Solar Lantern - 18650 Conversion

Howdy guys! I have studied this forum many times in the past few years as I have taken up Caving as a hobby and the knowledge levels here are astounding. I did a lot of searching but came up empty so I figured I would get some input from the experts on this idea.

I have an LED solar-charging lantern. It was an extreme cheapo that I picked up on ebay several years ago. No name or model on it that I can tell. The battery was useless so I never really used it.

The light source is basically just a cylinder full of LED's with a diffuser around it and reflector below it. The circuitry and batteries are in the top under the solar panels and the base is just a large empty space where you can store the ac/dc chargers.

I opened up the top to see what's under the covers. It appears to have 3 chinese made NiCd AA batteries connected in series and a simple charging circuit. The input is 9V, 250mA.

My first idea is to convert this to 18650. I have a ton of them that I've harvested from recycled laptop batteries and I use them in most of my flashlights. I really want to maintain the solar capability for SHTF scenarios with extreme power outages... but I also want to be able to utilize my regularly charged 18650 battery supply when I really need to use the thing and it isn't charged.

I was considering installing 3 18650's in parallel in the base and running some small white wires from the base to the top through the diffuser cylinder (shouldn't be noticeable). This should be roughly the equivalent of 3 AA's in series, but with much higher capacity right?

Questions (please go easy on me, I'm a flashlight n00b):
Is there any way to reuse the charging circuit? Would the solar panel supply enough current to charge 3 18650 batteries instead of 3 AA's?

Would the unprotected 18650 cells from laptop batteries be dangerous to use in this manner?

My other idea was to install the 18650 cells in the base with these battery holders. Then I could easily replace them instead of charge them in place. Then put in some better AA rechargeables and install a selector switch so that the lantern could be run from either power source.

Glad for any help! Thanks guys!

Moving this to the Flashlight Electronics, Batteries Included forum for more exposure for battery and electronic issues.

Bill

The algorithms and circuitry needed to charge up NiMH batteries aren't the same as what's needed for li-ion cells.

Li-ions are ~4.2v hot off the charger and 3xNiMH in series might be close at ~1.45v times 3, for 4.35v, but charging the li-ions back up using a NiMH charging circuit will be problematic.

Chris

Thank you for the input!

Note: The batteries are NiCd, not NiMh...not sure if that makes any difference.

That being the case... do you think it would charge 3 AA NiMh batteries? Maybe some good eneloop batteries or something? Or should I stick with some NiCd batteries? I've read that NiMh requires lower current charging, but the AC adapter on this thing only supplies 250mA and I can't imagine the solar panel supplies much at all.

steveh_131 said:

Thank you for the input!

Note: The batteries are NiCd, not NiMh...not sure if that makes any difference.

That being the case... do you think it would charge 3 AA NiMh batteries? Maybe some good eneloop batteries or something? Or should I stick with some NiCd batteries? I've read that NiMh requires lower current charging, but the AC adapter on this thing only supplies 250mA and I can't imagine the solar panel supplies much at all.

Click to expand...

Generally, we like to charge NiMH at over .3C, so a 2000mAh Eneloop at .3C would be 600mA. .1C would be 200mA. We do this because part of the NiMH termination protocol is via temperature and at such a low rate, the batteries never warm up enough to trigger that delta T temperature point and they can 'overcharge.'

You can find NCads still, so maybe that's the way to go, or just look for some lower capacity NiMH cells, where that charger current gets you closer to .3C, or above.

Chris