My theory on blowing bulbs

So yeah basically everyone blows their bulbs and the main theory is to blame it on DRLs. Now, I don't think this is the case. Being in Canada, every car here has DRLs and trust me they don't all have this problem.

 

However, one reasonable explanation for the bulbs blowing is that they are receiving too much juice! When I started upgrading my stereo, I looked into the alternator specs on the Legacy and I also did some testing with the multimeter. This alternator is rated at 130A and mine tested at 139A! The voltage at the alternator was 15V, 14.6V at the headunit, and also in the high 14s at the lowbeams! This is much higher than most cars out on the market. For example, even in my brand new S2000 I notice a very very slight dimming in the dash lights when I operate the power convertible top. A lot of cars get by with 60A alternators, so I'm not too sure why Subaru overengineered our alternators so much. Maybe it's because the car has power everything, heated side mirrors, heated seats, etc etc. But either way, I think the ridiculously high voltage has something to do with our bulbs burning out quickly. 12V bulbs are designed for 12V, possibly 13V, but definitely not 14.7V.

 

Thoughts?

wrong. your car should be putting out 14.7 volts running

I think you are onto something. Later (post '05) models don't have this problem.

 

A friend suggested a poorly performing voltage regulator. Haven't searched to se eif this is part of the laternator or, a separate module.

i think the lamp housing is incorrectly designed and the bulb gets too hot. or maybe it gets to cold. i think it gets too hot with not enough air flow on the bulb itself to cool it down some. some vw's do the very same thing. just constantly blow bulbs.

DRL runs the bulbs at half voltage. I think that is causing the bulds to die early as they were designed to run at 12v, not 6v

I have had my 05 LGT for almost 3 years with the same bulbs. Granted when I bought the car both bulbs were defective. I was about to pull out of the lot at 4pm in Nov. in New England when I decided to fire up the headlights and they did not turn on. What are the chances of having 2 defective bulbs in a brand new LGT?

 

There is a very good possibility that there was a huge batch of flaky bulbs. I work in media technology and we see bad bulbs from slide projectors, overhead projectors, and lcd projectors. These bulbs are either halogen to metal halide. Perhaps Subaru had a bad batch...

DRL runs the bulbs at half voltage. I think that is causing the bulds to die early as they were designed to run at 12v, not 6v

A long time ago I saw someone here that tested the DRL voltage at around 10V.

 

I suppose it's also possible Subaru had a bad batch, but that's pretty unlikely, since they don't make the bulbs themselves, and any major bulb maker would have worked the bugs out of their product a long time ago. Anyway I'm coming up on 1 year with my Osram Rallyes so I guess we'll see how the aftermarket performance bulbs do in my car.

I am not an EE but running slightly higher voltage would be preferred to slightly lower voltage. P=IV...so if you voltage drops you will draw more current which would likely cause more of a problem to a thin filament due to heat.

 

For me I think the cause may have been due to my on stupidity. All of my previous cars would beep if I left the lights on, but the Subie automatically shuts them off. Problem is when you start the car you have a much bigger load on the electrical system so the voltage is probably not regulated as well as it should be and dips due to teh load. Since the voltage is low the current is higher through the bulb....but what I think is worse is that the voltage likely fluctuates causing surges of current through the filament. Part of my reasoning on this was when I noticed another car that had DRL's had them tied to the trans. You could turn the car on and they did not light, only after you put the car in gear did they light. Maybe this is why some cars seem to be OK?????

Just an aside ... is it the law that you must have your headlights on in Canada while driving, whether it be day or night?

^^ DRL's are required in canada i belive.

As of now, I've had both OEM and aftermarket bulbs (Sylvania Silverstars) burn out pre-maturely.

i think MMS is on to something with the cold; my experience is blowing bulb after bulb, even fogs, in winter only. I have yet to change a single bulb in 50*F +.

I just replaced one of my replacements.

I am not an EE but running slightly higher voltage would be preferred to slightly lower voltage. P=IV...so if you voltage drops you will draw more current which would likely cause more of a problem to a thin filament due to heat.

Actually, that reasoning doesn't work because the power isn't constant.

 

The bulbs are resistors. V=IR is the formula you want. Assuming resistance stays fairly constant (it does vary with the heat of the bulb, but not enough to offset the result), when voltage increases so does current through the filament. The increased current increases the filament temperature, which could reduce the bulb life.

 

Not trying to be a jerk, just trying to help.

We have an OBXT05 and a LGT06. Both have burned out the bulbs within one year. The second bulb has burned out within one week of the first, on both cars!

I decided to buy PIAA bulbs thinking I would get longer life... I was wrong. I won't be spending that money again. I'm now using Sylvania Silver Stars.

 

BTW, I did disable the daylight running lights on both cars after the 2nd set of bulbs burned out... I just replaced the passenger side on my OBXT. Oddly enough, the driver has not burned out yet.

 

Cheers!

Actually, that reasoning doesn't work because the power isn't constant.

 

The bulbs are resistors. V=IR is the formula you want. Assuming resistance stays fairly constant (it does vary with the heat of the bulb, but not enough to offset the result), when voltage increases so does current through the filament. The increased current increases the filament temperature, which could reduce the bulb life.

 

Not trying to be a jerk, just trying to help.

Like I said I'm not an EE but I thought bulbs were rated in watts which is power, so I was thinking of the power being fixed but maybe that power rating is based at a certain voltage....because if you combine the two equations you'd have P=I^2R and if the P and R are constant then the I has to be too....so I guess you're right.

My 05 eats bulbs like candy but others dont do this at all. I think its something with the housing or overheating. When I last changed a low beam bulb it seemed that the clip/spring was less that snug. I bent the clip to be tight as hell. Im not ready to declar victory just yet but they have held up longer than usual. Im saying the issue is vibration due to design.

I only had one bulb go bad and that was when the fan was bad.....now that I said that though mine will blow.

 

To be honest...I am not that upset about the bulb life. I would rather have decent lamps than crappy one that last forever. The light output from these projectors is pretty good so a few bucks every now and then isn't a big deal to me.

I lost my stock bulbs within 3 days of each other.

 

Been 1.5 years since they were replaced

i got a fog light out.

 

maybe the same sorta relay problem for the fan is with the lights?

 

i still think its an issue with heat build up in the housing.

i got a fog light out.

 

maybe the same sorta relay problem for the fan is with the lights?

 

i still think its an issue with heat build up in the housing.

 

 

Ding ding, we have a winner

 

The projector housing got so hot it baked it brown, there just isn't enough air around the lamp to keep it at it's designed temperature.

 

My wife has an '02 LGT, and it is still on the same lamps it came with when we got it over 5 years ago.

 

Simple answer is to change to HID's

how about ventilating with a nice hammer?

That avatar's got to be barely legal, eh?

how about the rest of the pic from the avatar sent to my inbox?

Ding ding, we have a winner

 

The projector housing got so hot it baked it brown, there just isn't enough air around the lamp to keep it at it's designed temperature.

 

My wife has an '02 LGT, and it is still on the same lamps it came with when we got it over 5 years ago.

 

Simple answer is to change to HID's