Wouldn’t you normally want some insulation between these series cells? Looks like these cell wrappers are just laying next to each other - no fish stick ons / tesa / or even hot glue to separate them.
Wait…so each thermistor doesn’t press directly and firmly against the two cells? You’re saying they actually have pads between them and the cells?
Thermistors on their own are already bad enough. Being rounded they have very poor thermal coupling to the cells. And these being fairly large thermistors they have very slow response to changing temps. Add that onto the poor mounting you described and those sensors are practically useless. Any temp readings will be too low.
Those slotted cutouts increase the resistance of the connection between the cell’s terminals and the rest of the nickel strip. Not by a lot, but it only hurts performance and concentrates the current to four narrow strips. This will cause those points to get hotter than the rest of the strip. I don’t know by how much but at high power levels it could be by a lot.
The strip is also considerably weakened by those cutouts. Any flexing/bouncing from vibration and shocks will cause metal fatigue at the four narrowed locations.
I’d be very interested in hearing their reasons for using those cutouts as I can’t think of any benefits.
Ridiculous amounts of excess balancing wire too. With the high volume they do they can certainly get some custom harnesses made. All that excess wire just takes up valuable enclosure room and adds weight while offering nothing.
I disagree. As long as the ligaments connecting the center are have adequate cross section they will not be a limiting resistance.
Perhaps my typo threw you. I meant to say the contact resistance. The contact resistance of the strip to the cell is more of a concern for 1P high amp packs. This is the resistance that exists between two touching conductors and it is largely influenced by the surface geometry on a sub-micron scale. You get basically 0 resistance at the weld point but it increases as you travel radially outward from the weld. By providing more flexibility in the strip, the center can make better contact.
Yes, I think it is good practice to have more insulation or space your cells but I have seen a lot of packs like this. I imagine in normal operation it does not matter and the wrapper will be sufficient. In an extreme situation like a cell explodes or an adjacent fire, the cell wrappers can fail causing a cascade.
Not terrible as long as they’re all around that. Pack I just built was a new batch of p45b cells that were 3.5v. A bunch of p42a sitting around for a while only dropping 0.03v seems fine to me
That’s perfectly fine. The differences between the voltages of the cells is of much greater importance.
Some manufacturers are now shipping cells at 30% charge level in order to limit the amount of energy that can contribute to an accident during shipping so lower voltages will be more common.
Wanted to put battery build #1 here to see if it all looks good to you guys. Decided on a 18s4p build that needed to fix a Lacroix Nazare enclosure. Ordered cells from Liion wholesale, all came at 3.53v.
I ordered a Malectrics spot welder and 3s Lipo that was recommended by them. Welds look a tiny bit hot to me but that is the minimum that was required to get nickel to tear off leaving nickel behind on battery. I glued P groups together and wrapped with Fish paper. Decided on 8 welds per cell instead of 6, figured a tiny extra heat was worth it for a little extra security.
Soldering got better as i practiced but they all are stuck on there good. I pulled on each one to make sure it wouldn’t fall off. This is where I could improve most on my next build i think.
I soldered on all balance leads, covered in fish paper and then ran Negative discharge and charge leads on each side track and then covered in fish paper again since the S connections were touching them.
I dont have a charge port yet so I will charge it when I get that and monitor voltages during. I figured I should also wrap each horizontal segment in Kapton tape to cover things up and then stick the battery to the enclosure. Ill put some foam on top to take up the extra space as well.
Any chance you know where i can get a zbms or how long itll be till a restock? I dont mind paying for the good stuff, but i cant right now as its out of stock lol.
