For a tiny LiPo package, I needed a charger.
Sounds like an easy one? I beg to differ.
Rather than reinventing the wheel I thought it was a good idea to get some tiny, ready made USB charger. A suitable circuit with a MCP73831 should come cheap enough from the PR of C. For around €2.50, I thought I could expect just that.
I found one that was advertised as: 3.7V Lipo Battery USB charger JST plug 500ma output. It has a charge control LED that comes up when the battery is fully charged. - Sounds good. It arrived a few weeks later.
Just to be on the safe side, I took my meter (thou shalt check voltages) and was surprised that the USB-side seemed to be shorted to the charging side of the circuit. The meter read 5V on the charging connector. Way beyond safe for LiPos.
So two minutes a little prying later, I was in. And stunned.
Inside the plug
Carefully tracing the circuit (because my initial impression just had to be wrong), this turned out to be the schematic diagram:
This "charger" is outright dangerous. I can't even remotely meet the proper charging conditions.
I have no idea where the "3.7V" and the "500mA" in the product description might come from. Possibly from the fact that some USB ports are limited to 500mA and that the nominal voltage of a LiPo cell is 3.7V.
And what are all those unused solderpads for? Maybe the original design idea was good and some electrical engineering genius found a way to cut the cost. At the expense of a few burnt down houses.
I suppose the idea might me to babysit the charger and the pack and wait for the LED to come on. Then disconnect the pack immediately. - That just won't work for me.
Watch my rant about this piece of **** on YouTube.