Headlights Flare

crashthecar · 06-24-2005, 10:00 PM

Crazy problem comes and goes,
Driving along and the headlights flare brighter then drop to normal. It's not the high beam coming on, it's like the Alternator overcharges briefly and supplies more power.

It only affects the low beam lights no other systems.

Couple of nights ago it Flared and just kept getting brighter until it popped the filliments in the globes. didn't blow the fuse or damage any relays or wiring and when i put my spare globes in to get me home there were no more problems.

Last night it started to brighen up againbut didn't go as far to burn the bulbs this time.

I'm thinking of getting my Alt looked at as when ever I test it it's output is 14.2V normal and i don't know anything else it sould be. The battery is in good cond and less than 6months old.

You guys come across this before???

blkongry · 06-25-2005, 02:20 PM

I'd say it's the voltage regular. I think they are integrated into the alternator on nearly all cars now. They regulate that only 14V or so come out of the alternator, otherwise the faster you spin the alternator, the greater the voltage output, which would do exactly as you say. Now, I've never known anyone to have the problem so apparent that it pops bulbs, but theoretically, that's what it should do.

crashthecar · 06-26-2005, 05:01 PM

Alternator checks out ok...
Got it bench tested at the local auto elec.
He seems to think there is a regulator on the headlight circuit seeing as the rest of the car dosen't fluctuate, but has no idea about where (dosen't understand those damn Beemers!)
Anybod come across this in their cars?
Luke.

blkongry · 07:22 AM

I don't get it, if there is a good regulator in the alternator holding voltage at 14 or so volts, and the rest of the system doesn't fluctuate, then what would cause the power to the headlights fluctuate? It's already regulated, unless the power to the headlights is pulled from the alternator "pre-the-regulator", and I highly doubt that.

By the way, those bench tests don't catch all the symtpoms of a bad alternator/regulator. I had a friend whose Camaro had a similar problem, and his alternator/regulator checked out, but he couldn't find the problem. He just ended up buying a new alternator/regulator and it fixed his problem. Apparently those bench-testers only catch the major failures.

Jeron · Jeron's Garage

That's a good point it the alternator regulator is fine then how could a bad down stream regulator deliver higher voltage? That is unless the headlights are independently regulated, but why would they be?

crashthecar · 06-28-2005, 02:50 PM

It's got me stuffed...
is there a 12v regulator after the battery before the fuse panel?
so the car only gets 12v of the 14 that the alternator regulates battery charge at?
I'm grasping at straws here... Too tight to fork out for a new Alt just yet when it looks ok, and may not fix it.
Luke.

Jeron · Jeron's Garage

I think it is regulated to about 14V. I don't know what the headlights run on I just assumed the same V as the rest of the car. I suppose they might need a strict diet of 12v or less so they might have their own regulator and its is this regulator that is the problem but I doubt it.

I think blkongry's point was that the alt regulator gives 14v and it goes directly to the head lights and if the alt regulator is failing and it is going higher than 14v it could blow the bulbs. If this is happening I would be very afraid of blowing out other more expensive things.

Bentley shows the regulator on the alternator is removable and might be available in the aftermarket but is not an OEM replaceable part. Maybe remove yours, clean it inspect it and try to find a replacement.

Dave at Pelican Parts · Dave at Pelican Parts's Garage

Unless you have HID bulbs on the car (and their associated transformers and other $$$ parts), the headlights should be designed to run on "12 volts"... That is, they're designed to run on "about" 14V under normal operating conditions.

The voltage regulator is built into the alternator on these cars--I think!! It does act as a "choke" on the amount of voltage getting pushed into the system by the alternator. Left to its own devices (and wired incorrectly), the alternator would put out 16V or more when the engine was running at any reasonable RPMs. This will boil your battery, among other problems. The VR acts as a switch that turns the alternator off when the voltage gets too high, and back on again when the voltage gets low enough. This switching happens many times per second, so the system voltage stays pretty close to 14V.

If you think your alternator has been overcharging, I would check around the battery and check the battery itself. A battery that has boiled will spew acid, which isn't very good for your trunk. Nor, for that matter, for the battery. If the battery isn't one of the sealed types, you can add more water and bring it partway back. If it is sealed, I'm not sure what you do.

I find it difficult to believe that you would blow the headlights only by having too high a voltage in the electrical system. I think this would cause many other problems (e.g., boiling battery) that you would also notice.

It is normal for headlights to dim and brighten some as the car operates. It isn't normal for it to be a whole lot. I would look for other problems--bad grounds, water in the headlight housings, and so on.

--DD

blkongry · 06-28-2005, 04:33 PM

I've been kind of mullin' this over. If the regulator was having problems and failed, then voltage output should be a direct response to RPM and effect headlight brightness. Like Dave said, there is some normal variation in brightness (so we know it's tied into the alternator to some degree), but if you lost the regulator enough to blow the lights, then they should be directly tied to engine/alt RPM, and you should be able to see it when you rev the engine.

Now that's assuming the regulator totally blew. There's a strong chance you have a sporadic problem with your regulator, and you only get the voltage flare up where there is a specific load, temperature, and a variety of other circumstances. With that said, you wouldn't necessarily boil your battery because it wouldn't be a constant stream of power... just a sporadic one. Although, what won't boil your battery will most definitely pop your headlights.

Hmm, can you control the surge on the headlights? If so, then get a multimeter and start measuring voltage to the lights... vary the RPM and watch for flareup and voltage change. Headlights are just filaments... big resistors.... they just soak up power, so the more power, the brighter. If I remember right, an electrical unit will draw as much amperage as it needs, but over load the potential (voltage) and you'll burn it out. What I mean is that power is made up of voltage and current (P=IV), so if a part won't over draw current, then it is taking in too much voltage, so what ever your problem is, it's a voltage output surge somewhere in the car. Now I'm back to the fact that your only power supply on the vehicle is the battery and the alternator. Unless your battery is voltage spiking and popping your lights, which is pretty unlikely, it falls back on the alternator, which we all know has variable voltage output. Now it's back to the voltage regulator again.

I don't know, Luke, is there any way you can swap out alternators with a friend or make a deal with a salvage yard that you need to see if it works before you buy it? You need to totally rule that alternator/regulator out before you start chasing any other ghosts.

crashthecar · 07-10-2005, 02:56 AM

I bit the bullit and put the ALT in for overhaul on Wednesday,
The globes only blew once but the surging was becoming more frequent.
Guy's down at the Auto Elec said there were a few questionable bits in there but nothing that had failed totally.
I ended up with a new set of Diodes' a regulator and I got the bearings done while they had it apart just to save $$$ in the future.

Thanks for all your input guys, fingers crossed she plays nice now. I've not noticed it flare scince i threw it back together in friday night.

Luke.

blkongry · 07-10-2005, 02:17 PM

Keeping my fingers crossed for ya, but I think you took care of your problem and should be safe. I'd be really surprised if it wasn't.

Wayne 962 · Wayne 962's Garage

Alternators can be strange beasts, along with voltage regulators. What I would suggest in a situation like this is to run a volt meter from the battery into the dashboard area so that you can monitor it.

Also, with surges like these, you may have a battery that is failing. The battery has a tendency to act like a big capacitor at times, helping to absorb and regulate the system (never disconnect the battery while the car is running).

-Wayne