its totally okay to disassemble and reassemble the packs
Iâm having the worst luck with my battery builds. I just rebuilt the 12s4p with a new bestech D223 V1. Everything works as it should but when I plug in the balance wires to the bms, the bottom gets extremely hot!
Any ideas of why would be extremely appreciated.
@Chase test your leads. What your describing can happen when the balance wires arenât in the correct order. I bet thatâs the issue.
2 Likes
Damn you were right. I canât believe I missed that. Did it screw it up you think?
I doubt it. As long as you didnât try to ride it like that. Without a significant load, you were probs just really making one resistor work. Should be ok still. Monitor closely for the next few charges.
I just charged it up to 90%. Everything seems to be working fine, but shouldnât all the cells read the same voltage?
Donât think so. Think the bms has to balance all the cells. Pretty sure it will do that when 1 cell is at max capacity. It just takes some time. Can you post some pics of the new pack? And how did you do the series connections?
I think there must be some sort of language barrier with bestech because when I asked them why the first cell of the series is lower in voltage than the rest, they keep responding âmake sure all the cells are matchedâ before assembling. Their all of course 30Q. The reason some of them were different voltages before I assembled it was because some were brand new and some were slightly charged. I told bestech this but they just keep saying make sure all the cells are matched before assembling.
The new pack pics below
Started by adding new heat shrink to the cells because the super glue pulled a lot of it off when disassembling. Then added cardboard rings and fishpaper. The parallel connections are made with 10mm nickel strips. The outer series are connected by 12mm nickel strip supported by 12 gauge solid copper along the edge. Inner series are connected to a brass bus bar, then the series are bridges by two 14 gauge wires.
![image|375x500]
(upload://oKMIwUuTJ3LZ72qFHGhyQDmjqum.jpeg)
3 Likes
you could charge all the cells to the same level BEFORE assembly
But is that absolutely necessary for the bms to balance the cells correctly?
Itâs called float charging
Thanks for the link. Looks like it may just take some time to balance these.
holy hella dangerous looking all those cells without wrap together. looks like one of them is practically shorting across the top of a couple even in the pic. one big spark and then you knock the bong over onto all the cells and then you run out of the house screamingâŚrun away never come back.
4 Likes
Yes that did happen actually. I learned very quickly how dangerous of a situation I had created once one of the negative ends lodged itself inside of the positive groove of another causing about 4 nearby cells to go crazy and almost burn my table down. I can honestly admit that I didnât have enough hands on experience working with batteries to realize how dangerous these can be. Hopefully others can learn from my stupidity.
1 Like
Ok so I have been reading about it and it looks like you are right. One cell needs to be 4.2 for balancing to begin. The weird thing is that none of the cells go above 4.1 by the time the charger light goes green (when indicator reads 90%). So does this mean that it wonât ever begin balancing? And why does my charger stop at 90% (48.0 V) when my charger is rated for 50.40 V? First cell of the series is about 3.67 and the rest are right at 4.10.
I was racing through my current build when I saw this thread - decided to take an extra couple of weeks on my battery build - really glad I did I was about to do something stupid, I donât think I would have spotted it if I wasnât hyper paranoid about batteries now 
Good that makes me feel like maybe all this trouble is worth something
2 Likes
The same thing happened in another thread. To fix it he let the battery charge for a few hours when the light was green. It takes some time to balance. Let your battery stay in the charger when the light becomes green and the bms should do the rest. Donât leave the battery for 5 hours but see after an hour or less if something has changed.
Yeah I saw that post and tried that already. One cell got up to 4.2 V, 10 are at 4.1 Vbut the first one wonât change from 3.68 V. I talked to bestech and they said âcheck the cells in the first series because they Arlene abnormally low compared to the othersâ. But the cells in the first series are all brand new. Do I have to make sure they are all charged to the same voltage (or nearly the same) before assembling? I didnât do this before making the pack because I thought that was what a bms was supposed to do.
Pretty sure all cells has to be around the same voltage when you assemble it⌠Sadly. Donât know what you can do other than take everything apart again, charge all cells to max and assemble it again 