Solar powered sign


Hi all,

I am just working on a outdoor LED project and need to charge (26650) LiFePO4 Battery 3000mAh 3.2V through a solar panel.

The project is very simple; I already got;

8 x 20mA LED in parallel and
2 x 3000mA LiFePo4 cell (3.2V)

The only thing is that the solar panel would be better if it can tolerate the temperature up to 50’C and suitable for outdoor use.

Are below charger and solar panel compactible with what I am trying to achieve please? And any recommendation or suggestion would be really appreciated.

Thank you.

I am happy to buy below components all together.

Hi Su,

Welcome to the forum :slight_smile: Sorry for the delay in getting back to you, we’ve been a little short staffed this week.

We don’t have anything in the way of 3.2V circuitry for LiFePO4 cells. They aren’t as popular as the more common LiIon chemistry due to their lower power density, but it’s definitely the right choice for this application as they’re very voltage stable and temperature resillient. They’re like the NiCds of the lithium world.

I’d recommend avoiding using standard 3.7v LiIon/LiPo cells for this as 50°C is definitely near the upper limit of their safe operating temperature - and by the time you throw on some self-heating during charging and being inside a box in the sun it wouldn’t be great. Might even be worth oversizing the panel a bit and adding some fans if you did want to go down the LiIon path - you may also want to look into an adjustable charging IC as you can extend battery life (at the expense of capacity) if you reduce the charging cut-off voltage.

If you want to know more about charging LiFePO4 batteries, this guy has heaps of awesome information on his site:

Battery University has a little bit too:

You could develop your own charger using a microcontroller and some voltage/current sensing, or you can probably obtain one pre-made somewhere else. Element14 have a few LiFEPO4 ICs:

With that out of the way, the other part of the story is the solar panel. Yes, you’re on the right track with that 6V 2W panel. It’s definitely suitable for your application.

And yes, those products (if it weren’t for the heat) would be a good combination.

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