loading

Slow down a DC motor?

Here is another basic electronics question for all of you: What is the easiest way to slow down the RPM of a small DC motor?

Much appreciated!


sort by: active | newest | oldest
lawrences167 months ago

I've got a 1.5v DC motor that I'd like to slow down. I'm not sure how to slow it down and use a larger battery. I'm good with a soldering stick just need a little help.

Reduce the drive volts using a voltage regulator like an LM317.

Steve
Laral steveastrouk10 months ago

But this just varies the voltage like the divider. The PWM solution suggested is the best way to do it.

steveastrouk Laral10 months ago

You don't understand. Reducing the voltage is exactly what you need to do. Using a regulator gives you effectively a zero output resistance supply, so the motor runs extremely well regulated, even down to very low speeds, where PWM is often not very good. There are plenty of good reasons to choose PWM, but they aren't "Easy" as the OP wanted.

Laral steveastrouk10 months ago

Well regulated? It isn't me who doesn't understand. Operating any motor at lower voltages than it is designed for reduces torque as has been pointed out already, and causes the windings to overheat. PWM maintains almost constant torque even at reduced speeds because the full voltage is being applied in bursts.

steveastrouk Laral10 months ago

Torque is a function only of current in a DC motor, not of applied voltage, it is an amateur mistake to believe that voltage controls torque.

Overheating is NOT caused by running the motor at lower voltages, its caused by excessive current in the armature which in turn is caused by taking more torque than the motor is designed to provide from it. Since V=E+IR, where V is motor terminal voltage and E is the back EMF and I is the motor current and R is the armature resistance, as E falls (you slow the motor down by applying a mechanical load, I increases and the armature losses increase.

Available torque goes DOWN with increasing speed. Available power from a DC motor is maximum at the rated speed. Available torque is maximum at zero speed.

PWM is nothing magic. A regulated supply with effectively zero output resistance works JUST as well as a PWM system, only for larger motors it isn't very practical.

Get some good books on electric machines and read them.

The only thing I can conclude is that, if you have to rudely insult the intelligence of me or anyone else, in order to 'win' an argument, you've already lost the argument. Any point you made after that, whether it has any merit or not, mostly NOT, is invalid because you have lost all credibility at this point. Intelligent, knowledgeable adults make their point WITHOUT acting like trolls, and with logical explanations of the FACTS. They back up those facts with references to source material. They don't make the 'amateur mistake', to coin a phrase, of reading, but not understanding, a few articles they found on the net and then mixing and matching buzz words and ideas, while being rude and insulting, in a futile attempt to bolster their own ego, and "prove" their "point". That's all I will say. Next time I will just flag it as 'not nice' spam.

Bootz421 year ago

Funny I came upon this old thread... I am attempting to slow down a small rotating motor for a mobile. I hooked up a potentiometer but it slowed the motor down over a 3º-5º turn. Is there a certain potentiometer to use where I can get at least a 180º turn from 0volt to the 1.5v max? Or if I don't care about varying the speed how do I know what ohm resistor I could put in the circuit to slow the motor down by 25%, 50% or 75%?

Bootz421 year ago

Funny I came upon this old thread... I am attempting to slow down a small rotating motor for a mobile. I hooked up a potentiometer but it slowed the motor down over a 3º-5º turn. Is there a certain potentiometer to use where I can get at least a 180º turn from 0volt to the 1.5v max? Or if I don't care about varying the speed how do I know what ohm resistor I could put in the circuit to slow the motor down by 25%, 50% or 75%?

Jayefuu6 years ago
Simplest way:<br /> Wire up a potential divider (google it) with a variable resistor as one of the resistors. Attach the DC motor across the potential divider and then as you change the resistance of the variable resistor (also known as a potentiometer) the voltage across the motor will change, slowing it down or speeding it up.<br /> <br /> Harder but better:<br /> Use PWM (pulse width modulation) to send pulses to the motor, it will appear to run slower but will just be turning on and off quickly. To make it run slower you vary the ratio of off to on so it's off for slightly longer compare to on. http://www.discovercircuits.com/DJ-Circuits/simplepwm2.htm Here is a tutorial on how to use PWM to vary the speed of a motor using a 555 timer IC. 555 timers are quite cheap and should be no more than $1.<br />
Hey I have a question, why does my potentiometer only work as an on off switch? I'm doing the same except for a small black globe that makes it look like you have stars on your walls.
brandegor (author)  Jayefuu6 years ago
I like your idea of the potential divider because it allows variable speed, which would be way cool. Now I just have to sort out how to do it and/or try the other suggestions before selecting best answer.

The 555 is out of the realm for this project, and I want to keep it small so I'm not sure about a pulley or gear, but experimenting is fun.

Thanks - I'll be back.
lemonie6 years ago
Put some load on it.
What do you want to do?
Run something slower with the same power - gears / pulleys.
Just run slower - less Volts

L
 Couldn't you also just add some more resistance so that you don't have to fool around with gears and the math behind them.
Yes, but we don't really know what they want (yet). Resistance comes under "load" (physical) or "less volts" (electrical).

L
brandegor (author)  lemonie6 years ago
I should have been more specific about what I want, for sure! I'm making (or trying to make) a silly little gift - a lighted die (one dice) that will rotate much slower than the dollar store fan I swiped the motor from. As I said, I kind of need simplicity since I'm not terribly skilled at electronics. Thanks, everybody.
How about a pulley? Make or find a large-ish wheel, and mount the die on that. Connect the outer of the wheel to the motor pinion with an elastic band.

L
and resistors!
Adding resistance is always a bad idea, because the regulation of the motor gets completely screwed -it'll vary in speed much more as the load varies.

PWM is nice, and the best way to go really - I'd recommend the Fan controller ICs you can get like the Micrel MIC502 - add a single transistor to get a really nice PWM stage.

For simplicity though, the voltage reg is hard to beat.

Steve