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#68253 - 07/31/06 09:53 PM How does an Air Compressor draw...  
Cinner  Offline
Joined: Dec 2004
Posts: 78
Kelowna, B.C., Canada
How does an Air Compressor draw 15 amps at 120 volts 1 phase(on the nameplate) when it is rated at 6HP?

Air Compressor is a DeVilbiss Air Power.

I came across this compressor today.
Isn't it calculated:
120V x 15A = 1800W...1800 W/746=2.4 HP?

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#68254 - 07/31/06 10:13 PM Re: How does an Air Compressor draw...  
e57  Offline
Joined: May 2003
Posts: 2,876
Are you sure its not a dual voltage 6HP motor, that would be about 18A at 240???? (30A Circuit?)

But that depends on the motor, and applicable tables for frame, FLA etc....

I would double check the nameplate info, and what its really hooked up to.

Mark Heller
"Well - I oughta....." -Jackie Gleason

#68255 - 07/31/06 10:17 PM Re: How does an Air Compressor draw...  
gfretwell  Offline

Joined: Jul 2004
Posts: 9,105
I have one of those compressors and they had to give everyone a gift as part of the class action suit. (the 6hp is a lie) I got an air nibbler.
I did track the amps while it was coming up and it starts at about 11a with no air in the tank, as the tank fills it peaks at about 13-14a with 70-80psi in the tank and drops back off after that to 12 right before it pops off at 150psi.

Greg Fretwell

#68256 - 08/01/06 07:08 AM Re: How does an Air Compressor draw...  
IanR  Offline
Joined: Dec 2004
Posts: 328
Palm Bay FL USA
Well, I asked about this once. I was told that the buzzword was peak HP. Which we all know there is no real standard to measure for electric motors. You know, the inrush current when the motor starts is 37A.

37X120=4440W and at 750W/HP that is 5.92HP
So it is 6HP.

A completely worthless number as far as power output. But, they don't say the motor puts out 6HP. They just say 6HP, not defining that that is the peak electrical input power when the motor starts.
Kind of dishonest, but that's marketing for you.

#68257 - 08/01/06 09:42 AM Re: How does an Air Compressor draw...  
JBD  Offline
Joined: Jul 2001
Posts: 599
When trying to convert between W and HP - remember the 746W/HP is for INPUT watts while the motor nameplate is OUPUT horsepower so you need to include the efficiency and the power factor into your calcualtions.

1-ph Nameplate HP = (E x I x %eff x PF)/746
1-ph Input Amps = (HP x 746)/(E x %eff x PF)

#68258 - 08/01/06 12:43 PM Re: How does an Air Compressor draw...  
renosteinke  Offline
Cat Servant
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
Just another example of why horsepower ratings are just so much eyewash.

#68259 - 08/01/06 06:49 PM Re: How does an Air Compressor draw...  
gfretwell  Offline

Joined: Jul 2004
Posts: 9,105
Campbell Hausfeld (the company behind DeVilbiss) got sued over those "6hp" compressors. There was a class action settlement, $50 worth of stuff for every customer. It wasn't much of a consolation if you really thought you were buying a 6hp compressor. I knew what I was getting because I recognized the NEMA 5-15 cord cap.

Greg Fretwell

#68260 - 08/01/06 10:14 PM Re: How does an Air Compressor draw...  
gobblerhuntr  Offline
Joined: May 2005
Posts: 23
If you want to know anything about a DeVilbiss product, I got the connection. My neighbor is the materials engineer for the plant that makes all DeVilbiss products. He is at my house virtually everyday. They have been bought by Black and Decker recently and are having change overs to get to the B and D way of doing business. Don't know if that is good or bad.

I did tour the plant one day while we were riding motorcycles and I noticed several different items with the same motor. He says the motor was the same but the stickers are different. You can't imagine the different brands they make and the only difference is paint and stickers. The only one that had some differences enought to note were Snap-Ons and they weren't that different.

#68261 - 08/02/06 05:36 AM Re: How does an Air Compressor draw...  
Texas_Ranger  Offline
Joined: Dec 2001
Posts: 2,400
Vienna, Austria
Ouch! That HP rating reminds me of the oh so common PMPO rating on "HiFI" stuff!

From some German board:
Oh, I always thought PMPO was the pulse output in the instant lightning strikes the amplifier! *veg*

#68262 - 08/02/06 08:05 AM Re: How does an Air Compressor draw...  
IanR  Offline
Joined: Dec 2004
Posts: 328
Palm Bay FL USA
I know that we are not calculating using accurate formulas, ie 750W/HP vs 746
and we havent done the efficiency calculations, but it still makes our point using the approximations.

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