Help me understand diodes and capaciters in motor control circuits.

Hi everyone. Sorry if this has been covered many times but I’m having trouble understanding the purpose of and how to use capaciters and diodes in motor control curcuits. Specifically in the attached circuit, what would be needed and why. It is a 24v dc H bridge circuit with relays driving this motor (link below)

http://www.grainger.com/product/DAYTON-DC-Gearmotor-4UHD9?s_pp=false&picUrl=//static.grainger.com/rp/s/is/image/Grainger/2L011_AW99?smthumb

Again sorry, my electrical knowledge is very weak. Many thanks in advance!

I'm having trouble understanding the purpose of and how to use capaciters and diodes in motor control curcuits.

In the case of that circuit I can't see the need for a capacitor and the only place I would put a diode is across the relay coil to prevent high voltage spikes or back EMF from disrupting the circuit that drives the relay coil.

Freewheel diodes are used when the current is one direction (such as in the arms of an H-bridge), capacitors to decouple the supply (reduce the voltage spikes which can trash power semiconductors when they are driving heavily inductive loads).

You could add 4 diodes to that relay circuit, but relay contacts aren't so sensitive to high voltages as MOSFETs - a simple snubber RC across the motor is probably easiest.

The relay contacts are not the real problem, but the relay coil is. This is where the freewheeling diode should be placed to avoid damage to the control circuitry.

Didn't antbody notice the misconnection of the relay? You need to swap Either A1 & B1 OR A2 & B2 (not both) as right now as drawn you have a direct short. Other than that I agree with the above advice.

R

rdfeil: Didn't antbody notice the misconnection of the relay? You need to swap Either A1 & B1 OR A2 & B2 (not both) as right now as drawn you have a direct short. Other than that I agree with the above advice.

R

Well spotted +1