I wonder why they made it so low with such large cells?
Why did you end up pulling them?Signs are the BYD's got cycled fast, so I agree. I do know the one without the BMS board are slightly older. So at some point the 2nd board to balance was added to production but I dont think it solved the problem so all of these got pulled. Some BYD packs test good some have one bad cell.
as others noted is a sketch for someone post here for reading the CAN and converting to voltages. I just went Chargery but ended up pulling my six BYD packs.
With my Byd's I bottom balanced the packs, then charged them and added one or two headways to the runners..
Once the headways were added, the difference between the 3.65v cell and the lowest cell in the pack would be +-5amps in capacity.
Then the cells were paralleled, this took many hours and around 200 fuses... The byd bank is 2s12p packs, 1350ah usable..
I added two 8s qnbbm balancers and a 1amp jkbms for monitoring. This gives a total of 3amps active balance for 1350ah power wall..
The Byd's are cycled 3.4v to 3v per cell, at 3.4v they are out max 60mv and once a load is added they settle to about 10-20mv...
These byd's have been beaten up pretty bad, only having 60% capacity remaining... But if you parallel the cells and only charge to 3.4v and let them absorb at 3.4v they will stay in balance.
These degraded lifepo4 are now behaving more like a lead acid battery. They need time at absorbtion voltage to bulk up... If you try and charge to 3.65v per cell there will be a runner in the pack. Once the absorbtion amps have tapered off which take about three hours it only takes 4ah to push an individual cell from 3.4v to 3.65v..It just not worth the extra ah to fight imbalances.
This morning is a typical 20% discharge of my power wall and there batts are 10mv out of balance.
I also wouldn't be surprised if all the Batts came with the two board bms from the factory and the one board was removed because the Batts were going too far out of wack for the software...
The BMS can't keep more than 1 cell from going to high unless it is capable of moving more current out than is incoming. That said I think the bms in these packs could have been externally controlled through the canbus.I charged it so that 3 of the cells went over 3.60V, 2 of those were over 3.65, and I set my power supply for 0.50 amps hoping that the BYD BMS would keep the high cells from charging and allow the rest of the cells to catch up but it didn't work, the high cells kept increasing. Tried it on both of my BYD packs. So it seems that putting 12V to the BYD BMS doesn't do anything, unless it only happens above 3.70V which would make it fairly useless anyway since that's higher than they should ever get.
So now that the ANTs are a no go, what BMS will you be replacing them with?The next step in this Adventure of BYD pack.
The BMS I used, turned out to be junk. All four failed. The MOSFETs simply could not handle the current, even with 320 amps printed on the board and sticker. Geeze you'd think you could trust Chinese printers.
The BMS monitor works fine, but all the safety measures it provides are not satisfactory.
The next step is to add a 1S Balancer, a 4 AMP 1S balancer, it will be active and separate self contained unit in operation all the time, always balancing the cells.
This is what I am ordering:
View attachment 24943
I am getting 64 for my self, there is about a 12% discount if I order 100.
These will balance 4 amps between cells. Which in the balancing act, is huge. The "active balancer" on the BMS I had could only balance at 0.2 amps.
If you have a desire for a serious active balancer and want to save a few dollars, please PM me and I'll order the 100 and not the 64.
I am not bull shitting you, this is going to be ordered before the end of this week (October 16th, 2020). So don't dilly dally around. Expect $20 each with shipping.