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3S Battery Charger

Build your own Li-Po & Li-ion Balance Charger for under $10

Recently I purchased some 3S Li-Po batteries for a project I was working on. Unlike single cell batteries, batteries with multiple cells should be charged in a balanced way. This is to ensure that any single cell is not overcharged and hence possibly damaged.

Note that the battery has a two connecters. The 2 pin connecter is the output of all three internal Li-Po cells in series. The 4 pin connector is the charging plug and corresponds to the B-, B1, B2 and B+ connections as shown in the diagram below.

So rather than pay $30+ for a commercial battery charger, I decided to make my own using a 3S battery balancing board from AliExpress (Cost around $3).

One option is to connect the battery as shown above and feed 12.6V to P+ and P-. You should use a constant current source to limit the current to the mAH rating of the battery. The cells are fully charged when each cell is charged to 4.2V. You can check this with a volt meter.

To simply this process, my build displays the voltages across each of the cells on a OLED display. You can easily see when the battery is fully charged or if you have a faulty cell that fails to charge.”

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