# My new "5.75HP" Shopvac

Discussion in 'General Electronics Chat' started by strantor, Dec 9, 2013.

1. ### strantor Thread Starter AAC Fanatic!

Oct 3, 2010
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I just bought this shopvac. It claims 5.75hp. Hmmm... Let's do some math. 5.75*746= 4300W. 4300W/120V= 36A. So this thing should only be able to work on a 40A breaker. But what 120V load is on a 40A breaker? And what does a 120V 40A outlet look like? The shopvac's cord plug has a regular 15A pinout. I'm thinking this thing is over rated by a factor of 4 at minimum. I couldn't get it to trip a 10A breaker no matter what I tried. Grossly false advertising.

Of course I'm ignoring the elephant in the room; There is the work "peak" there. So I get it, that's not constant running HP. But still, it obviously never "peaks" in any mode of operation or else the breaker would trip. So are they taking inrush current, multiply by (120V/746W), and calling that "peak HP?" That's a completely meaningless number!

Now, further damning this claim, are they talking input power or output power? I figured they were talking electrical HP (input power) but if they're talking mechanical output power, that's even worse. I'm going to plug this thing into my killawatt and see how much power it actually draws. When I search for "universal motor efficiency" I am seeing estimates between 55% and 70%. I'll call it 55%. We'll see how much output power this thing ACTUALLY has.

2. ### wayneh Expert

Sep 9, 2010
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Yeah, I think they make some calculation of power required to stop the rotation of all moving parts or something goofy like that. Totally irrelevant to the user.

It would be so easy to introduce some standard measure in this industry, like cfm at a specified vacuum level, but people already know more HP is good, so that's what we get.

3. ### inwo Well-Known Member

Nov 7, 2013
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Here's an honest report.

"Most manufacturers of garage vacuums and shop vacuums are marketing their vacuums as 4 to 5 Peak Horsepower (PHP). Lately GarageVac had no choice but to follow this trend."

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Jul 18, 2013
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If you want to measure the maximum current, run it without any hoses or tank on input or output for maximum current draw.
I think they base it on the RPM factor of around 20Krpm.
Max.

Last edited: Dec 9, 2013
5. ### mcgyvr AAC Fanatic!

Oct 15, 2009
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Says 11.6 Amps max on the specs..
and that link above states its calculated from the inrush..
and per UL 1017 the "horsepower" rating cannot be include in the products marking.

6. ### PackratKing Well-Known Member

Jul 13, 2008
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" Horsepower " aside, a vacuums; actual performance, is rated on CFM of free air that the little motor / impeller can move...

Suction from the business end, depends solely upon the amount of air it is blowing out the exhaust, amplified by the size of the orifice / hose / it is pulling that air through...

Granted, HP. plays a part in making the impeller go 'round, and dogging the suction, makes the motor work harder and draw more amps.

CFM is generated by the RPM's, distance between the impeller plates, and the number of fins between them...

Last edited: Dec 10, 2013
7. ### russ_hensel Distinguished Member

Jan 11, 2009
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Actually an ideal motor, no matter how large, draws 0 power at no load, if you want to measure power you need a load.

Jul 18, 2013
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This is why I suggested maximum load, in a motor driving an impeller fan/pump type load, the load will be maximum when the inlet and outlet are completely Unobstructed.
Max.

Last edited: Dec 10, 2013
9. ### #12 Expert

Nov 30, 2010
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True. Maximum power in a fan happens when the fan can get the most amount of air into the intake. You'd be surprised at how much a 3/4 inch tall entrance horn will increase the current draw. The "ultimate" vacuum is a function of the design of the fan blade, not so much the RPM. Certain fan blades are designed to "unload" under high differential pressures. The vernacular is that they "paddle" instead of, "scoop".

Lawn mower horsepower ratings recently got government scrutiny. Mine was rated at 6.5 "reserve powers". After applying the torque rating and the 3100 RPM speed to a math formula, I found out it had 2.75 horse powers. No significant change in 50 years.

10. ### THE_RB AAC Fanatic!

Feb 11, 2008
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This is a common problem in advertised specs! That is 5.75 AMERICAN horsepower.

America has very small horses;

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11. ### wayneh Expert

Sep 9, 2010
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But not in Texas, home of the world's larges horse, of course.

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12. ### strantor Thread Starter AAC Fanatic!

Oct 3, 2010
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Numbers are in, verified by killawatt and fluke. With the filter and all hoses removed, it draws 10.8A. With clean filter, no hoses, 10.6A. Clean filter with hoses, 10.3A. Filter clogged with sheetrock dust + hoses fitted, 7.9A.

So I'll call 10.3A the normal running current. That works out to 1.66 electrical HP. Now, factoring in the best estimate of universal motor efficiency (55%), the motor puts out 0.91HP (mechanical).

I didn't expect there to be such a drastic change in current draw between dirty and clean filter. This could be a good way to implement a "time to clean the filter" alarm.

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13. ### strantor Thread Starter AAC Fanatic!

Oct 3, 2010
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oh yeah, and inrush current was 25.9A with filter off and hoses removed. So even using their ridiculous method of calculating "HP" would only put this thing at 4.17HP. They must have brought the winding temp down to -20C with liquid nitrogen like it was said in the link.

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Jul 18, 2013
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This would require some kind of low current over time, as any time it draws in anything large at one time will cause the current to drop drastically.
Confirmed by the rpm rising considerably!
Max.

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15. ### wayneh Expert

Sep 9, 2010
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So they inflated the real number by ~6X.

That's flagrant and far beyond mere stretching of the truth. I wonder if there have been any lawsuits on this yet. Seems like a class action would be a big enough potential payout to attract some hungry lawyers.

16. ### wayneh Expert

Sep 9, 2010
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A ∆P monitor would probably be a better way to detect fouling. You could watch for peaks of ∆P - which I think will happen when the flow in the hose and nozzle is unrestricted. If the peaks reach a high enough sustained level, time to buy a new filter. (I clean mine with a hose.)

This would help sell filters, so I'm surprised you don't see this "feature" already.

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May 11, 2009
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19. ### GopherT AAC Fanatic!

Nov 23, 2012
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Interesting that the average age was as high as it was. Then I realized the report was from 1980 - the pre Viagara period.

Here is the monster referenced in two of the cases. No wand for their wand.

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20. ### t06afre AAC Fanatic!

May 11, 2009
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That is a 1930 model I think. This is how the dustette looked around 1980. I have been quite puzzled how they managed to end up in that awkward situation. But I think I understand more about how now

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