Help me understand Li-Ion batteries!
June 14, 2010 2:34 PM   Subscribe

Battery and blinky light gurus - help me power my LED jacket! It apparently loves to eat batteries.

First off, thanks again to everyone who helped me with the first version of this question. I got some great suggestions, and ultimately ended up scrapping the existing LEDs for 8 cheapo AA powered (4.5V) Christmas Lights from Dealextreme. I lopped the battery packs off the 8 strings, hot glued the strings around the jacket, and soldered the leads in parallel to a PCB. I also wired a little 500ohm pot in between the battery lead, so I can turn it down when I'm indoors.

The battery problem still remains - I've tried a 6Ah battery and charger from sparkfun, as well as a 4 unprotected 18650 batteries (with this charger) in parallel in a protected battery holder. In both cases, the two battery packs worked well at first - lots of happy blinking hours until the battery protector kicked in. I was thinking I was a genius until I tried to recharge them - in both cases, the chargers start acting weird (blinking status and power lights). The batteries have a much shorter lifespan after this - perhaps an hour or so.

Am I somehow damaging the batteries, even though the circuits *should* be protecting them from overdischarge?

Bonus question - is it really unsafe to use multiple Li-Ion 18650 holders in parallel?
posted by cr_joe to Clothing, Beauty, & Fashion (5 answers total)
What you describe really does sound like overdischarge. In the case of the LiPo battery from Sparkfun, what kind of regulator circuit were you using? what "battery protector" do you mean?
posted by Mars Saxman at 2:57 PM on June 14, 2010

I am pretty sure nobody can answer this question without photos...
posted by DarlingBri at 3:06 PM on June 14, 2010

LED flashlights are kind of a ripoff, because they look bright when you test them in the store, but they are discharging the batteries at the maximum rate, in other words they are good for changing a fuse, but don't take them camping.

You need to regulate the current that goes to them.
posted by StickyCarpet at 3:24 PM on June 14, 2010

Measure the open-circuit (while not connected to a charger or a load) voltage on the batteries in question, and we might be able to conclude or rule out overdischarge.
posted by Myself at 3:41 PM on June 14, 2010

Response by poster: Thanks for the help!

The 18650 batteries are at 3.6V right now (after going in the jacket for a couple of hours, and after the weird recharge). The battery holder for these guys has circuit to protect the batteries overdischarge ( <2>5.0 Amp). As far as overcharging, the charger should take care of that. As an update, I've put only one cell in the charger, and so far no weird flashy charging.

The 6Ah battery (3 cells) is currently 3.6v (after going in the jacket and a failed recharge). It has a pcb after the three cells which I assume largely does the same thing.

Here's a couple of photos about the project: Photo 1 shows the guts. The + battery connects to a PCB with all the christmas lights in parallel. The - battery connects to a pot (to dim the whole thing) and then to the PCB. Photo 2 is the saddest possible picture of the jacket itself. It doesn't look very cool in the daytime with low batteries. :(
posted by cr_joe at 4:42 PM on June 14, 2010

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