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Old 04-15-2010, 02:06 AM   #1
Wild Horse
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Electrical conversion

I'm pretty dang good with electrical...120 and 12...but with converting, not so much.
So here's the question.

Scenario: Take a 12v light fixture and switch it to a 120v fixture, then put in a screw in base 12v bulb.

Wattage limit ? Gauge of wire an issue ? Bulbs are available from 50 watt incandecent to 13 watt fl or cfl. I'm pretty sure the issue isn't wattage, but amps ? If it's too much, will it simply blow the fuse ?

Inquiring minds wanna know !
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Old 04-15-2010, 02:28 AM   #2
ole dude
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Yep
Yep
Wattage will turn into amps
Yep, you at least hope that will happen
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Old 04-15-2010, 02:53 AM   #3
camper4
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Sounds like you are just changing fixtures so you can use screw base bulbs. So, all the wiring should be good as long as you keep the same size fuses that came with the unit.

One simple way to estimate your amp draw with a bulb is to take the wattage rating, and divide it by the volts. That will give you the amps draw for that bulb. Then you can go from there and see how many, of whatever size, you can put on each fused circuit.
Don't max out the fuse though. If you use FL bulbs, they can draw extra amps when they initally light up.
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Old 04-15-2010, 02:54 AM   #4
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That 12 volt bulb won't last very long on 120 volts. The gauge of the wire is sized for amperage. The smaller the volts, the higher the amps for the same wattage.
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Old 04-15-2010, 03:04 AM   #5
camper4
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SO, my response assumed you were using 12 volt power and just changing the fixture. If you are changing the voltage to 120, that is another set of issues.

The amp calculation is the same but...

You would need to check the voltage rating of the wire and the fuse box. I know the fuse box is not rated for 120v.

I believe you will need to change the wire and then go to a spare location on your AC breaker panel and add a breaker.
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Old 04-15-2010, 03:15 AM   #6
ole dude
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The way I read the post is to put in a 120v light fixture but still use 12v lights.
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Old 04-15-2010, 03:53 AM   #7
H. John Kohl
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Quote:
quote:Originally posted by Wild Horse

I'm pretty dang good with electrical...120 and 12...but with converting, not so much.
So here's the question.

Scenario: Take a 12v light fixture and switch it to a 120v fixture, then put in a screw in base 12v bulb.

Wattage limit ? Gauge of wire an issue ? Bulbs are available from 50 watt incandecent to 13 watt fl or cfl. I'm pretty sure the issue isn't wattage, but amps ? If it's too much, will it simply blow the fuse ?

Inquiring minds wanna know !
Thanks Ole dude,
I was reading it the other way until I reread it as just replacing fixtures.

Wild Horse,
Check the amperage of the fuse that protects the circuit that powers that fixture. That will tell you what wattage bulb on the 12Vdc circuit you can use. Also check what other bulbs are on that circuit because they can play into your calculations.

Reference Wattage and current. The two are attached.
Ohms Law says Power = Current times Voltage.

Hope this helps.


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Old 04-15-2010, 06:10 AM   #8
Wild Horse
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Thanks, that's what I figured. I'll go do the math in a bit.
I appreciate it.
Bill
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Old 04-15-2010, 07:12 AM   #9
firetrucker
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Bill,

There doesn't seem to be a big selection of 12 V screw base light bulbs, and the prices are high compared to the large selection of automobile light bulbs. Most seem to be higher wattage (more current), too.

Why do you want to go to the screw base bulb?

Would LED lights be a better choice?

Bob
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Old 04-19-2010, 02:00 AM   #10
Wild Horse
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My reasoning for going this route is twofold. First, we think the bright brass looks dated. Secondly, I've already got a set of replacement fixtures in my shop storage that are perfect. I checked yesterday, and the circuits are setup fine. Max on a 15 amp fuse will be a approx. 10 amps for now...less later when I switch to cfl bulbs. Will be installing them later this week...first, finishing up replacing all the cabinet hinges and pulls.

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Old 04-19-2010, 03:04 AM   #11
Wild Horse
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BTW, the 10 amp figure I got by using the 4-25 watt bulbs divided by 12 volts....and being as I won't short change myself ever with electrical or gas work, I'm going to even put in a lower amp fuse to double check it. The cfl's I'll end up with are 13 watts.

I am fortunate the monty is wired the way it is...they seem to keep the circuits very light.

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Old 04-19-2010, 12:40 PM   #12
firetrucker
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I'm not sure I have a clear picture of how many fixtures your putting in. I'd guess four, each with a 25 W, 12 V bulb. I think the wiring would support that, but I'd check the voltage at the fuse and the fixture when the light's on to see how much of a voltage drop there is. That would give you a better idea how much current the circuit would support.

Of course, the CFLs would give you a lot more light for the lower wattage and less draw on the circuit.

Bob
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Old 04-19-2010, 04:08 PM   #13
Wild Horse
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Bob, it worked out very well. It's 2-25 watt bulbs on one 15 amp circuit, 1-25 watt bulb on another 15 amp circuit and 1-25 watt bulb on yet another 15 amp circuit. Later I'll put 13 watt cfl's in to improve it even more.
Thanks everyone for the input....when I get a chance, I'll have pics posted.
Bill
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