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Help figuring out electric motors Answered

I'm trying to decipher the mystical language of electric motors and need some help.

I was at one of my favorite stores yesterday, a place called 'Industrial Liquidators' here in San Diego, and I was looking at their vast supply of electric motors. Big ones, small ones, battery operated ones, flat one, all in latest styles and fashionable colors. I know of plenty of uses for these things but I have no idea what it is I'm looking at. I would like to make my own rock polishing tumbler, so I'd like a motor with a bit or power and a slow rotation, but how can I figure out how strong and fast a motor is?

Maybe I'm starting at the wrong place. I must admit that I know next to nothing about electrical stuff. Pretty much the only thing I know about electrical equipment is that it only works when you plug it into a socket.

So that being what it is, can anyone direct me to a website that explains how to read these motor labels? Ya know the ones that say how many ohms, volts, amps etc.

Thanks for any help.



7 years ago

A fractional HP AC motor is all you need.

The pic shows how to slow it to your needs.


1031 rock tumbler.jpg

7 years ago

In AC motors the rpm is determined by the voltage times the frequency all divided by the number of poles.

Many people use washing machine motors, which you can usually get for free. Use your basic belt and pulley ratio formula to arrive at whatever speed you desire.

DC motor rpm is dependent on voltage level supply.

In either regard, be aware of how the motor was meant to be cooled! Most motors if slowed down will overheat and burn up, eventually.

If you look at the amperage rating on the motor tag, be sure to stay under that amperage level. If you load too many stones in the tumbler the motor will draw whatever amps it needs to function (turn the rotor). The amperage will continue to rise to infinity or until the windings burn up. So, be sure to use appropriate size overload protection as determined by the full load amp (F.L.A.) on the motor tag.

Use a basic "clamp" type ammeter to take readings while using the home made tumbler to actually see how many amps the system is requiring of your motor in order to function.

I am an old agate tumbler from the great lakes area and I share your enthusiasm for the beauty hidden within many rocks. Good luck with your project.

Most rock tumbling is accomplished with fractional size motors (those under 1 hp)

The speed of the tumbler is also dependent on the diameter of the tumbling tub.


10 years ago

Im using a motor from an old Montgomery Ward dryer for just such a project. Im not sure of the rpm's or such, but so far so good.


10 years ago

. For AC motors, the main specs to look at are:
  • Volts - usually 110(120), 220(240), or 440(480). 110 and 220 are usually single phase and 440 is usually 3-phase.
  • Amps - commonly given as Full Load Amps (FLA)
  • RPM - commonly 1200 or 1800, but can be just about any multiple of 60 (or 50 outside the US)
  • Frame - the physical size and shape of the housing and mounting flanges
. You should be able to find more info at any motor manufacturer's (eg, Baldor) web site.