# Inductive "kickback" Problem

#### Coach

Joined Jan 12, 2007
2
Hello,

I'm an avid reader but this is my first post. I am building an electromagnetic brake assembly on a motorcycle. The machining is going well but I have run into a circuit problem that I need help with, please.

The brake is 24v powered through a 12 to 24 step-up. After doing research in the archives and reading the FAQ I learned that the electromagnet may create inductive "kickbacks" that might damage my switching equipment. First question: Am I on track, is this an issue of concern?

So then I read about "commutating diodes" in a inductor commutating circuit at http://www.allaboutcircuits.com/vol_3/chpt_3/8.html. I'm not an electrical engineer but I found the the material very informative in a general sort of way.

But it led me to question 2: What type and size of commutating diode do I need and then where do I go to buy one?

In the attached rough circuit diagram there are two batteries with a cut-out relay assure one battery is always available for starting the engine.

Coach

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#### Ron H

Joined Apr 14, 2005
7,014
71 watts at 24 volts is about 3 amps. You can use a 1N5400 as the diode. Connect the anode to the negative brake terminal, and the cathode to the positive brake terminal.
One place you can get them is Jameco Electronics. It looks like you may have to buy at least 10 pieces, but they're cheap.

#### Coach

Joined Jan 12, 2007
2
Boy that was fast. Thank you.

Where in the circuit diagram would you suggest placement of the diode?

Sincerely,
Coach

#### Ron H

Joined Apr 14, 2005
7,014
Boy that was fast. Thank you.

Where in the circuit diagram would you suggest placement of the diode?

Sincerely,
Coach
I answered that, but maybe it didn't make sense to you. Does the brake have more than two terminals? What's the deal on the dotted line to the battery on the left?