DPRG mailing list archives: [DPRG] Motor Filter Capacitors

Thu Mar 22 10:25:43 CDT 2007

Eric,

How about this for a practical approach. (Theoretical discussion aside.)

Start with a 100nF or so ceramic capacitor across the motor and watch
the voltage with your scope. If the voltage spikes are too high,
increase the capacitance (within reason) until it looks manageable. It
may be better to put the capacitors from each motor pole to ground,
rather than across the poles, which will just pass the noise around the
motor.

The best solution is to use a separate battery pack for the logic and
motors, and optocouple the signals to the motor H-Bridges. I tend to do
this on anything that requires an electromechanical device.

Good Luck,

Rick

-----Original Message-----
From: dprglist-bounces at dprg.org [mailto:dprglist-bounces at dprg.org] On
Behalf Of Eric Sumner
Sent: Tuesday, March 20, 2007 2:18 PM
To: Dprglist at Dprg.Org
Subject: [DPRG] Motor Filter Capacitors

In the robot I am building for SMU, the servo controller crashes
whenever the motor has an instantaneous load (hard start, hits a bump,
etc).  I don't have any sort of filter capacitor across the motor leads.
I have several to choose from, how can I determine what the proper value
is?

  -- Eric
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