HAving just read the "alternator high output thread" made me remember something from my college days so here goes:

Why if the cars battery and system is 12v and the bulbs are rated at 12v don't they blow when used if the alternator is putting out 13-14 or even 15 volts?

All answers on the back of a postcard hehe:D

Thats cause its thye amps that blow fuses

Its like the mains power is 240v but you get different appliances with different amp fuses like 1A from low power stuff to 13A for things like irons.

Am I right or barking up the wrong tree?

Short answer - 12v is nominal figure .Actual voltage design for lamps is probabbly nearer 13.2 -13.8 volts.(I would suggest )

15V - Fried electronics (I would think), with certainly frying and (in the extreme ) possibly exploding battery .

A bulb will take at least 50% more voltage than it is rated at

All good answers that you think would make sense but nope:) the answer is a bit daft but keep guessing

No, it really is correct, the bulbs are designed to last for the usual 1000 or so hours at about 13.8V. If you were going to say it's something to do with alternators putting out AC you're wrong - by the time it gets to the bulbs (or any other part of the car electrics) it's been rectified and very effectively smoothed by the battery.

A theatre lighting tech once told me that the life expectancy of normal light bulbs in the near vicinity of their nominal operating voltage is roughly proportional to the inverse 11th or 12th power of applied voltage. That may not hold for 1.5 times the nominal voltage, though. I once had the regulator on my Skud Rapid pack up: the battery boiled dry as a result and the electrics were getting about 18-20 volts. I made the mistake of putting on the hazard lights and blew most of the indicator bulbs! Took me two stops at motorway services to find enough bulbs to replace 'em all - after calling out a local garage to bring a new battery :thumbdwn:

my guess is that the batery funtions as a capasitor, the higher voltage put out by the alternator work to charge the batery, but system stays nominal, im saing this cus if you take the battery out of a motorcycle the lamp would glow brighter as revs goes up and burns all the time.

also bulbs are basicaly a resistor that puts out heat (till it becomes incandecent) so it realy dont care about voltage but Watts (Watts=volts*amps) voltage might be comming higer but amps are less since the batery is storing energy.

well, thats my guess al least or it might be something more simple as all bulbs are inherently a resistor so it can only let so much electricity in.

you let me know oldschool i like this kinds of questions that make you think and ofcourse, ake you smart