starter motor current

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VARISTORS
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starter motor current

Post by VARISTORS » Wed May 24, 2006 9:22 pm

How does one determine the current drawn by a starting motor? No data
plate or name on the motor.

3Phase
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Post by 3Phase » Wed May 24, 2006 9:45 pm

Any idea of the horsepower, three phase or single phase???

dyarker
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Post by dyarker » Wed May 24, 2006 9:56 pm

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Dale Y

dyarker
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Post by dyarker » Wed May 24, 2006 9:57 pm

Estimate resistance of cable from battery to starter motor by looking up resistance per foot of that gauge wire multiplied by length. Measure voltage drop of the cable while cranking, then Ohm's Law.

I think I've heard figures like 500-600 Amps in-rush, dropping to 20-100 Amps depending on oil temp and engine size.
Dale Y

Robert Reed
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Post by Robert Reed » Thu May 25, 2006 9:25 am

Are you talking automotive starting motor? Althogh not every one has one, I used a DC current clamp probe to run checks. The results I got on a Ford 351c.i.d. engine was 200+ amps normal and closer to 400 amps under fault conditions. Don't know how much this varies from manufacturer to manufacturer.

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Post by gerty » Thu May 25, 2006 9:41 pm

Some other things that have an effect on the current draw is cubic inched, compression ratio, worn rings,valve timing. There is a commercial amp meter for this application that you hold against the battery cable. .J.C. Whitney used to carry them, can't vouch for their accuracy, best I can remember 300-400 amps was average..

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