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Re: Driving/Fog Lights
>I added some individual relays to improve the voltage reaching the
>headlamps on my 1986
>5000CS Turbo when I added some high wattage 9004 bulbs.
Good move, Now your light switch will last forever and you'll get a
whiter brighter light. NJT
>My nice new high wattage bulbs started burning out only after
> 3 -6 months of use so I went back to the standard bulbs wattage
>55/65W. Even with the stock bulbs I still was replacing the bulbs every
Hmmmmmm Read below......
>Most bulbs burn out when they are first turned on (cold) due to low bulb
>resistance and the fact that the inrush current is something like 5-10
> times the normal operating current.
Well not exactly correct, The cold resistance is higher than the hot
resistance but only buy a few %. Yes it's true that the inrush current
is higher than the operating current but this last's around 10
milliseconds. With Q/H bulbs this has to happen in order to jump start
the Redeposit cycle.
>I have measured this using a current probe and an oscilloscope. This is
>also true for most household light bulbs.
Yes but hosehold light bulbs are slightly different than Q/H bulbs,
namley household bulbs operate at a much lower temp. That's why hosehold
bulbs blacken over time and the Q/H bulbs remain crystal clear throughout
>Previously I had gone several years without replacing any bulbs. I
>theorized that the shorter bulb life was caused by
> 1. (lousy bulb manufacturer) or 2. The relays I added had lowered the
>voltage source resistance enough that the inrush current was being
>increased. Eventually this burned out the bulb sooner than when
>I had the stock wiring with all of the added resistance from the fuse
>box through the headlamp switch and out to the lights.
I would vote either lousy bulbs, abusive handling, OR what I'm voting
for, the glass envelope came into contact with body oil's which etch the
envelope making microscopic fissures in the glass leading to stress
>Any one else had this sort of problem with lights burning out? Just one
I have had 80/130's on relays for a year now and I hav'nt had to change
Sorry for the long post but as a Motion Picture Cameraman I kinda have to
know how light bulbs work.