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I'm looking to power about 10m of RGB LED strips (60 LEDs / meter) from a battery of some sort. Max current draw for the 10m run is 36A @ 5V.

My initial thought was to get a ~12V RC Car battery and run it through multiple DC/DC buck converters to get it down to 5V (probably get 8 rated at 5A or so) but I wanted to make sure I wasn't missing another, possibly cheaper, option. Runtime doesn't have to be super long... I'd be happy with anything beyond 20 minutes.

Also, note that 36A is absolute worst case scenario. Everything full white. In reality, it would probably average 1/2 - 1/4 of that... probably even less. But, obviously, I want to design for beyond max possible current to give some margin of error.

Battery needs to be rechargeable. Are there any other good (and hopefully cheap) options for providing that much power?

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  • \$\begingroup\$ Getting that much current is easy. Getting it at 5V is not. Can you make the circuit work at some multiple of 3V7-4V2 instead? \$\endgroup\$
    – Ignacio Vazquez-Abrams
    Nov 5 '13 at 0:32
  • \$\begingroup\$ Sadly, the LED strips (and the controller) require a regulated 5V. Why is it easier at those multiples? \$\endgroup\$
    – Adam Haile
    Nov 5 '13 at 0:37
  • \$\begingroup\$ Like I mentioned, I figured I'd have to run it through a regulator. \$\endgroup\$
    – Adam Haile
    Nov 5 '13 at 0:39
  • \$\begingroup\$ Because those are the multiples that Li-ion batteries come in. \$\endgroup\$
    – Ignacio Vazquez-Abrams
    Nov 5 '13 at 0:39
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    \$\begingroup\$ Thats exactly right. Each RGB element is rated at 20ma, there's 3 per LED, so 60mA each. That's exactly what they are rated at. \$\endgroup\$
    – Adam Haile
    Nov 5 '13 at 2:17
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Since you said cheap........ Any car repair place can get you a used car battery that has one weak cell. Sometimes just for the asking. Car batteries get 12V from 6 2V cells in series. So charging it at 13.8V yields a 10V output. A simple buck converter fed from this setup will get far beyond 20 minutes, even with full load demand. The buck converter will tolerate batteries that get worse for awhile as well. If that requires too much weight or size for your application then consider feeding the buck converter from a 12V 12AH lead acid cell used to power UPS. Be careful to use an off the shelf charger, or provide some temperature sensing to limit charging current if you build your own charger. Your full load demand could make the battery's internal temperature rise so it will not tolerate as much charging current.

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  • \$\begingroup\$ +1 for old car batteries, you won't get more electrons for your money. Easy to charge in the field if you arrived at the field in any sort of vehicle too ;) \$\endgroup\$
    – John U
    Feb 18 '14 at 21:36
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36 Amps 5V is about right for the 5V line of a scrap ATX off an old desktop computer. Does it have to be battery?, the downconverters for 12V to 5V are usually much smaller; just a few amps each, and probably not best suited to parallel grouping.

White LED which I've tested all had a threshold near 2.6V and a normal operating voltage near 3.1 to 3.3V. The reason for the 2.6V is the eV of a blue photon, so absolutely all should be about the same. Those would work straight with 3-ish volts off the lithium batteries which you can get this year in a cylindrical case about 6cm long. Mine are labelled "TR18650" which I think is the type and "5200mAh" which is lots, if it is not a lie from the marketing dept. You'd want to make something with copper foil to bypass the 1 Amp rated wires on a cheap type of battery holder. Supposing that you put four of those in parallel, and if necessary add more groups of four in parallel, that could give you as much current as you like at "about 3 to 4" volts, which is what I think your white LED need.

To charge that group, you'll want 4V not 5.

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