This afternoon we made our first light from a car battery (other than an auto light, of course).

Actually, we made light twice, once with a 12 V 50 watt halogen light, and then with a 50 watt DC bulb. We didn't have a fixture for the halogen, so we wrapped and taped a wire around each of the little posts on the lamp, hooked those to battery cables, and then put the cables on the car battery. Brightest 50 wattlight I've ever seen. While trying to buy a fixture for this light, a guy at a builders square store said it was a 12 volt AC, not DC, light. The packaging didn't say one way or another, and we called the company and found that it doesn't exist anymore (I bought it cheap at a dollar store).

With the DC light bulb, we simply screwed it into a cheap lamp, and wired the plug to the same wires we had had on the halogen, and then put the battery cables on, and it worked.

We let both lights burn only for a few seconds each, as we were using wire from AC appliances (I cut the cord off a fan that no longer worked). I am assuming we need to get a heavier gauge wire to convert an AC lamp to run on DC.

Now that we have proved to ourselves that this works, it seems to me the next thing I want to learn about is fuses, since putting a fuse between the battery and the lights is important. Any thoughts about this? (We are trying to rely on off-the-shelf-at-the-auto-parts-store components.)

-- robert waldrop (rmwj@soonernet.com), August 03, 1999

Answers

Sounds interesting,

You might want to check out dc fixtures at an RV supplier - good luck.

-- Kristi (securxsys@cs.com), August 03, 1999.

You can use AC light bulbs with a DC power source, just remember that when doing that, the current will be higher than advertised for AC operation. The best way to explain is to take a 120 volt AC light bulb for example. To keep the bulb burning at its rated wattage while operating on 12 volts DC you'd find that the bulb will take TEN TIMES the current on DC than on AC (120 volts divided by 12 volts = 10).

Use a multiplier of ten to figure the DC current operation for your lights and use the correct heavier gauge wire and fuses for your system. Then you can compute the correct overall current load you're expecting and then you can figure the battery sizes to properly power your system.

As far as any life reduction of using AC lightbulbs on DC power, yes there will be an impact. An AC bulb is made of thinner filament wire than an equal wattage DC bulb. Under the higher current operating levels of DC operation and bulb designed for AC will not live as long.

If things go bad and stay that way you may run out of small AC lightbulbs. So I would recommend that you design your system around 12 volt automotive lightbulbs (tail lights are very good) for two reasons.

First they're relatively cheap now and so are fixtures. Go junkyard shopping on an "all you can carry for X-dollars day". Take a big bag and some wire cutters. Harvest all the taillamps and bulbholders you can. You should have more than enough for your needs with one large garbage bag full, as well as lots of strange looks from the yard operators. The second reason automotive bulbs are a good bet is that if things go down and stay down, there are going to be lots of abandoned cars available for scrounging parts like light bulbs, off of.

WW

-- Wildweasel (vtmldm@epix.net), August 03, 1999.