# How to calculate smoothing capacitor value?

I'm using two DC motors on my project, and i need to filter the noise that they generate, most of people recommend to use one capacitor on the V terminal, and one on the GND, but how do i calculate the capacitance of it?

Motor specs:

Gear ratio: 100:1
Free-run speed @ 6V: 320 rpm
Free-run current @ 6V: 80 mA
Stall current @ 6V: 1600 mA
Stall torque @ 6V: 30 oz·in

Just follow the instructions in this tutorial: Pololu - 9. Dealing with Motor Noise

Basically you don't calculate it because you do not know how much interference you have and you don't know how much smoothing you need. These things are never calculated professionally you use what normally works and if it dosen't you go for larger values until it does.

Ok Thanks

And if you do want to calculate you use dV/dT = I/C
(or put another way I.dt = C.dV).

One thing you may need to consider is the ripple current rating, exceeding this can
cause overheating/degrading of the capacitor. Low ESR capacitors are always best
for this reason.

Hi,
Try 0.1uF capacitors across each of the motor terminals, keep motor leads short, try and route them way from other wires.

Tom......

MarkT:
And if you do want to calculate you use dV/dT = I/C
(or put another way I.dt = C.dV).

But that only calculates the effect not how much effect you need.