Battery Christmas lights

Running Christmas lights off batteries (DC power)

Photo by Mike Mullen  

This page was the original hook-up on the web for battery Christmas lights!

Way back in the 1990s this page showed readers how to re-wire Christmas lights to run off batteries, since battery-powered Xmas lights were extremely rare.  The article also turned readers on to LED Xmas lights, which were new and extremely rare at the time.  (LEDs are important when running lights off batteries, because you get up to sixteen times the battery life vs. regular bulbs.)  Nobody else was talking about these things back then.

Some years later, LED lights that were pre-wired for DC came on the market.  That made things easier, but you still had to buy the lights, a special battery pack, and a special charger.  And I was here to hook up readers with that combo.

But around 2011, lots of companies started to make battery-powered LED Christmas lights that you can just pop normal AA batteries into.  Now you can just head to Home Depot, Target, Amazon, or Christmas Lights Etc. and buy a set off the shelf that runs on three AA batteries for about $9.  Problem solved.

Sources for battery LED Xmas lights

• Big box stores.  I know for sure that you can get LED battery lights at Home Depot and Target, and probably others as well.  Now you know this product has really gone mainstream! 
• Specialty Online Shops.  These include Christmas Lights Etc. and LED Christmas Lights.  I ordered four sets on Dec. 6, 2011 from the former, and they work fine.  Also, Christmas Light Source has 12V strands, while the other two guys don't.
• Amazon.  Amazon has everything these days.  Several options to choose from now, and I expect more in the future.
  
• Imaginary Colours / Inirgee.  These guys used to be just about the only game in town for this kind of product, so props for that, but they've since been leapfrogged by their competitors.  Inirgee's site is ugly, hard to navigate, and their products are frequently out of stock.  But they do have strings prewired for 12V, which hobbyists will appreciate.
  
  

Use LED lights!

I can't emphasize this enough:  Use LED lights when running your lights off batteries!  They use 90-98% less electricity than standard lights, and you'll get around sixteen times the battery life.  Instead of 15 minutes with old-school lights, you'll get four hours with LED's.  I just ran a test with a big battery and got only two hours on a set of old lights, and a whopping 31 hours with LED's.  Both strands were 20 bulbs each.  Dude/dudette, use LED's.

What kind of batteries to use

AA batteries

Most LED strands wired for batteries take three AA batteries.  In my experience, rechargeable NiMH work just fine and give great runtime, despite their initial lower voltage than alkalines, so I recommend (and use) NiMH.

12V batteries

Most folks will prefer to use simple AA batteries, but if your home is already wired for 12V (like an RV or off-the-grid house), or you just want to wire up a 12V battery because it makes you feel cool, then you can buy strands pre-wired for 12V.  The only sources I know for 12V as I write this are Christmas Light Source and Inirgee.

A 12V NiMH rechargeable battery pack and charger will set you back about $20 each.  You can get them from Amazon (battery pack, charger) or Powerizer (battery pack, charger).  If your battery, charger, or lights need connectors, you can get those at Radio Shack or Powerizer.

You could make your own pack out of AA or AAA batteries, but then you'd have lots of batteries to charge.  But hey, it's your life.  If you go that route then that would be 10 NiMH's (10x1.2V=12V), or 8 alkalines (8x1.5V=12V).  Radio Shack has battery holders for that purpose.  If you're connecting multiple holders together, connect the opposite colors together (red+black).

Running a 120V AC Xmas lights off batteries

If you don't want to buy a battery-powered set, there are two ways to run your normal (120V AC) Xmas lights off batteries.

The first is to use a 12V battery and an inverter.  An inverter is a little device that converts electricity from DC to AC (or less technically, from battery-type to wall-type).  You connect a 12V battery to the inverter, and then just plug your Christmas lights into the standard AC outlet on the inverter.  It's like a mini-power plant.  You might choose to go this route if you already have a ton of regular (AC plug) Xmas lights and you don't want to buy all-new battery-powered lights.

Radio Shack has inverters as cheap as $14.  You can also probably find good inverters on eBay.  Note that many inverters come with a cigarette-lighter plug.  If the inverter is an all-in-one device, you'll run wires from the inverter to the battery.  If the lighter plug is separate, then chop it off and attach the wires to your battery source.  It expects 12V input, which could be met by a battery pack or ten 1.2V NiMH batteries.

The second way to run AC Christmas lights off batteries is to rewire them, as I explain below.  But it's such a hassle that you probably wouldn't want to rewire a whole bunch of them.

How much runtime you'll get from your batteries

Calculating electrical use is easy. The formula is simple:

Volts x Amps = Watts

Usually we'll abbreviate. (e.g., 2.5V = 2.5 volts, 25W = 25 watts).

You don't even have to know what volts, amps, or watts are, as long as you know the formula.

When you use a watt of electricity for an hour, that's a watt-hour, or Wh. An amp of electricity for an hour is an amp-hour, or Ah. Batteries store such a tiny amount of electricity that they're usually rated in milliamp-hours instead of amp-hours (mAh). 1800mAh is the same as 1.8Ah.

A typical 50-bulb strand of (non-LED) Christmas lights uses 25 watts. So each bulb uses about half a watt. (Remember that, we'll use it later.) Now we need to see how much electricity is stored in a battery.

A typical rechargeable AA battery (NiMH) puts out 1.2V and is rated at 2200mAh. Remembering that V x A = W, we see that a single battery has a capacity of 1.2V x 2.2Ah = 2.64Wh. But the lights use 25 watts. So you'd need ten batteries to power your lights for just one hour. Ouch.

You have four options for getting more runtime out of your batteries:

• Use LED lights instead. LED's use 90+% less electricity than regular lights. So your batteries will last around 16 times longer.
  
  
• Use fewer bulbs. Who says you have to use 50 lights? Use only 25 and then your batteries last twice as long. Use even fewer lights and get even more battery time.
  
  
• Use more batteries. The more batteries you use, the more energy you'll have.
  
  
• Use higher-capacity batteries. NiMH D-cells store up to 11,000mAh. You could also use a small lead-acid battery or a rechargable pack used for camcorders or remote-controlled toy cars.

My preferred solution is to use LED lights. That way I don't have to limit the number of lights I use or deal with buying and recharging a gazillion batteries. LED's offer other advantages: They don't burn out (not for about ten years, anyway), and they're rugged -- they don't break easily like regular flimsy Christmas lights.

All Christmas lights are made in China

If you wanted to buy "Made in USA" lighting strands, you can't.  They don't exist.  And even if you could find a brand that was assembled in the U.S., the LED bulbs themselves would certainly be manufactured in China.  I don't like supporting Chinese slave labor, so I try to buy all my stuff second-hand on eBay and at thrift stores.  (I just got a set of LED holiday lights at Goodwill last weekend for $6, thank you very much.)  Here's an article on the lack of U.S.-made Xmas lights.

Beware of lead in the wires

Christmas light wiring contains lead.  Some sources say that all electrical cords have lead.  Some are quick to say that the amount of lead is so small that it's not harmful, but the head of the CSPC says, "The scientific literature is abundant and has established there is no safe limit for lead."  This is no joke, as a friend of mine's child got lead poisoning from the old house they lived in and had to undergo treatment, and now the parents will always wonder if she suffered diminished cognitive capacity, since there's no way to know what her ability would have been without the exposure.  So, don't let your kids handle electrical cords, and always wash your hands after you do so yourself.

Running the lights from a bicycle generator

Some readers have asked about powering the lights from a bicycle generator instead of batteries, so they've always got power for their lights when riding around without fussing with batteries. Well, let me tell ya, fussing with a generator is a lot harder than fussing with batteries.  Plus your lights will go off every time you stop.

One problem with generators is that you need a way to regulate the voltage, because otherwise the lights would continually get brighter and dimmer as you pedaled faster and slower — and they'd blow out completely if you went too fast.  I also don't know where to get the generator, mounting bracket, and voltage regulator, so until someone clues me in on all those things, you're best off powering your lights the easy way:  with batteries.

Rewiring Christmas lights to run off batteries

Here's where you get to play mad scientist. Many devices run off only AC or DC, but lights aren't picky and will run off either.  The trick is just to rewire the strand so the bulbs get the proper voltage.  That voltage is the voltage of your battery or battery pack.  Here are your choices for battery voltage, depending on what flavor and color of lights you're rewiring.

• White, blue, or green 3.3V LED's:
  • 6V (five 1.2V batteries) for lights wired in series of two
  • 12V (ten 1.2V batteries or one 12V battery pack) for lights wired in series of four
• Red, orange, or yellow 2.0V LED's:
  • 6V (five 1.2V batteries) for lights wired in series of three
  • 12V (ten 1.2V batteries or one 12V battery pack) for lights wired in series of six
• NON-LED lights (old school "normal" 2.4V Christmas lights)
  • 2.4V (two 1.2V batteries) for lights wired in series of one
  • 4.8V (four 1.2V batteries) for lights wired in series of two
  • 9.6V (eight 1.2V batteries) for lights wired in series of four
  • 12V (ten 1.2V batteries or one 12V battery pack) for lights wired in series of five

We're gonna use standard (non-LED) bulbs in our example below because I had an old set lying around when I got the impulse to write this article.

A wall outlet supplies about 120V, so if there are 50 lights in the strand, each bulb gets 2.4V. The bulbs actually want 2.5V, so supplying them only 2.4V makes them just a tiny bit dimmer, but not much, and the reduced voltage makes them last longer anyway.  In our example below we'll supply 9.6V to our strand with batteries, which will power four bulbs (4 x 2.5V = 10V). Before you start screaming that four bulbs isn't enough, don't worry, in a minute I'll show you how to wire several sets of four together.

Most Xmas bulbs are 2.5V but some are different, and they could be more or less. Usually the voltage is printed on the box the lights came in or on a label on the strand. If they're LED lights then every color has a different voltage; white LED's are generally ~3.5V. If you can't find the voltage, check with the manufacturer. Also, don't assume that if a 50-bulb strand has 2.5V bulbs that a 100-bulb strand must have 1.25V bulbs; it's more likely that the 100-bulb strand is just two 50-bulb strands wired together.

Anyway, here's how to wire four 2.5V lights together:

But what if you want to power more than four measley lights? Easy, just create several sets of four lights and hook them all together. You can have as many sets of four as you like, though the more lights you have the quicker the batteries will run out. Here's how to wire three sets of four bulbs together.

Here's what it looks like with actual lights:

STEP 1: Make three sets of four bulbs each
I tied up the slack so the lights would be more compact.  There's nothing special between each bulb, just a continuous wire.  Remember that the outer wiring jacket has lead and you should wash your hands when you're done playing with wires!

STEP 2: Connect all the "heads" together.
That is, make sure the beginningof each set is connected by a wire.  Normally you'd wrap the power wire around the other wires, but I made the wire separate here so it's easier to see how the wiring works.

STEP 3: Connect all the "tails" together.
That is, make sure the end of each set is connected by a wire.
Normally the return wire is also wrapped around the other wires.
I made it separate so it's easy to see how it's wired.
Note the battery pack is actually eight batteries even though only four are visible
(the other four are on the bottom; it's two batteries deep).

This set would last almost two hours on a set of eight AA 1.2V NiMH batteries with 1800mAH capacity each (like the kind Radio Shack sells). Remember that each bulb uses half a watt-hour per hour. So 12 bulbs use 6wH per hour. Our batteries store (8 batteries x 1.2V x 1800mAh = ) 17,280mWh, or 17 wH. Therefore our 17 wH battery pack will power this 6-watt strand for almost three hours.

So there you have it, three ways to get Christmas lights to run off batteries!

You might also like How Christmas Lights Work from HowStuffWorks.com.

I'd like to give extra-special thanks to my good friend Jerry Chamkis (inventor of the Kosmophone) for teaching me about electronics so I could know how to do this kind of stuff myself. Thanks, Jerry!

Links:

• Technical data and practical info about LED Christmas lights

Last update: April 2013