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# how do i make a table lamp battery operated? Answered

Do I just cut off the plug? I want to use a 40 watt bulb, and keep the switch. I can't/don't want to use LED's. thanks, ap

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## Discussions

What if I am using an led bulb? Now that we have them, what can they handle?

i guess my question is, what part of the lamp requires AC current? If i match battery/resister/watts, can I just cut the plug off, and wire in a new set-up?

what kind of bulb you using? If it's incandessany just measure the resisance of the filament, use ohms law, and fine out the voltage required. If it's a flourecent lamp there's probably a transformer inside of the lamp or wallwart. In the case you should just give up (good luck with those words of motivation)

yeah, it's just an old-school desk lamp. I'm trying to set it up for theatre use (no plug available), and want it to still look like a "real" lamp. so i can just put a meter on the bulb, get the resistance that way, and then supply the volts? (i'm asking this next bit cause i'm a noob) there's no magical "all 40 watt incandescents are X ohms"?

unscrew the lightbulb
put one probe on the tipe and one end on the threadings
R x V = 40
where R is the resistance your meter reads in ohms and V is the voltage that your battery needs to supply.
make sure when you read the resistance your fingers don't touch because your body acts like a resistor.

awesome. it seemed easy enough (in my optimistic - yet to be electrocuted - head). thanks a lot for your help!

. You don't have to go to all the trouble. If it's a standard incandescent bulb, then it takes ~110V (in the US). . Running on DC, your switch may not last as long, but it should work. If it crackles or makes flashes, replace with a sw rated for higher voltage/current. Really shouldn't be a problem. . Wiring in US house appliances is rated for at least of 250V (maybe higher, been a while since I checked) - as long as you stay below that, you're OK. Insulation can't tell the difference between AC and DC. . An incandescent bulb does not care if it's getting AC or DC.

. I think that's exactly what you need! I didn't see anything that actually said that's a "standard" screw on it (there's a designation for that base, but I can't remember it), but I'd bet it is.
. Wire a receptacle to your battery and you don't have to change anything but the bulb.
. I think incand bulbs are designed to run at the rated voltage. The specs for lumens will be at the rated voltage. You can run them over-voltage so they put out more light, but they burn out faster. Or run them under-voltage and they last longer, but are dimmer.
. Great job searching. You found that fast. ;)

. BTW, that 12V bulb is just a lamp for a 12V device (eg, big flashlight) with a 120V base on it. You may want to make your own.

Correct me if i'm wrong, but wall power provides AC current, and batteries provide DC current, so I think you'll need to use a transformer.

. Incandescent bulbs can swing both ways. If he has a fluorescent, then it's a problem.

also you would need a bunch of batteries to be hooked up in series for enough voltages. What he needs is an inverter, not a transformer.

. OIC. That will work, but inverters are not terribly efficient and will waste battery power. If he doesn't want to change the bulb, it might be the best option (a 120V battery can be dangerous, especially in a DIY project).

. You will have to change to bulb to match your battery voltage and you may have to change the socket to match the new bulb. All the wiring and switches will work (as long a your battery voltage is <100V).