Hello, I'm new to this depth of electronics. Sorry in advance for a story. I recently purchased "The art of Electronics" and have been watching Khan Academy to help me figure out a solution to my problem and have only understood a fraction of what I've read. Please excuse my inaccurate terminology and other ignorant things I may or may not say.

I have a vehicle that I want to swap out the poor factory headlight for one that provides a better light pattern (while looking more aesthetically pleasing) but want to keep all factory wiring intact to make swapping back easy if it doesn't work out. It so far has proven to be beyond my knowledge.

The connector at the light has:
2- key-on switched 12.6v supplies (High beam, Low beam)
2- key-on switched 12.6v supplies (running lights)
2- 35.5v inputs (from a module to turn on the low and high beams while the engine is running)
2- grounds

I originally tried using 2- 36v relays and the result was the light would flash on and off like a slow strobe light). I didn't originally check for current and the relays had no specifications on the coil other than being 36v. Probing with my multi-meter, the current at the 35.5v input from the module to ground is 17.8ma. So I'm assuming there isn't enough current to keep the coil energized?

Then the idea of using a transistor with the 35.5v at the base and the 12.6v at the collector for the relay's coil. It appears no transistor is manufactured for up to 50v (I think I saw some 30v). I didn't have much luck finding a small affordable stolid state relay either.

I'm not sure what direction to go at this point and I'm hoping I may get some assistance from here.
Attached is the transistor circuit I had planned on my child's tinker cad that I now don't believe will work.

 

Your proposed circuit should work; there are plenty of transistors with a rating of over 50V (Vc-e). The other transistor parameters of importance are Ic, the maximum collector current, the power rating and the gain (Hfe).

If you assume that the relay coil draws 100mA (from the 12Vdc) and the transistor has a gain of at least 20, then you need to select a base resistor value that will pass 5mA (35/0.005 = 7kΩ). Based on a 100mA relay current, the transistor will dissipate less than 1W when switched on.

One other observation on your circuit, the 8 LEDs are wired directly to the 12V, the circuit should have some resistance in series (or other current limit/control) otherwise you might end up supplying excessive current through them.

 

Hi Turbo,
Check out this edited image, let us know the answers?
E

 

What scheme did the original system use for that 35.5 volt signal to control whatever was the light previously?? That does not seem like a standard voltage at all.
So if you investigate as to how it was done with the original lights, that should be the scheme to copy.

 

Thank you for your time and responses.

The 2 switches and LED's are more of a visual representation of what is going on in the circuit and the child's program I made it in is limited so I included what I could.

The 12.6v supply represents the battery, switch 1 is representing the key-on switch, Switch 2 is the "high beam" switch.

The 12v relays I have on hand are a 12v 30a Bosch 5 pin. The coil resistance is between 73.3 and 83.3 ohms when I measured a few I have. They are overkill and a smaller 10a relay should suffice. The circuit is fused at 7.5a.

The LED light I will be using is of Chinese origin with sketchy specifications. Leaning on the higher side its 13 or 14, 3 or 5w cree leds and 75w@12v with both high and low on. (I tried connecting my multi-meter in line to measure the current but it wouldn't function for some reason?)

The 35.5v input through my multi-meter measured 17.4mA. The resistors in the image are 1k but since I still do not fully understand the math I included them knowing I would need to figure it out.

I agree the voltage is unusual. The original light has some kind of sealed light module behind the projector lens. I also do not have the light to investigate, it was trashed by the prior owner.

**Regarding my first post, there are actually 3 connectors to the light, (2 connectors are switched 12v and ground for the running lights) the 3rd is a 6 pin with only 4 wires, 2 switched 12 and the 35v inputs that only have voltage when the vehicle is running. I was assuming the ground is through the chassis contact because there is no ground in the connector. Attached is what the factory low and high beam portion looked like.

 

I was planning on using one of the grounds on the running light connector for what I was trying to accomplish. Looking at the attached picture, I don't see how it could be a chassis grounded unit. Is it possible the 35.5v supply is really a ground and I am seeing some back feed voltage or something?

 

Interesting looking light assemblies. What sort of vehicle, and is there any vehicle service information available?
I am guessing that the 35 volts is intended as some sort of control signal, and I suspect that the effort to measure that current caused the source to believe it was seeing a fault condition.
How are those " the poor factory headlight for one that provides a better light pattern " headlights controlled?I see that they seem to be sealed packages.
I suggest checking that 35.5 volt wire when the existing lights are connected and switched on. The voltage relative to the vehicle common will provide the information needed to suggest a working control method.