Help me harness electricity: LED's

downer

So I'm currently working on my halloween costume, and would like to incorporate some lighting effects into it. What I'm thinking is about 3-5 LED's (maybe more). I have access to soldering irons, etc.. but, I've never done any wiring or anything. I'm willing to learn, and I'm sure I could get a handle on it. Does anyone have any pointers or how-to's?

Thanks!

MetroidZoid

Might it be easier to find short strings of LED Christmas lights and cap the ones you don't want to use?

E: Forgot to specify, I think you can find these for table top Xmas tree set ups that run off a battery pack.

vonPoonBurGer

I'd recommend against Christmas lights for a couple of reasons. First, with a string of Xmas lights you're likely going to have way more lights than you need, and jury-rigging a shorter string may be unsafe. Second, most Xmas lights work on wall voltage so powering them could be a challenge. Third, if you're using a string of incandescent (non-LED) Xmas lights, heat could an issue. And fourth, most Xmas light bulb housings are large and difficult to work with in a costume.

LEDs, by comparison, solve all those problems. They're low-power, you could easily run a significant number off a 9 volt battery. They don't produce significant heat, so you can stick them in a costume without worrying about anything burning or melting. You can have as many or as few lights as you need (within limits determined by your battery power source), and if you run the wires smartly in your costume they'll likely blend in well.

Wiring LEDs is really not that hard, you just need the following:

• a bunch of LEDs
• a 9-volt battery
• a 9-volt battery connector
• resistors (Which resistors do you need? This calculator will tell you, and also tell you how best to wire everything up.)
• soldering iron and solder
• electrical tape
• lots of narrow-gauge insulated wire

Leave the battery disconnected while working (of course), wire everything up as per the diagram by stripping insulation as needed and twisting wires and leads together. If you're not sure how long to make a wire, make it extra long. It's easy to bundle up extra wire and tuck and/or tape it down under your costume somewhere, but it's a lot more work to splice in an extra length of wire if the length you used at build time turns out to be too short.

Import points to remember. The positive (red) lead goes to the resistors before it goes to the LEDs. Running your LEDs straight off the 9 volt battery would fry them, the resistors step the power down to safe levels. Resistors do not have a polarity, so it doesn't matter which way you wire them up. LEDs do have a polarity, though, so be sure to connect the incoming voltage to their positive lead. When you buy bare LEDs, they have two wires coming out the bottom, one will be longer than the other. The longer wire is the positive lead, and power coming out the positive (red) lead from the battery should go into the positive (long wire) lead of the LED, after it's been through the resistor.

Once everything is wired up and you've double-checked your assembly against the wiring diagram, connect the battery to test it. If you hear no pops, crackles, fizzles, or hisses, see no open flame and smell no smoke, and all your LEDs function with a steady light, then you've got everything wired correctly. Congratulations! Apply a small amount of melted solder to each twisted wire connection, both for good conductivity and to ensure that the connections won't come apart during assembly or use. Wrap any exposed sections of uninsulated wire/leads/solder in electrical tape, then install it in your costume.

The LED calculator gave me this schematic for 5 2-volt drop, 20 milliamp LEDs (typical-ish values for red or green non-superbright LEDs) running off a 9-volt power source, and calculates power consumption of the circuit at ~36 mA. According to Wikipedia, a typical alkaline 9-volt battery has 565 mAh, or in other words I think you'd be able to run those LEDs for over 15 hours off a standard 9-volt battery (565 mAh / 36 mA =~ 15.7 h).