Slowing down a Motor

yaggy

Well-known member
Joined
Mar 23, 2008
Messages
5,402
Reaction score
189
Location
Pennsylvania
24VDC Motor, about 20RPM

I need it to run at about half that speed.
I'm thinking a 5Kohm potentiometer but I'm just not positive
that it's a viable solution. I want to do it right.
A pot would be the best component, as having the freedom
to tweak the speed is a big big plus.
 
Seems like a logical solution to me. It can be hard finding a correct motor for some of these old games.
 
Slowing motors down with resistors can be problematic. Heat generation is one issue, both generated by the resistor and within the motor. Lowering voltage is going to have a profound effect on the torque output of the motor, with the motor's physical load remaining the same, the windings will run hotter. Also the motors stall speed will be much lower, depending on the load, the motor may not be capable of turning the load with reduced torque output, or may fail to spin up, from a stop, under load.

Usually you can get away with resistors for very small changes in speed, but trying to half the speed will likely give you the troubles mentioned above. So much depends on the motor specs and the load it's running.

Really the best way to control motor speed would be a Pulse Width Modulated scheme. Actually PWM motor controllers aren't very complicated and are pretty easy to build, there's schematics available online for a build-your-own, kits you assemble yourself or pre-assembled controllers. Here's one example: http://www.electronickits.com/kit/complete/motor/ck1400.htm (note: I don't know this specific product or vendor, just an example plucked from a google search)

PWM controller is probably your best bet.


D
 
Do you have an idea of what kind of current it is pulling? A simple pot controled PWM circuit seems ideal for this. Use a power transistor that can handle your voltage/current with a 556 circuit and you are good to go.
 
thank you very much, i may end up with the PWM as a permafix, but for now i guess it won't hurt to at least try a pot, i'm just not sure what value it needs to be. these are for light-duty targets, nothing heavy.
 
the targets are moving way too fast on a game i have.
everything else checks out.
 
Your biggest issue with a pot will be the heat buildup. I would go with at least 50% derating on the power handling.

If you use an ammeter to see how much current the motor is pulling, you can figure out what the power and resistance you need for your pot.

If you need help figuring that out, post up the numbers and I can help you out.
 
I doubt that you'll get too far with a pot as others have mentioned. Maybe good for testing, but I think a pot would burn out eventually. Motor control is "one of the things I do". If you post up the voltage, unloaded current and stalled current I can help out. Oh. I see the voltage is 24V. Cool. What's the current when the shaft is disconnected? What's the current with the target attached and moving at full speed?
 
slowing a motor down with a variac or resistor will not only damage the pot or resistor , chances are you will cook the motor windings. a slow down is usually acheived by gear reduction
 
Back
Top Bottom