ForumElectric: Electrical forum, Electrical engineering, electrician, power plant, energetics, wires

brainfarth · Joined: 15 Jul 2007 Posts: 3

I remember making a speed controller for a motor back in high school that consisted of a single winding of wire around something. Then an arm in the loop would run back and forth along the winding to give greater or less resistance. I've tried to find information on the net about specific windings, wire size and voltages with no success. Does anyone know where I can find this information?

-Brainfarth

JRaef · Joined: 05 Aug 2006 Posts: 56 Location: California, USA

You are describing a "variable resistor", often called a Potentiometer or "Pot" for short. They are widely available, why do you want to make one? Your HS experiment was likely done to help you to understand the principals involved, but to make one like that could be very dangerous. The materials to do it right would be difficult to attain at the retail level. You would need some high resistance wire, NiCh most likely, and an insulator to wrap it around, something to insulate the wraps from touching each other, then a conductive device of some sort for the slide assembly.
Here is what an old fashioned one looks like, it gives you an idea of the principal. In reality they make then round so that the "slide" has less distance to travel and the entire thing can be a lot smaller.

Here is what the insides of a Pot look like, you can see that the principal behind it is the same.

brainfarth · Joined: 15 Jul 2007 Posts: 3

I dont see how it could be dangerous since my voltage range is between 12v 10amps to 0. I have fabricated a turning jig for welding with a 12volt dc motor turning it. Unless you can think of a cheaper alternative from maybe radio shack. As I recall, the windings on the pot were coated and tightly packed together. And we sanded the contact side with fine sand paper to make contact with the armature.

JRaef · Joined: 05 Aug 2006 Posts: 56 Location: California, USA

You hadn't said it was 12VDC in the beginning. yes, that would not be as dangerous.