Mon 06 Jul 2020 08:30:14 AM UTC

Solar Lithium Battery Charge Controller

I’ve been rolling the idea around to make a WiFi weather station with an ESP32. I’d like it to be solar powered and use an 18650 battery, since they’re pretty easy to get a hold of. Of course, a battery charge controller is needed to make sure I don’t end up with a garden fire.

At first I just hooked up a standard lithium charge controller between my 5-6V solar cell and the battery. It worked quite well, charging the battery at around 250 mA. However, since the charge controller is designed for USB input, I wondered if it was maybe sub-optimal for solar.

I started looking around for an MPPT (maximum power point) charge controller for single cell lithium packs and found that a certain chip, the CN3163, was used in a few of them.

As you can see below, it’s pretty simple to use. You just have to be sure that you don’t exceed the 6.5 V input limit. A simple zener diode can take care of spikes, or a buck converter can handle a panel that outputs higher voltages. I found the english datasheet and have it available here.

CN3163 Typical Application Schematic

The best part is that it is super cheap and an SOIC-8 package. So totally hand solder-able!

Next step would be to design a little board and make a few. Question is, do I just use headers for batter connection or make an all in one package with a battery clip?