DC Motor help

[versimilitude]

hi there,

I'm looking for some help with a small project i'm building. My electronics knowledge is basic (but growing!) and my DC motor knowledge is non-existant so i'm hoping someone might be able to help!

I am looking to use a 12V DC Motor (perhaps this one **broken link removed**) running off a 12V supply. It only has to run in one direction and at a constant speed. It will be triggered by a potentiometer so that once it reaches a certain resistance the motor will start.

Am i being far too simplistic to think that a potential divider circuit feeding into a transistor of some form would be enough to do this? Or does it require more circuitry and protection than that?

Any help would be most grateful! Thanks!

 

[stevez]

Others who might respond have far more expertise in this area than I but here's a couple of thoughts.

A. There is likely to be some inductive spike from the motor that might damage a transistor. A diode or diodes, appropriately connected, can help to solve the problem.

B. A transistor that will handle the required current ( I did not look at the motor) may require more current from the pot than it can supply.

C. An op amp configured as a comparator - or a comparator might be a good way to accomplish the triggering - taking the load off the pot and it will be on or off - not between. The output might drive a transistor so that it's full on or off - easing the demands on the transistor heat sink. A small transistor might operate a relay that has the current handling needed. The relay can also produce inductive spikes so protection is still required.

I have some old Radio Shack books that have lots of circuits for driving small DC motors and I am sure that such simple circuits are published elsewhere. The hard work is done for you so you should not have to struggle.

Hope this gives you a start.

 

[Styx]

bushed DC machine with a need to spin at a fixed speed & direction with a "pot" used to turn it on/off (not for speed control)

simple solution is

battery +
    ||------------
Motor stator     Diode
    ||------------
   FET
    ||
battery -

Then drive the FET from a comparator (powered from the same 12V) with the +ve input going to a voltage-divider (with some pos-feedback) and the -ve coming from the POT

you "could" feed the POT directly to the gate of the FET but you would be dependent on the gate-threshold level AND also run the risk of sitting the FET in its active region

 

[versimilitude]

Thanks for the replies guys. That should give me a start. I can give it a go now and see how I get on!