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FS8205A Mosfet Battery Protection

Not so much a circuit I build this week, but rather a commercially bought circuit/shield that I thought I'd have a crack at repairing. I ordered some 18650 battery chargers which also double as a power supply (claimed 3V-1A and 5V-2A output).

Everything looked wonderful until I didn't read the many warnings on both the board and the website and stuck an 18650 battery into the holder with the wrong polarity. ZAP!! Burnt finger for me, and magic smoke production for the charger.

Always read the fine print

I suppose a normal person would throw the whole thing in the bin and look for a commercial replacement at many times the cost. But after taking a closer look at the broken board I thought that only one component looked completely spooked by the experience - a little 8-pin TSSOP package sitting on the edge of the board. I couldn't tell what the label was through the charred remains, but in an un-fried version of the same board it seemed to be a FS8205A Mosfet Battery Protection IC. The cost of a new charger/power supply is around AUD 3.81, and cost of 10pcs FS8205A is around AUD 0.77, so no problem - order and wait.

When the chips arrived, it was simply a matter of de-soldering the fried chip using a hot air gun, and then plonking on the replacement and re-soldering. I do enjoy the SMD soldering and if you are a little wary of it then order one of the many practise kits available and have a go - it's not that difficult. A pair of comically large enlargement glasses can help as well.

Normal operation

Fried guy

De-soldered old chip with keen replacements in the background

Re-soldered and ready for action

The end result is a working charger and power supply, and a glow of satisfaction for it's owner. Nice one.

Postscript: the "un-fried" charger went "fttt!" as well with the same component at fault, and this time I didn't put the battery in the wrong way, so obviously a bad batch of mosfets and probably the reason for offloading stock cheaply to unsuspecting Tasmanians half a world away. Anyway, a desoldering and resoldering session ensued and now I have two perfectly fine chargers/power supplies!