Motor Madness (or "When is a horsepower not a horsepower?")

[Roger Chandler]

David,

the motor on my 14" bandsaw [Tiawanese} went out, I replaced it with a baldor with identical spec............no comparrison......the baldor just has so much more torque and will cut through a piece of wood that the other motor that came with the saw would stall with............American made, baby...........gotta love it!

[Josh Bowman]

David, it comes down to Volts and amps in reality. Craftsman is famous for "peak HP" ratings. Here you have a little motor that produces 5 hp! Well it does, but not in the way we use it. The 5 hp is "break HP" or to say it differently, it's the max amps drawn as the shaft is slowed to a stop (sometime before it burns out). So that creates a unit of measure that is not very useful. But Amp draw or better yet wattage can be used for comparison. These units should give you the average draw of energy as the motor is used. You may also have a defective motor. I'd take it back and swap for a different one and see if it gets better. Or better yet, take it back and re install the old one and never look back.

[David DeCristoforo]

"...take it back and re install the old one..."

Done. The old motor is back in the machine and the new one is going to gather some dust whilst I ponder it's fate... I wonder about the "peak" ratings thing though. I understand how this would apply if I were comparing say a 2HP router to a 2HP table saw motor. But these two motors are pretty much identical so I did not think that would apply. FWIW, the voltage and amperage specs on both are the same.

[phil harold]

Pretty simple explanation ..........

Not as simple as that

A Shetland pony can pull twice its weight, while a draft horse can only pull half its weight...

[Craig Matheny]

Made in China could explain a lot lack of quality control for one. There are only so many parts to a motor that can be modified. You checked the caps and swapped them motor to motor so they should be good, my understanding is the power and the torque is created by the magnets and the windings if the wingdings are done with cheaper material or the unit got wound on Friday afternoon then that can be the problem i simple twist in the winding can break the wire. I believe the best advise was return the unit and get a new one see if it iany better if it is not then they are not built internally the same and by looking inside you can not tell.

Good Luck

[Paul Williams]

My bet is on thinner copper wire in the windings of the new motor. Less copper equals more resistance so the same amp reading for two motors with vastly different efficiencies. You could stick a meter across the windings of the two motors and see if the resistance of the mew motor is higher than that of the old.

[Jeff Bratt]

There is a lot of garbage around when it comes to HP ratings - the numbers on routers and shop vacs are all lies. (My webpage documenting all these shenanigans.) However, the ratings on induction motors are generally pretty reliable. And you said the motor nameplate ratings for voltage and amperage were identical. It could be that the old one was just rated conservatively.

The math is actually not fuzzy at all: HP = torque (lb-ft) x speed (RPM) / 5252. I guess it's possible that the motors were different designs (internally), which can affect the torque curves. But that would be unusual for general purpose motors that are used in WW machines. Is there any more info about the different motors from the nameplates? Do you know the manufacturers of the two motors?