Any ideas on how ot implement a snubber circuit on a DC motor that is controlled by two relays (so the direction can be reversed)?

(Circuit Attached)

Thank you.

 

Back to back zener diodes just above the operating voltage of the motor. I'd also put caps across the diodes and the motor itself.

This will take care of higher voltage transients, what exactly are you trying to filter out?

 

Thank you for that. Any chance you could sketch out what you wrote in a small schematic? I just want to be sure when I put it all together.

I am trying to reduce the EMI noise from the motors (http://forum.allaboutcircuits.com/showthread.php?p=271920#post271920)

Thank you again.

 

Back to back simply means connecting the two anodes (or cathodes) of the zener diodes together then attaching the remaining loose leads across the motor.

 

What is the effect from doing this... what do the back to back zener diodes do?

 

It helps to limit the amplitude of spikes/noise created by the motor. With babck to back zeners it will be limited to the zener voltage of the reverse biased diode plus the forward voltage if the forward biased diode. eg. 12V zener will limit the voltage to 12V plus 0.7V of the forward biased diode.

 

I'd also suggest putting a capacitor across the motor terminals, it might help catch a little of the hash that DC motors often create.

Anything between 0.01uF - 1 uF would be fine so long as it's rated at or preferrably somewhere above the operating voltage of the motor.

In all this I've forgotten to ask - are you having a serious noise problem, something minor or some unexpected operation?

 

With regards to capacitor voltages it is a good rule of thumb to go for a voltage double what you are using for a supply.

I think this thread is linked to his EMI on USB thread.