I almost didn’t respond to the seller when he refused to send a pic of the pack because he didn’t want to open the case, but I was intrigued, and he was only 15 minutes away.
He told me the pack was custom built by someone on the esk8 forums (Not a fkn chance)
I still hadn’t seen inside it at this point, but I test rode it and it checked out. After chatting for a bit he said I could take the complete for $200.
I still think I got an insane deal, but it needs a lot of love.
One of the motors is running sensorless. The vesc checks out, and I got continuity on the adapter, so it’s gotta be a broken sensor wire near the motor.
I have a set of elofty dd’s but they’re 58kv so I would want this to be a 12s setup.
How bad of an idea would it be to reconfigure the battery to 12s4p?
The cells are spot welded on nickel strips. Iv’e built a couple packs, but never tried removing and re-welding a cell. I wanna figure this out before I buy a bms
Also, I’m gonna wrap it in fish paper and kapton tape the exposed connections, so don’t freak out.
He also drilled out the battery cover to balance charge externally (idfkw) so I’ll have to deal with that too. I’m on the fence of either parting it out or making it a solid beater board.
So… I recycle cells. It’s a shit ton of work. First i pull all the nickel off - shit can any that get damaged in the process. Charge and capacity test them - shit can any that act weird, heat up, or test low. Let them just sit for a week to a month at full charge with the date, voltage, capacity, and internal resistance in sharpie. Then retest voltage and IR - shit can any that drop too many volts or if the IR test comes back high.
Those that survive are sorted by capacity and IR and matched into p groups. I use a repacker spreadsheet that takes the best of a large pool of cells and makes packs with similar resistance and capacity for the entire battery. Then i clean up the cells: sand off any welds or nickel, rewrap if there is any damage (damage wrap means look under the wrap), fish paper rings, stacked and silicone into pgroups. Skip any of it and all the work you put into the pack becomes waisted as you tear it apart and have to start over.
Unless you are a masochist like me, the investment in the tools to do it are more than just getting new fresh cells imho. Making packs from fresh cells has a way lower bar for entry and has a bigger payoff. I only do it because I have consumer guilt about tossing them, and I like learning all the ins and outs of batteries.
Ps. the balance connector on the outside is a red flag to me, the pack may already be having problems or it wasn’t kept balanced and could have worn some of the p groups unevenly. Idk, could be nothing but something seems off imo.
Pretty much that will get you going, testing capacity is the most time consuming and i would highly suggest no skipping it. Does your nitecore have a capacity test mode? If it does I would take the readings with a grain of salt, same with any non lab grade IR test output.
They will vary from test to test, or even from cell holder to the one adjacent. They will let you know if something is way off but never get you super repeatable results. My capacity testing on the same cell can vary by 200mah from one test to another. So these will get you in the ball park.
For the Internal resistance (if your charger has that) you should use the exact same cell holder, setup, and procedure for every test. Fully charged, rested for a few minutes, tested in the same spot, tested with the cell making as perfect contact with the tester as possible. Better the match the better the pack will balance. I get super anal about this so remember i am an amateur, and this is advice.
Voltage is a different story, the voltage readings are usually very consistent, and because of this they tell you a-lot about the cell health. If you don’t have a good multimeter, this is a good excuse to get one. (Fluke) if you can get consistent thousandths of a volt you are probably getting good voltage readings. I made a tester for voltage and IR because my charger/tester was too inconsistent. Probably just me being anal again ¯\(ツ)/¯
Lots of decent tutorial type videos on youtube but don’t just watch one guy, some chick may have a better vid that points out something dude one forgets or doesn’t think is important. Hit a bunch of sources and remember that 99% of the packs those guys make wouldn’t last 100miles in a skateboard - we are hard on our packs
You can do an internal resistance check with just a multi meter, some leads, and a component with a known resistance that you measured (don’t just assume that the stated resistance is correct).
Side note: As for multi-meters, yes the Fluke ones are great, but they’re overpriced these days. Here: https://www.amazon.com/gp/product/B071JL6LLL/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1 is a much cheaper and just as good alternative for anyone who doesn’t have a multi meter yet. That meter is the same model my university started ordering to replace dead fluke multi-meters as well as the meters they ordered to make our equipment more covid friendly.
From a rank amateur who’s pulled a pack apart before, don’t do it bro. It’s an exercise wrought w danger. Especially when u already have a bunch of half finished builds lying around lol. Realistically, it’ll end up sitting around for months or years half baked bc you’ll get tired of the massive amount of work it takes to rebuild a pack as outlined above.
Buy some new cells and build a new battery w a daly bms (20 amps are pretty tiny) bc fuck external balancing.
Also, buy some tesa tape and line the enclosure and lid. Carbon fibre is conductive.
This is a good point, a lot of the features and protections that i require as an electrician aren’t really necessary and are just a cost premium for this or household use. Save a buck, that meter looks dope.
Ha! Didn’t mean to talk you out of it, just help set your expectations. I think it’s fun but im not entirely sane. I don’t break down and rebuild packs as a service, totally amateur. I don’t think it would make a very good business model anyway, too much time involved and too many unknowns. I could find no bad cells or 10 in your pack and it would take me two months or more to get it rebuilt… if i can.
I get free power tool cells from dead work batteries and occasionally someone gifts me a dead ebike or eskate pack. I have a little solar setup that my subpar cells go into but with the price of lfp cells getting lower each year i may give that up soon and just recycle the low capacity ones. Its got me by my sunk cost fallacy now though, so i keep at it.
It really is fun to get everything working again though so as long as you go in without expecting unrealistic results. More of a back burner rainy day project imho. And once you do the big dangerous part of pulling all the nickel series connections it is pretty safe… ish. If you already have the stuff to try, recycle accepts loose cells as well as packs made up so you can give up if it just isn’t your thing with no penalty
Replacement fuses are also apparently a lot cheaper for them. I’ve never needed to replace them but I do distinctly remember my professor getting very upset over people using the wrong meters in the wrong lab. The analog lab was more likely to have students blowing the fuse on a meter while the digital lab you would need to actively try to blow the fuse on the meters since the circuits were lower current and lower voltage.
Also I completely agree with it being a pain in the ass to rework cells when you aren’t certain on their health. I went through it with a battery pack only to fuck up with the BMS and have all my balancing work undone because the bad/ blown BMS allowed for unequal discharging. Had some cells end up bellow 3.3 volts if I remember correctly. It has since sat in the closet not being messed with because I didn’t want to bother with it anymore and also it seemed like it would be a bad idea to try mess with the cells bellow their nominal voltage.