For the past year or so, I have been testing 18650 Lithium-ion cells from recycled batteries in order to re-use them to power my projects. I started out testing the cells individually with an iMax B6, then got a few Liitokalaa Lii-500 testers and some TP4056 modules for charging, but the testing still took way too long for my liking. This project has been a long anticipated one for me, and I am now able to test 36 cells and charge 40 cells simultaneously.
All the testing carried out with this test station followed this test protocol.
A fair amount of people in the community of people re-using laptop batteries use the OPUS BTC3100 testers, but those were a little expensive for me. When I found the Liitokalaa Lii-500 testers for under $20 each on Aliexpress, I ordered 6 more to complement the 3 I already had, as well as 50 TP4056 chargers, and some 4 cells holders. The power supplies I used were from Aliexpress as well – 12V 30A and 5V 60A, but a better option would have been to used server power supplies.
I’m sure that almost everyone that has a basement lab is looking for every way possible to get more space, so using up a ton of desk space with a charging and testing station is not ideal. Such is the case for me, so I decided to make my testing station a sliding drawer underneath my desk.
Building this was fairly straightforward, but required a lot of time. I designed some 3D printed clips to hold the 10 4 cell holders and the 9 Liitokalaa Lii-500s to the plywood that I used as the base.
I connected the BAT+ pad on the TP4056 modules directly to the cell holders, and ran wire through the holes in the battery holder to connect the other end to BAT-. This was a very elegant solution, and only required 1 wire per slot, 40 in total.
Power lines for the TP4056s and Lii-500s were made out of 3 x 18AWG wire from old Christmas light string. I stripped the insulation, and twisted them all together using a clamp and a cordless drill.
I lined up the positive wire just in front of the TP4056s, and the negative wire was connected directly to the USB ports, which are grounded. To connect the 5V line to the IN+ pad of the TP4056s, I used leftover resistor legs, which were the perfect length. Connecting 12V power to the Liitokalaa chargers was done with the same Christmas light wire, as well as some DC barrel connectors, and plenty of 3mm heat shrink to protect against shorts.
Moving on to the AC wiring for the power supplies, I got a fused power socket with a switch, and connected it to each of the power supplies. All the AC wiring is done on the underside of the plywood, and is secured using some 3D printed cable clips, printed out on my i3 style printer. I attached the power supplies to the board using 3D Printed brackets. A small voltmeter was added to the 5V and 12V power supplies for a quick check of the voltage.
After plugging in the power cable and turning on the switch, everything worked great!
One thing that I noticed as I was charging 18650 with these TP4056 modules was that they got pretty hot (too hot to touch) at the CC part of the charging curve. The TP4056 modules are linear chargers, so they ‘burn off the extra voltage as heat’. If you start charging your cell that measures 3V at 1A from a 5V source, then the power wasted as heat inside the chip will be (5V-3V)*1A = 2W. I started by adding some small 8x8mm heat sinks to the TP4056 chips, and then adjusted the output of the 5V power supply as low as it could go. In this case, it was 4.9V. Now, they never get too hot to touch.
Project by: Micah Black
Written By: Micah Black