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Discussion Starter #1
Sorry to talk techie but...

I finally wired in my headlight relays today. I didn't use the Eastern Beaver setup because my setup (dash, DRL, spots, aux powerlet, USB chargers, voltmeter, battery tether switch, separate fuses for each headlight/beam) is a little complicated so I put it all onto a PCB mounted in a little sealed box under the front side cowling.

But, I notice a very small flash in both indicators (on the instrument panel) when I switch between hi and lo beam. My relays switch off and on when toggling between beams.

I'm a teensy bit worried I should have put diodes back across the relays to dissipate the back EMF when the relay coil collapses. Does anyone know if the Eastern Beaver relays, or other, use diodes for that purpose?
 

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Some automotive relays have diodes already fitted inside, others have resistors across the coil.

An internet search on the relay part number should help determine what yours have - otherwise a check with an ohmmeter might tell you (no guarantee on that).

The problem with diodes is that it requires the installer to wire the relay according to the pin numbering correctly. The relays effectively become polarity conscious.

Personally, I'd add the diode. I don't know how effective a resistor is at suppressing the back EMF.
 

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Discussion Starter #3
Yeah my relay's don't have diodes inbuilt - I checked because I've done the PCB layout differently (current flow direction through the coil) between hi and lo beam as it's pretty tight in the small space I allowed myself.

I'm not looking forward to removing the relay box to add diodes, but I think I'm going to have to. I don't like seeing other things being affected...
 

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Scott, I just found this: Relays

Scroll down and read the bit on suppression and how the diode can affect relay speed. I learned a bit tonight - and I am/was an electronics tech.
 

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There has not been a single report of a problem being created by the induced current from the relays throwing. Adding a diode can result in shorter relay contact life according to Jim Davis at Eastern Beaver. I think you have a solution in search of a problem. Every time time this is discussed, a lot of theory is put forth but there is no practical problem in using ordinary relays to power the headlights.
 

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Discussion Starter #6 (Edited)
Scott, I just found this: Relays
Indeed an interesting read, regardless of whether or not I have a problem, thanks for that!

There has not been a single report of a problem being created by the induced current from the relays throwing. Adding a diode can result in shorter relay contact life according to Jim Davis at Eastern Beaver. I think you have a solution in search of a problem. Every time time this is discussed, a lot of theory is put forth but there is no practical problem in using ordinary relays to power the headlights.
The "read" above does indeed go into the "shorter relay life with a diode" and the reasons for. I'm not looking for trouble - or additional effort :) I was concerned about the flash from indicators on my instrument pod when either of my relays switches off. At this point I'll assume it's from the energy of the collapsing coil - the induced energy transferring over through all those wires running together in the left side switch harness. I'm just trying to prevent switch problems (and add features) rather than create different problems :)

I was wondering if this flash is seen by anyone else who uses relays for their lights. I've used beefy 40A relays because this circuit also powers my "accessory" circuit. I think Eastern Beaver uses 20A which of course is perfect for the intended use.
 

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Everybody using unmuffled headlight relays mounted near the turn signal wires will get a flash on the LED indicators when they change beams. It's the nature of the setup. When I had LED turn signal lights, they would flash too. Again, there is absolutely nothing to worry about. The induced current is much too small to hurt anything. There has not been a single report of a problem.
 

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Discussion Starter #8
Oh good - so I won't climb in and remove my relay box, and get all "cat scratched" up again - good news :)



And before anyone mentions it - the fuses and relays are very easy to get at to replace, but the box mounting, well...

 

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I wonder

Would a capacitor across the terminals allow the transient to go to ground? Probably less likely to present problems down the road than a series diode. A zener diode across the terminals would also clamp the voltage. Depending on the resistance of the coil, a series resistor would also help limit current.

Or you could just leave well enough alone. LED's can take a pretty high current transient, so long as the duration is short. The failure mode seems to be thermal.
 

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Much ado about nothing.
 
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