I don’t believe you would throw an 84 cell pack in the trash because 1P-group has been 3.65V vs. 3.83V twice, and you found a faulty cell in the P-group. The second P-group was low (3.78V vs. 3.83V) when I checked it this last time, and the BMS has clearly failed.
So you guys are saying that if your BMS fails you would just toss the whole pack and start over. Right.
Then again, everyones entitled to their opinion, and I did post to get opinions. I’m not selling this battery to anyone else, I’m the one riding it, and I’m not throwing it in the trash to start over without at the very minimum trying to fix it.
You can do what you want and you know best in which conditions the pack is.
You wrote that multiple p groups have been out of balance. For me out if balance is as minimum 0.2V differences from other p groups. Something a „normal“ (not a smart bms) can’t out balance.
If that is the case than your p groups will drift also in future because there is not only the one p group which had the optical damage somehow fucked, the other packs might have a defective cell (or cell with higher IR) as well.
With this said for me personally it wouldn’t make sense to spend a day reworking that pack just to face the same situation after 10 rides.
If the drift wasn’t that big as we thought it is, than rebuild it if you think it makes sense.
@Andy87 I do plan on reworking the pack and seeing what happens. Do you have any other suggestions other than the ones I noted to give the pack an opportunity to work properly? I may very well end up throwing the whole pack away if it continues to give me issues, but I’m going to give it a shot at least to rework it.
LLT smart BMS’s have a temp sensor internally and externally. I have the external one taped on the side at the middle of the brick. I’ll remember to screenshot to record the info one day.
You don’t. You cab also just shrink wrap and only fishpaper the sensitive parts. Either way over protecting us never a bad idea but in this case choose what is most appropriate and you feel safe with.
I personally opted with fishpaper in the middle between parallels> one strip of kapton to hold it tightly together> pcb>the shrink tubing
There’s a similar amount of solder in each blob. Just one is beaded up like water on a lotus leaf because the nickel doesn’t want to stick to it.
I’d say take the wires off, and work on the solder blob that remains on the nickel until it’s good, then put the wires back. That way you’re not fighting the wires sucking all the heat out of your joint while you’re working.
and keep your tools clean. The oxide that starts to crust over your soldering iron makes it hard to solder well. It should flow almost like mercury, not like mmmm… drippy candle wax?
It’s going to have cell level fusing via the positive terminals each having their own nickel strip spot welded to them, which is then folded over, and on the folded side, a fuse wire would connect it to the negative side of the next parallel string.
The holes in the pack are for threaded rods that keep the pack held down in compression to an aluminum baseplate, which will in turn be mounted to a trampa deck. This will all be 3d printed in PETG btw.
Alright, I’ll work on getting a better solder puddle(?) tomorrow before I solder any more wires. I didn’t use any additional flux this time; I thought the flux in the solder would’ve been fine, but lesson learned.
I’ve been tinning my tips . I think I’ll also need more heat then.
Yeah, it’s usually fine for copper, but nickel is significantly more stubborn. I actually have some special acid-based flux that I use specifically for nickel because it’s more aggressive than the regular stuff.
Yup. I made the busbar part (nickel ladder and soldered wires etc) before welding to cells.
Mostly cos my soldering finesse and care is average (also cos I like to drink beers while I work ) and that way I don’t have to worry about too much heat near the cells while making series connections
Careful to tape over the bullets on completed p groups while you work tho.
. I think I’ll also need more heat then.
) and that way I don’t have to worry about too much heat near the cells while making series connections
