How to build an esk8 / ebike battery with 18650 cells.
My waiting paid off, fogstar wholesale had an offer on 30Q cells, as they are local i popped in. 84 cells for £230.
This is my first time playing with 18650, its incredible to thing these 2 batteries are roughly equal in capacity
I dropped the 10awg wire busbar idea in favor of copper strip. I wanted more rigidity, the cable was too flexible and also hard to solder. I 3d printed some bus bar channels in abs, and glued them with abs slurry to the holders.
Then came the boring repetitive job of glueing it all together, I have adhd-pi, this almost killed me. Every cell is glued at 8 points! I can safely say this isnt coming apart.
Next i 3d printed a press jig for creating the fuse links, this worked well. I then 3d printed a holder to hold the fuses in place for soldering to the bus bar.
Finally, I sanded, cleaned and fluxed the cell terminals. Then i clamped and glued the bus bars in place. I bent the fuses so they are in contact with the cells terminals, then off i went with the scary task of soldering. The ts-100 @ 24v with largest tip does the job with ease. 2-3secs max. Im about half way through the soldering now
Right im finally done.
I attempted to do multiple terminations for equal current paths with multiple 14awg ro 10awg, but it quickly got very annoying, so i just staggered + and – after reading a research paper confirming what id suspected, that it helps with balancing. Im glad i used the large bus bars, the surface area for thew glue makes it all rock solid. I used xt150s inside the case as i wanted to make maintenance and upgrades easy. balance connections are 22awg to DB9.
I 3d printed an enclosure using PETG. Its very much form over function for version 1. The print failed part the way through due to retraction clogging, so i instead stopped printing the holes and instead drilled them afterwards, ill add louvers later. I successfully reinforced the weak print joint with a hot air station. The xt90, xt60 are glued in place with abs slurry onto a seperate 3d printed holder printed with ABS, the holders are them bolted to the petg enclosure.
Cooling is via 4 sunnon maglev fans @12v, the primary goal for thw cooling was to enable fast charging with less degradation, but ill be using them whilst riding too, with temperature control circuitry. My esk8 already has a 12v and 5v buck in the rear, so ill run another cable from to the battery. My chargers PSU is 12v too, in both cases the 12v for the fans is supplied via the xt60.
Vibration Isolation is via 15mm rubber bobbins.
First charge i took the lid off and watched the temperatueres with an infrared thermometer, no issues at all.
Then to test, i did two loops around draycote reservoir, after 10 miles it has discharged approx 30% exactly exactly where i expect to be. The acceleration is as immense as with the lipos. I then dismantled, tested every joint. All perfect.
All in all im very happy with my design. Part of me wants to build a more integrated design, but this approach was easier to design, maintain and with all the deck flex sould be more reliable. Oh and i also have lots of clearance.
I made a video on how i solder cells with a ts100, theres so many bad tutorials on youtube i thought id dilute them.
thanks for reading! hopefully it will help someone else.