DIY 220V Scale Lithium Battery Upgrade

If you're interested in converting a 220V electronic scale to run on a lithium battery, keep reading.

The electronic scale we're going to DIY this time has a "three-prong Pi-shaped" socket. It powers the main chip through a 9V transformer, rectifier, and then a 7805 regulator.

If you want to convert it to lithium battery power, you'll need a lithium charge-and-discharge module with 5V, 2A output and built-in protection, as shown below.

Silkscreen marked MHCD42P, this module comes with a power switch, which makes DIY much easier. Single click to turn on, double click to turn off, and it supports simultaneous charging and discharging. You can take a larger tactile switch from another discarded circuit board, which makes switching even more convenient.

The nice thing is, there's even an external soldering pad for the switch connection.

Once you've connected the wires, secure them with super glue. You can use 18650 batteries for the power source.

After installation, you can test the scale.

This scale is very sensitive—anything weighing 0.3 grams will register the same no matter where you place it on the weighing pan.

Next, check if the charging works properly. When the battery shows 75%, the charging current is about 0.3A, which definitely includes the scale's operating current.

Now it's much more convenient—you're no longer limited to using it near a power outlet.

Done.