is there any protection needed for relay?

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Forum Name: Relays
Forum Discription: Relay Diagrams, SPDT Relays, SPST Relays, DPDT Relays, Latching Relays, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=37140
Printed Date: May 13, 2025 at 11:38 AM

Topic: is there any protection needed for relay?

Posted By: friscodanco
Subject: is there any protection needed for relay?
Date Posted: August 10, 2004 at 6:11 PM

I wired together a fuel pump kill switch using a couple of relays which I have connected to 12v from the car. Besides a diode, is there any other protection needed for the relays? Do I have to worry about the relays overheating, controlling current, etc... ?

Replies:

Posted By: Installerny99
Date Posted: August 12, 2004 at 8:36 PM

no need to worry about the relay over heating, its always a good idea to have your power supply fused if some thing were to go wrong it would blow. but on that same note it depends on how yuor relay is wired. is it normally closed or open?

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InstallerNY99

Posted By: hotwaterwizard
Date Posted: September 03, 2004 at 12:39 AM

What about the EMF field that the relay coil produces as the field colapses?

I recommend a Diode Reverse Biased as a Ground path to protect your electronic device connected to the same power source.

If you want to see what I am talking about try this little experiment.

As you know 12vdc will not shock you.

Touch both sides of the Battery post and nothing happens.

(CAUTION THIS WILL GIVE YOU A SMALL JOLT)

Now hold both of the stripped ends of the wires to the Relay coil in each of your hands making sure you are touching the wires touch them to the battery posts for a second and remove them while still touching the wires.

This is why they connect a Diode across a relay in circuits like this one. posted_image

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John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !

Posted By: SPOTTYJ
Date Posted: September 03, 2004 at 8:24 AM

Hotwaterwizard:

Excellent post! posted_image

Question, I will be installing a wiring harness with a relay soon.

https://ewylie.com/jeep/auxfuse.htm

How do I attach the diode to the relay? What I mean is the relay has posts and the diode I am looking at has bare ends.

https://www.radioshack.com/product.asp?catalog%5Fname=CTLG&category%5Fname=CTLG%5F011%5F002%5F006%5F000&product%5fid=276%2D1661

Do I solder the diode leads to the relay, or do I splice the diode leads into the wiring going into the coil/

Thoughts?

Posted By: hotwaterwizard
Date Posted: September 04, 2004 at 2:03 AM

Just hook it in across the Bare wires that go to the relay coil. It does not have to be right at the Relay.

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John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !