Peak horsepower?

Brad Buchanan · Feb 25, 2013

Greetings to all.

I was abusing my bod on my bowflex this morning and was looking at a shop vac in the room.

The label stated '6.5 peak hp'. The vac is a 120v. plug in.

A little quick math concluded that 6.5 hp should be in the neighborhood of 5320 watts.

I know that advertisers can engage in enhancing their product, called 'puffery' or the like but this seems like outright lying.

This seems to be the case for many power tools and the like, domestic or foreign.

How can they get away with this??

Brad

dr sportster · Feb 25, 2013

I got 4849 watts at 115 volts the thing would draw 42.1 amps. NO WAY the cord would sart melting. Got an Amprobe?

David G · Feb 25, 2013

Its got to be a derived value, cannot be actual HP

RayP(MI) · Feb 25, 2013

I would assume that they get that by blocking off the intake, and letting it suck away. Yeah, way too much power for a conventional 110v outlet/fusing!

I have an amp meter - now I can't wait till I get home to check this out on my shopvac.

Dean · Feb 25, 2013

Peak HP is calcualted at peak voltage (indeed, probably peak to peak) rather than RMS voltage.

It is a true measurement but a rather meaningless one.

Dean

guido · Feb 25, 2013

Hello Brad Buchanan.

Your vacuum rated at (PEAK) 6.5 horses
should draw 4849 Watts at 120V?... NO WAY!!!
It probably meens that while starting will draw that much. Staring a motor will take 3 to 6 times its rated running amps, even if it is for a split second. May be that is were the unrealistic number comes from! Get an amprobe reading and you'll know the REAL numbers. How can they state that much H.P? I agree with you!
CRAZY!!!
Guido.

David G · Feb 25, 2013

Ray, it actually draws maximum amps at full flow and minimum when plugged off.

Ted in NE-OH · Feb 25, 2013

The government sued the small engine companies a while back for their lying about their horsespower ratings and now they are rated differently.

Dusty MI · Feb 25, 2013

Peak horsepower is the amount of power a motor is putting out just before it stalls.
The horsepower that we are used to is the amount of power that a motor can put out continually without harming it.

Dusty

Bob M · Feb 25, 2013

Is the "6.5 peak HP" claim a lie? Technically no. But is it deceptive - absolutely yes! Here's the deal:

The peak HP rating is calculated using the peak watts drawn the instant the switch is closed. In this case, 6.5 HP works out to about 4,850 watts. This is about 41 amps at 120 volts.

But this condition exists for less than only half a cycle (1/120th of a second) after the switch is closed. And a 15 amp household outlet can provide a half cycle surge like this without tripping the breaker.

Now as the motor accelerates the amps, watts and thus HP rapidly drop off. In less than a second the wattage has dropped to around 1,800 (15 amps) or about 2.4 HP. And if you take into account motor efficiency the actual MECHANICAL horsepower delivered at the motor shaft is probably less than 2 HP.

----

Another point: The motor draws this 6-1/2 HP only the instant after the switch is closed. But since the motor shaft is stationary when the switch closes, the mechanical HP developed the instant the switch is closed is actually ZERO(!).

Gotta love sales hype!

Peak horsepower?

Brad Buchanan

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dr sportster

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David G

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RayP(MI)

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Dean

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guido

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David G

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Ted in NE-OH

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Dusty MI

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Bob M

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