All groups are consistent except group 1.
I’ll replace the group, test it with the old BMS, then swap the BMS if necessary.
I’ve got over my popped welds issues since getting a Maletrics.
I’m fine at series connections (though I could practice with copper braid more).
BMS wiring and BMS settings are the main place I feel my knowledge is lacking.
I’m also pretty tempted to sell off everything related to pack building and just buy a skyart or duck pack. But then I think of my sunk cost fallacy…
So I’m now trying to get my head around the cause of the sag:
Some cells are bad (the P-packs saging the most according to the BMS I’d say), they had similar capacity and IR before putting them in a pack
Nickel is not welded properly to the cells (tho 4.2V sag at 50A is like 210W, that would be noticable on the temperature?). I have 10mm 0.2mm nickel linking the p-pack then another folded 0.2mm nickel strip to make the series connections… At this sag it would mean I have a 0,09 Ohm resistive load somewhere, which I’d say is possible?
Cold joint on a weld, tho I’m 98% sure my connectors and series connections are welded properly with no cold joint
Murata VTC5A cells dont behave like Sony cells ? (@Battery_Mooch is that possible?)
There’s a lot of mass available to spread out the heat and the pack is thermally insulated, preventing us from feeling the heat. Temp sensors can give us a very, very rough idea of the temps but often not in locations that really help us.
The pulsed nature of esk8 pack use allows high heat generating periods of riding to get averaged out too, hiding the fact that so much heat is created.
Anything is possible but cells from the major manufacturers are stunningly consistent. In my testing the Murata cells were essentially identical to the previous Sony-manufactured VTC5A’s.
IMO Murata would haven been stomped silly by the huge customers they inherited if anything changed when they bought Sony’s factories.
Yeah I was just throwing ideas never know 
So it leaves me with bad spotwelds or cells, now to find were and which ones… Should have shown them on here before welding the series…
That’s what I thought about the heat, would have to try it longer at high use to be able to see anything…
Thought about attaching thermocouples to each p-pack to find the culprit(s) but again, placing them near enough to sense anything useful would not be feasible…
I haven’t done all the math, but the sag feels right if using 10mm nickel for the series connections. Most use 2x 12awg or 2x 14awg copper wires for the series connections. I wonder if you could solder some copper series connections on top of the existing nickel and see if the sag improves?
On top it’s already 12AWG copper wire, should have mentioned it
Some pictures are there
Has been taped and shrink-wrapped since then
Yeah that looks pretty good regarding the series connections. How did the welds look? Which welder?
I as an idiot didn’t take any pictures when welding…
They didn’t look over burned at least
If a remember correctly I was welding with a kWeld (and a big ass lead acid battery) at 27 joules, more than that and I was burning through the nickel, wrote the values down somewhere but can’t find it, it’s been more than 6 month since I welded spotwelded the p-packs so I might be off.
It was alos stored a while in P-packs at storage voltage (3.64-3.67V/p-pack) before doing the series connection the voltage didn’t change since I left them tho
What cells? Did you get pics of the pack construction?
Lishen LR2170LA
uhh, I have a ew pics scattered around but not a lot. I’m terrile at picture taking. I think some are in my build thread.
Is this the correct amount of solder? I don’t like the placement of these two (cyan). Should I move them or are they good? Also I can’t get this excess flux off, will it cause a problem?
Those solder pools look fine to me
Thx, I’ll carry on.
For the next time, you can add those solder pools before you weld the nickel to the group, that way you don’t have to watch out for heat transfer.
Ahhh, excellent idea, thx
The easiest way to clean that flux off is after the solder has solidified but while the joint is still hot. A rag or a paper towel should remove most of it
Rosin flux isn’t really corrosive though, i don’t stress too much about cleaning it off.
If you really want to clean it off after the fact, isopropyl is your friend.
This was my main concern. Thx
do you think it would be possible to do the series connections compeletely before welding? On my last (first) pack, i felt like i was either putting too much heat into the cells or not getting the solder to wet out into the wire totally.
can someone around here help me understand? 
and is there a way I can healthily squeeze some more range out of my 12s8p p42a?
This is correct. Above 40.8v, you have 100% available on tap.
From 40.8 to 35, the available battery current will linearly decrease, until there’s none available.
You can still ride it in that range, but the lower it gets, the more sluggishly it will accelerate until at some point, it basically won’t have enough power to move at all.
The farther apart you set the two cutoffs, the more gradual the process will be.
If you set them really close together, the cutoff will be more abrupt - you’ll have plenty of power, until you don’t, and then you will have no power.
