How do I connect a light dimmer circuit to a DC motor?

[dfgsdfg]

I found a light dimmer switch with a slide potentiometer on it.... and I want to use it to control the speed of a dc motor... all the circuit has is 2 wires... 1 from the ground of the transistor and the other on the switch... now how do i connect the power plus the motor? I tried connecting 1 wire of the circuit to one leg of the motor, then the other leg of the motor to the power, then the power to the other circuit wire.. if that makes any sense... basically like you would attach a switch to a potentiometer...

i really suck at electronics, can anyone help?

[EdisonRex]

Unless you like smoke and fire with your light show, don't try it that way.

First of all, a light dimmer is an AC device, and high voltage as well. Those slide dimmers work by clipping parts off of the AC sine wave, but the voltage stays at line voltage. Not being sure what DC voltage your motor wants, or how big it is, I am still quite sure that a DC motor will not spin in any direction under 60 (or 50) cycle AC. It'll make a real loud buzz, before smoke starts coming out of it.

What you need to control a DC motor is, unsurprisingly, a DC motor control. Depending on the size of the DC motor, you can either buy an RC motor speed control or build a fairly simple one. I think the LM298 motor driver does a good job too and is pretty cheap. Determining the size of a DC motor usually involves reading the label on the side of the motor, although not all DC motors have nameplates. Size/diameter of the shaft sometimes helps. Pictures help too.

Hope this helps (and saves your motor).

[JovianPyx]

Well, a proper DC motor control circuit (basically a controllable current source) is the best way to accurately and repeatably control a DC motor.

However, I think that for a noncritical application you might be able to get away with using an AC lamp dimmer - but I think there would be crappy properties. In the process, you would also abuse a transformer.

So take the lamp dimmer output and run it through a transformer (such as a 12 volt transformer) that has rectifier diodes and a big filter cap at the output. The output then becomes DC assuming the cap is big enough. Our hypothetical DC power supply would probably have a range of 0 to 15 or so volts.

Basically, this is a very crappy variable DC supply. Did I mention it is crappy? Part of the crappiness will manifest in the transformer getting warm. If it's big enough (enough amperes) then it won't get as hot and might be tolerable. The transformer may also buzz depending on the dimmer setting and the construction of the transformer.

Choosing a transformer will largely be guesswork.

It's a crappy idea, but it might work.

[blue hell]

[JovianPyx]

Yeah, I've heard of pulses being used with constant DC for model trains. The power supply pulses when the train goes slow (creep) because a low constant voltage won't provide sufficient energy to start it from a dead stop. As the train speeds up, the voltage is more of a constant voltage with pulses on top of the DC level. Each pulse goes from wherever the DC level happens to be to the rail.

Bottom line is that there are several good ways to control a DC motor, my point was that using an AC dimmer as I described would be a variable DC supply that could drive a DC motor, but the method is crappy for more than one reason.

[EdisonRex]