Running LED strip off batteries

November 9, 2016 7:15 AM

I would like to run some portion of one of those cuttable LED strips off of a battery or batteries. Is this possible? How do I calculate how to do that given that these strips use 12v DC converters to run when plugged in?
posted by OmieWise to Home & Garden (7 answers total)

If they run off a 12V wall-wart, they'll run off a 12V car battery (or similar). Or they'll run off 8 AAA, AA, C or D cells (for varying lengths of time.) They might run (dimly) off fewer batteries, but basically, you'll need to get them 12V from somewhere.

It's possible to run LEDs, even lots of them, off fewer batteries (i.e. at lower voltages), but the strips you buy that are designed to run at 12V, won't run well at lower voltages without some significant modification.
posted by spacewrench at 7:28 AM on November 9, 2016

Expanding on spacewrench: Standard alkaline AAA, AA, C or D cells are 1.5v each. Stack them up until you get in the ballpark you need. Rechargeables tend to run a little lower voltage per cell, but probably close enough to get you where you need to go, and the only down-side of going lower is that the light will be less bright (higher may burn things out, but there's probably a bit of margin there, ie: I'd expect 4 rechargeable cells to work with a 5v strip).

Other option is find 5v strips (they exist) and run them off of USB battery packs.
posted by straw at 7:35 AM on November 9, 2016 [2 favorites]

You can get USB battery packs with 12v outputs, like this one (I have used that particular model of battery for 12v power and it was fine.)
posted by moonmilk at 7:47 AM on November 9, 2016 [1 favorite]

Here's something I learned doing just that: LED wattage ratings are for the light emitter alone and do not include the power circuit. For the same light rating the cuttable strips have a small fraction of the battery operating life compared to some other LED lights. This is due to resistors that are used in the strip configurations.

In general, it seems that the heavier bases with heat sinks run much longer on a charge.
posted by StickyCarpet at 7:48 AM on November 9, 2016

Response by poster: Y'all are awesome! StickyCarpet, did you find a different LED solution that worked better? I'm not wedded to the strips.
posted by OmieWise at 7:50 AM on November 9, 2016

I bought a pack from IKEA, cut the wire before the transformer and wired them into my boat's 12V system. Been working great for years.
posted by humboldt32 at 7:56 AM on November 9, 2016

Most individual LEDs use about 2v. You can wire them in series to add up to the voltage you're supplying, so a 9v battery can run 4-5 LEDs in series. Then, you can put a few additional series of LEDs in parallel, powering a lot of lights with a small 9v battery.

If you use too _few_ LEDs in series, then they will be overwhelmed by the voltage and burn out quickly. If you use too _many_ in series, then they will not turn on and/or will be dim. Lesson: start with more LEDs in series than you think you can power, then remove one at a time until they glow.

If you use too many LED _series_ (run in parallel with each other), then they will overheat and deplete the battery. Lesson: start with one or two series, and if the battery doesn't get warm, you can add more. Or do the math about the amps loads.

You can order the individual LEDs from any electronics supply company; they aren't expensive. Connecting them, you'll want a battery holder and some way to make the connections between them. Honestly, I think a small breadboard might be a good way to do this, depending on your specific applicaiton. If you want to make a long chain, then you can still start with the breadboard; then an inexpensive soldering iron, some solder, some wire, and wire strippers are in your future -- along with a quick YouTube video on "how to solder".
posted by amtho at 8:00 AM on November 9, 2016