Re: PIAA Tech's bulb failure theory

[steveb@falcon.kla.com (Steven Buchholz)]

> I've had 2 PIAA 85w H3 bulb failures within 20 hours of use on my A6QW and
> after the second one, had a lengthy discussion with their tech.  He feels
> that I may be creating a power surge by shutting off the engine before I
> turn off the lights. He says that with a lot of accessories on, this "surge
> of power" can be overheating the bulbs, and that it happens so fast, it
> goes right through the fuse.
> 
> Now, I'm not an electrician, but I have my feelings on this and thought I'd
> ask if anyone more eminently qualified could shed some light on this
> theory.  As an aside, both bulbs failed in the same manner. I use them in
> my low beams. Filaments seem OK, but farther down the shaft of the
> assembly, there are 2 metal leads soldered to the wires coming out of the
> glass envelope (bulb) that somehow burn away and leave a mass of fluffy
> crystalline stuff in their place.
> 
> What do you think?  TIA
> 
... Although I'm not a lighting engineer, I am an EE and I do understand 
incandescent lightbulbs to a certain degree ... so I'll pitch a couple 
pennies ...

If it were me I'd tell the PIAA tech to take a flying leap!  When you shut 
off the car with the lights on they are already warmed up and so their 
resistance should be fairly high.  Incandescent lamps have a surge problem 
when they're turned on ... and this should be a much greater surge than 
anything you'd see due to the fact that the load on the electrical system 
is reduced when you shut the engine down.  The other thing that is true 
is that the car automatically shuts off the low beams when you shut it 
down ... and is probably one of the first loads to be removed ...

Based on your description of the result I'm thinking that you have a little 
too much contact resistance at the plug, and this is generating excessive 
heat that is conducted up the wire into the envelope.  Did you replace the 
headlight connector when you installed the bulbs?

HTH!
Steve Buchholz
s_buchho@kla.com
San Jose, CA (USA)