Electronics advice: LED costume battery replacement

The Hackspace Electronics
1

I’m trying to modify a friend’s LED wing costume (pictured) so that it runs off USB power, or failing that some rechargeable source rather than the 3xAA cells it currently uses.

led_wing
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It draws quite a lot of power, pulling 1.75A out of a fresh set of AAs, and this pulls the battery voltage down to 3.65V. The circuit is very simple; it’s just the battery and LEDs all in parallel so far as I can tell, like this:

led_wing_circuit
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My assumption is that the AA cells and wires provide all the current limiting.

My ideas so far have been to drop the 5V USB voltage with a couple of big diodes and a 0.2 ohm resistor, or to use an LM2596-based buck regulator module with the same resistor. Both of these work, but the diodes or LM2596 get unacceptably hot. The LM2596 gets up to 70°C, which is no good for something that has to be worn or held in a pocket without a carefully designed enclosure.

The other option is to run this directly from an 18650 cell, which is close to the desired voltage - but then there would be no deep discharge protection on the cell.

Does anyone have any ideas before I throw in the towel and just buy a crate of AA cells?

2

Worked in led costume design for a while and had this exact problem. Research at the time indicated the cheapest good method was a ‘buck converter’ which is a cheap switched dc-dc board usually used for RC vehicles.

I think they often/always have discharge protection too. This is from memory of a project 10 years ago, so mainly just saying that’s the term to google.

While I’m here, the other major issue with led costumes is that chained leds often fail high so you can get overheating due to one failing and the ones following that in the chain getting unreasonably hot.

3

You can get 18650 cells with ‘built in protection’, which provides low voltage cut-off in the cell, then run it directly from that maybe?

BAK N18650CK 18650 Battery | 18650 Lithium-ion Batteries | Fogstar UK is a good example

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RC vehicle stuff sounds like it’ll come well packaged as well which is a plus, so thanks for the tip. Protected 18650s are a new one to me as well, so thanks both for the suggestions!