(John) wrote in message ...
60 amps X 28 volts = 1680 watts
1680 watts/746 watts/hp = 2.25 horse power
Since the alternator is about 50% efficient you will need at least 5
HP drive for full output.

The alternator speed is the ratio of the pulley sizes x engine RPM.

Which on an O-320 is between 3 or 4 to one, so the alternator
will spin at about 8000 RPM.
The alternator should be a bit more than 50% efficient, I think.

Dan



On Sat, 29 May 2004 17:53:02 GMT, Nathan Young
wrote:

I want to build a teststand where I can test an alternator.

I plan on fabricating a test stand for the alternator.
I have a variable voltage source capable of driving enough current to
'drive' the field.
I have a dummy load to sink the output current.

What I need is a variable speed electric motor to drive the
alternator. But I am not sure how much horsepower is required to
drive a 60Amp alternator @ the equivalent of 2500 RPM at the prop.

Which brings up another question. What is the typical ratio of prop
RPM to alternator RPM? I am thinking it is 2:1.

Alternatively rather than wasting a bunch of my time - is this
something I could just buy from an alternator repair shop?

Thanks,
Nathan