Led light turn on at specific Voltage

Diver300 said:

If the vehicle is detecting faults with 10 V and the lamps off, what current is flowing? Is there any digital signalling going on?

What is the voltage with and without the lamps connected?

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The 10v is the vehicles can bus. I'm not thrilled to find this out but it is what it is and I need a viable solution which is easy to implement.

I'm not aware of a mechanical relay that triggers at specific voltage or does one exist i can just use and wire in. Seems like the zener option is not viable without testing a dozen diodes and resistors all which I have to order to experiment with.

CANbus does not run at 10V. LIN bus runs at somewhere near 10 V, but it doesn't provide power. Just because a car has CAN or LIN or any other serial communication bus has nothing to do with how it controls the lights.

It doesn't appear to be a practical solution to have 10 V as the voltage level to turn a lamp off and 12 V to turn in on.

It is impossible to suggest a circuit without knowing exactly what it needed. If there is 10 V in when the lights are turned off but connected, the current that they take is important. If a circuit were to take too much or too little current, the car's electronics could regard the lamp as faulty.

How much current do the existing lights take when connected to the car and turned off? If you are measuring currents, you might as well measure the current when turned on.

65mA @ 12V when the lights are working. Didn't measure off.

This is not a normal car, the ECU operates in this manner, we can keep talking about it but it doesn't change the fact this is the way the vehicle operates. I'm not looking to debate this any longer. I'm not trying to be rude but if you are going to keep asking me the obvious than perhaps there is is futile. The facts do not change how this ECU CAN Bus operates and like you I was just as surprised it is 10V but that is not standard but this vehicle is not standard either. I also don't care about CAN bus errors for the lights. This custom setup is going to throw errors for other reasons so having lighting errors will be ignored and not impact anything.

So having said that, let's focus on a solution. I need a simple trigger mechanism to only pass 12v despite the constant 10v on the line.

Interesting discussion, and I'm tipping somewhere in here is the reason I can't use LED lamps on my caravan, tried it once and as soon as I turn on the Parkers (and van sidelights) the electric brakes lock on!
Gone back to good old glowing filaments.

djmixalot said:

The 10V is the computers can bus, it does not change the fact it is using 10v for its bus.

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CAN is an independent network it does NOT run on a power feed.

If you won't do the requested tests to diagnose the cause of the problem, there is no point continuing.

Another suggestion. As you are not taking advice so far given is to reverse enineer the original light to understand how they work.

Les.

djmixalot said:

if you are going to keep asking me the obvious than perhaps there is is futile.

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10 V when turned off is far from normal. Therefore the current that the lamps take in that state is far from obvious. It may not matter how much current the lamps take at 10 V, but we don't know if it does matter or not.

What is the current when the original lamps are connected and turned off?

These are vehicle tail lights. Some people will advise against changing them at all because of safety or local regulations.

I am just very worried that 10 V when off isn't correct. All other tail lights that I have come across are supposed to work at 10 V and meet their specified light output at that voltage. Many cars will see the voltage dip below 10 V at times, although I realise that with an EV there's no starter motor which is the main cause of voltage dips in an ICE car.

You need to take more measurements to find out how the car works with the original lights and tell us before the the situation become obvious to us.

djmixalot said:

I also don't care about CAN bus errors for the lights.

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Lights can't cause CAN bus errors. However electronic control units can see problems with lights, and information about those problems can be sent on a CAN bus.

The problem here is that if the car's control unit detects an error, it will probably behave differently. The control unit will almost certainly have some overload protection, and it applies 10 V when turned off for some reason.

If I suggest a circuit that takes 5 mA with the lamp turned off, and the control unit decides that 5 mA at 10 V is too much, then it might stop the lights from working after that. It could even be that 5 mA is too little current.

Tex260Z said:

Interesting discussion, and I'm tipping somewhere in here is the reason I can't use LED lamps on my caravan, tried it once and as soon as I turn on the Parkers (and van sidelights) the electric brakes lock on!
Gone back to good old glowing filaments.

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Could you tell me a bit more about that? Can you tell me what vehicle it is, and what brake controller you are using?

Did the LED lamps that you were using have the same LEDs for sidelights and brake lights, just lit more brightly for braking, or were they completely separate?

Are you in America? The relevance there is that American trailers have the same lamps for stop and turn.

Voltage trip relay :

https://www.pc-s.com/pdf/multitek-dc-voltage-trip-relay-m200.pdf (this is 24V, maybe they have 12 V buss
solutions).





Regards, Dana.

Diver300 said:

Could you tell me a bit more about that? Can you tell me what vehicle it is, and what brake controller you are using?

Did the LED lamps that you were using have the same LEDs for sidelights and brake lights, just lit more brightly for braking, or were they completely separate?

Are you in America? The relevance there is that American trailers have the same lamps for stop and turn.

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Mercedes W164 ML320CDI 4 Matic, only changed the Brake/Stop lamp bulbs, not the indicators or side/clearance lights.
Redarc electric brake controller.
We live in Melbourne Australia, did a trip to our property in Gippsland, about 3 hours, I actually forgot to turn the parking lights on which also turns the sidelights (on the side of the van) and the tail lights, going down, so no issue.

However, when we were leaving to return home I realised the parkers (which are also the daylight running lights on the Merc) were off when I was checking that everything was secure, so when I got back in the car i turned them on, went to pull away and the car wouldn't move. I soon realised the van brakes were full on, turned the electric brakes down to minimum (from about two and a half), and the car would move but brakes still dragging badly. After a lot of investigation I unplugged the van from the car and the problem went away, (not a real solution).
Eventually I got around to turning the car lights off, and bingo! problem solved.
Luckily we got home before dark, and the next day I swapped the lamps back and did a test, all good, put the LED stop & tail lamps back in, back to locked brakes.
I figure it must be something to do with a resistance measurement, but at 76 I really don't give a rats, pretty sure the glow plugs will see out the rest of my caravanning days.

Diver300 said:

What is the current when the original lamps are connected and turned off?

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More important still, what voltage is across the original lamps when they are off??
I'm pretty sure it will be less than "10V".

How about posting the ECU (BCM for lighting??) make, model and part number?

Tex260Z said:

Mercedes W164 ML320CDI 4 Matic, only changed the Brake/Stop lamp bulbs, not the indicators or side/clearance lights.
Redarc electric brake controller.
We live in Melbourne Australia, did a trip to our property in Gippsland, about 3 hours, I actually forgot to turn the parking lights on which also turns the sidelights (on the side of the van) and the tail lights, going down, so no issue.

However, when we were leaving to return home I realised the parkers (which are also the daylight running lights on the Merc) were off when I was checking that everything was secure, so when I got back in the car i turned them on, went to pull away and the car wouldn't move. I soon realised the van brakes were full on, turned the electric brakes down to minimum (from about two and a half), and the car would move but brakes still dragging badly. After a lot of investigation I unplugged the van from the car and the problem went away, (not a real solution).
Eventually I got around to turning the car lights off, and bingo! problem solved.
Luckily we got home before dark, and the next day I swapped the lamps back and did a test, all good, put the LED stop & tail lamps back in, back to locked brakes.
I figure it must be something to do with a resistance measurement, but at 76 I really don't give a rats, pretty sure the glow plugs will see out the rest of my caravanning days.

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Thanks for that. I guess that you have the Redarc controller brake input connected to the trailer brake light connection.

I've looked at the signal connection on the Redarc and it is a bit over-sensitive for some conditions, as you found. It only takes 0.7 V and a few microamps to turn on. That can be activated when it shouldn't be in a couple of ways.

1) If the trailer earth isn't very good, and there is a lot of current being taken by trailer lights, the point where the trailer brake lights connect to earth can get above 0.7 V. If that happens, and you have ordinary brake lights, the raised earth voltage could turn on the trailer braking.

2)With combined LED brake/tail lamps, the circuitry is powered from either the tail light connection or the brake light connection, usually with diodes. There is a sensing circuit that detects if the brake light connection is at a high voltage and makes the lights brighter. When the tail lights are on, there's nothing to make the brake light connection stay at a low voltage, and it's quite easy for leakage to make it go above 0.7V but still be low enough that the lamp stays on its lower brightness.

On your caravan, a resistor of 500 Ohms between the brake connection and ground would almost certainly reduce the voltage enough that you could use the LED lamps. It's either the car's trailer brake feed that has a sensing circuit or the LED lamps seeing if the brake light is on with a sensing circuit, which is feeding out a tiny current.

I recently had a similar challenge with the illuminated "Pony" in the front of the Ford Mustang Mach e GT. It's an EV with a LIN bus. Three wires to the pony labelled 12, 0 and LIN. There was no signal we could figure out or capture on the LIN bus to turn this on. I opened it up to find an odd diffuser (that's another story) but there was a small circuitboard to control the serial bus and switch the LEDs on/off.
All this to ask, are there 2-wires or 3-wires to the lamp and is there any circuitboard inside your light module or haven't you disassembled it enough to find a circuitboard.

Forget it, i'm moving on to my own solution to make this work, it is clear some in here are more concerned about making a point, than accepting the facts, and providing a solution.

I'll leave with this, I'm blown away with the attitdue by some who are so addamant to disprove something they don't comprehend or understand, simply because they have never seen it before so in their view it must not work that way. This kind of attitude would get your fired where I work, but hey each their own.

I hope in your own personal lives you learn to accept facts as they are, and help the next time someone provides them rather than trying to disprove them with your personal conjecture.

Happy New year to those who tried to help.

djmixalot said:

than accepting the facts,

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Facts only exist after verification by testing. Without tests they are assumptions.

Goodbye.

Tex260Z said:

Mercedes W164 ML320CDI 4 Matic, only changed the Brake/Stop lamp bulbs, not the indicators or side/clearance lights.
Redarc electric brake controller.
We live in Melbourne Australia, did a trip to our property in Gippsland, about 3 hours, I actually forgot to turn the parking lights on which also turns the sidelights (on the side of the van) and the tail lights, going down, so no issue.

However, when we were leaving to return home I realised the parkers (which are also the daylight running lights on the Merc) were off when I was checking that everything was secure, so when I got back in the car i turned them on, went to pull away and the car wouldn't move. I soon realised the van brakes were full on, turned the electric brakes down to minimum (from about two and a half), and the car would move but brakes still dragging badly. After a lot of investigation I unplugged the van from the car and the problem went away, (not a real solution).
Eventually I got around to turning the car lights off, and bingo! problem solved.
Luckily we got home before dark, and the next day I swapped the lamps back and did a test, all good, put the LED stop & tail lamps back in, back to locked brakes.
I figure it must be something to do with a resistance measurement, but at 76 I really don't give a rats, pretty sure the glow plugs will see out the rest of my caravanning days.

Click to expand...

Tex, can you tell me what what type of LED lights you tried on the caravan. Have you got a photo or a link or something?

Diver300 said:

Tex, can you tell me what what type of LED lights you tried on the caravan. Have you got a photo or a link or something?

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Thanks very much for that. Those lamps are most likely not going to conduct at all when the voltage is only just high enough to activate the Redarc controller.

Just to show how easy it is to misunderstand things, I thought that you were talking about complete LED lamp assemblies, not just replacement bulbs.

I think that a lot of this thread has been misunderstandings.

Diver300 said:

Thanks very much for that. Those lamps are most likely not going to conduct at all when the voltage is only just high enough to activate the Redarc controller.

Just to show how easy it is to misunderstand things, I thought that you were talking about complete LED lamp assemblies, not just replacement bulbs.

I think that a lot of this thread has been misunderstandings.

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Can you clarify my understanding of the problem.
This is my undestanding at the moment after carfully re reading the thread.

1 - You have replaced the existing rear LED light clusters on the vehicle with different LED rear light clusters.
Four of the LEDs in these clusters remain on all of the time. This did not cause a problem with the caravan brakes.
(I originally thought this was when the brake problem started.)

2 - With the original plug in filiment bulbs on the caravan there was no problem with the electric caravan brake coming on when the side lights were turned on.

3 - You replaced only the stop and tail light filiment bulbs (5 / 21 watt) (NOT the turn signal bulbs. ) in the caravan with LED bulbs. This is when the problem with the caravan brakes coming on when only the tail lights were on switched on.

Les.