I have a few single phase AC motors laying around that my grandpa scrounged from dryers or something. I figured I'd make a wet tumbler with one but I was curious about speed control.

 

I can gear the RPM down to approximately where I want it with pulleys but it would be nice to be able to fine tune the speed, which would in turn allow me to use different size drums for different sized batches and stuff.

 

Can I just put a rheostat/pot/whatever inline to dial down the voltage? Or am I asking to ruin my motor?

 

The motor is a capcitor start, does that make a difference?

I don't think a rheostat on an ac motor would work unless the motor was designed for multiple speeds. Otherwise it'll overheat from lack of cooling.

 

Just check that the motors are single phase and multiple speed. Otherwise look up vfds.

 

I did a fair amount of reading about this before I built mine. But I went the DC motor route. Find a free treadmill on cl and you're more than half way there.

 

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maybe heavyopp will chime in, he makes a bunch of these.

 

Personally, I dont see the reason for speed control - I dont think the speed is really that important ( as long as it isnt going so fast that centrifugal force keeps the materials in the same spot....which I would imagine would be pretty friggin' fast ! )

Unfortunately I can't check much of anything on this motor I have in-hand, it's a GE motor but I guess it's too old for the part number to come up in any searches. In fact the wiring labeling is such gibberish that I'm lucky the old cord was clipped instead of disconnected or I'd have no idea what the terminals mean. The other motors are scattered in other houses so I can't examine.

 

I'm aware of frequency drives but I'd probably try to find a DC motor before going down that path.

 

I guess the comment on speed is a good point. I was trying to hit 30RPM exactly (I think that's what the thumbler runs) but that's probably not critical.

If you use a shaded pole motor you can vary speed with a rheostat.

Capacitor start or run motors can only be changed with a speed tap if they have one.

In short, most single phase motors aren't amenable to changing their speed.   It is doable, but a common dryer motor isn't going to be capable.

 

If you have 3 phase motors, you can use a Variable Frequency drive that runs off 120v.  

 

You're better off just adjusting the speed on what you want to turn with belts and pulleys.  

 

If you have steppers or servos that's a whole different thing.  You need a controller and driver for those.

 

I might have a highly geared motor laying around the shop...we use a bunch of low RPM (7 to 15RPM) motors that have an AC speed control.

You need a DC motor like others have said, from a treadmill

 

You can set your RPM from the pulleys -- Realistically what size drum are you going to use?

 

6" and 8" but most likely you'll just use a 6" because the cost of 8" fittings is a little crazy

 

4" pipe won't have enough room inside to actually clean anything

 

I forget the exact RPM but the difference between 6" and 8" isn't much -- 8" being slower -- something like 72 rpm for 6" and 55 for 8" 

 

Both clean fine 

 

I do have cast iron pulleys with 1/2" bore sized for a 1725 rpm motor if you need -- Whatever I paid for them is what can have them for

 

I bought them in bulk to save but don't expect to build any more tumblers

It's possible to vary the speed of an AC motor with a rheostat.  What actually happens is the motor no longer runs at the "synchronous" speed matched to the 60 cycles-per-second electric that's powering them.   Lower the available current (with a rheostat) and the motor will begin to slip or fall behind it's synchronous speed.   This is common in AC fans. 

 

But it's terribly inefficient and causes the motors to run hotter than designed.  

 

VFD's are expensive.  I'd go with a belt an pulley.

Thanks, all. It looks like I'll be in the ballpark with a 6" drive pulley. Then I'll leave all those other cans of worms firmly closed.