CANBus Source Triggered Relay - 2014+ Jeep Cherokee Forums
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post #1 of 18 (permalink) Old 05-11-2017, 08:49 AM Thread Starter
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CANBus Source Triggered Relay

Along with getting those KL shirts up on the store, the wife finally listed an item I have been making and selling to friends for some time.... I thought some of you may be interested.

These are to help eliminate relay chatter from tapping into a CANBus hot source (like your high beams hot wire). Running even low current LEDs directly from these sources can cause the lights to flicker and faults or diagnostic (lamp out) messages.

There is no magic here... I simply make these relay connectors with a small capacitor to smooth out the DC the relay coil sees and a diode to block coil decompression and isolate the CANBus.

We have used these on our JKU for years where we have some auxiliary lights that come on with our high beams and some others that come on when we go into reverse. We also have a bypass/manual trigger where you can use a switch for these lights as well.

We are also using one of these to activate our new Rigid lights that we just put on the KL when we hit the high beams.

...anyway, I just wanted to share these are available now in case they might help someone. You can see or order them HERE

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post #2 of 18 (permalink) Old 05-11-2017, 09:51 AM
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Ok... my curiosity is... piquée...

I'll be tapping into my high beam wire, to trigger a relay for some auxiliary lights, soon. This is the first time I hear of such a device, and also the first time I hear tapping into the high beam wire could cause... something...

Electronics semi-noob here so be gentle please, haha. What are potential problems of tapping into this wire ? In my case, I would only want to trigger a relay.

Thx...

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post #3 of 18 (permalink) Old 05-11-2017, 10:01 AM Thread Starter
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Ok... my curiosity is... piquée...

I'll be tapping into my high beam wire, to trigger a relay for some auxiliary lights, soon. This is the first time I hear of such a device, and also the first time I hear tapping into the high beam wire could cause... something...

Electronics semi-noob here so be gentle please, haha. What are potential problems of tapping into this wire ? In my case, I would only want to trigger a relay.

Thx...
The high beam is not run on a solid 12v source... it has a PWM (pulse width modulated) source. This is used by the computer to detect when lamps are out or damaged. There are only a few relays I have found that will stay activated when using this type of hot. Most will chatter (bounce on/off very fast) or buzz. Even though they buzz, some will stay activated enough to turn on what-ever you are running, but the relay will get hot and not last long.

Provided you find a relay that will stay activated, you are adding circuitry that changes how the computer views the lamp circuit. It may be okay, or it may throw a diagnostic message. In the case of JK fog lights I have seen the computer deactivate the circuit all together.

By adding the capacitor and diode to the relay's circuit we can isolate and protect the CANBus side while smoothing out the voltage the relay sees which stops the chatter.

It's not really any magic, and I even post a picture of how the circuit is made. I have just been asked so many times to make these I finally did. If you want to go "science fair project" and make your own I'm happy to help with that too.

Hopefully this helps, let me know if you are still confused.
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post #4 of 18 (permalink) Old 05-11-2017, 10:08 AM Thread Starter
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Also, the PWM is only active for the lights when the car is running... I have seen people test by just turning on the light while the engine is off and think they are okay and then as soon as they turn the engine on it the relay chatters and the lights flicker.

(This actually happened to me on our JKU when I first realized the need for this in 13').

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post #5 of 18 (permalink) Old 05-11-2017, 10:08 AM
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The high beam is not run on a solid 12v source... it has a PWM (pulse width modulated) source. This is used by the computer to detect when lamps are out or damaged. There are only a few relays I have found that will stay activated when using this type of hot. Most will chatter (bounce on/off very fast) or buzz. Even though they buzz, some will stay activated enough to turn on what-ever you are running, but the relay will get hot and not last long.

Provided you find a relay that will stay activated, you are adding circuitry that changes how the computer views the lamp circuit. It may be okay, or it may throw a diagnostic message. In the case of JK fog lights I have seen the computer deactivate the circuit all together.

By adding the capacitor and diode to the relay's circuit we can isolate and protect the CANBus side while smoothing out the voltage the relay sees which stops the chatter.

It's not really any magic, and I even post a picture of how the circuit is made. I have just been asked so many times to make these I finally did. If you want to go "science fair project" and make your own I'm happy to help with that too.

Hopefully this helps, let me know if you are still confused.
Got it... well, 65% of it, roughly

Ok... so in the KLs, the high beam circuit is used to activate the projector shutter motor (or coil most likely). I could be wrong but I wouldn't think it is monitored, because of this special application (activating a shutter, not feeding a light source).

Oh and I am a complete PWM / CANbus noob, so this is all interesting to me.

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Last edited by Mark_; 05-11-2017 at 10:11 AM. Reason: edited to add the word coil
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post #6 of 18 (permalink) Old 05-11-2017, 10:21 AM Thread Starter
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@Mark_

I don't know this for sure... but I think the diagnostics are much more simple than that. I think the system is just measuring the impedance. This is why adding more stuff can trigger messages or faults. I am aware some devices have additional circuitry in them to report more intelligent responses than "bad", but I don't know which ones or exactly how.

To be completely honest, it's these unknowns that prompted me to just use these anytime I am tapping into a source wire. It's my way of getting the signal and doing my best to leave the CANBus stuff alone.

Another full disclosure: If the system was measuring current it could still have issues with the added relay. This said, I have used dozens of these and never seen this. It has fixed all CANBus related flickers, chatters, buzzes, and messages to date.

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post #7 of 18 (permalink) Old 05-11-2017, 10:34 AM
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@Mark_

I don't know this for sure... but I think the diagnostics are much more simple than that. I think the system is just measuring the impedance. This is why adding more stuff can trigger messages or faults. I am aware some devices have additional circuitry in them to report more intelligent responses than "bad", but I don't know which ones or exactly how.

To be completely honest, it's these unknowns that prompted me to just use these anytime I am tapping into a source wire. It's my way of getting the signal and doing my best to leave the CANBus stuff alone.

Another full disclosure: If the system was measuring current it could still have issues with the added relay. This said, I have used dozens of these and never seen this. It has fixed all CANBus related flickers, chatters, buzzes, and messages to date.
Fair enough, and thanks for taking the time to explain.

I will tap into the high beam wire for the relay, as many other members here have done - with no known (to me) problems - to trigger a relay for added lights. I will put my ear to the relay and watch closely for any sign of... whatever abnormal. And if I notice anything, expect a call from me

Would you ship to Canada (yes of course I'd cover the extras) ?
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post #8 of 18 (permalink) Old 05-11-2017, 10:55 AM Thread Starter
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[SNIP]Would you ship to Canada (yes of course I'd cover the extras) ?
I'm happy to try... As I'm sure you know, it's tricky. I sold a set of wheel spacer/adapters here and they went to Canada. It became a rather troublesome ordeal for both me and the buyer. I'm also happy to help you make your own.... It's not like I'm getting rich off of these things. It's more about helping. I mean yes, we do make some money, but not really when I add the value of my time if you catch my drift...

.
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post #9 of 18 (permalink) Old 05-11-2017, 11:13 AM
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I'm happy to try... As I'm sure you know, it's tricky. I sold a set of wheel spacer/adapters here and they went to Canada. It became a rather troublesome ordeal for both me and the buyer. I'm also happy to help you make your own.... It's not like I'm getting rich off of these things. It's more about helping. I mean yes, we do make some money, but not really when I add the value of my time if you catch my drift....
Well that sucks (the wheel adapter situation).

I've thought about this before when members have shared ideas or designs on the forums ; instead of getting something made and shipped, doing it ourselves and sending a little... courtesy/royalty fee for the idea. Haven't done it yet but considered it when a member offered to make/sell front tow hooks for non TH KLs and I realized shipping those over here would be... costly... lol. Haven't commited to those yet though.

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post #10 of 18 (permalink) Old 05-11-2017, 11:15 AM Thread Starter
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@Mark_ The better option is just getting together somewhere and exploring/wheeling then it's just a hand-off! Seems like a good excuse for a road trip as any!
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