Simple Circuit Question

[mummydude]

Hi and thanks to you all!

I have an old game that I am trying to fix.

I do have some electronic knowledge, but figured I'd ask you experts about this:

I've got a simple circuit..

One size 'D' battery. One very general and standard old electric motor (with permanent magnets inside...the kind you see in old games and in kids' science sets and such) The other item is a variable resistor..or rheostat..or a 2 pin connected potentiometer. This item is bad. I bought a 5k ohm one at Radio Shack and all I got was an on/off switch basically.

So my question is, with that simple circuit, what size/ohm potentiometer should I get in order to evenly change the speed of the motor?

Again, thanks!

 

[heathclf]

Pot

Well, my first suggestion would be to get a hold of an ohm meter, and see what the value of the original part was, that way, you know you're money.

Just by guess though, you want a 5 or 10 ohm, with many turns. That way it's very adjustable. More than likely you'll only use a few ohms, but with a 5 or 10, you know you have plenty, and with 5+ turns, you should be able to dial it in without a problem.

If you can't find one like that at radio shack (which wouldn't surprise me, a 10ohm pot is not a normal thing), then check out digikey.

Hope it works out for you.

 

[Willbe]

One size 'D' battery.
electric motor
a variable resistor
what size/ohm potentiometer
to evenly change the speed of the motor?

If you want to go down to zero speed the ends of the pot should be across the battery and the motor power is picked off the wiper.
To get reasonably linear control the current through the pot should be >5x the motor current out of the wiper.
If the motor has to start under load (as opposed to a fan, for example) this circuit may exhibit motor starting problems.

 

[mummydude]

Much Thanks to both of you

I'll go and check out digikey..

Wow, all the way down to 10 ohms..

That's why I thought I'd ask the experts..


Again, Thanks for your time and wisdom

 

[heathclf]

I just hope I didn't lead you astray. Again, not knowing the exact current draw you're expecting, that's my best guess, but I'd be surprised if I was off by much.