How do I match 48 cells together? What order?

[TommyHolly]

Hey everyone,
My system is almost ready to put back together. I’m trying to figure out how to match the cells together and follow the advice I was given here. Any advice on the order?

I’m designing a 12v 1,200Ah 3P 4S system with four batteries. Each 12v 300Ah battery has 12 cells and the entire system is comprised of four batteries of 48 cells total, making a 12v 1,200Ah system. The cells are CALB brand, 3.2v 100Ah LiFePo4

Per everyone’s advice, I charged and performed a capacity test on each and every single cell over the last few weeks. I now have an order of my worst cell at 82.893Ah to my best cell at 90.345Ah. The vast majority of them are approximately 84-&5Ah each.

Here is an excel chart of the way I’m designing the system:

I was told to match the best cell with the worst one. However, I have 3 cells in parallel and the other groups of 3 form a 12v battery for the 4S part. Here is my guess. I’ll label the parallel ones in parentheses and a dash for the 4S series connections.

Battery One: (1, 48, x) - (5, 44, x) - (9, 40, x) - (13, 36, x)

Battery Two: (2, 47, x) - (6, 43, x) - (10, 39, x) - (14, 35, x)

Battery Three: (3, 46, x) - (7, 42, x) - (11, 38, x) - (15, 34, x)

Battery Four: (4, 45, x) - (8, 41, x) - (12, 37, x) - (16, 33, x)

What do I do with cell #’s 17 through 32??
Do I match the cells in a completely different way instead? I’m guessing I follow that same order and drop cell #17 together wity #1 and #48?

The final version may look like this…
Battery One: (1, 48, 17) - (5, 44, 21) - (9, 40, 25) - (13, 36, 29)

Battery Two: (2, 47, 18) - (6, 43, 22) - (10, 39, 26) - (14, 35, 30)

Battery Three: (3, 46, 19) - (7, 42, 23) - (11, 38, 27) - (15, 34, 31)

Battery Four: (4, 45, 20) - (8, 41, 24) - (12, 37, 28) - (16, 33, 32)

How does that look?

 

[time2roll]

I would want cell groups in series to be the same capacity.

Battery one: cell group A = group B = group C = Group D

Same for battery two. Although if battery two is lower capacity than battery one that is OK.

I would plug the values into an excel spreadsheet and fit them as best I could. The diagram seems to indicate each cell group was configured to exactly 300 Ah.... it that by actual values or by some miracle that it all worked out?

 

[NVS]

Hey everyone,
My system is almost ready to put back together. I’m trying to figure out how to match the cells together and follow the advice I was given here. Any advice on the order?

I’m designing a 12v 1,200Ah 3P 4S system with four batteries. Each 12v 300Ah battery has 12 cells and the entire system is comprised of four batteries of 48 cells total, making a 12v 1,200Ah system. The cells are CALB brand, 3.2v 100Ah LiFePo4

Per everyone’s advice, I charged and performed a capacity test on each and every single cell over the last few weeks. I now have an order of my worst cell at 82.893Ah to my best cell at 90.345Ah. The vast majority of them are approximately 84-&5Ah each.

Here is an excel chart of the way I’m designing the system:

I was told to match the best cell with the worst one. However, I have 3 cells in parallel and the other groups of 3 form a 12v battery for the 4S part. Here is my guess. I’ll label the parallel ones in parentheses and a dash for the 4S series connections.

Battery One: (1, 48, x) - (5, 44, x) - (9, 40, x) - (13, 36, x)

Battery Two: (2, 47, x) - (6, 43, x) - (10, 39, x) - (14, 35, x)

Battery Three: (3, 46, x) - (7, 42, x) - (11, 38, x) - (15, 34, x)

Battery Four: (4, 45, x) - (8, 41, x) - (12, 37, x) - (16, 33, x)

What do I do with cell #’s 17 through 32??
Do I match the cells in a completely different way instead? I’m guessing I follow that same order and drop cell #17 together wity #1 and #48?

The final version may look like this…
Battery One: (1, 48, 17) - (5, 44, 21) - (9, 40, 25) - (13, 36, 29)

Battery Two: (2, 47, 18) - (6, 43, 22) - (10, 39, 26) - (14, 35, 30)

Battery Three: (3, 46, 19) - (7, 42, 23) - (11, 38, 27) - (15, 34, 31)

Battery Four: (4, 45, 20) - (8, 41, 24) - (12, 37, 28) - (16, 33, 32)

How does that look?

Here is a program I use for making balanced battery packs from 18650 cells. My largest pack being 7S 140P.
Just enter each cell ah separated by a comma and it.

rePackr - 18650 pack builder

 

[TommyHolly]

I would want cell groups in series to be the same capacity.

Battery one: cell group A = group B = group C = Group D

Same for battery two. Although if battery two is lower capacity than battery one that is OK.

I would plug the values into an excel spreadsheet and fit them as best I could. The diagram seems to indicate each cell group was configured to exactly 300 Ah.... it that by actual values or by some miracle that it all worked out?

Ok so divide them by cell groups. Every 12 batteries will form a group then is what you are saying.

How do I divide those 12 to form a battery?(1, 12, 6) - (2, 11, 5) - (3, 10, 7) - (4, 9, 8)???

The diagram was based on the original nominal rating of the cells being 100Ah each. Since these are 6 years old and abused formerly having no BMS, they are much less now.

The average capacity is about 85Ah for each cell. The worst one was just under 83Ah and the best was just over 90Ah. So the total actual capacity of the system is about 1,020Ah and if I evenly distributed the cells (like my plan in my first post above) each battery would be approximately 255Ah instead.

 

[TommyHolly]

Here is a program I use for making balanced battery packs from 18650 cells. My largest pack being 7S 140P.
Just enter each cell ah separated by a comma and it.

rePackr - 18650 pack builder

Very cool!
But I’m having problems using it. I keep getting errors.

To test it and make it simple, it asked me to input mA for each cell separated by a comma. So I put in 85001, 85002, 85003, 85004 and so on…

I input 4 as the number of cells in series.
The capacity part I’ve tried putting in 300Ah, I’ve tried blank, I’ve tried entering 3 as the number of Parallel cells??? No matter what I get this error.
“Please specify a number of cell in parallel or capacity”

Also, do I enter in the value of all 48 cells and it tells me how to make 4 batteries in a 3P 4S configuration? Or do I just pick 12 cells at a time to see how it arranges them for one single battery??

 

[Sojourner1]

When doing your capacity test did keep track of cell voltages? What if you have runners mixed in you parallel configuration won't you be short changing you capacity of the batteries themselves? Or are just assuming once you build the batteries packs the the cells are going stay fairly balanced?

You said these are used batteries.

 

[TommyHolly]

When doing your capacity test did keep track of cell voltages? What if you have runners mixed in you parallel configuration won't you be short changing you capacity of the batteries themselves? Or are just assuming once you build the batteries packs the the cells are going stay fairly balanced?

You said these are used batteries.

I did the following.
1. First I top balanced all the cells in parallel, then I disconnected the cells and took readings twice a day for 2 weeks. This was a standing resistance test to get an idea of internal resistance of each cell.

2. Next I individually charged each cell to exactly 3.65v until the charger said 0.000A for an hour. Then I performed a capacity test.

3. Before the capacity test started, I recorded the reading directly from the Capacity tester (which was always slightly higher than what my multimeter would say.) I set the low voltage cutoff to 2.6v and the test would usually run for around 4 hours and 20 minutes… I recorded the exact time it took and the capacity in Ah of each cell.

I’m not sure what “runners” are? Keep in mind all the cells passed over 80Ah which people here said is the lowest capacity you should have before you throw away the cell.

The system was installed on my boat and not working properly. It had no BMS and originally a 4S 1P system of 12 batteries consisting of 4 cells each battery. The only thing installed was a QNBBM Lithium Battery Balancer on each cell and that was it.it had all sorts of problems… it water from a leaky hatch dripping on it, many connector lugs had bad crimps, it had random cables connected to random spots which effected the batteries differently, it had no monitor system… so these cells were used and abused which is why people here said to conduct a full capacity test before I do anything else. And luckily they all passed.

When I rebuild the system, each 3P 4S battery consisting of 12 cells will be made with its own Overkill Solar 120A BMS, connected with bus bars and new cable measured identically, and will be connected through a smart shunt and all wired properly. (See other posts on this forum from me)

Each battery of 12 cells will also use the QNBBM Lithium battery balancers in addition to the Overkill Solar BMS.

 

[Sojourner1]

When you had the cells in a 4s1p configuration could you see the individual cell voltages while charging? Mostt cells will stay fairly balanced to each other till you get near their full capacity and that is when you'll see the runners.. the cell that will rise in voltage very fast. Hence balancing boards or high voltage disconnect with the bms.

 

[MisterSandals]

to conduct a full capacity test before I do anything else. And luckily they all passed.

Can you post a list of your cells and their capacities? I'd be interested in seeing the capacity distribution.
So far, based on the capacity testing and cell matching that I did almost 2 years ago, what you proposed in your OP sounds spot on.
In my experience, the cells that deviated the most from the average capacity were on the low side, overwhelmingly. So the lowest capacity cells need all the help they can get. Pairing #48 (worst) with #1 on the first pass, and then with #17 (the best of the last 24 cells) makes the most sense to me.

Ideally you'd want the sum of the 3 cell "pairs" to equal each other. After all, its that capacity that is important to staying balanced the most.

 

[TommyHolly]

When you had the cells in a 4s1p configuration could you see the individual cell voltages while charging? Mostt cells will stay fairly balanced to each other till you get near their full capacity and that is when you'll see the runners.. the cell that will rise in voltage very fast. Hence balancing boards or high voltage disconnect with the bms.

When the cells were in the original 4S 1P configuration, the voltages of all cells were the same (I never took one individual cell out to test it by itself.) The entire system would drop from 13.6v immediately down to 11v within about 2 minutes.

So by “runners” you are referring to cells which don’t charge or discharge at the same rates as the others??

 

[TommyHolly]

Can you post a list of your cells and their capacities? I'd be interested in seeing the capacity distribution.
So far, based on the capacity testing and cell matching that I did almost 2 years ago, what you proposed in your OP sounds spot on.
In my experience, the cells that deviated the most from the average capacity were on the low side, overwhelmingly. So the lowest capacity cells need all the help they can get. Pairing #48 (worst) with #1 on the first pass, and then with #17 (the best of the last 24 cells) makes the most sense to me.

Ideally you'd want the sum of the 3 cell "pairs" to equal each other. After all, its that capacity that is important to staying balanced the most.

Ok, so my plan on the original post matching #1 with #48 and #17 is a good plan? That way the capacities would all average out all four batteries to about 85Ah each.

However, some people said to match the best 12 in one single battery?? This would create 4 batteries with different averages in each. One battery would have an average of 88Ah and the worst would be around 84Ah if I did it that way.

Here ya go:
Capacity Tests:

• 1st number: Cell Number written on the actual cell to keep track
• 2nd number: Starting Voltage on cell according to the Capacity Tester leads. (It showed 3.65v each time on my multimeter)
• 3rd number: Time with a 20A load
• 4th number: Total Ah Capacity of that cell

#1: 3.692v, 4:17, 85.638Ah
#2: 3.691v, 4:27, 88.819Ah
#3: 3.687v, 4:19, 86.258Ah
#4: 3.694v, 4:24, 87.942Ah
#5: 3.687v, 4:25, 88.292Ah
#6: 3.692v, 4:24, 88.012Ah
#7: 3.694v, 4:22, 87.253Ah
#8: 3.690v, 4:20, 86.700Ah
#9: 3.685v, 4:26, 88.574Ah
#10: 3.694v, 4:22, 87.161Ah
#11: 3.684v, 4:18, 85.909Ah
#12: 3.693v, 4:21, 87.070Ah
#13: 3.688v, 4:09, 82.996Ah
#14: 3.686v, 4:16, 85.182Ah
#15: 3.685v, 4:20, 86.536Ah
#16: 3.691v, 4:17, 85.421Ah
#17: 3.685v, 4:17, 85.595Ah
#18: 3.689v, 4:16, 85.313Ah
#19: 3.696v, 4:20, 86.707Ah
#20: 3.692v, 4:14, 84.590Ah
#21: 3.691v, 4:30, 89.820Ah *
#22: 3.694v, 4:18, 85.907Ah
#23: 3.691v, 4:25, 88.384Ah
#24: 3.690v, 4:21, 86.755Ah
#25: 3.692v, 4:20, 86.346Ah
#26: 3.686v, 4:17, 85.614Ah
#27: 3.686v, 4:18, 85.986Ah
#28: 3.688v, 4:24, 87.937Ah
#29: 3.693v, 4:29, 89.270Ah
#30: 3.689v, 4:33, 90.762Ah
#31: 3.689v, 4:25, 87.938Ah
#32: 3.692v, 4:22, 86.863Ah
#33: 3.689v, 4:18, 85.746Ah
#34: 3.690v, 4:27, 88.998Ah
#35: 3.691v, 4:22, 87.373Ah
#36: 3.690v, 4:14, 84.63Ah
#37: 3.693v, 4:18, 85.826Ah
#38: 3.696v, 4:25, 87.956Ah
#39: 3.692v, 4:28, 89.163Ah
#40: 3.708v, 4:32, 90.104Ah
#41: 3.718v, 4:14, 84.400Ah
#42: 3.697v, 4:19, 86.068Ah
#43: 3.685v, 4:20, 86.271Ah
#44: 3.690v, 4:19, 86.111Ah
#45: 3.691v, 4:28, 88.908Ah
#46: 3.692v, 4:25, 87.874Ah
#47: 3.692v, 4:29, 88.641Ah
#48: 3.692v, 4:27, 86.633Ah

 

[wholybee]

All said and done, you will have 12 groups of 3 cells each. Your goal is that the Ah capacity of all 12 are the same.
To do this, start by pairing best to worst. When you have 12 pairs, you will have 12 cells left. To place the 3rd cell, do a best to worst pairing again. The pair with the highest Ah, with the single cell with the worst.

 

[MisterSandals]

One battery would have an average of 88Ah and the worst would be around 84Ah if I did it that way.

Thats actually not too bad. But the biggest consideration is at the cell triplet level within each battery. If one cell triplet capacity is lower than the rest, it will charge and discharge faster which will limit the entire battery on top and bottom ends.

This would create 4 batteries with different averages in each.

Yea, this does not sound optimal. I'd want series batteries of equal capacities.

1st number: Cell Number written on the actual cell to keep track

This is why i recommend labeling/naming your cells with letters (A, B, C...) because your ranking are also numbers. And the position of the cell in the battery is also a number.

4th number: Total Ah Capacity of that cell

Those look excellent for a set of used cells from a formerly misbehaving battery bank. Even a simple matching like your OP suggested should be just fine. (48, 1, 17) ...

 

[MisterSandals]

All said and done, you will have 12 groups of 3 cells each. Your goal is that the Ah capacity of all 12 are the same.
To do this, start by pairing best to worst. When you have 12 pairs, you will have 12 cells left. To place the 3rd cell, do a best to worst pairing again. The pair with the highest Ah, with the single cell with the worst.

What you are describing is for 36 cells. And what you are describing (as far as i can tell) is what the OP is proposing in the OP.

 

[wholybee]

@MisterSandals my mistake, yes that would be for 36 cells. Attached is the "ideal" pairing. The capacity of the 16 groups ranges from 260-261Ah. It works out very well!

Matching on other parameters would be much more difficult, possibly beyond the ability of a DIYer, and the would not yield much gain. In parallel, the cells will be held at the same voltage, so "runners" will not be as much of a problem. All 3 cells will hit the min/max voltages at the same time.

 

[MisterSandals]

Attached is the "ideal" pairing. The capacity of the 16 groups ranges from 260-261Ah. It works out very well!

So any of the rows can be combined with any other 3 rows?

It looks good if this is what you propose. Nice work.

 

[TommyHolly]

All said and done, you will have 12 groups of 3 cells each. Your goal is that the Ah capacity of all 12 are the same.
To do this, start by pairing best to worst. When you have 12 pairs, you will have 12 cells left. To place the 3rd cell, do a best to worst pairing again. The pair with the highest Ah, with the single cell with the worst.

I'm not sure I'll have 12 groups of 3 cells each?
Each of the four batteries will consist of 12 cells, in a 3P - 4S configuration. So in total it will be 16 groups of 3 parallel cells.
But I understand what you mean.

In my original post up top, that is what I did. I paired the best with the worst, added those to the first 3P cell of the first battery, then moved down to the next battery and paired the best with the worst to that first 3P cell. Then I went to the second 3P cell of each battery in order. Then when all four batteries had the best and worst cells matched, for the third CALB cell in the 3P I went back to the first 3P cell of the first battery and added #17 and then moved to the second battery's first 3P cell and added #18...etc (Take a look up top please and see if what I plan makes sense.)

 

[TommyHolly]

Thats actually not too bad. But the biggest consideration is at the cell triplet level within each battery. If one cell triplet capacity is lower than the rest, it will charge and discharge faster which will limit the entire battery on top and bottom ends.


Yea, this does not sound optimal. I'd want series batteries of equal capacities.


This is why i recommend labeling/naming your cells with letters (A, B, C...) because your ranking are also numbers. And the position of the cell in the battery is also a number.


Those look excellent for a set of used cells from a formerly misbehaving battery bank. Even a simple matching like your OP suggested should be just fine. (48, 1, 17) ...

OK, so by saying "not optimal" you are recommending that I don't put the 12 best together in one battery, and that I evenly spread the cells across like in my OP, is that correct?

I'll label them accordingly like you said.

The cells will even test slightly higher for capacity since I set the cutoff at 2.6v instead of 2.5v because the capacity tester would always register a slightly higher voltage then my multimeter. I tried 2.5v low cutoff on two of my spare cells and I only got another 0.3Ah capacity out of it which wasn't much. I took the safe route and kept the low cutoff at 2.6v and tested them all at that to keep apples to apples comparisons.

 

[TommyHolly]

@MisterSandals my mistake, yes that would be for 36 cells. Attached is the "ideal" pairing. The capacity of the 16 groups ranges from 260-261Ah. It works out very well!

Matching on other parameters would be much more difficult, possibly beyond the ability of a DIYer, and the would not yield much gain. In parallel, the cells will be held at the same voltage, so "runners" will not be as much of a problem. All 3 cells will hit the min/max voltages at the same time.

Awesome!
This matches very closely with what I had in the OP. It looks like you adjusted a few of the cells slightly to make sure the end result of all the rows is as close as possible. I didn't know that was the intent. PERFECT! I'll use your chart, thanks.

So even though my system was originally a 1,200Ah nominal capacity.
According to your numbers, I have about 261Ah in each group of parallel cells and each battery. So 261Ah x 4 = 1,044Ah system roughly.

Later on, I'll use this number when I make another post to ask people what I should set my Victron Smart Shunt and Solar Controller settings to.

 

[Shale MacGregor]

12 batteries in parallel, then in series, 1044 avg got to within a tenth