12v relay kickback?

Thread Starter


Joined Oct 17, 2011
Hi everyone,

It's my first time working with a 12v automotive relay. Do i need to concern about any kickback from the coil?



Joined Jun 19, 2012
It depends on what you are using to drive the relay, if you are driving it with a semiconductor, then yes, you should include a diode across the coil, in reverse bias connection.
This diode will act as a current path when the switch opens, it should be rated for the coil current X 2 at least. Without the diode, the voltage will rise until *something* provides a current path for the inductive spike, usually that *something* will be your semiconductor blowing up.


Joined Jul 31, 2013
Relay coil suppression is a more complex issue than is commonly supposed. A simple diode is said to be the worse solution as it slows the relay release, encouraging arcing, and can shorten it's operational life. If the relay is controlled by another relay or a simple switch don't bother. The low impedance of am automobile supply line will soak up any back emf. Of course if it is to be switched by a solid state device, in spite of the drawbacks, the reverse bias diode is a common solution.
There are several informative articles on the net about it. Goggle "relay coil suppression" or similar. here's one: http://www.te.com/commerce/Document...v&DocNm=13C3264_AppNote&DocType=CS&DocLang=EN

Thread Starter


Joined Oct 17, 2011
Thank you all for the insightful information. Can you guys let me know the right protection?

1. Relay will be activated by connecting the coil directly to a 12v source.
2. Relay will be activated by a 5v->transistor->12v.

Thanks again.


Joined Jul 18, 2013
Probably not needed if it is not being switched, i.e. Energized all the time.
Although presumably you will remove power at some point?
If so there will still be a spike at power down.