Hi,

Setup is very simple, updating led lights on a vehicle, the older 3" round led lights have been replaced with new ones.

This vehicle put out a constant ~10.2v on the lights wiring. (turn signals, brake lights, 3rd brake light) when the ECU drives the circuit to ground the voltage goes from ~10v to 12V and the lights light up accordingly.

The older lights, lets use turn signals as an example, would turn on when you activate the turn signals. When the turns signals were off they remain off despite the 10v.

These new round led lights have about a dozen led in this 3" round light. Due to the fact there is ~10v on the turn signal wiring, it lights up about 4 of the 12 led at all times. When you actually activate the turn signal, it turns on the other 8 led on and off as expected but these 4 remain on all the time.

The goal is to make the new lights work like the old lights. So a modification is needed for each of these lights. I'm looking for a clean solution since this needs to be done on each of the lights.

1. Running resistors in serious dimmed the 4 led which were on all the time but than none of the lights work when the turn signal is turned on.

2. Added a pair of diodes schottky but it made no difference.

Was thinking a comparator would be ideal however its all IC mounted and not ideal. I'm thinking maybe Zener diode would be the best option.

Thoughts?

 

Welcome to AAC.

While a zener might work, you also might experience issues with warnings about bulbs being out as the ECU doesn’t see enough current flow in the off state.

A small relay might work if it is selecting so the must make voltage is appropriately above 10V but not the higher 12V of activation. The relay coil would still be a load, just not operating. I can’t guess about the service life of the relay.

Of course, you would use the same signal as was being sent to the coil as the source of the power, connecting the one side of it to both one side of the coil and half of the NO contacts, then one side of the LED light to the other half of the NO contacts. Whether this is the positive or negative shouldn‘t matter and convenience of wiring would help make that choice.

I am not certain you could make this work because of the critical 2V spread, but you could also try connecting the coil through a resistor to drop the input voltage to match a particular relay’s must-make/must-break spread.

 

Thanks for the feedback.

What i was thinking was using a 12v zener and using it so only the reverse bias voltage when it is supposed to work when the zener voltage hits (12v) passes through and that way the 10v never reaches the lights. Or am i over simplifying it? The ECM doesn't care if the bulbs are burned out or not b/c I have it disconnected completely to simulate an open and no error occurs and i'm not concerned about that at all.

Just looking for a simple solution knowing i have a postive and negative wire at each of these lights (turn signals, tail lights)

The relay idea sounds good as well, but do you know where i can find such a relay with these specs that are not overly priced and sized?

thanks

 

If you had to recommend a zener what would you recommend, these are led so draw is not much but i'm looking for something that will last

 

Thanks for the feedback.

What i was thinking was using a 12v zener and using it so only the reverse bias voltage when it is supposed to work when the zener voltage hits (12v) passes through and that way the 10v never reaches the lights. Or am i over simplifying it? The ECM doesn't care if the bulbs are burned out or not b/c I have it disconnected completely to simulate an open and no error occurs and i'm not concerned about that at all.

Just looking for a simple solution knowing i have a postive and negative wire at each of these lights (turn signals, tail lights)

The relay idea sounds good as well, but do you know where i can find such a relay with these specs that are not overly priced and sized?

thanks

Well, here‘s the rub. Most standard relays have a must-make (also called operate) voltage of 75% of the rated voltage and must-break (or release) is 10%. This means a 12V relay has an operate voltage of 9V. This is 3V, so there should be enough room for your application, but it will have to be shifted down with a current limiting resistor and it must be less than 1.2V to guarantee the release, so you’d have to do something with the relay itself* adding in a bigger resistor to the coil once it was made. No big deal, but more complex than first glance, and it would require some testing to be sure it acts as expected.

*One strategy might be using the NC contacts to add a resistor in parallel to drop the non-operating resistance to match the needs of that state and when the relay operates it removes the parallel resistance raising the total resistance to the point that the 2V drop of not operating produces a <1.2V signal on the coil. When the relay releases, it puts the additional resistor back in parallel to ensure it will operate when the 12V is applied again.

 

If you had to recommend a zener what would you recommend, these are led so draw is not much but i'm looking for something that will last

What is the total current drawn by the lamp?

 

I'm trying to picture this and how it would look, you are saying i would have to take a sealed relay apart to modify it. It seems like this could be an issue itself if i'm going to use a small relay which is sealed already.

How about the zener diode option not being concerned about codes is there a long term issue with this? and How would you do it and is my idea sound to use just the reverse bias?

 

I'm trying to picture this and how it would look, you are saying i would have to take a sealed relay apart to modify it. It seems like this could be an issue itself if i'm going to use a small relay which is sealed already.

How about the zener diode option not being concerned about codes is there a long term issue with this? and How would you do it and is my idea sound to use just the reverse bias?

You don’t have to take anything apart. You would just connect the additional resistor through in parallel the NC terminals. When the relay operates, the parallel resistance would be disconnected and the total resistance in line with the coil would increase.

The zener could work just fine. I would use something rated for twice the expected current draw to be safe. You should try it.

 

I just tested and its 0.065A @ 12V

What zener diode would you recommend and is my logic of using just reverse bias sound?

 

I just tested and its 0.065A @ 12V

What zener diode would you recommend and is my logic of using just reverse bias sound?

Well, there is a problem. A 12V zener has some resistance which will make its output less than 12V. Looking at some datasheets I find to expect about 4Ω, so with your lamps you would be losing something around half a volt. Will they light fully at that voltage?

 

Your best bet is to just try a 1N5349 diode and see if it behaves as you would like. These are ubiquitous, cheap, and rated for 5W so plenty of room for error. Give it a shot.

 

What you are thinking will not work. (placing a 12 volt zener in series with the load)

A 12 volt zener will drop 12 volts across it leaving nothing for the LEDs. To work the way you want the voltage would have to go from 10 to 24 volts.

You need a different approach.

 

Several questions, going back to the start, as I just saw this thread. Is that 10 volts with no load except the meter? What is the voltage with the new light and the 4 LEDs illuminated? Are those 4 anywhere near full brightness?
AND, what is the reason for replacing the lights?
If the old lights still function it would be good to know at what voltage they illuminate. Likewise, check the new lED lights to see what voltage they illuminate at. A lot of the LED lights are driven by a pulsing signal, so the 10.2 volts could be just a peak reading.

 

Can you show how the old lights are wired and where you measuring this 10.2V when off? My understanding of your description seems very unlikely to me.

 

Sounds like my wife's old Hyundai. Daytime Running Lights (DRL). Headlights were lit dimly whenever the car was running. When you switched the headlights on they went on full brightness. This is a safety feature, one insurance companies like to see. The way the Hyundai DRL lights ran dim was via a modulated source. PWM or Pulse Width Modulation would supply power on and off very quickly with a shortened ON time. The overall average voltage was what lit the DRL's. When you turned on the headlights PWM either went to 100% on time or another circuit activated at full voltage.

When you talk about a car's electrical system, a 12 volt system, when the engine is running, runs at about 13.6 volts. After startup it can run as high as 15 volts, though I've never seen one run that high. I HAVE seen 14.5V on occasion. So all this must be factored in. If you're using some sort of comparator circuit to determine the voltage that comparator needs to have a constant regulated reference voltage. Otherwise at 10 volts DRL ON and the engine starts and the voltage runs as high as 14 volts, the 10V can appear to be 12V (approximately without doing any math).

Are you SURE your 10V is a solid 10V? Or is it PWM? PWM engine running or engine off will still see the fluctuation in voltage unless the car's computer monitors the output and modulates the PWM accordingly. You COULD be chasing a rabbit down a hole. No matter how far in you reach the rabbit just goes deeper.

 

Well, there is a problem. A 12V zener has some resistance which will make its output less than 12V. Looking at some datasheets I find to expect about 4Ω, so with your lamps you would be losing something around half a volt. Will they light fully at that voltage?

Yes at 12v+ they light fully i think even at a slight lower voltage if i recall when i just hooked up a battery that was 11.8V they light fully

 

Your best bet is to just try a 1N5349 diode and see if it behaves as you would like. These are ubiquitous, cheap, and rated for 5W so plenty of room for error. Give it a shot.

Thanks im going to order some now

 

What you are thinking will not work. (placing a 12 volt zener in series with the load)

A 12 volt zener will drop 12 volts across it leaving nothing for the LEDs. To work the way you want the voltage would have to go from 10 to 24 volts.

You need a different approach.

Really, my understanding of a zener diode is when the breaking point hits it allows for reverse bias of the zener voltage.

Can you elaborate a little more on what you mean?

 

Yes, that is correct, but the diode will always have the breakdown voltage across it after it breaks down.

It is not a switch that closes at the breakdown voltage.

 

Several questions, going back to the start, as I just saw this thread. Is that 10 volts with no load except the meter? What is the voltage with the new light and the 4 LEDs illuminated? Are those 4 anywhere near full brightness?
AND, what is the reason for replacing the lights?
If the old lights still function it would be good to know at what voltage they illuminate. Likewise, check the new lED lights to see what voltage they illuminate at. A lot of the LED lights are driven by a pulsing signal, so the 10.2 volts could be just a peak reading.

Yes 10v with meter only no load, with the new or old led lights connected it is still putting out a constant 10v.

voltage with new lights 4 led lit is that 10v, the 4 appear to be about 80% brightness.

The old lights illuminate only at 12v