Protecting sensitive electronics and modules from a collapsing relay coil.
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Tuned
Joined: Feb 2025
Posts: 294
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From: Brighton, IL
Protecting sensitive electronics and modules from a collapsing relay coil.
I just recently post edited an article on my running board lights over on the 99-03 diesel section.
i added this link to that thread and wanted to include it elsewhere as I believe it might help others with newer vehicle that have a VSM, BCM, etc. and are thinking about doing something similar to what I did. I am not trying to preach to the choir, but if you’re unaware this article should be interesting.
One of the better articles I’ve found on relays
In my other article over on the Diesel 99-03 section I mentioned using the dome light to energize the relay coil for running board lights.
But, as I learned while planning out my project, when a relay coil collapses it can cause a severe and high voltage spike of high voltage that can reverse direction harming sensitive electronics upstream. I was not about to find out knowing that the dome light is controlled by the trucks VSM.
When you open the above Link, drop down quite a ways to Configuration (on the left margin) - and then scroll down to “Relay with diode across the coil” (also in the left margin) and there is a full explanation of the how, why, and what to do……as shown in my photo below the Link.
I hope it proves to be an insightful read
Big Horn
i added this link to that thread and wanted to include it elsewhere as I believe it might help others with newer vehicle that have a VSM, BCM, etc. and are thinking about doing something similar to what I did. I am not trying to preach to the choir, but if you’re unaware this article should be interesting.
One of the better articles I’ve found on relays
In my other article over on the Diesel 99-03 section I mentioned using the dome light to energize the relay coil for running board lights.
But, as I learned while planning out my project, when a relay coil collapses it can cause a severe and high voltage spike of high voltage that can reverse direction harming sensitive electronics upstream. I was not about to find out knowing that the dome light is controlled by the trucks VSM.
When you open the above Link, drop down quite a ways to Configuration (on the left margin) - and then scroll down to “Relay with diode across the coil” (also in the left margin) and there is a full explanation of the how, why, and what to do……as shown in my photo below the Link.
I hope it proves to be an insightful read
Big Horn
Cargo Master
Joined: Apr 2003
Posts: 3,476
Likes: 224
From: Frequently frozen MN
I just did a google on this and there are lots of articles discussing using a diode across the coil to suppress damaging voltage. I knew that from electronics classes, but I've never dpne it, so I don't know what would be a good diode to use. There are other protection items such as a metal oxide varistor (MOV) that will limit the voltage between power and ground. Zeners do the same thing, but they're kid of slow from what I understand.
hj
hj
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bald59
1957 - 1960 F100 & Larger F-Series Trucks
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Sep 5, 2023 08:49 AM
