amps = 1 HP is an oversimplification intendee to correlate rated
engine power with alternator power output.
However, keep in mind that many engine ratings are based on "raw" power not
shaft output power at the very end of the power train.
A typical 4 HP small motor will not produce 4 times 746 watts of energy at
the point of work being done.
Nor is the power output fixed at all speeds; and the alternator output is a
curve not a linear function.
The Balmar data is only an approximation. A 100 amp alternator would require
a belt capable of transmitting 4 horse power of rotational energy.
A alternator capable of putting out 100 amps at low speed, fitted with a
good quality, tight belt will stall a 10 HP motor running at idle speed
because at that idle speed the motor is not putting out 10 HP.
If you are going to pick nits to this extent, at least agree about which
side of the centerline you are going to split the hairs. :-)))
Cheers
arild
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