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[DPRG] Motor noise caps

Subject: [DPRG] Motor noise caps
From: Ed Koffeman edk at kinetric.com
Date: Fri May 24 16:03:35 CDT 2002

Hi, Clay.

If the motor case is connected to a metal chassis, then it helps to go from each terminal to the case.

The main reason to have the caps is to suppress RF noise, when using radio control.

I wouldn't worry too much about it on a robot, unless you really notice some sensitive A to D conversion noise (but it'll much more
likely be coming from motor current variations, PWM etc.).  A 433 Mhz RF link probably wouldn't be affected, but could be.

Don't go too high on the capacitance value since that does tax the PWM drivers a bit (youll get current spikes), and smaller caps
actually have less impedance at high frequencies than physically larger ones (to simplify things).  A value of .01 ufd would be
typical.  Never use electrolytics, and of couse not polarized ones on reversing motors anyway.

Ed Koffeman


----- Original Message -----
>From: "Clay Timmons" <ctimmons at cadence.com>
To: <dprglist at dprg.org>
Sent: Friday, May 24, 2002 2:12 PM
Subject: [DPRG] Motor noise caps


>
>
> A question to my fellow robot builders.
>
> I've often seen a capacitor placed across motor terminals
> which is supposed to help suppress the high freqency noise
> coming from the sparky little motor brushes.  I'm looking
> for opinions on this...
>
>
> Which is better; a single cap across the motor terminals
> or two caps, one from each motor terminal to the motor case?
>
> What size caps should be used?
>
> Are such caps appropriate for motors being drvien with PWM?
>
> Do these caps really help?
>
>
> Regards,
>
> -Clay-
>
>
>
>
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