@JohnA I’ll do some more research then. It just make more sense in my mind to average the capacities but maybe I’m looking at it all wrong.
What are you charging/discharging with durring testing? All I have are 2 imax b6 hobby chargers and it takes FOREVER at 5amp charge and 1 amp discharge to test all 60+ of my cells. I’m only discharging, charging, and then storage-dischaging. Its takes me a long time and idk how I’d get more than one capacity test in every cell before going insane.
yea I believe I’ll have more capacity than I’d ever want so I was planning on setting my charge and discharge end voltage pretty conservatively to preserve this battery for as long as possible. From what I understand, it dramatically lengthens the life.
Doing all of your testing on 2 max b6’s would suck… I got one of these : https://www.amazon.com/gp/product/B07428G1G2/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1
I soldered some alligator leads on the battery terminals, and then I do the fast test profile. It takes a while because it discharges them at 0.5 Amps to 2.8v (I think thats the cutoff) and then it charges at .5 amps and records capacity. It seems to work really well as far as the cycling and capacity readout, but the internal resistance measurement doesn’t seem good enough to be useful (not repeatable). Then after they are charged, I run another fast test, interrupt them an hour and a half in and see if any of the cells dropped weirdly fast or anything. (have had a few that test over 3000mah but some reason most of their capacity is in the 3.2-3.6v range instead of the 3.6-4v range). Lastly I just unplug and group the cells up.
I would be weary about the 5 amp charge on your Imax. I was doing 5amp to test some cells, and they handled it fine (no warmth or anything), but the lower the current the better. I think its best to charge lithium batteries at 1C so roughly 2.9 amps or so. I believe their original charger was just 1.5-2 amps. It is nice to know though that we can have regen be 5A per cell and they can easily handle it.
Thats how Tesla is able to get their million mile battery, they only charge up to 80% unless the driver explicitly changes the setting to fully charge for a trip. These cells seem pretty durable though (as far as fire safety), i’ve destroyed over 10 by now. My last test was over charge to 4.4v and then puncture with a screw. It puffed and smoked but no fire. One of my other cells I fully charged, put between 2 aluminum blocks for cooling and discharged to 2v. after 12 cycles it was down to 1200 mah, but still wasn’t puffed over 1.5mm. Hopefully in real world use they last.
@JohnA it been a minute. Been making any progress on your battery durring this quarantine? I’ve made some discoveries and think I’ve finally settled on the best way for me to connect batteries together. Spot welder was a bust, I had a good go at it but couldnt maintain consistent results and I’m not confident in my soldering ability on aluminum, I know this lithium is very sensitive to heat and I couldn’t stand the thought of roasting all my cells because I couldn’t solder fast enough…
So I came to this conclusion as pictured… aluminium bus bars that clamp the terminals with all-thread. The picture is just my proof of concept which proved to be a super solid joint on each battery terminal. The final product should be simpler and cleaner because I need 3/16 flat bar aluminum for the perfect size spacing between cells but none of my local metal suppliers had any, I improvised by cutting strips of 1/8th and 1/16th aluminum bar and it worked very well despite the complexity of the many cuts and holes to drill but I am very confident in the integrity of the whole thing. Have got some 3/16th bar on order and will get to cutting away soon as it gets here. Only thing that slightly worried me was puffing cells during cycling but I will probably throw a 1/16th plate in the middle of each P pack to allow for some room for expansion.
Yeah, I have been able to make a lot of progress during these last few weeks! I finished my second pack and am getting ready to seal them up in their battery boxes. I also got them on the bike bike and so far so good :).
What kind of soldering iron do you have? If you have enough power the alu solder I linked to flows pretty well. But your pictures of those bus bars look very legit. I think they should be plenty strong. It does look like if they puff too much during cycling the cell tabs could be stressed, but I think you are okay because your buss bar thickness is good. Maybe just leave some space between each p group with a thin piece of foam? Also I would be sure to sand the bus bars when you do your final install so insure a great contact.
Here are some pictures of my second pack, and what they look like on my bike!
Looks great!! Glad its going smooth for ya! You riding trails on that beast or mainly using it for commuting? My iron gets pretty dang hot but I think I’d rather go this route since I’m already invested and I can more easily swap out a dud cell later on if I need to. And yeah I was planning on using a brass wire wheel on all the tabs and bus bars with my dremel before final assembly and possibly using some conductive grease to help the connection as well. I figured with all the surface area of contact on top and bottom of the battery tabs, the resistance should be well under what I need for the current flow. Only gunna have 6 cells physically bolted together for my p groups so the total puff and cell tab flex should be pretty minimal but I’ll probably cycle a finished P pack and measure to make sure.
@JohnA I got freakin sent… lol idk how I got up with out a single scratch on me while doing about 15mph, but I wasnt hurt a lick despite wearing absolutely no protective gear. I just so happened to be cutting the corner off a 90° sidewalk turn through the grass at a park when I think the vibrations of going off road disconnected my can bus, locking up the wheels. Idk if I can configure the fail safe to coast but weather or not I can, I am definatly soldering my can bus pins in place once I swap everything over to the new deck. The drop through deck already had a weak spot that I had some what patched but I think when the drive wheels locked up, my weight shifted forward quickly enough to finally snap it. The new MBS board will work great though.
