> Date: Wed, 24 Jan 2018 00:59:48 +0000 (UTC)
> Working on a belt sander project using a 130V PMDC motor off a treadmill. The 
> control board got crushed so I need a simple cheap adjustable speed control. 
> Anyone have something laying around they want to get rid of? Need 115Vac 
> input. Thanks Dach.

Is this permanent, or temporary/intermittent use?

I’d put a full-wave bridge rectifier as close to the motor as possible, and 
just call it a 120 VAC motor. Put a standard plug on it. Then you could plug it 
in to a wide variety of AC power control devices, as Lee suggests.

Then, it sounds like a job for a good old-fashioned variac transformer. They 
aren’t cheap brand new, but you can sometimes find them cheap in surplus or ham 
radio estate sales.

If you don’t intend this to be permanent, you could put your variac in a box 
with a volt meter and a couple standard AC outlets. It can be handy that way 
for so many things.

Lee’s ideas will still produce AC, and so would work fine for a universal 
(series-wound) motor, but probably not for a permanent magnet motor, which will 
just try to go forward and reverse at 60Hz and make a loud hum before it burns 

But if you rectify what goes into your PMDC motor, SCR dimmers should work 
well. Older drills used SCR phase control, but I think newer ones use PWM, 
which will probably make a better speed control than an SCR phase-control will 
— but it will still require rectification for a PM motor.

So, rectify that puppy, and lots more options become available!

:::: Jan Steinman, EcoReality Co-op ::::

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