I kept threatening that I would get back to another battery holder build. I finally did and made a couple of different kinds. Unfortunately. I neglected to take any pictures while building this first one, but it's not rocket science. Each 3 cell holder has all 3 cells in parallel. The end of one holder is hot glued to the next holder until I have 4 in a row. I made two sets of them. Then I used some 14 awg transformer wire from a failed motor wind and soldered it to the solder tabs between two battery holders. This connected the first holder to the second holder as well. I made lengths of wire that are a little more than 2X the length of the battery holder solder tabs. Once I had one side completely soldered together. I then did the other side. That left a small gap between the two halves of the pack. I then folded the wires over so that the two halves were back to back. That gave me two sets of 12 cells each per side. I then soldered the bottom ends of the 14 awg wire together and pinched the bent in half parts together. A few more bits of soldering onto the folded over section of the wires for balance wires and I was nearly done. Then came some 14awg silicon wire for the battery leads. A little hot glue to secure things in place and it was finished. I've been running this battery holder for 24 hours at least now. I made a small load tester out of some old blow drier parts. I didn't have a way to load test all the used laptop cells I have until I scrounged one up from old blow driers. This battery holder worked exceptionally well with the load tester and allowed me to test 24 cells simultaneously. Of course I can also charge 24 cells at the same time too. I put my celllog on the balance port and watched for cells to reach 3 volts. Once that happened, I quickly pulled all the cells out of the holder and checked their individual voltages. Invariably, One set would run down faster than the others in the 4S series. Whatever ran down first to 3 volts was when I stopped the test. What I noticed is that despite their being 6 cells in parallel times 4 in series that a weak cell could be found anywhere in the pack when I checked them one at a time. As a result, the cells that had lower than average voltage were obviously the weak ones. The rest I considered to be "good". I have culled probably 30 cells from the several hundred I have. I'll pull my 20S2P packs out of my scooter and load test them too. I'm curious to see how many have gone bad...if any.
This pack is 4S6P.
This battery holder is 6S6P. It's the prototype for the 24S packs for my moped build. I started out with 3 battery holders and hot glued them end to end into a long strip. Then I made 3 more strips. Then I took 2 of them and hot glued their long edges together...times 2. That gave me my two halves. I was wondering how I was going to connect those inner solder tabs to anything and then came up with a foldable interconnect. I soldered the long "leg part" to the individual tabs in the sets of 3 cells. Then once all 4 sets of interconnects were done, I collapsed the whole thing at those large bends. I had to flatten out the bend a little to get the two halves to close up, but it worked very well and since I made sure all my solder joints internally were well flowed and not starved for solder, nothing broke apart. Once it was all collapsed together, I soldered the folded part together and the exposed end solder tabs.
This is the interconnect part. I made 6 of them in case I screwed one up, but that didn't happen.
A couple of views between the two halves before I collapsed them together. The top half and the bottom half are on separate interconnects that don't meet in the middle. There's about 1/2" gap between them. They can't short together in the middle of the pack.
This is the " back end" of the pack where the top row connects to the bottom row to make the 6S series.. That scuffed up 14 awg transformer wire sure came in handy for making interconnects! The extra long end was later bent over and buried in hot glue between the two halves after I soldered a balance wire onto it.
This is the battery lead end. I later shortened those ends by a good bit. When I made these up, I didn't really know how long I should make the ends for attaching the battery wires.
With all those batteries going back and forth in the pack and on both sides, it would be easy to lose track of which way a cell should go and create a dead short. Every slot in every battery holder is labeled. 2 batteries dead shorted end to end would be a very bad thing! More than likely, it would be 6 batteries with one of them backwards. How long would it take for that single cell to go thermonuclear?
And the final product...complete with an XT60. Some of the balance wires are longer than others, Any slack was stuffed back inside between the two halves and then hot glued in place so they can't move. At every solder connection for the balance wires, I hot glued them in place too. I suppose if you pulled hard on the balance cable you could pull it loos, but it's buried in quite a lot hot glue. Same for the ends of the battery leads after I closed them up in heat shrink. I've got 36 18650s charging in this battery holder right now. Assuming 2600mah per cell and there are 6 in parallel, well that's 15.600mah times 6 sets in series or 93,000mah. This thing is going to take a good while to charge up! I maxed out the charge current on my balance charger, but it will still run for hours.