What is the true HP

Is there a way to tell true HP from the below info.

Thanks


115 VAC / 60 Hz / 2 HP, 3450 RPM Motor
4600 RPM Cutter Head Speed
Start-Up Amps = 16.0 / No Load Amps = 7.0
Power Cord Type: 16 Gauge / 62” Long
Power Plug Type: 3-Prong / Grounded
Features Overload Protection & Lock-On Switch

About 840 watts, no load, so somewhere around ONE horsepower. depending on the efficiency (power factor).

Thanks Jim can you give me the math break down of how to figure this out for future reference?

I've known that with Sears tools you always cut the stated tool HP in half or just read the build plate on the motor. This is the 8" Harbor Freight Jointer. I was curious about it. On other forums it seem some people have had good luck with it. As much as I like Grizzly a 72" jointer is to long for my shop. Sometimes bigger isn't always better.The older model 66" one would have fit much better. Sunhill is the only one I know of with a jointer that is 66" long now. The Harbor Freight Jointer is 52" long & has the old style fence that is hooked to the end of the in-feed table & this works ok, I have become accustom to a center mounted fence.

Bart, it's roughly the voltage (120) times the amperage (7), divided by 746, which would equal 1.126 HP, but that's if the motor is 100% efficient (and it's not).

Here's something I found at http://www.elec-toolbox.com/Formulas/Motor/mtrform.htm:

Bart Leetch said:

Thanks Jim can you give me the math break down of how to figure this out for future reference?

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Bart,
Vaughn covered it pretty well.

746 Watts equals one horsepower - not accounting for any power loss due to bearing friction, induction losses, etc. Most induction motors are around 70% efficient, if I recall correctly (Been many years since my E&M courses), so the 1.12 hp Vaughn and I cited could be as low as ¾ hp.

The 2 hp rating on the plate would be the 'locked rotor' rating, or the fictional horsepower developed just before the motor melts.

Jim DeLaney said:

...the fictional horsepower developed just before the motor melts.

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Very eloquently put, Jim.

Royall Clark said:

That was one of the things that turned me off to sears tools years ago..... The started rating their machines at peak hp or the amps drawn at start up. Fooled a lot of beginners buying there first TS or what have you. I do find a lot of other makers getting on the same wagon now too

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Royall this is the same when it comes to amplifiers. The only real measurement of power is watts measured in RMS (root mean squared) but that is a low number but real, if you look at hi fi's at a furniture store and the likes Walmart for one, you find on non branded goods they put peak music power or just watts on their own which then is totally meaningless especially when the figure is huge like 100's and yet its a tiny device and the total power consumption is nothing.

Rob Keeble said:

Royall this is the same when it comes to amplifiers. The only real measurement of power is watts measured in RMS (root mean squared) but that is a low number but real, if you look at hi fi's at a furniture store and the likes Walmart for one, you find on non branded goods they put peak music power or just watts on their own which then is totally meaningless especially when the figure is huge like 100's and yet its a tiny device and the total power consumption is nothing.

Click to expand...

Good analogy! Andin the case of amplifier watts, more and better are completely independent terms that don't necessarily coincide.

Re: Sears, not all their stuff is rated by max developed HP anymore. Many of their newer machines state the same HP the motor plate does....now whether or not you believe the info stated on plate is another matter!