Is Porter Cable lying about the HP on their compressors?

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hockeyoligist2

Senior Member
My brother bought a new Porter Cable 6 hp 25 gallon compressor. He wants me to run a dedicated receptacle about 5 foot from the panel in his garage. He said the name plate says 120 v 15 amp.

How is this possible? Unless it really isn't 6 hp, it should be about 45 amps, right? I'm going over to check it out tomorrow.
 

kbsparky

Senior Member
Location
Delmarva, USA
Porter cable and most all the other manufacturers routinely "lie" about the hp capacity of air compressors. They base their rating on the locked-rotor amps of the motor, and translate that to an advertised "HP" rating. Pure bunk.

If you look carefully at the motor nameplate, you will find that the "hp" rating is actually blank, or marked "special". It would conflict with their advertising if they were to put the real hp rating of the motor there.

Using the code book's table on motors full-load amps, you should be able to figure out what the real hp capacity of said compressor is.
 
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mcclary's electrical

Senior Member
Location
VA
My brother bought a new Porter Cable 6 hp 25 gallon compressor. He wants me to run a dedicated receptacle about 5 foot from the panel in his garage. He said the name plate says 120 v 15 amp.

How is this possible? Unless it really isn't 6 hp, it should be about 45 amps, right? I'm going over to check it out tomorrow.

the simple math comes out to 37.3135 amps, but there's lots of unknown factors that could "plug" into the equation.
 
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Sierrasparky

Senior Member
Location
USA
Occupation
Electrician ,contractor
Gota Love those S or SPL motors. I have a compressor that is 5 HP 220 has "s" I once put a amp meter on it and what happens is that it will pull the amps of a 5 hp motor but only for a very short time.
 

brian john

Senior Member
Location
Leesburg, VA
THe peak HP is based on lock rotor or the point just prior to reaching lock rotor, a tool manufacture told me this at a woodworking show. So it ain't necessairly true, but based on what I have seen close to true.
 

mxslick

Senior Member
Location
SE Idaho
The compressor motor horsepower caper reminds me of how car stereos were touting "300+" watts per channel and using the 12v battery source and a tiny IC chip amplifier. :roll: Simple Ohm's Law will tell you is just isn't possible that way.

The real high-power car stereo amps of late use switching power supplies to step up the DC voltage to the power transistors to get a true high power capability. But the 12v DC source current draw is of course pretty high.
 

david luchini

Moderator
Staff member
Location
Connecticut
Occupation
Engineer
I don't believe that "horsepower" on this type of compressor means "Electrical Horsepower."

I think it relates to "hydraulic horsepower," which relates to gallons per minute x psi. Or more simply how much air is required to fill the tank based on the demands of air flow being placed on it.
 

LEO2854

Esteemed Member
Location
Ma
My brother bought a new Porter Cable 6 hp 25 gallon compressor. He wants me to run a dedicated receptacle about 5 foot from the panel in his garage. He said the name plate says 120 v 15 amp.

How is this possible? Unless it really isn't 6 hp, it should be about 45 amps, right? I'm going over to check it out tomorrow.

Here is the largest compressor on the porter cable web site at 5.4 amps it need a 240v 30A cir.:)
 

LEO2854

Esteemed Member
Location
Ma
My brother bought a new Porter Cable 6 hp 25 gallon compressor. He wants me to run a dedicated receptacle about 5 foot from the panel in his garage. He said the name plate says 120 v 15 amp.

How is this possible? Unless it really isn't 6 hp, it should be about 45 amps, right? I'm going over to check it out tomorrow.
Heres a link to the largest compressor i could find on the porter cable web site
http://www.deltaportercable.com/Products/ProductDetail.aspx?ProductID=11529
 

kwired

Electron manager
Location
NE Nebraska
I don't believe that "horsepower" on this type of compressor means "Electrical Horsepower."

I think it relates to "hydraulic horsepower," which relates to gallons per minute x psi. Or more simply how much air is required to fill the tank based on the demands of air flow being placed on it.

Isn't horsepower X amount of torque over Y amount of time no matter what the input power is derived from?
 

Rick Christopherson

Senior Member
I don't believe that "horsepower" on this type of compressor means "Electrical Horsepower."

I think it relates to "hydraulic horsepower," which relates to gallons per minute x psi. Or more simply how much air is required to fill the tank based on the demands of air flow being placed on it.
Conservation of energy dictates that you cannot get more pneumatic power out of a compressor than the electrical power you put into it. A compressor simply converts electrical power into pneumatic power, less losses. A motor is the same in that it converts electrical power into mechanical power, less losses.

To the original poster, this compressor (based on the nameplate of 15 amps at 120 volts) is simply a standard retail cord-and-plug portable load. Even though the nameplate indicates 15 amps and it has a NEMA 5-15 plug, it should be installed on a 20 amp circuit. It will function on a 15 amp circuit, but voltage drop can be an issue during start-up on a long run.

Edit: By the way, a reasonable estimate on the actual horsepower of the motor is obtained from Hp = I x V x pf x eff / 746, with powerfactor and efficiency both estimated at 0.80 unless the nameplate states these values otherwise. This gives a typical 120 volt, 15 amp motor a maximum horsepower of 1.5 Hp.
 
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hurk27

Senior Member
The problem with this false advertising is we have to deal with customers who believe in these ratings, vacuum cleaners, audio equipment, compressors, and even hair dryers (I have one that states 1800watts but pulls only 11.5 amps)

in one case I had a customer who just wouldn't understand I could not wire his older 5hp 60gal air compressor to a 120 volt 15 amp receptacle so he could just plug it in any where, and he used the ratings of his portable 6hp air compressor to back his argument, and trying to get him to understand the difference was fruitless, because of this I lost this customer, who most likely won't be back because even if he does learn the truth, he would be too embarrassed to call again.

What if this was the load the inspector in this THREAD was rejecting, based on the HP rating? as we can see we can have some problems with even code on this.

As I have said before this needs to be address by UL, and the Federal Trades Commission, to stop them from being allowed to advertise inflated ratings.
 
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hockeyoligist2

Senior Member
Well, I went over to my brothers house. The motor on the compressor doesn't have a nameplate. The guard just says 6hp 15 amp. He had a spare 20 breaker so I ran a piece of pipe and fixed him up. I checked the amp draw and it was 15 amps. No way it has 6 hp.
 

templdl

Senior Member
Location
Wisconsin
Maybe there is hope for truth in ratings

Maybe there is hope for truth in ratings

The compressor manufactures are doing the same things that the small engine manufacturers have been doing for years and that is to miss state the horse power.
But as I understand it because of a class action law suite now the small engine manufactures are just stating the displacement of the engines or the torque both of which are not easily to exaggerate.
Just maybe those compressor manufacture who miss state their HP ratings will be forces to follow the same truth is rating methods it appears that the small engine manufactures are doing at the present time.

Here's and excerpt from an article at http://www.gazette.com/articles/horsepower-34878-mowers-engines.html
"The shift away from horsepower ratings came after a lawsuit in Illinois claimed that engine manufacturers were over stating the horsepower of lawn mower engines.

In some cases, the lawsuit alleged, identical engines were labeled with different horsepower ratings, misleading consumers into believing they were getting more power by purchasing more expensive models.

Briggs advertised one engine as having 6.75 horsepower and yet told the Environmental Protection Agency the same engine had 3.6 horsepower, an 88 percent overstatement, according to the lawsuit.

Since at least 1997, engine manufacturers Briggs, Tecumseh, Kohler, Toro and Kawasaki have reported horsepower ratings to the EPA that were significantly lower than the ratings advertised to the public, the lawsuit said."

And article from the Washington Post states: Article: Familiar Horsepower Rating No Longer Standard; Small-Engine Makers May Cite Torque, Cubic Centimeters or Nothing at All
 

LEO2854

Esteemed Member
Location
Ma
Well, I went over to my brothers house. The motor on the compressor doesn't have a nameplate. The guard just says 6hp 15 amp. He had a spare 20 breaker so I ran a piece of pipe and fixed him up. I checked the amp draw and it was 15 amps. No way it has 6 hp.

If it say's 15 amps the thats all you need plug it in and take an amp reading.
 

SOG38

Member
Location
USA
Compressor HP

Compressor HP

IMHO
As I recall from investagating long ago the running HP is the HP at the compressor to deliver the cfm to replinish the tank. The motor RPM, say 3600 is stepped down to say 600 rpm.
A 1 HP motor would be delivering 6 HP to the compressor. This is of course for the belt driven compressors
Then the motor is slightly larger to ensure it isn't running at full load with the losses. I always measure to see what is needed for a power circuit. It is misleading.;)
 

Rick Christopherson

Senior Member
IMHO
As I recall from investagating long ago the running HP is the HP at the compressor to deliver the cfm to replinish the tank. The motor RPM, say 3600 is stepped down to say 600 rpm.
A 1 HP motor would be delivering 6 HP to the compressor. This is of course for the belt driven compressors
Then the motor is slightly larger to ensure it isn't running at full load with the losses. I always measure to see what is needed for a power circuit. It is misleading.;)
No, as I stated earlier, the law of conservation of energy prohibits such tricks. You cannot get more power out of a system than what you put into it, regardless how you manipulate that power. Changing the rpm does not alter the horsepower. Thinking otherwise is what leads people into believing they can create perpetual motion machines, or free energy motor/generators.
 
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