I’m trying to help my daughter with a school science project, in which I wanted to take a bunch of Christmas lights out of the string they came in, and use my own wires and a battery to make them light up. I decided to use a 9-volt battery, because the 1.5-volt D cell I originally tried was only good to light one, or two very faintly. However, the very thin wire I was using started to get hot and smoke when I tried touching the ends to the 9-volt. So I’m guessing that I need something thicker - does anyone know just what thickness of wire I’d need to safely conduct 9 volts? How about 18, if 9 doesn’t look bright enough to me?
Wow, it must be really thin. The wire they come with is less than 22 gauge, so is already pretty thin, so I’d suggest using the same gauge. If the wire is getting hot, it seems you may not be wiring the circuit correctly.
The voltage isn’t what matters. What matters is the current. This isn’t to say they are completely unrelated, because, especially with simple devices like Christmas lights, the more voltage you have the more current you’ll have as well.
Are you connecting the lights in series or parallel?
Do you have access to a voltmeter? Alternately, do you know what type of bulb it is? Bulbs are rated for a particular voltage and current. If you exceed the recommended voltage per bulb, too much current will flow and the bulb will burn out.
It’s hard to give you a specific number without knowing how much current you are drawing.
There’s a wire chart here:
If you are using say 24 gauge wire and it’s starting to smoke, then you know you’re up around the top end of how much current it can handle (about half an amp). That might give you a rough idea of how much current you need to be able to handle and what size wire you might need to handle it. 22 gauge for example would handle closer to an amp, and 20 gauge would handle about 1.5 amps. Replace 24 gauge with whatever wire size you are actually using, and go down a few numbers in wire size and you should be ok.
Get a better idea of the current draw and you can get a more exact answer from that chart.
Remembered one other important thing after hitting submit.
If these are LED lights, they are much more sensitive to how they are driven than regular bulb type Christmas lights. With the light bulb type, the more voltage you use, the more current you’ll get, and the brighter the bulb will be, nice and simple. LEDs don’t have a nice linear relationship like that. As you increase the voltage, LEDs will stay too dark to be useful for much longer than a regular bulb, then will all of a sudden go from too dark to see to so bright that they overheat and burn out over an extremely small voltage change. With LEDs you need something to limit the current, or you have to be very careful about the voltage. With Christmas lights, LEDs are typically driven without a current limiter, and they rely on the voltage being divided across multiple LEDs to get a fairly exact voltage across each individual LED.
And yes, the wire I’m using is extremely thin. I started with the intention of using a household-type 120 v AC wire, but when I stripped away the insulation, I found it to be made up of about a dozen thinner strands, and it was impossible to twist it together with the wires that came out of the Christmas light bulbs. So I pulled a single strand - very thin - and was able to get it working OK - for one bulb on a D-cell, then 2, but dim. Then I added some more lights, but since I knew I didn’t yet have the power, didn’t test them, so it is certainly possible that my connections aren’t 100% right at the moment. Then I got the 9-volt battery, and I connected the ends of the wire, and got the smoking (but the bulbs didn’t light). So I’m figuring I need to get a thicker wire.
You can probably tell what voltage the bulbs expect by how many there were in a strand. If the lights plug into 120 volts and there are 30 bulbs per strand, each bulb expects about 4 volts.
If you hook them up in series, the total voltage will be divided over the bulbs. So if you have 2 bulbs in series connected to 9 volts, each bulb gets 4.5 volts. If there’s a transformer or a controller of some sort in the stand, then the actual voltage may be a lot lower.
The voltage actually divides proportionally according to the resistance of each bulb, so it will only divide evenly across the bulbs like that if you use identical bulbs.
You can get hook up wire at Radio Shack (as much as I hate to recommend them for anything). Auto parts stores will also have relatively small gauges of wire.
On preview I see that they are 2.5 volt bulbs. If you hook four of them in series to a 9 volt battery you’ll get 2.25 volts per bulb which is pretty close to their operating voltage.
Great web site - I wish I had seen it before embarking on this project.
Still doesn’t tell me exactly what type of wire to get, though. Hopefully that “hook up wire” that engineer_comp_geek mentioned getting from Radio Shack will be good.
solid telephone wire (4 solid wires, what you would run in walls or tack on baseboards) or doorbell wire is inexpensive and available at building supply (they will maybe sell by the foot and you buy what you need) and most hardware stores.
Mostly the smallest wire you find in telephone or signal wire is 20 or 22 gauge. It should be plenty to carry a few small Christmas lights. My guess is that you have too little load and it is too close to a dead short. e=IR If R is very small, even a t9 volts, I will be large. with excess draw, the battery will get hot too.