Back EMF Protection

[shane23]

Hi guys, I was hoping you could help me with a query regarding using diodes to protect against back EMF in relay circuits. I am using a IMO TY4 12v delay on timer to delay my intruder alarm autodialler from triggering for approx. 20s. The alarm manual states a diode must be connected across the coil , but it doesn't give any values. I would be very grateful for any advice.
Thank you, Shane

 

[Hero999]

It's not very critical, just use the 1N4001 and make sure it's connected in reverse with the power to the coil, anode to - and cathode to +.

 

[crutschow]

Just about any diode or rectifier will work.