£1 Lithium Ion Battery Charger

One cheap PCB from an auction site. 1 scrap bit of copper pipe. 2 bronze pennies. Put them together and charge up a 18650 Li ion cell.

If like me you have a stash of rechargeable 18650 Lithium ion cells (perhaps from a defunct laptop battery) but no battery holders, here's how to make your own. First remove the spring terminals from a dead lantern battery using aviation snips. 

Find a scrap bit of copper pipe 22 mm OD (approximately 3/4" ID). Trim it to the combined length of the battery and terminal and then cut in half lengthways using a hacksaw. Each halfpipe will make one battery holder.

British 1p coins have exactly the right diameter to fit inside the halfpipe. Pre-1992 pennies are best because they are made of solid bronze instead of copper clad steel. Make a big hole in one of the pennies to feed through the connection from the spring terminal. Make a small hole near the edge of the other penny to attach a copper wire.

Clamp the drilled pennies to the halfpipe using hose clips and solder them in place using acid flux and a propane torch. An easy way to clean up the copper after soldering is to place in a mug with a scrunched up ball of aluminium foil, add a heaped tablespoon of bicarbonate of soda, top up with boiling water, and leave to soak for 15 minutes.

Solder a black wire to the spring terminal (negative) and a red wire to the penny at the other end (the positive terminal). Put a big round solder blob in the middle of the positive terminal to improve the connection to the cell and facilitate removal. There are your battery holders. Easy!

To make a battery charger, just solder the red and black leads to the BATT+/- terminals on the charger board. I got this PCB on eBay for US $1.58 (£0.98). It can be powered by a mini USB cable and features a TP4056 chip which is a generic version of the LTC4056 Li ion charger chip.

Linkbacks

Dangerous Prototypes