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Relays and Protection Diodes

Printed From: the12volt.com
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=146155
Printed Date: October 17, 2021 at 4:16 PM


Topic: Relays and Protection Diodes

Posted By: niksfish
Subject: Relays and Protection Diodes
Date Posted: April 23, 2020 at 12:00 AM

Hi, how are you doing?

I'm making this post just to learn more. I want to use a relay in my motorcycle, and I'm not sure if I should use a diode in anti-parallel for spike protection. The solution is easy, in case of doubt I should use one. But... most automotive relays don't have a built in diode, only special ones. Why is that?

The idea is to use a diode in anti-parallel with the coil of the relay, to protect the electronic circuit from spikes (mainly transistors and chips), like this image:

posted_image



Replies:

Posted By: niksfish
Date Posted: April 23, 2020 at 12:17 AM
In case you were wondering, my motorcycle is a Honda NSR 150 RR from 1998. The original wiring doesn't use a relay, and I want to add two of them for the headlights, so I don't have a drop in voltage.

In case that you want to know, Daniel Stern explained all of it in deatil in his website. I already measured my instalation and I have a 2v voltage drop in the wiring and switches of both low and high beams, so I need it. Daniel didn't mention anything about using diodes for protection.

This would be my circuit:

posted_image
The thing that I want to protect the most is the CDI unit. That is, the computer of the bike. As you can see, it is in parallel, not in series with the coil. So I guess it won't affect it. But, I can't find any info about it.

A guy in another forum told me that the only part affected would be the switches. So, by using a diode, the life of the original switches is increased.

What do you think?




Posted By: eguru
Date Posted: April 24, 2020 at 7:25 PM
If you are serious about protecting the CDI from spikes when the relay is de-energized, don't use garden variety rectifiers (like 1N4000 series).
Use Schottky diodes (like 1N5819).




Posted By: niksfish
Date Posted: April 26, 2020 at 4:39 PM
eguru] wrote:

If you are serious about protecting the CDI from spikes when the relay is de-energized, don't use garden variety rectifiers (like 1N4000 series).
Use Schottky diodes (like 1N5819).
Why is that? I saw a lot of people use the 1N4000 series for that purpose

BTW I found the answers:

https://www.autoshop101.com/forms/hweb2.pdf

This pdf explains the basics in relays. There are two comonly used ways to add protection to the circuit on the relay: the diode method and the resistor method. A lot of relays don't have any protection because the computer itself has the protection.

So, resistor is what for example, my mom's car has. It has a few cons, but anyway it's used in practice.




Posted By: eguru
Date Posted: April 26, 2020 at 7:47 PM
The use of 1N4000 diodes is fine for wired-or logic in order to prevent backfeeds.
The 1N4000 diodes can't respond quickly enough to suppress spikes that can damage your electronics.




Posted By: Ween
Date Posted: April 26, 2020 at 9:27 PM
Some info on relay coil suppression
https://www.te.com/commerce/DocumentDelivery/DDEController?Action=srchrtrv&DocNm=13C3311_AppNote&DocType=CS&DocLang=EN




Posted By: jonas2
Date Posted: October 09, 2020 at 4:48 PM
niksfish wrote:

Hi, how are you doing?

I'm making this post just to learn more. I want to use a relay in my motorcycle, and I'm not sure if I should use a diode in anti-parallel for spike protection. The solution is easy, in case of doubt I should use one. But... most automotive relays don't have a built in diode, only special ones. Why is that?
Bosch makes automotive relays with both diodes and resistors. This might help you make a choice, though very long after the fact....:oops:

https://www.boschautoparts.com/en/auto/relays/mini-relays

Sorry if I might be misunderstanding your goal, but that link is pretty good for choosing a possibly appropriate one.





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