HP/Amps

My new edge sander was delivered today, Grizzly 6x80. In the version of the manual on the website they list it as 1.5 HP 16A/8A. But in the manual that came with it and on the nameplate on the motor it says 1.5 HP 20A/10A.
Now I should probably run a dedicated 220V line to it regardless, but for the time being I thought I was going to be fine on my 20A 110V circuit. I just think it's very weird because if it's really drawing 20A then why are they calling it 1.5 HP? 20A should give 2 HP. I was under the impression that they couldn't lie about the amps, but HP ratings were more fudge-able. It's a 1725 RPM motor, and looking at the motors Grizzly has in their catalog the 1.5 HP 1725RPM model draws 17A, whereas the 3450RPM draws 15.6. So I suppose that can explain a bit of why the number is higher than I expect, but not all of it. Have they just found a new source of really inefficient motors?
I wired it for 110 and it ran fine with no belt on it, but that doesn't really mean anything. I need to build a stand for it and get it up on that before I start bolting on all the tables and whatnot so it's going to be a while before I can test it under load.
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On Sep 11, 12:45 pm, snipped-for-privacy@yahoo.com wrote:

756 watts per HP @ 100% efficiency. Most electrical motors run around 90% or so. Sooooo let's call it 1000 watfs per HP 12.5 amps at 120 V will get you your horse-and-a-half. 6.25 amps at 240 V
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Robatoy wrote:

I think that's a bit optimistic. Baldor's "premium efficiency" 3HP motor gives 85% efficiency and 96% power factor.
Their more typical 3HP motor gives 78% efficiency and 85% power factor for a total efficiency of around 66%.
Chris
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I allocated 1000 watts for 1 HP. Close enough for giggles.
Hell, I have 6.5 HP vacuum which draws 10A!! How is THAT for efficiency, eh? <G>
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Robatoy wrote:

With a K&N, that bad boy might do _10HP_! <G>
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Not meaning to nit-pick but that is 746W=1HP
wrote:

756 watts per HP @ 100% efficiency. Most electrical motors run around 90% or so. Sooooo let's call it 1000 watfs per HP 12.5 amps at 120 V will get you your horse-and-a-half. 6.25 amps at 240 V
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That should be fairly close to typical. The 3HP motor in my cabinet saw claims to pull 14 amps at 240v
Tom Veatch Wichita, KS USA
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er... isn't the starting current somewhat higher than the running current - (Back EMF and such?)
What's your fuse rating? If it's a slo-blo spec that would usually indicate that a startup surge is expected and it will draw considerably more juice at switch-on than when performing. In this case you can't relate ampage to horses.
Is this what we're talking abiut, or have I missed the point? (Sorry, I'm not really familiar with 110 v stuff 'cos we don't have it here in domestics.)
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snipped-for-privacy@yahoo.com wrote:

Horsepower ratings aren't always all that precise, and motor efficiency can lead to higher max draw.
I suspect it's simply an inefficient motor. Also, it's likely that the motor will hardly ever actually draw the rated amount. Most shop tools (except for dust collectors) aren't running anywhere near full load.
Chris
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But marketing departments making specs sound as good as they can is right up there with death and taxes. The Sawstop contractor saw actually says 1-3/4 HP which I've never seen anything say.

I found this link which says the minimum efficiency for a NEMA "Design B" should be 79%. I don't know what a Design B is.
http://www.engineeringtoolbox.com/electrical-motor-efficiency-d_655.html
Even at 75%, 20A at 115V is well over 2 HP. Or going the other way, 1.5 HP at 75% is 13A, which is exactly what my table saw says.

The manual actually has a page where it says the machine will draw 10A on 220V under normal use. Which doesn't make any sense, but that's what it says.
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Maybe they stamped the motor with a ball-park reading, with a clamp on ampmeter it will only draw 8A when on full load... I like grizzly tools, they've been good to me. Lots of luck

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Before adding special circuits I would first plug it in to what you have and try it out during actual use.
On a 15 amp circuit I run a radio, lighting, 12 amp dust collector and a 15 amp router, no problem at all unless the compressor comes on. typically your heaviest amp draw is going to be when you start the machine, usually you don't work on the machine until it comes up to speed and the amp demand goes down.
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Watts=volts x amps. 1HP t6Watts. Double the voltage then half the amps. It is 240 volts and 120volts in residential. 110volts and 220 volts went the way of the Doh-doh bird long ago. Using old numbers with newer equipment will do funny things to your mathematical calculations compared to real world measurements.
Stu

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That's definitely what I'm doing, and I built the base for it and got it setup. Seems to run fine. The one set of 4 ft lights on the same circuit barely flicker when it starts up. It starts up fine with the spindle sander next to it running too, but that's just rated at 2.5 amps. Still, if the manual is to be believed that should have brought upon the end of the world. The dehumidifier is also on that circuit, but we're getting to the end of the season where it's needed. Before you know it I will be freezing my ass off in there again.

I can say that a TS and a space heater on a 20 amp circuit is a no go :) Well, it's a go.. to the panel to reset the breaker.
Anyway, I raised the topic not so much in regards to what I need to do to make it work, I can deal with that. It was more that I have definitely heard on the wreck that you can't trust the hp rating, but the amps were more reliable because that gets tested by UL. And I just wonder if the marketing departments haven't figured that out and now you can't trust anything.
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Might I also add that there isa 20" fan blowing on my circuit also.

A space heater tends to use a constant higher amp so they will tend to use most of the amps that they are rated at.. Electric motors tend to use more amps getting up to speed than they do during actual usage.
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snipped-for-privacy@yahoo.com wrote:

UL tests that the amps don't ever go higher than the nameplate. They don't test whether they go as high as the nameplate.
I've heard a few stories of drill/jigsaw/etc manufacturers padding the amperage rating to make the tool seem more powerful. No evidence that it actually happened, but it sounds like something someone would do...
Chris
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