Halogen bulbs 12vdc vs. 12vac

[pizza]

I have a halogen bulb that is normally used with a small 12vac transformer. I can also light this bulb straight off a car battery that's 12vdc (the battery of course runs down very quickly). My question is, "Do I harm the bulb by using 12vdc on it, since it's primarily used with that 12vac transformer?" And "Are there halogens that are made specifically for 12vdc applications"? Thanks

 

[Lewish]

I think you will find that the life expectancy is about the same. Please realize however, that a car battery is about 12.6 volts fully charged and about 11.9 or discharged. But if the car is running, the bulb will see closer to 14 volts.

Yes, there are halogen bulbs designed for DC use. Usually they are ruggedized, assuming that the user will be using them in a vechicle which will shake them around.

The wattage rating of the bulb will determine how fast your battery runs down.

Lewis

 

[230842]

First question: Bulb performance is not dependent on current type (ac or dc) provided that voltages have same values.
Second question: there are different kinds of 12 V halogen bulb depending on its us (car or home applications) rater than on current type. That differences mainly affect to mechanical arrangements. Julian

 

[pizza]

THANKS!

 

[BrianR]

For small (<150W) incandescant lamps, the supply voltage has the greatest influence on the life of the lamp. Generally the change in life is related to the 12th power of the voltage difference from the design nominal. ie. running the lamp at 5% overvoltage halves its life and 5% under voltage roughly doubles its life. The RMS AC voltage is equivalent to the DC value. I think there can also be minor adverse effects running off DC, due to ion migration from the filament.

 

[jbartos]

Suggestion: Consider Vrms=(pi/(2 x sqrt2)) x Vdc = 1.11 x Vdc