Pairing Cells for a 2P 8S battery

[natec]

I just received my 16 EVE 280AH cells and accompanying data. I plan to bulk charge in the 2P8S arrangement and the shift to 16P for top valence. My question is on the best way to pair up the cells based on the test data I have. Should I focus on matching resistances? Resistances at low SOC or mid SOC? Attached is the data…

any help is appreciated.

 

[Steve_S]

No attachment there.
I can only tell you what is common knowledge, unmatched & unbatched cells (Bulk Cells) do NOT make for good parallel combinations.
280AH cells can discharge at 280A for one hour and take 140A for 2 hours to charge (max limits).
LFP Nominal Voltage is 3.200 with the active working voltage curve of 3.000-3.400 for bulk or 2.800-3.500 for Matched & Batched.
IF Matched & Batched you can pair them according to the printout with cell serial numbers.

Most vendors only sell Voltage & IR Matched cells at Resting storage voltage.
This is NOT Matched & Batched ! which is a 3 Full Cycle at varying Amperage & Load/Charge rates with sampling taken every 10 minutes through the cycles and then they matched so that all cells have same IR & Impedance at the various voltage points. Typically this adds up to 50% cost above the cost of Bulk Cells.

Top Balancing can be done in sets, such as 4 or 8 cells at a time. Remember that more cells in parallel the longer it will take for them to charge and it is already fairly slow at low amperages. You can do them in batches and let them settle in parallel while doing the others. Once all 16 are topped & settled, you can put them ALL in Parallel and top off again and it is faster doing it this way. Myself, I use a TekPower TP1540E which outputs CC up to 40A and then switches to CV mode as it's finishing up. I allow the cells to saturate @ 3.650V to the point where they do not take less than 2A.

Do download the Luyuan Tech LFP guide from my Signature, there is a lot of info & refs in there to help you. Grab the voltage chart too (the downloadable PDF is hi-rez). When you are ready to setup your system, you will have to Voltage Calibrate everything, so there is a link for that in my signature as well... All Lithium Cells are very finicky and not as forgiving as Lead. FLA deals in Volts, where Lithium deals with Millivolts !

Good Luck

 

[natec]

No attachment there.
I can only tell you what is common knowledge, unmatched & unbatched cells (Bulk Cells) do NOT make for good parallel combinations.
280AH cells can discharge at 280A for one hour and take 140A for 2 hours to charge (max limits).
LFP Nominal Voltage is 3.200 with the active working voltage curve of 3.000-3.400 for bulk or 2.800-3.500 for Matched & Batched.
IF Matched & Batched you can pair them according to the printout with cell serial numbers.

Most vendors only sell Voltage & IR Matched cells at Resting storage voltage.
This is NOT Matched & Batched ! which is a 3 Full Cycle at varying Amperage & Load/Charge rates with sampling taken every 10 minutes through the cycles and then they matched so that all cells have same IR & Impedance at the various voltage points. Typically this adds up to 50% cost above the cost of Bulk Cells.

Top Balancing can be done in sets, such as 4 or 8 cells at a time. Remember that more cells in parallel the longer it will take for them to charge and it is already fairly slow at low amperages. You can do them in batches and let them settle in parallel while doing the others. Once all 16 are topped & settled, you can put them ALL in Parallel and top off again and it is faster doing it this way. Myself, I use a TekPower TP1540E which outputs CC up to 40A and then switches to CV mode as it's finishing up. I allow the cells to saturate @ 3.650V to the point where they do not take less than 2A.

Do download the Luyuan Tech LFP guide from my Signature, there is a lot of info & refs in there to help you. Grab the voltage chart too (the downloadable PDF is hi-rez). When you are ready to setup your system, you will have to Voltage Calibrate everything, so there is a link for that in my signature as well... All Lithium Cells are very finicky and not as forgiving as Lead. FLA deals in Volts, where Lithium deals with Millivolts !

Good Luck

Steve,

Thanks for the reply. Data from the supplier is now attached (mobile mishap). These are cells and data from Luyuan. I'm planning to assemble (electrically at least) in the 2P8S configuration shown at the bottom of page 10 of Luyuan Assembly Guide you pointed to, managed by a REC Q BMS. Is this a bad idea? I'm a little deep in the design and procurement to make a change now. I recognize that without matched cells it might not optimally use the pack and may take a hit on capacity, but is there more that I should know before proceeding?

As for "matched" that is the product that I requested/purchased, but from the data I can't tell:


Nate

 

[Steve_S]

The new versions are the matched ones at EVE factory.
The REC BMS is used by some of the members, few have had issues for their particular application, but that stands true for most BMS' as these are all "compromise" devices.
If you use the Ri1 column and match the cells that way, the numbers are close enough, they are never exactly the same. (not prismatics anyway). The cells also all above 290AH capacity so you'll get the 280 per cell without issue.

Your working voltage is essentially 2.800-3.500 for Matched & Batched.
They will still start to deviate during charge above 3.400 but not serious, it's normal.

Have fun

 

[natec]

The new versions are the matched ones at EVE factory.
The REC BMS is used by some of the members, few have had issues for their particular application, but that stands true for most BMS' as these are all "compromise" devices.
If you use the Ri1 column and match the cells that way, the numbers are close enough, they are never exactly the same. (not prismatics anyway). The cells also all above 290AH capacity so you'll get the 280 per cell without issue.

Your working voltage is essentially 2.800-3.500 for Matched & Batched.
They will still start to deviate during charge above 3.400 but not serious, it's normal.

Have fun

Thanks so much for getting back to me! The adventure begins...

 

[lekeola]

Steve,

Thanks for the reply. Data from the supplier is now attached (mobile mishap). These are cells and data from Luyuan. I'm planning to assemble (electrically at least) in the 2P8S configuration shown at the bottom of page 10 of Luyuan Assembly Guide you pointed to, managed by a REC Q BMS. Is this a bad idea? I'm a little deep in the design and procurement to make a change now. I recognize that without matched cells it might not optimally use the pack and may take a hit on capacity, but is there more that I should know before proceeding?

As for "matched" that is the product that I requested/purchased, but from the data I can't tell:
View attachment 53006

Nate

Hello, I wanted to make a battery purchase on alibaba and luckily I am chatting with Amy, plz share hr experience on thier EVE cells, thanks in anticipation