Unusual battery from solar lights - AA size

[David WE Roberts]

Just taken apart a solar light and it has a single battery which is marked LI-ION 14500 3.2V 400mAh.

Same size as a 1.2V -> 1.5V AA cell.

Which means I can't charge it on the usual AA charger, nor swap in another AA battery to see if the battery is knackered or the solar charging isn't working.

Lights were working but stopped after some time in the shed.

Google shows some for sale by sites with 'solar' in the name.

Buggered if I know how to charge it to see if I have flattened it by leaving the lights switched on but not charging - can presumably only half charge it with a normal AA charger.

I will give it a kick with a charger and put the meter on the solar bit to see if that is putting out any current.

Cheers

Dave R

[Brian Gaff]

They go with a nice bang if overcharged apparently. Probably sold the balance to Boing for their new plane.. grin.

Brian

[polygonum]

You could use one of these to charge it:

If it is not completely broke. :-)

Dozens and more out there!

[Harry Bloomfield]

David WE Roberts expressed precisely :

You can buy 1/3 , 1/2 and 2/3 size AA cells, it is probably 2x 1/2 size cells in the same package.

[Andrew Gabriel]

You can do a reasonable job with a regulated bench supply with current limiting. Charge at 4.2V max, limited to 200mA current max (half the mAh capacity). The battery should not get hot (usually not even slightly warm - charging Li-Ion batteries is very efficient if the battery is working). Stop charging when the voltage is 4.2V (typically 2 hours). That's not fully charged, but it's enough to see if it's still working.

To get nearer fully charged, you would continue for another hour after it reaches 4.2V, but voltage shouldn't go any higher. You must not overcharge these batteries - they can't take it.

Some failure modes cause the battery to explode like a firework. I would suggest experimenting with the battery someplace where it will do minimal damage if it goes wrong.

Never try and charge it from anything which isn't designed for the purpose. Never short it out.

If the battery has gone completely flat, some chargers will start by charging it extremely slowly for up to an hour, before switching into regular charging. This typically applies where the battery is providing the supply for the logic which is controlling its charging (like in a mobile phone).

[The Natural Philosopher]

that is a bit strange. For LI ion

Normally they are flat at 3.2 charged at 4.2 and halfway (and rated) at

3.7..

cant charge it at all mate.

what you need is a car battery and about ...hmm., you don't want to put more than half an amp - about a 22 or 27 ohm resistor, roughly. Or a 6W

12v bulb, in series with the battery.

Depending on whether its really Li-Ion or LiFePo the voltage should slowly rise to either 4,2v, if its Li-ion, or about 3.3v if its LiFePo.

When it gets there, stop.

Its more or less charged.

[The Natural Philosopher]

Not if its lithium. 3.7V for Lithium ION and 3.3v for lithium IRON

Very simple to charge. Don't charge at MORE than the 1 hour - 400mA in this case - or let the terminal voltage rise aboove a givemn value -

4.2v for LI ION and IIRC about 3.4V for LiFe.

And dont cahrge LiFe on a LIIon charger either.

LiFe doesnt normally go bang.

[David.WE.Roberts]

Just as well I didn't read all the comments yesterday!

Stuck it in an AA charger to see if I could get it to move at all, forgot about it over night, and remembered this morning.

Took it out, checked it, and it was about 4.2V.

I checked the solar panel thingie yesterday and it was chucking out 3.2V.

So I suspect (seeing as they are sold on line as described on the battery) that they are regular Li-Ion AA batteries which are only charged to 3.2V because that is as high as the cheap and cheerful solar circuitry goes.

Anyway, it is back in the light, the LEDs glow, it is out in the garden on test.

We shall see how it goes long term.

Cheers

Dave R