12 slot charger with under $15 cost

Since at a point I needed to charge a very large amount of batteries and the chargers I had were insufficient (a 6-slot and an 8-slot), I thought to build one of my own, out of scrap materials...and with more slots.

The only things that I did buy were the Li-ion single cellcircuits, that's where the $15comes from.

Everything else was scrap, parts recycled from various other things (springs from industrial batteries, plastic pieces from power tool and laptop batteries, wood from remaining materials of other big wood-based projects, wires form UTP cable).

I powered it initially with a PC PSU, since I had many of them. But sometimesthe current was too high (in the case of damaged cells) it could exceed what the PSU could handle and in that case I coulduse a 5V/40A PSU from another retired project, whichcan handle the load of 12 cells in any condition and of any kind.

This is the final result:




Detailed information on the construction steps can be foundhere.

Nice. Good ol TP4056's

Just a couple of suggestions:
* If you have to replace the TP units, I would suggest going with the TP5100's. They can take a larger input voltage range, waste less energy, and are more consistent from unit to unit
* The wires that go to the coil spring side would be better if it was soldered to the battery end of the spring, or very closer to it. This reduces a lot of induced resistance/voltage-drop caused by the poor conductivity/ohms of the spring.

The TP5100 would be able to use the 12V rail of the PSU, thereby decreasing the change of so much voltage drop the units start going nuts. I've had that with the 5V rail on my own PSU, and others as well.

Now to just add an arduino with lcd screen to show you the voltages of the cells (just make sure the Pos connections are isolated otherwise you may get smoke)

Thank you for the suggestions. If the TP5100 can be powered from 12V it would be very nice since the PC PSUs today are built to provide most of their power on the 12V rails. The V-drop, in the case of bad cells gets near 4.2V at over 8 cells mostly. But that's nothing for the 40A unit (never drops below 4.8V), so I don't consider it an issue. I would prefer to power from the PSU though, it's more convenient.

The side LCD for now I considered enough, just to make sure the input does not drop too much.
As for the wires, they are like that mostly because it was an emergency build (I had to quick charge 240 cells), they definitely can be improved.
Voltage meters on each cell sounds like a nice idea; I will certainly consider that if I'll make an upgrade.

Here's a list of the TP5100.

"Input voltage: DC 5-18V (5V-12V is appropriate)"

Emergency builds are always great. Sometimes your best ideas come out at that time.

If you go with voltmeters per cell, make sure to get the ones that can be calibrated. They will have a trim pot on them. Also, make sure they are 4 wire variants, so you don't pull power from the charging circuit. Which, those aren't as cheap and harder to find as the mass of voltmeters on eBay are the $1USD 2 wire non-adjustable variants.