Real horsepower or marketing lies

[Jimbo]

I have an old Sears compressor with a one horsepower electric motor. It was sold as a "one horsepower" model about 30 years ago. The current draw is 6.5A@240V / 13A@120V.

I saw a new Craftsman compressor that looks very similar, belt drive, two-cylinder, single stage. It was "rated" at SIX horsepower on the label. The motor itself (GE) had the HP label blank, but the amperage rating was similar to my old one. There was some fine print mumbo-jumbo about ratings. ***?

 

[XS650]

In the tool news groups, over rated horsepower ratings are often called "Sears Horsepower"

I think what they di they take starting inrush current times voltage, which is a instantaneous momentary power into the motor and calculate power from that. It's nonsense.

All you can do is look at voltage/current ratings and output and hope they didn't lie too much about those.

My brothers ancient Sears 1 hp air compressor puts out more air than my 15 year old Campbell Hausfield 2 hp compressor. The present version of my compressor is rated at 5 hp, same basic motor, same current draw.

[ March 19, 2004, 01:56 PM: Message edited by: XS650 ]

 

[jsharp]

I discovered this very thing lately while looking at compressors to get a rough idea of what motor and pulley size I'll need to use an old CH pump I want to rebuild and use as a stationary compressor in my shop.

The horsepower numbers on current compressors are looking like audio amplifier wattage ratings in the 60's and 70's, before the FTC put a stop to it. My 2hp Sears made by CH in the late 70's delivers about the same amount of air as a current "5hp" model, and the current crop of single stage 6-7hp consumer grade compressors are really at most 3hp units.

If you want to determine the real motor hp, look at the motor full load current on the unit. Find a US built industrial grade motor with a comparable current rating and it will give you a pretty good idea. Expect to be shocked. Your 5hp Chinese "compressor duty" motor will probably draw about 7.5 amps at 230 volts. Which makes it in real life roughly a 2hp motor.

There's a reason the Chinese can build a "6hp compressor duty motor" and sell it for $99 instead of the $250 or $300 it should cost. They lie...

 

[XS650]

quote:

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Originally posted by jsharp:


There's a reason the Chinese can build a "6hp compressor duty motor" and sell it for $99 instead of the $250 or $300 it should cost. They lie...

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Sears is, and I believe rightfully so, credited with being the first major company to dishonestly rate their elecrical consumer grade motors. Last I checked, they aren't a Chinese company. The Chinese put whatever labels their Western distributors want on their motors.

[ March 19, 2004, 03:30 PM: Message edited by: XS650 ]

 

[jsharp]

quote:

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Originally posted by XS650:

quote:

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Originally posted by jsharp:


There's a reason the Chinese can build a "6hp compressor duty motor" and sell it for $99 instead of the $250 or $300 it should cost. They lie...

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Sears is, and I believe rightfully so, credited with being the first major company to dishonestly rate their elecrical consumer grade motors. Last I checked, they aren't a Chinese company. The Chinese put whatever labels their Western distributors want on their motors.

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I don't know about Sears or where the the motors come from for products manufacured for them, but I'm sure they're imported as are most of the motors used on Devilbiss, Porter-Cable, and CH consumer grade compressors. I was looking at the raw motors from assorted suppliers. The Chinese and other imported motors are typically far overlabeled compared to something made here by someone like GE.

It wouldn't surprise me a bit if Sears was the first to do it, but I know it's really common now from what I've seen in the last couple of weeks of looking. Check a place like Harbor Freight if you want to see what I mean. A "5hp" motor for $99.

I suppose the distributors and sellers can have any hp label they want put on any motor but they can't lie about the electrical ratings and get through testing for UL compliance for instance. That was my point, to use the electrical labeling to determine true horsepower. As far as the labeling is concerned, if you know enough to design and manufacture a motor, you *exactly* what the real horsepower is. Any other labeling, even if it's requested by your purchaser, is a lie.

I've bought thousands of power supplies from offshore suppliers and discovered the nameplate output rating means little. Run them at full load and close to 100% of them will fail in less than 2 years. Run them at 60% rating and they seem to last pretty well...

[ March 19, 2004, 11:17 PM: Message edited by: jsharp ]

 

[doitmyself]

Gentlemen,

Please read this! Just this month (March) a class action suit was settled regarding mis-labeling of air compressors. You might be eligible to get "something" back if you bought a mislabeled compressor over the past several years.Go to:

www.aircompressorsettlement.com for more info.

A good site about evaluating aircompressor ratings is at http://truetex.com/aircompressors.htm

[ March 20, 2004, 10:37 PM: Message edited by: doitmyself ]

 

[XS650]

quote:

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Originally posted by doitmyself:
Gentlemen,

Please read this! Just this month (March) a class action suit was settled regarding mis-labeling of air compressors. You might be eligible to get "something" back if you bought a mislabeled compressor over the past several years.Go to:

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I can't collect because to do so I would effectively be saying that I was dumb enough to have believed the ratings.

 

[jsharp]

quote:

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Originally posted by doitmyself:
Gentlemen,

Please read this! Just this month (March) a class action suit was settled regarding mis-labeling of air compressors. You might be eligible to get "something" back if you bought a mislabeled compressor over the past several years.Go to:

www.aircompressorsettlement.com for more info.

A good site about evaluating aircompressor ratings is at http://truetex.com/aircompressors.htm

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Wow, this is great. From the first link - Manufacturers agreeing to this settlement include Campbell Hausfeld, DeVilbiss, Ingersoll-Rand Co., and Coleman Powermate, Inc

IOW, pretty much everybody that makes and sells consumer grade compressors in the US.

I'd expect to see the HP numbers to drop back under 2hp on about all these 120V units. Just where they were in the 70's before HP inflation took off. Now if they could work on the SCFM @ pressure ratings and apply this to 240V units too, we'd be all set.

[ March 20, 2004, 11:34 PM: Message edited by: jsharp ]

 

[jsharp]

quote:

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Originally posted by XS650:

quote:

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Originally posted by doitmyself:
Gentlemen,

Please read this! Just this month (March) a class action suit was settled regarding mis-labeling of air compressors. You might be eligible to get "something" back if you bought a mislabeled compressor over the past several years.Go to:

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I can't collect because to do so I would effectively be saying that I was dumb enough to have believed the ratings.

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You mean you weren't buying that 350% efficiency all thse newer units seem to have?

 

[fractal]

quote:

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Originally posted by Jimbo:
I have an old Sears compressor with a one horsepower electric motor. It was sold as a "one horsepower" model about 30 years ago. The current draw is 6.5A@240V / 13A@120V.

I saw a new Craftsman compressor that looks very similar, belt drive, two-cylinder, single stage. It was "rated" at SIX horsepower on the label. The motor itself (GE) had the HP label blank, but the amperage rating was similar to my old one. There was some fine print mumbo-jumbo about ratings. *** ?

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First a definition. 1HP = 755 watt.

Next, no motor is 100% efficient. Hence a good "rule of thumb" is 1hp = 10 amp at 120v, 5 amp at 240v. Of course you use real numbers when it comes down to the nitty gritty, but the rule of thumb will keep you in the proper ballpark.

So, while a 5hp motor may not take the full 50 amps of 120v, it certainly can't deliver 5hp pulling 6.5 amps.

 

[anon12]

Most of the commercial grade compressors, usually 2 stage that I have looked at have a 5HP motor that draws around 25 amps at 240 volts single phase. These 5 to 6 HP ratings on consumer grade compressors are wildly optimistic.

 

[1 FMF]

this is funny, because I bought not too long ago a central pneumatic 20 something gallon compressor from harbor freight, primarily because it had the size tank I wanted, was oil lubricated and ran on 110/120v. It is rated at 4hp, HF still sells them for $169 I believe.
Maybe 120v x 20amps (max) = 2400 watt
2400 / 746 watt per hp = 3.217, so maybe they round up

 

[Jaybird]

Although HP seems to be the way lots of folks shop for a compressor, isn't the SCFM rating what one should be paying attention to?

 

[XS650]

quote:

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Originally posted by Jaybird:
Although HP seems to be the way lots of folks shop for a compressor, isn't the SCFM rating what one should be paying attention to?

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Yes, although you should probably take that with a grain of salt too.

 

[Crashbox]

I liken the consumer-grade compressor HP ratings to those on vacuum cleaners!!!

 

[Steve S]

quote:

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Originally posted by 1 FMF:
this is funny, because I bought not too long ago a central pneumatic 20 something gallon compressor from harbor freight, primarily because it had the size tank I wanted, was oil lubricated and ran on 110/120v. It is rated at 4hp, HF still sells them for $169 I believe.
Maybe 120v x 20amps (max) = 2400 watt
2400 / 746 watt per hp = 3.217, so maybe they round up

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Metric watts

 

[BIRD DOG]

never go by hp only go by the pump cfm not scfm not a true rating. I think to many get hung up on hp. most hp ratings are rated at peak hp not a real good way of rating just good marketing. for example i own a 7.5 hp 27cfm at 90psi compresor if rated by home depot,sears or other junk places to buy compresors it would have some crazy rating of 27hp. be aware of what is out in the world and do your homework.