The battery builders club

[ZachTetra]

Trim your corners!
You can grab the nickel with pliers and roll them to get the nickel off

[YeetMeat]

Will do chief

[Jujo]

@ZachTetra

roll them to get the nickel off

@YeetMeat But try not to short it out with the body! Had my first sparkles doing that

[lazopm]

Is this too much fishpaper and kapton?
My p groups are separated with fish paper like this:

Then I added a layer of fish paper on the sides and the top.
Finally, wrapped everything with single layer of kapton

Is there any concern of overheating? I tried searching and haven’t found any cases.

[ZachTetra]

Nah more is better in our case, cells shouldn’t generate that much heat or you’ll have other problems anyways

[Simeon]

What do you guys think? 12S3P P42A with 100A LTT smart bms

[bwahl602]

It’s chunky! That’s for sure. Looks plenty capable. I would draw a max of 90 from that and expect some sag. 60-75 are more reasonable numbers.

Any reason you decided to discharge through BMS? I’m sure that 100a cost a bit and it’s big

I would recommend fishpaper between P groups in the future

[Simeon]

It’s actually pretty small and light for a mtb battery pack (just shy of 2,9kg). 135A peak from the cells should be the theoretical limit. The bms is a chunky one bacause the cusomer wanted a super safe pack.

@bwahl602

I would recommend fishpaper between P groups in the future

And there is fishpaper between the P-groups ofc

[bwahl602]

That’s the mfg rating. 30 amps per cell max if you’re not monitoring temps

[Flasher]

@bwahl602

not monitoring temps

It’s an LLT bms, dual thermistors that tell the bms to cut if heat is too high.
I had a thermistor drop out of between 2 pgroups and landed very close to a MOSFET on the esc. Result:
“It’s a bird…it’s a plane…no it’s a cutout”

[Common_good]

Hey you cool cats and kittens. Made some more progress. Re-flowed that main terminal without issue

Wired the charge leads and bms although due to my inexperience laying out the battery there are several balance leads crossing. Once I’ve confirmed that everything is wired correctly, I’ll secure the wires and insulate any crossovers w fish to solve that issue.

And now, the moment of truth. I’ve quadruple-checked my wiring and I’m confident everything is correct. Any tips before I attempt to charge (aside from taking the pack outside and having the fire dept on standby)?

[ShutterShock]

I’m assuming that you checked polarity and all the voltages with your multimeter already?

[Common_good]

I have confirmed polarity and voltages at the main terminals. I’ve seen some builders confirm voltages from main neg and progressively check each p group which I haven’t done beyond the first few. I got the correct voltage of 37.x when I checked the mains as I have the cells at nominal.

[ShutterShock]

I usually check all the way down, but before I plug in the balance connector, it sounds like you’re good to go to me lol

[Common_good]

@ShutterShock

before I plug in the balance connector

Hmmm… If you’ve wired the bms incorrectly, can simply plugging the connector in cause a short?

[ShutterShock]

Yep lol

If your balance leads were in the wrong order you’d be out a BMS pretty much, usually a resistor pops

[Common_good]

Fack… I have a few spares but that would’ve been a bummer. Glad I took my sweet time to make sure it was wired right

[ShutterShock]

Good job haha I always measure my balance connector like three times because I blew up the very first one I did a few years ago by doing it wrong and had to wait a month

[Common_good]

Main pos terminal and then each pin starting at the last cell?

[ShutterShock]

Um well I usually try to measure from the lowest voltage (cell 1) and go up (cell x) to make sure they’re going the right direction, I don’t remember off the top of my head if it’s pos or neg lol whatever works really