DIY CN3791 MPPT Lithium Battery Charger Guide

In the previous two DIY articles, DIY Security Camera Repair & Solar Upgrade and DIY Off-Grid Solar System with MPPT Controllers, we covered how to build a solar-powered security camera and an off-grid solar PV system. This time, we're continuing along those lines by showing you how to DIY a CN3791-MPPT 4A lithium battery charging module combined with a battery protection board and a light control switch.

You can use the CN3791 chip, which reportedly has MPPT functionality. Then, you can combine it with a DW01+8205 battery protection circuit and pair it with a light sensor for automatic control.

The circuit schematic looks like this:

Battery protection board DW01+SC8205A

For the light control circuit: when solar power is available, the battery won't output power to the LEDOUT port; when night falls and there's no sunlight, the light will automatically turn on.

You can use S8050-J3Y-NPN transistor or AO3400 NMOS, if you use AO3400, the power consumption should be lower.

The PCB design looks like this:

As shown in the PCB image, the BAT-TEST port is used to test battery charging. When the battery connects through this port, it won't charge through the protection board directly.

Here's what the board looks like:

Next, it's time to wire everything for charging.

One important thing to keep in mind is the limitation of the CN3791 chip: the input voltage must be higher than the MPPT voltage because the battery voltage has to be below 4.00V to enter charging mode.

To simulate solar power, use 13.8V. The charging status will look like this:

And that's it.