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Dimmer for a 12V 50W halogen

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florida

New Member
I’m looking for a schematic or tutorial for a dimmer capable of controlling a 12V 50W DC halogen spotlight. Commercial dimmers are expensive specialty items that won’t work for my application. There is no commercial dimmer that is saltwater proof. The dimmer will control a 2 mil CP spotlight and will be used for marine navigation. Lately I’ve been using a rheostat from an old truck heater; it generates way to much heat.

Thanks for the help.
 

Sceadwian

Banned
A simple 12 volt 5 amp PWM circuit encapsulated in hot glue or epoxy would work fine. However if I'm not mistaken halogen bulbs don't like being dimmed.
 

florida

New Member
Thanks, great idea

Dimming lowers the temperature causing carbon to build up on the filament. Running it full blast for one minute for each hour of dimming is supposed to alleviate that.
 

florida

New Member
Sorry to bump this thread but when it was approved by mod. it didn’t show up on new post. It was buried on page 5 of the Electronic project forum. See above post.

Thanks
 

kchriste

New Member
Forum Supporter
If you changed R2 to 100Ω and replaced T1 with a suitable FET, it'll work OK. Or you could replace R2 with a 100Ω 2watt and replace T1 with a better transistor. I prefer using the FET myself, if for nothing else, than reducing the power dissipation in R2.
 
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bountyhunter

Well-Known Member
You could use a free running 555 timer with adjustable duty cycle driving a P-FET (high side drive) to the lamp to dim it. I would set the osc frequency to maybe 500 Hz ballpark. If the on resistance of the P-FET is low, the FET wll not need a heatsink. Here is an example circuit, you would want to make the 4.7uF cap smaller to get faster oscillation frequency. This one is designed to make a headlight flash as a warning light. The 30k/100k resistors can be varied to change duty cycle.
 

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