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?

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.

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.

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.

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)

Just another example of why horsepower ratings are just so much eyewash.

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.

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.

Ouch! That HP rating reminds me of the oh so common PMPO rating on "HiFI" stuff!

From some German board:

JBD,
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.

IanR,

You are correct that their advertising was based more on "inrush HP" rather than delivered output.

But, I am concerned that too many people do not take into account the EFF and PF when they are trying to compare input amps with nameplate (output) horsepower.

I think this law suit established there was no way to come up with 6hp, no matter how much they cheated.
http://www.aircompressorsettlement.com/faq.php3

"But, I am concerned that too many people do not take into account the EFF and PF when they are trying to compare input amps with nameplate (output) horsepower."

A very valid point.
My apologies

Even a terrible engineer can't stretch the facts to imply that inrush current equates to HP, because the speed is essentially zero at that point, so the HP formula cannot work. HP does NOT relate directly to current, otherwise you could rate a transformer as having HP! Current relates to torque, and torque relates to HP, but the HP formula is Tq x RPM/5250, so if RPM is zero, everything else is zero. There is another explanation though.

In college in the '70s I worked for Sears selling bench power tools (table saws etc.) when they began using the marketing term "develops __HP". Being an inquisitive sort and an EE student at the time, I asked an Emerson rep one day what they meant by "develops" (Emerson was making all of the Sears brand tools at that time). He explained that they meant that when the load increased the slip to where it put the motor into Break Down Torque (BDT), the total HP could be "recalculated" at those values. Well on a Design B motor, BDT can be as high as 220% of FLT and even though speed would be lower in order to achieve that torque level, the total "recalculated" HP at that point came out to be higher than the "old" HP rating. For example, we had been selling a 1HP motor on the belt driven table saw one day, then the next shipment came in with the EXACT same motor and the literature said "develops 1-3/4HP". So at it's rated 1750RPM it was 1HP, which meant 3ft.lbs. of torque. That meant that BDT was 6.6ft.lbs. and occurred at about 80% speed (1400RPM) so at that point was theoretically 1.76HP! This of course was BS because in order to "develop" that extra HP it was no longer at rated speed and rated speed has everything to do with how a circular saw blade works, but apparently the marketing dept. had no qualms about it.

You could rate a saw like that, or for that matter any machine with a direct drive where a nincompoop operator 'controls' the torque by feeding into the work like a bloody maniac, ignoring the tortured screams of the mechanicals. How long before overheating or breaking a shaft or blade? How long before you fire his ass? A 4-pole @ 1400 rpm? The cooling fan runs too slow, it's less efficient electrically and there is more heat to dissipate.

But for a compressor to run at 220% rated, they'd have to deliberately change the drive ratio, making the machine useless for anything but brief operation and/or making it unstartable. I bet they didn't do that! - Badge Engineering by Marketing - much cheaper!
What we have here is a deliberate lie designed to mislead the consumer. An air compressor is sized by the user on how much air is needed for the job in hand, such as paint-spraying or portable air tooling. A 'below spec' machine usually gives lousy spraying results or an inability of airtools to work at the required speed or endurance.

In these circumstances the maker got off very lightly indeed by being able to fob off tricked buyers with some crappy low spec tools. The tools he actually bought the compressor for don't work properly!
A full refund plus damages, a few million dollars in fines plus the CEO locked up 2-10 would have been more appropriate. That's what you get for fraud isn't it?

Alan

What you get for fraud appears to be inversely proportional to what you can afford to pay for lawyers.