capacitors in parallel with motors

is it needed to put a capacitor in parallel with the motors in order to prevent unwanted noise back to the controls or is this only in ac circuits? I heard someone mention this topic but i am confused

Well just starting off Ive done a thread on this and I think pretty overwhelmingly the answer was that its illegal to use capacitors directly with the motors, This is for FIRST right? That being said, If not I recommend (Its a pretty good summery and covers exactly what you are looking for). Here this says it perfectly.

Bypass capacitors help filter the electrical noise out of your circuits. They do this by removing the alternating currents caused by ripple voltage. Most digital circuits have at least a couple of bypass capacitors. A good rule of thumb is to add one bypass capacitor for every integrated circuit on your board. A good default value for a bypass cap is 0.1uF. Higher frequencies require lower valued capacitors.

Regardless of the legal standing, it is not necessary.

The Victor speed controllers are adequately protected from any sort of feedback the motors could produce, assuming they do not already have filters in place within the can (I suspect most do). Adding your own filters will not yeild any benifit.

Andy A.

Adding filter caps will almost certainly cause problems. If you add a big enough cap it will probably make your controls sluggish…

I think that in order to be large enough to make sluggishness a cause for concern, the cap would be HUGE. I don’t really want to spend the time on the math, but I suspect that it would have to be far larger than most readily available caps.

Now that I think about it, yes, yes it would have to be. Still, not a great idea.

A capacitor would only cause a sluggish response if it were in series with the motor. In that case, the motor would at times see a reduced voltage as the capacitor charges, and at other times see a higher voltage then the victor is outputting as the capacitor discharges. It would have to be a very large capacitor to be noticible, which means that it would probably be of the electrolytic kind. And we all know how much they like reverse current when you try to drive backward! They are used on large motors, such as in Electric cars. Because the starting current on a large motor is so high, it can draw the supply voltage very low and give poor performance. A large capacitor (or several smaller ones) can be used in series with the motor to keep the voltage from dropping to severely under acceleration.

If the capacitor were in parallel, bridging the positive and negative terminal, the function would be to filter out all the noise that a motor produces. They are common on DC motors. Typically, they are very small, on the order of 1uf or smaller, and of a type that isn’t harmed by reverse current. My guess is that most of the motors we use already have filters installed in side of the motor can. In any case, it doesn’t matter because the Victors are not going to mind either way.

-Andy A.

I do not think that there are any motors that have a cap already built in, but i could always be wrong, and the VICTOR is a motor controller designed specifically to deal with providing power to a motor almost completely isolated from the rest of the cicuitry, that said i’m pretty sure that whatever company manufactures them has engineers who have thought of the ways that they could best reduce electrical noise caused problems when the VICTOR is used correctly

Capacitors are not only not needed but also illegal. The Speed controllers have built in noise suprression to prevent any nasties from ending up back at the RC.
The effect of haniing a big cap across the motor just compounds the start current and run responses. Don’t forget that a capacitor looks like a dead short when discharged. When a capacitor is charged to some voltage and the supply voltage is reversed, the charge must be removed before the new voltage will charge the cap. This precludes using electrolytic capacitors which can’t have a polarty reversal without spectacular self destruction. Some motors (in the far distant past) have had small caps installed, internally, across the brush assembly to try and quench brush noise. Currently supplied motors do not have any of these internal components to my knowledge.