Harbor freight "3 HP" motor

Dec 16, 2006 13 Replies
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I have a particular vacuum pump that I may rewire for single phase. Right now it has a big old 3phase 2 HP motor. Very big for the HP on the nameplate.



Harbor Freight sells 56 frame motors that they somewhat vaguely refer to "use with compressors rated for 3 hp that were previously rated for



5 HP".

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Is that really a "3 HP" motor that can put out output comparable to that big old "2 HP" 3 phase motor. Note that I want to replace a 2 HP rated motor with a "3 HP" rated motor, ie one more nominal HP is added.



The FLA rating on the HF motor (15A) is similar to FLA rating on the real 3 HP Baldor motor that I have on my compressor (16 A):



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but the HF motor is a lot smaller than Baldor.



i
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G

These are probably rated for "compressor duty cycle". If you go into the store you'll see "100% duty cycle" motors that are a hell of a lot bigger for the same amperage/HP.

I noticed this a couple of weeks ago, as the local store got in an assload of motors and I was wondering why the different sizes.

-gc

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T

I have been informed that 'one HP hour', draws '746 watthours'.

746 divided by 110 volts would be 6.78 amps, which an electrician also told me (6.8 amps per HP, rule of thumb), is what a one HP motor draws on 110v. I have noticed that all these 'cheapo' motors on sale any more, especially the 1 HP or larger, don't come near matching the amperage draw necessary to generate the power they claim. A real 3HP motor, on on 110v, would draw 20.4 amps. Which in turn would require a dedicated circuit, #10 wire, and a limited run. Startup draw would be considerable more. Especially against a compressor that hadn't vented and was starting against the full remaining pressure. Amperage draw on 220volts, for a 3 HP motor, would be half or 10.2 amps, each leg. Still, startup would again be higher. "They don't make them like they used to", sure applies to 'cheapo' electrical motors...and their false ratings. One can understand why good motors are expensive, yet worthwhile. Worse yet, the watchdogs don't seem to give a darn. If you have noticed #12 wire is a touch smaller than it was 20 years ago.
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D

Should work OK for other than continuous duty, subject to caveats re anything from Harbor Freight. You surely know better than to expect Baldor quality from HF, but you probably don't need Baldor quality for your application. Pick yer pony, take yer ride.

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S

Iggy,

It seems like I recall you having a VFD. Why not stay with the existing

3 phase motor?

I bought a HF 20" drill press. Immediately noticed about the motor are the bearings. I'm kiind of surprised the motor is doing so well, compared to the amount of noise the bearings make. Sooner or later I'll have to replace it with a real motor.

Steve

Ignoramus22371 wrote:

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C

When a friend needed a NEMA 56C 1/2 hp motor for his vacuum pump I searched the web and found

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Definitely had the best prices at the time, so we crossed our fingers and ordered one. Came quickly, fit up okay, runs quiet and cool, is definitely bigger than the old one and kind of looks "clunky" if that is possible for a motor :-), but has been running several hours a month for 1.5 years evacuating auto a/c systems in his shop. Just a thought if the hf motor isn't exactly the frame configuration you need.

-- Regards, Carl Ijames carl dott ijames aat verizon dott net (remove nospm or make the obvious changes before replying)

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S

Thanks Carl. I'll check them out.

Steve

Carl Ijames wrote:

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I

OK I found something reasonable.

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i
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----- Losing faith in humanity, one person at a time. ----

Huh ?!! Losing faith in humanity, one Govt at a time !!! Why blame the victims of sell outs !

SF service factor is worse number than heat rise . Heat rise is how hot you can run it . 40C means it will burn up quick .

HF motors are as bad as any today .... Since theres no quality , you buy on price . A HF 2 pole motor :

1 HP = true 1/3hp , 3HP = 1HP , but draws like a 2 hp !! ( gets hot ) big heavy core and big copper windings keep heat down . China motors have small core , large air gap , etc etc . Hand tools are balanced by drilling holes in rotor ! Bad idea , it increases "reluctance" , lowers the coupling to the field , raises heat ...

HF band saw has a bad motor , wont pull ..

Gene Cash wrote:

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L

No. "Heat rise" is how hot it will run above ambient. 40C is a pretty normal figure for continuous duty motors.

And you ran these on a dyno to back up your observations, right?

That's a pretty common method of balancing intermittent-duty motors. The Chinese didn't invent it.

LLoyd

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G

Eh, just killfile this wanker and be done with it.

-gc

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L

On 18 Dec 2006 19:44:39 -0500, with neither quill nor qualm, Gene Cash quickly quoth:

Yes, everyone, please!

-- Losing faith in humanity, one person at a time.

Gene, I adore your sig. May I steal it? Thanks!

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U

I killfied the D F last week and glad I did. Steve

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