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Tool Talk Discussion Forum

motor HP ratings.

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James in North

07-24-2006 19:40:11




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In regards to the table saw thread below, it could be that the HP rating on the Home Depot saw motor is the maximum possible rate of energy consumption by the motor and the Grainger website Bus Driver listed shows the rate of energy output(useable horse power) by their motors. I know some compressor manufacturers used to list the maximum possible rate of energy consumption as the HP on their motors. I think they tested them just at the point where the motor was about to burn up(I'm not joking). In reality, the rate of energy output was significantly less due to inefficiency/heat loss and reduced current.

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Bernoulli

07-25-2006 17:59:44




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 Re: motor HP ratings. in reply to James in North Carolina, 07-24-2006 19:40:11  
Motors vary in efficiency, but generally are about 65% efficient. That gives manufacturers one way to lie - just use 100%. The next way is the amount of watts consumed when the lights go out - just claim that converted to HP. 12.3 Amps at 110VAC is generally accepted as 1HP. This makes a 1.5HP motor the practical maximum on a 20 Amp circuit since it will draw 18 amps at peak operating draw. It draws more than that at start, but your slo-blow fuse or CB will handle that. CH apparently lost a class action suit (lying about HP) a couple of years ago and had to compensate some compressor buyers who could prove they qualified. Your motor will give more effective power, run smoother and cooler if it can be wired 220VAC. Try it - you'll like it.

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Joe(TX)

07-25-2006 10:01:13




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 Re: motor HP ratings. in reply to James in North Carolina, 07-24-2006 19:40:11  
Air compressors and saws etc are rated at peak hp. Most other motors are at contiuous hp at a certain temperature rise. Most air compressor motors you can divide the hp by 3 to get the contiuos hp



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Robert in W. Mi.

07-24-2006 22:02:50




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 Re: motor HP ratings. in reply to James in North Carolina, 07-24-2006 19:40:11  
It takes very close to 10 amps on 120V to make one hp... (half that on 220V) Just look at the name plate on the motor and do the math!!

Robert



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Jerry/MT

07-25-2006 15:05:10




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 Re: motor HP ratings. in reply to Robert in W. Mi., 07-24-2006 22:02:50  
Actually it's a little more than 10 amps at 120 V, it 's a little over 11 amps.

Since HPin = 0.7457 x (Amps x Volts)/1000,

Amps = 1 HPin X 1000/0.7457 X 120V = 11.175amps



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James in North Carolina

07-25-2006 11:50:59




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 Re: motor HP ratings. in reply to Robert in W. Mi., 07-24-2006 22:02:50  
Robert, did my post tick you off or something?



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Robert in W. Mi.

07-25-2006 18:24:01




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 Re: motor HP ratings. in reply to James in North Carolina, 07-25-2006 11:50:59  
Not at all, why would it????

Checking the name plate is the "only" way to know what the motor really is...

Robert



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IH2444

07-24-2006 21:39:08




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 Re: motor HP ratings. in reply to James in North Carolina, 07-24-2006 19:40:11  
I agree with you James. Yep 5 HP, would be the smokin HP :)
I just wish they would go back to the continuous or %duty cycle straight HP measumements for electric motors.



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Coloken

07-24-2006 20:42:49




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 Re: motor HP ratings. in reply to James in North Carolina, 07-24-2006 19:40:11  
Maybe, but I think they just lie. Like my friend has what they call a 5HP compressor. It plugs into a regular 110 volt plugin. Run on less than 20 amps. Wonder what they would call a genuine one horse motor?



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IH2444

07-24-2006 21:49:00




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 Re: motor HP ratings. in reply to Coloken, 07-24-2006 20:42:49  
I have a sears 3 HP buzzer (oiless) compressor. Don't laugh it was a gift and it blows air. I did put it in an adjacent shed and plumbed it into my workshop though. Noisy sucker.
Anyway mine is 3 HP and draws less than 20 amps, maybe it won't just stall and smome long enough to qualify as a 5 hp ?



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