Dash light dimmer

[doc g]

I need some help with figuring out a dimmer for my dash lights . The rheostat burned out . I looked up the spec's and found it was supposed to be 32V,500 ohm,5W. Bought one and put it in. It just turns the lights on and off. Then I checked the voltage and found someone had converted the dash lights to 12V. How do I figure out what the correct spec's are for the rheostat now that the system has been converted to 12V? I assume I need more resistance, roughly 3X more as V is 1/3 of what it was?..............Pat

 

[Genesis]

Nope - 1/3rd the resistance.... For the same wattage lamp, you draw three times the current at 12V as 32/36, and thus you need 1/3rd the resistance since the filament resistance (hot) is 1/3rd as high, again, assuming equal wattage consumption from the bulb.

 

[doc g]

Karl,
They come in 100ohm,250ohm,500ohm . What I really need is about 167ohm. Should I go with the 250 or the 100Ohm?..................Pat

 

[Genesis]

Depends - how much dimming do you want? If a lot, then 250 (which should turn them nearly if not totally off, but may be twitchy at the top end.

If less, then the 100.

I'd probably do the 100; I will be at the boat today (I have a 12V panel and that rheostat) and can look at what mine is spec'd at if the specs are on the electrical prints.

 

[doc g]

That would be great ,thanks!!!!