# How can I switch something from being AC powered to battery powered?

I'm doing a project that involves using Christmas lights outside and there's a high chance I won't have an electrical outlet nearby. Is there a do-able way for me to rig this thing up to a battery so it can light up for maybe half an hour?

sort by: active | newest | oldest
Jack A Lopez3 years ago

Like others have said, this can be done using an inverter powered by a battery. The only thing I have to add is some hot, explicit, pictures of this actually being done; i.e. xmas lights being powered by an inverter being powered by a battery. The reason you are getting pictures is because I already took them, for a related discussion, here,

Anyway, I don't know what the power requirements of your xmas lights are, but, as you can see from looking at the pictures, the string of 100 white LED lights I was using required about 1 watt on the AC side. On the DC side, power consumption was about 5 watts, meaning like 4 watts of quiescent power for the inverter, and 1 watt for the load.

Well, those numbers are approximately correct. The measurement of 1 watt on the AC side is a little suspect, since it is on the very lower end of the measurement scale of my power meter. It might be like 1 +/-2.

Anyway, it should be easy enough for you to measure the current flow (in amperes) from your battery powering-your-inverter-powering-your-lights, and of course current flow on the DC side is the number that matters for estimating how much run-time you're going to get.

3 years ago

Nicely presented Jack, the 5 watt drain out of that battery should easily run those lights for more then a half hour as requested by our gal's question.

3 years ago

Yeah. That black brick in the first picture is a sealed lead-acid battery. It weighs about 2 kg (4 pounds), and has a rated current capacity of about 5 ampere*hours. So the naive calculation says it could supply half an ampere for 10 hours (i.e 5.0 A*h = (0.5 A)*(10 h) ), but that's probably wildly optimistic.

The legends say it is "bad" to drain a lead-acid battery, even one of the so-called "deep-cycle" kind, more than 50% its rated capacity. So that's a condition to try to avoid, much like "crossing the streams". That's also bad, again for technical reasons.
;-) http://en.wikipedia.org/wiki/Proton_pack#Crossing_...

A discharge of 20%, or two hours, is probably more realistic, if it is desired to actually re-charge the battery and use it again.

I obtained the pictured, 12 volt, black brick from a big pile of dead batteries I found at my local recycling center, a place that used to be called, "the dump", in the days before "recycling" became fashionable. Most people go there to drop things off, not to pick up.

Anyway, finding a discarded battery that would actually take a charge, that was a stroke of good luck, and I would NOT expect magic like that to be repeatable. A pair of 6-volt lantern batteries, wired in series to give 12 volts, or even a stack 8 D cells,
http://en.wikipedia.org/wiki/Lantern_battery
http://en.wikipedia.org/wiki/List_of_battery_sizes
would also work, and might even be cheaper if this is just a one-time thing. Or even for something that only gets used twice a year: once on Christmas, and once on April Fools Day.

Of course, I am not going to ask what this thing is for.

3 years ago

Of course, that would be rank and crude ..... though, I also would like to know maybe by private message.

BTW we never considered if her lights are more extensive and draw more current. After all US home outlets are meant to supply up to 15amps :-)

BikeHacker3 years ago

Use a transformer.

3 years ago

I wonder how to use it ?

Maybe as a high wind anchor.

A circuit diagram would be a wonderful addition !

iceng3 years ago

Hi new member

Xmas lights can run on DC.

What is the DC voltage or battery you want to use.

The reason we need to know .... is with lower voltage the lights may need to be rewired to fit the voltage.

Instructables is a DIY site. If rewiring is not your thing.

A car battery and a \$30 inverter can do what you want.

A

kjsrocks3 years ago

just a simple 12volt batery and inverter

schel3 years ago

HI, Regular string X-mas lights are usually little incandescent bulbs..they want AC power. If it has a transformer and is possibly LEDs then YES, you can run it on DC / battery power. If they are indeed little incandescent bulbs, then you might could get a few minutes from a fully charged 12vDC car battery. If you have a car battery and can do this, you'll need this thing that turns DC power into AC power, which is what yer lites probably are wantin' its called a 12 v power INVERTER...a small one will do for your needs. pick one up just about anywhere..even auto shops.

3 years ago

Ooops meant to say...With an Inverter you could power a lot of x-mas lites for hours n hours. ..without one ...you might get 4 minutes or so.

mpilchfamily3 years ago

What kind of Christmas lights are they? Many can be wired directly to a battery you just have to use less of the lights. Otherwise use a 12V car battery and a power inverter to give you the mains power the lights are designed to run on.