Voltage Drop in Headlamps

[Projek01]

hey, i noticed that my h4s on my toyota are dimmer compared to the civic h4s so i decided to check the voltage. it read 11.20v at the bulb (car off) and my battery with the car off is 12.60v. is there a easy way to raise the voltage. even silver stars look yellow on my car. thanks.

[SorrGwa]

voltage with car on should be 12-14.4

voltage with car off should be above 10 but below 12

hmm, check to see if ur alternator is charging right?

no whirley noises right? (bad ground usually gives u a whirley noise.

[Projek01]

hahaha wtf, thanks for the help but its not my charging system. its my headlamp voltage. and isnt battery voltage supoosed to be like at 12.5v?? with 10v you would not be able to start your car.

[benyl]

Get a wiring harness and run the head lights directly off the battery. Sounds like the stock wiring harness is old.

http://www.suvlights.com/

[Weapon_R]

Are you using the same bulbs as the civic?

[handsomebassman]

Originally posted by Projek01
with 10v you would not be able to start your car.

Ive started my truck many times when the battery charge was below ten, i think 7 and a half was the lowest tried. It has a batt gauge as well, thats how i know.

[benyl]

starting a car has nothing to do with voltage. It has to do with amperage. You can start a car with a 9V battery if it has enough amps.

[Projek01]

^ wow, i think hes is right. my voltage droped to 11 and i could not start my old beater. i guess its all about amps

[Zero102]

You will always see a small voltage drop in your headlight wiring, or any wiring for that matter.
If you were really gung-ho, you could run some #10 wire down to the headlights, right from either the battery or fuse box (fuse the wire you run of course), and install relays at the headlights, using the old headlight feed as the switching power for the relays. I've done it on a few cars with really terrible headlight wiring.
This will get you very close to battery voltage at the headlights.

The idea here is that the output of a halogen bulb varies proportionally to the 3/2 power of the applied voltage. Meaning a small drop in applied voltage means a big drop in output.

Check the voltage with the car running. If it's below 13.5V, consider adding relays, or upgrading the wiring. If it's 13.5V or above, then the wiring is good enough. Keep in mind, the higher the applied voltage, the shorter the bulb life. It's a double-edged sword really.

[Zero102]

Oh yeah, and on the whole voltage amperage starting topic,
It has a lot to do with the internal resistance of the battery, as well as the starter wiring, other electrical draws, and the starter motor in the vehicle in question.
A lot of times when the open cell voltage of a battery declines (from 12.5 to 11, or maybe even as low as 7), the reason is that the battery is beginning to fail. When this happens, you will see a greatly increased internal resistance. So, when you try to start the car, even though the open-circuit voltage was 11V, it could drop to 4-5V under load.
On the other hand, you can have a perfectly healthy battery in a poor state of charge (for example, down to 7V), with very little internal resistance, that can still provide a very high current when required to (such as when starting the engine).

I'd rather not get into it much farther, because it starts to get really lengthy.

[FiveFreshFish]

Basic wiring:

http://www.rallylights.com/useful_info/headlamp_wiring.htm

[barbarian]

Originally posted by SorrGwa
voltage with car on should be 12-14.4

voltage with car off should be above 10 but below 12

hmm, check to see if ur alternator is charging right?

no whirley noises right? (bad ground usually gives u a whirley noise.

What do you mean by whirley noises?

[SorrGwa]

Originally posted by barbarian


What do you mean by whirley noises?

from experience, weather or not its a bad ground from the stereo or from some area of the engine, i always get feed back thru the stereo.


I was helping trying to diognose all possible lose ends that could lead to the voltage drop to the headlights. but if its an old car, chances are the wiring is old and frail... some cars were known to have bad wiring due to the manufactuer using a smaller gauge wire just to save 50lbs in total of weight off the car.

[HiSpec]

whirley noise means bad ground loop.

also a simple ohms law math. a decrease in voltage means increase in current. so there must be a fault along the wiring harness to increase the wire's resistance allowing higher draw in current.

[Projek01]

for the wiring harnesses, do i need 2 of them or does the harness do both lamps? do you guys think installing that is easyer than installing a amp or stereo. thats all i have done on a car. thanks