Arduino Fio DEV-10116 — small fire when charging

[lfsc]

Background info:

I am working on a project that uses Arduino Fios as the brains of four model wireless windmills. The rotation of the windmill hubs generates voltage (less than 2v) that connects to a shield. The shield consists of a rectifier, capacitor, and pulldown resistor, and sends the windmill voltage to an analog pin. Every few milliseconds, each Fio wakes up from sleep, measures the voltage from the windmill, and compares it to the previous voltage. If the voltage is different, it wakes up the attached Xbee radio, transmits the new voltage value, and then puts itself and the Xbee back to sleep. The windmills operate wirelessly during the day, powered off an [Adafruit 328 Lithium Ion Polymer, 3.7V, 2500mAh battery . At night, they are charged in parallel to a 5v, 2.0a power supply via barrel plugs connectors in the bottom of the windmills. Those connectors are plugged into JST connectors at the CHG 5v + and – through-holes on the Fio board.

https://i.imgur.com/jP3xfqT.jpg

https://imgur.com/GkYCL8T.jpg

https://imgur.com/4HrqEI8.jpg

The Incident:

I have been having some trouble with charging reliability. After significant discharging, the windmills sometimes fail to charge the batteries. When I have taken them out, the microcontroller still works, but the charging circuit is dead. Frustratingly, it tended to start working again after a few hours or days, so I hadn’t pinned down the source of the problem. However, the other day, I opened a malfunctioning windmill, and there had been a small fire, originating at the LiPo charge management controller ( [datasheet).

https://i.imgur.com/CxC0o9A.jpg

https://i.imgur.com/88tmIRE.jpg

Upon closer inspection, the other Fios all show some degree of bubbling or scorching at the same location.

https://i.imgur.com/TKBvP1J.jpg

https://i.imgur.com/TPYf4dD.jpg

Speculation:

It seems that there is some circumstance in which there is a rapid discharge/short circuit at the charge controller. I would tentatively link it to charging after heavy use i.e. the battery is more discharged than usual. Could there be a conflict between the batteries’ safety logic and the charge controllers’? Did I improperly spec the battery for this board? Has anyone else encountered this? And how can I go about fixing this? Should I upgrade to the V3? I don’t mind spending the money, but I don’t want to drop $150 if it won’t solve the problem.

Any help would be greatly appreciated. Thanks!](https://cdn.sparkfun.com/datasheets/Components/General%20IC/33244_SPCN.pdf)](Amazon.com)

[TS-Chris]

Hello, and thanks for posting and including your photos.

The only thing we have seen that causes the charge controller chip to fail like this is if one of three things happens:

- A battery is connected with backwards polarity.

- A power source is connected with backwards polarity.

- Your power source exceeds 6 volts, even briefly.

I don’t think that the protection circuitry inside the battery would cause an issue as it’s designed to limit charge and discharge current. Most lipo protection circuits will also prevent the battery from over discharging as well but I don’t know if your battery has that protection or not. The charger IC will also limit charge current to prevent damaging the battery or itself so I don’t know what could be causing your problem.

The only thing I can think of is your power supply that you use for charging might not be regulating properly and could be drifting above 6 volts at sometime during the charge cycle and causing the IC to fail.

You might try a better power source as your charging power supply.

The Fio V3 uses the same charger circuit so there isn’t an advantage to using the V3 over the original. It’s also more expensive than the Fio. As long as the Fio is working for you (other than the charge issue) I’d stick to using it.