That air compressor says it's 5 or 6 horsepower.
Well, not quite!
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Updated 2/4/08
Sure, there's a big sticker on the tank, with a big "6 HP" on it. But if you look at the nameplate on the motor itself, the place where the horsepower is supposed to be listed, it is either blank, or says "SPL". (Someone's Probably Lying?) A closer look at the big sticker on the tank may even reveal some fine print saying "peak" horsepower.

We're talking about portable electric compressors here, that run off of an ordinary household outlet, 120 volts.

This is one case that I've reported to several "consumer protection" type agencies over the past years. Knowing what I do about electrical and mechanical things, I immediately had to take a second look when I saw these compressors on the floor at a local home center. The motor on it was physically way to small to be anywhere near 5 real horsepower, but the store's poster advertised it as "5 hp".

I made note of the electrical ratings on the motor, When I got home I ran the numbers, and taking into acount the efficiency and power factor of the motor, I concluded it was actually a 1-3/4 hp. unit, 2 hp. max.

So what's happening here is an outright
lie. And it's several different manufacturers doing it. The air compressor manufacturer does not make the electric motor, but buys it from a motor manufacturer. The motor manufacturer knows it could get in trouble by putting a false horsepower rating on the motor, because there are standards for determining horsepower. If someone were to take that motor off of the compressor and use it in another application, the truth would come out. So to stay out of trouble, they don't mark the hp. rating on the motor. And they also call it a special "air-compressor duty" motor, and say 'do not use in any other application', or something to that effect. Gee, I wonder why?

So it's the air compressor manufacturers that are twisting the truth. Obviously the motor manufacturers are aware of it, but have their butts covered.

My complaints about this fell on deaf ears, for the most part. One manufacturer sent some papers to the consumer protection agency, with charts and graphs, explaining basically that if you can make a motor put out 5 hp. long enough to get a reading, then it's a 5 hp. motor. Uh Huh. But the agency accepted that answer. I don't imagine that anyone at such an agency would know a horsepower from a watt.

The truth is,
1 horsepower is the amount of power needed to lift a weight of 33,000 pounds a distance of 1 foot in one minute, or 550 foot-pounds per second. And a motor rated at 1 (real) horsepower could do just that. Also, most electric motors are capable of producing two or three times their rated power during start-up, just for a second or two, to get up to speed. This is probably where the "peak horsepower" rating comes from, but really has no useful purpose for the consumer.

Additionally, a standard wall outlet (120 volt) can produce only 1800 to 2400 watts of electricity. (Volts X Amps = Watts.) A commonly used formula for converting watts into horsepower is 1000 watts equals 1 horsepower. This accounts for losses in the motor. So a
15 amp wall outlet can run 1800 watts or only 1.8 hp., and a heavier duty 20 amp outlet, as you might find in your kitchen, could run 2400 watts, or 2.4 hp. So any appliance that runs on regular power, and claims to be more than a couple of horsepower, is BS!

Early in the 2000's, I read that there was a class-action lawsuit about the air compressors, and the manufacturers agreed to cut the BS, but I still see them for sale every day, all the way up to 6.5 hp. now. I recently found an imported unit that is brave enough to actually list "5hp" on the motor itself, but acording to the electrical info on the motor, same crap, it's 2 hp. max. I did file another complaint about this matter.

Update 5/17/07: My complaint did help somewhat, at least on the local level. Now all of the units that have "peak hp." ratings on them now also have a notice put on by the store (Mills Fleet Farm) explaining that the peak rating is a fake, and listing the real horsepower. The exception is the imported unit that outright claims to be "5hp." as stated on the motor label itself. No notice on this one!

Another thought to consider if you plan on using compressed air to run power tools is the
tremendous inefficiency associated with compressing air. Check out this page ! <airloss>

Additionally, "shop" type vacuum cleaners seem to have caught this illness too. 6.6hp! Yeah, right!
More on that on another page.

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