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11-26-2011, 12:50 AM   #1
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## Understanding electrical specs...

I just bought a new (biggest name brand top of the line) chainsaw chain grinder that was advertised as having a:"Single phase, 115V-AC, 60 HZ, 3 amp, 285/300 watt, 3400 RPM direct-drive motor, 0.38 horsepower." but when I took the guard off, the motor had a sticker that reads: "4.2A 200W 115V 60Hz 3400rpm motor."

Did I get a much weaker motor than advertised???

11-26-2011, 01:25 AM   #2
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This is where knowing your electrial math helps....

Watts is voltage times current.....

So, if it's a 3A motor.....@ 120Vac, then that would be 360 Watts

Hmmmmm....that does not match......

Ok.....lets look at the 4.2A @ 115Vac...so, 4.2 x 115 = 483 watts.......

Oh boy....not very close to 200w......'

Did you get a weaker motor? Based on the above #s', I would say you got a Chinese motor....Weaker? Well..........maybe it was lost in translation....

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 11-26-2011, 10:09 AM #3 Civil Engineer   Join Date: Mar 2009 Location: Boston Posts: 5,637 Rewards Points: 4,854 When computing the HP of a motor, you have to account for efficiency and startup issues. In your case, the original specs state that the motor draws 3A, which could mean that at full load, the motor draws 3*120 = 360 watts. This is not the actual available power, which is always going to be less due to efficiency losses, so the actual available power may be close to 285/300 watts as shown. The numbers on the actual motor don't make a lot of sense. However, when sharpening a chainsaw blade, you don't need a lot of power, you need a tool which has a sharp file of the proper size, accurate adjustments for the various angles, and a good grip on the bar. Too much power will ruin the blade quickly. I sharpen mine using a clamp on, hand drawn system that works very nicely.

 11-26-2011, 10:33 AM #4 Newbie   Join Date: Nov 2011 Posts: 2 Rewards Points: 10 That's why I asked, I ran the math on an online calculator and the numbers didn't make sense to me (they still don't). The grinder is made in Italy, but the motor in Guangdong... I just got the grinder and haven't run it yet (snow on the ground gas in the small shop I have). So I was just setting it up and wondering as to the difference in advertising/reality? Thanks. I guess it comes down to whether I want to believe the Wattage figures or the amperage @ voltage figures.

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