Inside an eBay cordless tool charger - with schematic

A look inside the extraordinarily lightweight 21V "2A" battery charger, often supplied with generic unbranded cordless tools.

The charger is instantly notable for how lightweight it is. Literally just 60g or 2oz. It puts out a current limited supply of around 500mA, and uses a standard USB 5V 2A chip, but with the transformer wound for 20V at lower current.

The end of charge indicator is very simple and mainly triggered by the battery pack's BMS turning off its charge transistor or the voltage gradually creeping up to near the charger's output voltage.

The charger does work, although I wouldn't want to guarantee its life expectancy due to the pointless level of cost cutting and badly positioned foam mounting system in the case.


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