Determining Motor HP?

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  #1  
Old 04-11-07, 09:35 PM
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Determining Motor HP?

I have an older three phase motor that looks like it may be about 5 HP but...the nameplate is missing and some old motors are deceptively large for their rating. Is there a simple way of figuring out how many HP it's capable of? Maybe something like measuring the starting inrush current at no load and then using some sort of rule of thumb to get back to rated current?
I would appreciate any suggestions.

Thanks,

Bob
 
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  #2  
Old 04-11-07, 09:50 PM
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Are there any identifying markings on the motor at all such as make, model or serial number?
 
  #3  
Old 04-13-07, 10:04 PM
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Ben,

There are only rivet heads left where the nameplate used to be, although there is still a GE logo on it. I guess if I wanted to bad enough I could lock the rotor with something and measure the locked rotor current. That would give me something close to the "Sears air compressor equivalent HP" and dividing by two or so would at least be in the ballpark of real HP.

Thanks,

Bob
 
  #4  
Old 04-14-07, 04:21 AM
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Is this motorcurrently installed and running?

You could do the same test as above but not lock the rotor and measure the FLA. Or you could look inside the starter and get the starter size and heater part number and call a supply house and ask them to look it up for you.
 
  #5  
Old 04-14-07, 11:23 AM
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No easy way to measure this, old motors tend to have great starting currents, maybe 10 times running current.

If you want to use the motor try it, and if the temp nt rises higher than 160F it is OK for the job. (It may take long time to reach this temp.)

Then put in a motor protecting switch adjusted to the mesured amp. + 5%

dsk
 
  #6  
Old 04-16-07, 07:18 AM
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Thanks for the replies. I'll probably try connecting it to a load and measuring the current and temperature.

Bob
 
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