Remote Living > Lighting
LED battery substitution
dnix71:
I have 2 different "Commercial Electric" brand LED battery powered flashlights (aka "torch" to those in the UK). The smaller of the 2 uses 3 AAA alkaline or carbon-zinc cells and has a base which is the same diameter and threads as a common palm torch sold everywhere here for $1.99US under no name. Even the battery holders between the two are interchangeable if you bend the springs a bit.
The palm torch has it's on-off switch in the base and the other, like it's bigger cousin, has a push button on the side.
The largest torch uses two 3.7v lithium cells in a series pack.
Since a AA battery is pretty much the same length as a 3 AAA pack, I tried a AA size 3.2v LiFePO4 cell in a AA battery holder in the two smaller torches and they both work. I clipped off the wires on the AA holder and added a bead on solder top and bottom. It takes a little bit of practice to get the replacement pack seated on the springs but once done the lights work as well from one higher voltage cell as they did from three lower ones.
The smaller light has 9 LED's, the larger has 16. There are versions of the palm torch sold here that have 7, 5 or even only 3 LED's. All the palm torches work for hours on alkaline AAA's, but the 16 LED torch really should have had a bigger battery pack.
A 3.2 LiFePO4 cell is pretty near the safe discharge limit at 3 volts, which is also the minimum voltage needed to light the LED's so if you use a rechargeable cell it shouldn't be ruined if you run the light until it quits. A single LiFePO4 cell is cheaper here than 3 AAA's, so it's an affordable hack.
Simen:
LiFePo4 cells has a discharge limit at 2.5V, and a charge limit at 3.65V. (As opposed to 3.00V/4.20V for most other Lithium based rechargeable cells.) ;)
Harold in CR:
My Son sent down 3 Home Depot special single LED lights. They are unbranded, 5 inches long and have the end switch.
I took out the triple battery holder and took 1 laptop lipo battery, cut a piece of PVC pipe and split it down the side, and slipped it over the lipo cell. I then took a freshly charged lipo cell, and did a discharge, bleeding off that 4.15 v, down to 3.9.
Doesn't take much and, the LED seems fine. At night, this light can illuminate things over 100 yards away, no problem. The end switches are junk, so, I need to figure out a switch. IF I tighten the end too far, the switch doesn't function, so, I back it off until it works OK, then run a couple wraps of vinyl tape around the joint.
RandomJoe:
Very cool. I have quite a few of those little "unbranded"-style LED flashlights, will have to go get some AA LiFePO4s. Never even thought about that... (The only LiFePO4s I have so far are A123 packs, so a bit large...)
I've wondered what's up with the switch on the end of these flashlights too. Seems remarkable they'd make what's otherwise a very nicely machined item only to use such a ridiculously flimsy switch. Every single one of mine has gone bad.
I also have a light like the large one, actually had a second a while back that I gutted. Both used six AA NiMHs in a soldered-together pack, wonderful lights while they worked but the batteries were awful. Died in a hurry. Had to do surgery to get the base opened, they were WELL glued, but might be able to put the second back together with a new cell type inside.
I don't know whether to be disappointed or happy - so disappointing to see otherwise-useful kit basically destined for trash/recycle because of short-sighted design decisions, on the other hand long as I can intercept the stuff I do get lots of nice goodies to tinker with free of charge! :)
RandomJoe:
That's quite impressive... Went by Home Depot and got some Hampton Bay-branded cells, two for $13, rated 1AH. Out of the pack they measure 3.45V, and work a treat with the small LED flashlights. What really surprised me was that I can't tell the difference between the LiFePO4 at 3.45V and the AAA pack at (unloaded) 4.27V.
Fluke meter says they are drawing 60mA with the LiFePO4, and 120mA with the AAAs. There are 9 LEDs in parallel so I was expecting closer to 180mA, and would have thought they'd be noticeably dimmer at only 60mA. The LEDs ought to last forever at this rate! :)
Now I just need to fashion some sort of 2-cell holder to try them in the larger LED light, and a holder / jig for the charger. I have a Cellpro Multi4 which should charge these just fine - has a preset all ready for them - I just need to connect to the charging harness.
I am curious about battery sizes though. Reading the OP, and some other posts I found online, I got the impression an "AA-sized LiFePO4" was actually the size of an AA - would even fit in an AA holder. The ones I got are in fact the same *height* as an AA, but are noticeably fatter than even my highest-capacity NiMH cells, which are already quite a tight squeeze in an AA holder. Are there several sizes of these things running around?
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