Headlight voltage question
 

I've searched, but can't find the answer.

Does anyone know the voltage specs for the high beams on a 1997 blazer with composite headlights? The voltage to mine is 10.98V, which seems low to me.

when dealing with voltage it should all be the same as your battery voltage, unless you have a voltage drop in the line like a bad connection somwhere. Amps is the only varible that should change on a power consuming device like a light.
low voltage higher amp draw
higher voltage lower amp draw

Ideally it should be the same as the battery voltage, but that won't happen with the small gauge wiring used on the headlights for the Blazer. I would expect slightly less than 12v with the engine running, possibly even down to 11.5, but 10.98v is terrible. I guess I could rewire it with a heavier gauge, and maybe even use a relay.

voltage shouldnt make a diffrence your amps will be higher cuasing the wires to create more heat

I'm not talking about the supply voltage, I'm talking about the measured voltage at the load end. Voltage drop on a smaller gauge wire, like the one to the headlights, is normal and expected, but the measured voltage on my truck is lower than it should be, IMO.

I was hoping someone knew what the acceptable voltage range is, that's why I posted this. I didn't measure the voltage on the low beams, I'll try to do that today for some comparison. It's my understanding the DRL module controls the high beam voltage, but I don't know if it can cause a slight undervolt. I would think it would either work or it wouldn't, but I don't know for sure.

There has to be specs somewhere, showing the gauge of the headlight wiring. Engineering had to come up with an acceptable voltage range for the headlight. This stuff exists somewhere, but it may not be available to the general public.

My quest continues...

The wiring is size with 2 things in mind. Cost vs "will it work good enuf". The wiring size is causing a voltage drop. But the drop isnt so severe as to hinder the bulbs ability to put out enough light to satisfy the DOT. Lights are designed for 12 volt dc. That information is available on each manufacture's website.

Following OHM's law, In order for the same amount of work (or light) to be performed, If voltage drops, amperage must go up. Wire size restricts the maximum amp draw. Force too many amps through a wire and you let the magic smoke out. If the voltage at the bulb is lower than battery voltage then energy is being wasted in the form of heat going through the wire.

The relay solution works. Use the existing wire to control the relay that is being supplied by larger sized wire. (FUSE THE WIRES!) I did this upgrade on a truck of mine. It does make a difference.

I put Silverstar Ultra's in it, so the stock wiring is choking even more. I'll have to do the relay later, right now the wife is in a remodeling mood :icon_doh:

I like the silverstars - except for their short life span.