12 volt dimmer switch

[RKaniefski]

Does anyone know of a 12 volt dimmer switch I can use on my 5ver to dim the 12 volt light in my toilet room. In the middle of the night the light is too bright. I would like to add a dimmer switch to dim it at night and have it work normal any other time. There is no 110 volt supply in there. Does Radio Shack carry any kind of switch I can use in this situation ?

 

[RustyJC]

Any Radio Shack rheostat with an integral on-off switch should work so long as it's rated for the amperage your light draws. To calculate this, add up the total bulb wattage (if your light fixture has more than one bulb) and divide by 12 volts - the result will be the minimum amperage rating the rheostat must have.



For example, if you have a single 60 watt bulb, 60 watts divided by 12 volts equals 5 amps.



Rusty

 

[Badunit]

I don't think RS sells anything that could handle a 5A current or anything even close to that. Maybe you'll have some luck trying something from this link:



http://www.motorhomemagazine.com/forums/index.cfm/fuseaction/thread/CFB/1/TID/636459.cfm



As an alternative, RS does sell power resistors which you could wire to a switch. They get pretty hot, though, so be careful that they have room to breathe if you go this route. I'd wire it up, turn it on, and see just how hot it gets before placing it in the wall.



http://www.radioshack.com/category.asp?catalog_name=CTLG&category_name=CTLG_011_002_014_004&Page=1



Wattage of a resistor is calculated as W = I*I*R where I is the current and R is the resistance. As an example, a 50 ohm 10W resistor can handle 0. 45 amps. 10 = 0. 45*0. 45*50.



For your project, figure out the resistance of the light from the equation R = V*V/W where V = 12 volts and W is the bulb wattage. A 12V/60W bulb would have a resistance of R= 12*12/60 = 2. 4 ohms.



Say you want to decrease the current by a little more than half. You would put three 1 ohm 10W resistors in series with the bulb. Using 14. 4V for the maximum voltage (to be on the safe side which is always important when fire might be the result if you're not) The total current would be 14. 4 Volts/(1+1+1+2. 4 ohms) = 2. 7A. Wattage dissipated by each 1 ohm resistors would be 2. 7*2. 7*1 = 7. 3W each. They'll get hot but they are rated for 10W so should be okay.



All this said, I'd think an RV light would be less than 60W since a 60W bulb draws so much current. The link above suggests it is really 18W. If that's true, it will make this easier to do.

 

[RustyJC]

The 60 watt figure I picked out of the air was for illustration only - I used it because it was evenly divisible by 12 volts. The actual amperage for which the variable resistor must be rated is, as I said, determined by actual bulb wattage divided by 12 volts.



Rusty

 

[Badunit]

I kind of figured it was for illustration purposes only.

 

[klenger]

I bought a 12v dimmer control from Camping World, but can't find it on their website. I used it on the fan above the stove to control the fan speed. It was intended for lighting. I think it was about $20.

 

[juicedcummins]

Does the light have a switch right on the side of it ?{not the wall switch ] If so slide it the other way and it should act like a nite-light. [at least mine does. ] Then turn on wall switch.

 

[RKaniefski]

OK, thanks guys. I think I will just make some kind of cover for the light lens to tone it down at night, then remove it for other times. Thanks for all the input.

 

[Slough]

We just put in one of those round battery lights that you push on the lens to turn it on. POP Lights are found around here at home depot. had this one for a long time. mount it anyplace or just set it on the counter top.

 

[Badunit]

The low tech solutions seem to be the winner here. I guess there's no point in my suggesting at this point that someone make a pulse-width modulated dimmer that would also conserve electricity? The cost would probably be just a few bucks worth of parts (a potentiometer, a 555 timer, a power transistor, a few capacitors and resistors, a heatsink, and something to mount it all on), if someone had the gumption to design it.



Another low-tech idea would be to install a separate small lamp on it's own switch or that plugs into a 12V outlet. This is similar to the battery powered push-on lights suggested before but would be tied into the camper electrical system. I made one that plugs into the phono jack 12V outlets in my Coleman pop-up. I use it as a night light for the kids. It is just a small lamp installed in the end of a phono plug. Looks really sharp.

 

[Prairie Dog]

You cold also get a cheap headlight switch with the integral dimmer for the dash lights. The dimmer section could easily handle your load.

 

[klenger]

How about a night light that uses an LED? I know my Rv monitors sure put out enought light at night to see by. You wouldn't even need to turn it off; just let it run all the time.