Solar Li-ion battery charger - is this safe?

[BatteryCharger]

I want to build a solar li-ion 18650 charger. I have a bunch of solar cells that I will put together up to about 8v, then build an easy voltage regulator from an LM317 to 4.15v.

Is this safe to do with unprotected batteries as long as the voltage is always stopped at 4.15? This is not meant to fully charge them, just to top them off.

On the other hand, is there a better way to do this with some kind of li-ion charging chip that is easy to use for somebody who solders like a 4 year old? :ironic:

 

[mdocod]

in theory it should work fine, I would personally not hesitate to try, but I would have a volt-meter on it frequently during the first few test runs to make sure it's not over charging. Another consideration is charge rate, I don't know how big these panels are, but you'll want to keep your charge rate to a maximum of about 1C, with 0.7C being about ideal, but more than likely, you'll be dealing with much slower charge rates if you have small little hobby panels

 

[BatteryCharger]

Yeah, it will only be about 200ma max.

Can anyone tell me roughly how much juice would be left in a li-ion at 4.15v? Above 90%?

 

[SilverFox]

Hello BatteryCharger,

Roughly 95%.

Tom