[DIYguy]

Just thought I would jump in here. I have a very good supplier (has become a friend) in Hong Kong. He works for a company that sells all types of batteries. He has been very trustworthy and worked hard to help me get rare batteries and special orders. He gave me inside info on untrustworthy trader on Taobao also. I even sent him 50$ US as a token of my appreciation for his personal help and hard work. He would not accept it. . and promised to always do his best. Just some background to put it in perspective.

Anyways, I asked him about these packs. He tells me that A123 paid money to have them scrapped and that this company that took them sold them to Chinese market. His company bought some packs and tested them. He said that several had dead (zero volt cells) some cells were found at about 1 volt and some seemed fine. He said that because of this, they decided it was not worth the effort and worried about warranty issues even if sorted. So, maybe they weed them out, but it does explain the price point . . . which is "too good to be true".

[JRP3]

I'm guessing they don't weed them out and you are taking a gamble, and it's probably worth buying some extra pouch cells to replace any potential bad ones. Replacement may not be easy with the laser welded bus bars.

[Batterypoweredtoad]

If you look at the cells it looks like the bussbars wrap over the top of the tab and the center 1/3 of the top of the tab/bussbar are welded together. It looks as if some work with a dremel would make the cell removable (after cutting the straps). Reattaching a new cell to the bussbar would be interesting.

[Plamenator]

I have a strange problem with my 78 Winston cells of 90Ah each.
At 3-12A they charge OK up until 3.35-3.40V when some of the cells suddenly jump to 4.00V in a matter of minutes.

I tried to individually discharge those cells and it takes just a few minutes to go from 4V to 3.28 where they start discharging really slow - takes hours to get from 3.28 to 3.20.

Then I try charging at 12A again and some other cell does the same trick.
Any ideas?

[DIYguy]

Originally Posted by Plamenator

I have a strange problem with my 78 Winston cells of 90Ah each.
At 3-12A they charge OK up until 3.35-3.40V when some of the cells suddenly jump to 4.00V in a matter of minutes.

I tried to individually discharge those cells and it takes just a few minutes to go from 4V to 3.28 where they start discharging really slow - takes hours to get from 3.28 to 3.20.

Then I try charging at 12A again and some other cell does the same trick.
Any ideas?

This is the behavior of cells which are fully charged. You need to decide on a balance/charge strategy (top or bottom) if u are not using a balancing bms. If you are, then implement it I guess.

As for the voltage at which the upper charge knee is evident, perhaps these cells are slightly different chemistry than the old TS or maybe your volt meter is off a bit. ?? Either way, this is full behavior.

[Plamenator]

Thanks for the quick reply.
I use a balancing BMS - http://www.elektromotus.lt/en/products/bms with a 4kW Elcon charger that are interconnected via CAN.
I think it uses top balancing with a small shunt on each cell to parallel some of the current.
Voltage is correct - I measured it both with the BMS and with a multimeter.

I always assumed a cell should charge quicker when it exceeds 3.35-3.40V but not that much quicker! Further not all cells jump to 4.00V, only a few but as soon as they get to 4V (while the rest stay at ~3.40), the BMS stops the charging process.

[DIYguy]

Originally Posted by Plamenator

Thanks for the quick reply.
I use a balancing BMS - http://www.elektromotus.lt/en/products/bms with a 4kW Elcon charger that are interconnected via CAN.
I think it uses top balancing with a small shunt on each cell to parallel some of the current.
Voltage is correct - I measured it both with the BMS and with a multimeter.

I always assumed a cell should charge quicker when it exceeds 3.35-3.40V but not that much quicker! Further not all cells jump to 4.00V, only a few but as soon as they get to 4V (while the rest stay at ~3.40), the BMS stops the charging process.

I'm not familiar with your BMS, but my best guess is that it is trying to top balance but will need a few charge/disharge cycles to get the job done.
Verify proper function of the bms (check for balance current) and do some cycles. Perhaps the cells are far enough apart at the top that your system won't do it in one shot.

Also, just my opinion but, if u r relying on BMS to shut down charger, install a completely separate voltage and/or AH counter as redundant backup to shut down charging in case of failure.

Good luck.

[JRP3]

Those voltages don't sound right, especially for TS cells which have more room above 3.4V than CALB cells, and my CALBs don't shoot up that fast at those currents from 3.4V. You may have some funky cells there, keep an eye on them.

[DIYguy]

Originally Posted by JRP3

Those voltages don't sound right, especially for TS cells which have more room above 3.4V than CALB cells, and my CALBs don't shoot up that fast at those currents from 3.4V. You may have some funky cells there, keep an eye on them.

Ya, for sure. That's why I was wondering about the DVM.
Suggestion, if u have a spare cell, if not, remove one from the BMS and charge it from below the knee to see behavior. There may b some influence there from the BMS. Also, double check all the settings in the BMS relative to chemistry, shunting, charge control etc.

[Erikvonhalle]

My dream is to have a BMW electric. If anything happens to my z3 I might convert it also. I am so pleased you are pioneering the way for me. Please post more.
Evh
Oak Ridge, TN