Recycled Single Cell Charger

Well, I wired up a test battery to the pcb, and it charged up. It took around 4/5 hours, which was as I expected, its an old 2.2Ahr battery and the charging current is limites to 500mA.

I took a few voltage measurements along the way to check it was actually charging, and it stopped around 4.2V.

Next step is to connect a recycled battery to it and take some proper voltage/current measurements. Then its finished and I'm good to bung it in a project.

Ive hacked apart my first Makita battery and extracted 4 candidate cells, the rest are nackered by the looks of it.

Well, components have arrived, pcb is assembled with tweezers and a distinct lack of breathing hard and at first power-up it seems to work.

I'm getting around 4V at the battery connection, and a healthy 5.04V at the output. Tomorrow I'll connect a test battery and see if it explodes..................

My pcbs have finally arrived after mucho anticipation, bit of a bargain, Seeed studio had a Chinese New Year offer of free delivery, so for two projects, 20 pcbs, £13 to my door.... Not too shabby...

Now to order the components.. To Farnell!

For the charging circuit I selected the MCP73832 Microchip LiIon /LiPo charger, this will charge at a selectable rate up to 500mA, is very small, 5 lead SOT-23 package and is around £0.40.

For the Boost circuit I selected the Texas Instruments LMR62421 Boost convertor, as these can deliver up to 2.1A, up to 24V out, is a 3mm x 3mm QFN package, and costs around £0.87.

The charging circuit is as follows:

The Boost Circuit is as follows:

I've ordered the PCBs from SeeedStudio and am now playing the waiting game, hoping it works!