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station240's 18650 projects
Concept for battery charger for LiFePO4 pack.
For a single cell just connect a 5V switchmode PSU (eg ATX computer powersupply) to the input of TP5000.

However I want to charge the 4S 12V pack without needing a BMS, so I came up with this.
T2 is simply a transformer constructed with an equal number of turns for each of the 5 input/outputs.
The original output components are either re-located or tossed into the junk box.
I've got some pre-dismantled transformers that will suit.

In reality the PSU output has extra parts, filter inductors, feedback components etc.
The feedback circuit just needs to be tied onto one of the new outputs.

Why I chose the TP5000
a) Has the ability to modify charge current and voltage. 4.2V or 3.6V, 100mA to 2A
b) Found some cheap here I ordered 5 so asked for and got a small discount on top of that.
c) Uses an inductor so it's a buck based circuit, hopefully more efficient and less heat.
d) Has a full size LED, and pads to solder it into. Hence can be made neater and easier to see the status.

Plenty of time to construct the extra circuitry needed, which I plan to bolt to the output of an ATX PSU.
Couple of things on my shopping list for the new year.
Pre wired 4 slot 18650 holder, only have 3x single holders at the moment.

Cell frames/holders for 26650 cells, if I can get my hands on some of those.

Finally found a suitable resistor for a discharge tester, 2.2ohm 20W
Did a high current discharge test on a 18650 A123 cell the other night.
Cells are rated for 30A continuous discharge current, so that what I did.

Used 82cm length of 0.36mm copper wire, a calculator I wrote was used to work out if it was suitable.
Cell got barely warm, the wire got very hot.

Safety followed for this test:
1) Conducted outside on concrete path.
2) Bowl of water next to cell.
3) Wire soldered to positive end of cell, left unconnected to other end.
4) Other end of wire gripped by pliers and touched against negative of cell.

All in all successful test, cell did not overheat, nor did the wire unsolder itself. Both things I was worried about.
Will repeat with a second test, one I have the charger to fully charge the cell, and because I forgot to attach the multimeter's temp probe.
Should also measure the voltage under full load, see how it compares to the datasheet.
Are you still looking for these cells?
I think I have at least 4, although some of the text on the cells is slightly different. They were out of a dewalt power tool battery.
They are dame colour as your photo and have following text.

They have LR1865AM APR18650M1A

They were all harvested at 3.29 volts.
Let me know if they are useful to you.
                                                Choose LiFe  Wink

                      May all your batteries be fully charged and perfectly balanced  Cool
Yes still after more cells, need a few hundred more.
LR is Lishen, somehow involved in the new owner of A123.
Gotten a few things over the past few months, been too busy to document it all properly.

Got given a very rusty ammo box with random tools in it, no prizes for guessing what that is used for.
Big box of random cables, three big AC contractors to re-purpose, and some new electronics I ordered.

got six 36V Dewalt packs off ebay, didn't expect to get 1x A123 pack, 2x Samsung pack, 3x Sanyo pack
So end up with:
9x A123 26650m1-N LiFePO4 3.3V 2.5Ah (one had leaked and is dead)
39x Samsung IFR18650-11Q LiFePO4 3.3V 1.1Ah (one has clearly overheated and is dead)
30x Sanyo UR18650RX 3.7V 1.95Ah  in varying poor states of charge (some already binned)

The one A123 pack is good, bar the mess the leaking cell made. I will rewrap the cells later.
The Samsung packs are wired in 10s2p, so the current is shared over two cells.

The Sanyo cells have issues, for a start they were wired in 10s1p with 10 dummy cells. Probably had a hard life. They are also 3.7V Lithium cells, so not much use to me at the moment.

So far I have recharged all the LiFePO4 cells, and didn't that take ages. Not capacity or resistance tested them yet. The TP5000s arrived obviously.
Going to shift all this onto twitter, the almost complete lack of interest here is depressing.

< twitter link there

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