Recycled Single Cell Charger

This is a single cell battery charger/boost convertor circuit

Similar projects worth following
I recently bought some Makita drill batteries on Ebay that were faulty, they won't charge. After taking them apart, I discovered that there were only one or two faulty cells in each battery. I shall attempt to build one good battery out of the batch, but I decided to build a circuit to use spare single cells in projects, as this seems to be a good way to get cheap powerful batteries.

The Design Specifications for this project are:

Must be charged from a micro USB plug.

Must deliver up to 2A.

Must be as small as possible.

Must be as cheap as possible.

Must boost the battery voltage to 5V.

Must be able to use most single celled LiIons.

Must have a charging LED.

I haven't included a battery protection circuit, as a lot of batteries come with them built it, for my drill cells, I bought a set of ten protection circuits off Ebay for a couple of pounds.

  • Still attached to eyebrows...

    FrazzledBadger04/03/2015 at 12:17 0 comments

    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.

  • It liiiiives

    FrazzledBadger03/30/2015 at 19:50 0 comments

    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..................

  • Pigeon Messenger from China finally arrived!

    FrazzledBadger03/16/2015 at 20:11 0 comments

    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!

  • Component Selection/Design

    FrazzledBadger02/23/2015 at 06:14 0 comments

    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:

    R1 sets the charging current to 500mA, and the LED lights up when charging is in progress.

    The Boost Circuit is as follows:

    I managed to squeeze the pcb into a footprint of 11mm x 30mm, which should easily be small enough to be directly mounted on the cell, and is not much wider than the micro USB socket.

    The use of planes instead of tracks should allow for a large current flow.

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

View all 4 project logs

Enjoy this project?



FrazzledBadger wrote 03/31/2015 at 08:28 point

Sorry I'm half asleep this morning, the 2A referred to the boost voltage output from the LiIon battery, not the charger.... Its been a while since I wrote the specifications and my memory is foggy nowadays...

  Are you sure? yes | no

FrazzledBadger wrote 03/31/2015 at 05:16 point

Thanks for the reply, this is true, but there are plenty of chargers out there that will deliver it, my ipad charger has USB out and will deliver up to 2.1A for example.

  Are you sure? yes | no

O. Alan Jones wrote 03/31/2015 at 01:26 point


How are you going to get "up to 2A" from a a micro USB plug? Are you going to be using a powered usb hub also? Just curious. I like your project. USB 2.0 will only give you 100 to 500 mA.

  Are you sure? yes | no

Similar Projects

Does this project spark your interest?

Become a member to follow this project and never miss any updates