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# This switch....(again)

#1
05-03-11, 07:53 AM
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Join Date: Oct 2007
Location: Illinois
Posts: 111
This switch....(again)

I am not sure what amp I actually need for this switch. It completes the circit up to 6, 12 volt light bulbs and a small ceiling exhaust fan. It needs to be NORMALLY OFF. It is in a pop up camper. The watts on the bulbs are probably 30-50watts. (im not at home). I ordered a 5 amp switch but a couple people on the pop up forum said that wont be enough. This is the switch I had......I dont know what amp it was and it doesnt say on it. What size do I need? Any help is appreciated.

#2
05-03-11, 10:01 AM
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Join Date: Oct 2002
Location: Hamilton County, Ohio
Posts: 4,296
Simple formula is watts divided by volts. Ex. 30 watt bulbs times six bulbs =180 watts. Add an extra 40 watts for the fan and you have 220 watts. 220 divided by 12.8 volts (battery) = a tad over 17 amps.

That's why your amigo's are telling you to use a bigger switch.

#3
05-03-11, 02:26 PM
Member
Join Date: Oct 2007
Location: Illinois
Posts: 111
really? wow. So a 15amp breaker in my house can run several outlets, lights, ceiling fans, and tvs but I need a 20 amp switch to run 3 small over head lights and a small fan? Well I dont get it but I have no idea what Im doing lol. thanks....

#4
05-03-11, 02:37 PM
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Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,944
That's because the voltage in the house is 120V, ten times higher than the automotive voltage 12V.

A 50W bulb in the house: 50 watts / 120 volts = 0.42 amps
A 50W bulb in the RV: 50 watts / 12 volts = 4.2 amps

#5
05-03-11, 06:28 PM
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Join Date: Dec 2010
Location: Cressona, Pa, USA
Posts: 2,546
You could always use it to operate a contactor which in turn will switch the lights. (and make the unsuspecting jump if you get a very large one)

#6
05-03-11, 09:41 PM
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Originally Posted by Justin Smith
You could always use it to operate a contactor which in turn will switch the lights. (and make the unsuspecting jump if you get a very large one)
Think more along the lines of a starter or battery interlock solenoid.

However it would be less involved and cheaper to just use a switch rated for 20A, and "make it fit" if necessary. I also don't think the wattage is as high as the OP is guessing. IIRC camper lights use either 1156 bulbs which are 21 watts, or JC-10 halogens which are 10 watts. That's going to put the lighting load at 5-10A, not 15-20. If the OP wishes, he can change out the bulbs for LED, which will not only make it virtually impossible to start a fire, but they will draw significantly less power. Their tradeoff though is their cost.

Djsrcy, out of curiosity, does this camper have an onboard battery/charger/generator or does it use the umbilical pin on the trailer plug to pull power from the tow vehicle?

Last edited by JerseyMatt; 05-03-11 at 09:58 PM.

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