Used CALB cells

[toverb]

Hi form Norway.
I have got hold of a bunch of blue CALB 100 Ah LiFePo4 cells from a condemmed car for a real low price (about 20$ a piece). I think the cells are more than 5 years old, but testing them I see that they still deliver about 90% capacity. The cells are somewhat different in capacity, and also how they discharge.
I intend to install 20 of them for domestic use in my boat and plan to do a 5P 4S installation with a manual monitoring system.
This should give me a useable capacity of about 350 Ah in 12V (I intent to carge them with not more than 13,8 V and not discharge them to more than 80% DOD).
Question: How shall I pick which cells to use and what should I look up for?

 

[gnubie]

Cells in series (strings) should be closely matched to maximise the amount of power you can pull from them. If they are mismatched, and you have a BMS!, they will still work but you'll be losing capacity as the BMS will see that one cell is going too low and disconnect the string to prevent a cell from becoming over discharged or even worse, reverse charged. One way to match cells would be to bring each cell up to fully charged and then discharge it while monitoring the power output using a watt meter.

Parallelled strings do not necessarily need to be closely matched as each string will share the load according to its effective impedance.

 

[svetz]

Perhaps this tool would help with matching?

 

[HighTechLab]

I would parallel your strings before putting them in series - this makes balancing so much easier. So you would make 4ea 5p1s strings then tie it together to be the 5p4s.

If you do it this way you only need a 4s balancer/monitor as it can't pull any single cell out of range, it would have to pull 5 cells out of range.

I would try to make each parallel string of 5 cells average out in capacity, e.g. if you have a 100ah cell and a 90ah cell, then put those together in parallel to get 95ah average capacity, then series with another group of equal average capacity.

you don't want to series up differing capacity for a variety of reasons - if one group of 5 gets near full and the other 3 groups are at 80%, then you will have to stop charging to prevent overcharging that one group - Meanwhile you have 3 other groups that are only 80% full - leading to wasted capacity.

I suggest with unbalanced cells this balancer: https://www.electriccarpartscompany.com/12V-4S-Lithium-Battery-Balancers-Equalizers because it can move up to 6 amps, and after I have done some testing once everything is in balance, it shuts down and has a negligable idle draw (The self discharge of your cells wastes more power than the balancer)

This balancer does not have low battery cut out or any "smart" features, it simply shuffles the power around the cells. I would suggest using it in conjunction with a monitoring device that has these "smart" features.

Your real benefit with that balancer is that it can move so much power between cells that it can make up for the mismatched cells.

Here is my YouTube video installing a 16s balancer very similar to the one I mentioned above. Take note my battery bank is a 16s1p but it still has a large demand for balancing (My cells were used as well.)

 

[Danny]

Hi form Norway.
I have got hold of a bunch of blue CALB 100 Ah LiFePo4 cells from a condemmed car for a real low price (about 20$ a piece). I think the cells are more than 5 years old, but testing them I see that they still deliver about 90% capacity. The cells are somewhat different in capacity, and also how they discharge.
I intend to install 20 of them for domestic use in my boat and plan to do a 5P 4S installation with a manual monitoring system.
This should give me a useable capacity of about 350 Ah in 12V (I intent to carge them with not more than 13,8 V and not discharge them to more than 80% DOD).
Question: How shall I pick which cells to use and what should I look up for?

I am currently using used Calb 180ah in 4s. I'm thinking the safest way do do it is organize each 4S group by AH. Here is the cheap discharge tester I use.

 

[toverb]

Thanks for the feedback.
I intend to put 5 cells in paralell first and connect 4 such blocks i series.
I have tested all cells and the difference I see is that some are "stiffer" on top - i.e. keeping the voltage high longer while some is better on the low side. They are quite similar regarding total capacity. I am testing them in av 4s setup after a top balance of each individual cell and they deliver between 1100and 1150 Wh.
Should I choose cells that have similar chrasteristics in each 5 cell paralell block or will it be OK to put in one of the "stiff on top cells" in these blocks.
(I'm not sure I explain this right, but these "stiff on top cells" seems somewhat better than the others). Or is it better to put these cells together in he same block?
Regarding capacity testing: I just have equipment to test in a 12V setup. I have not found a good inexpencive low voltage cutoff relay capable of cutting off the load at say 2,5 V. This makes it somewhat difficult to get exact messurements of each cell, but switching them around I have got an OK view of them.

 

[HighTechLab]

I would stick to cutting out at 3.0v. From 3.0v to 2.5v, you only get 2-3AH out of these, however you start getting on the steep drop off of the discharge curve and risk stressing the cells to a point of causing damage.

There are "Smart" bms that can send a cutoff signal when a cell drops too low, Will has mentioned them in videos before.

 

[b.james]

I found the active cell balancer that Will did a video on useful when there is a weak cell in my pack . Especially suited to boats with daily solar in and nightly out.
It feeds current from the high cell to the low cell as they are discharging and then when the solar kicks in again they all go up equal too. Keeps mine within 30mV.

 

[toverb]

I have bought two of the active cell balancers and will try them when the pack is ready. I will try them but if I need more capasity may be the ones that HighTechLab use is better .
So, 30 mV difference between cells is OK?
I only intend to do cutting off at 2,5V when I test the cells. In operation I will not go below 80% DoD.
I will also aim at a setup where the 4 5p blocks are as similar as possible.

 

[HighTechLab]

I have bought two of the active cell balancers and will try them when the pack is ready. I will try them but if I need more capasity may be the ones that HighTechLab use is better .
So, 30 mV difference between cells is OK?
I only intend to do cutting off at 2,5V when I test the cells. In operation I will not go below 80% DoD.
I will also aim at a setup where the 4 5p blocks are as similar as possible.

Sounds like you got it figured out. Oh and the balancers I linked can be "stacked" in case you change your system voltage, and with 6 amps of balance current possible, they are more powerful than any other balancer I know of. If you order from ECPC let them know I sent you haha, I was trying to work with them but negotiations fell apart. I still recommend their products.

 

[TCgreg]

I would stick to cutting out at 3.0v. From 3.0v to 2.5v, you only get 2-3AH out of these, however you start getting on the steep drop off of the discharge curve and risk stressing the cells to a point of causing damage.

There are "Smart" bms that can send a cutoff signal when a cell drops too low, Will has mentioned them in videos before.

Our 12v bank has LVCO at 12v (3v/cell) and our max charging is 13.6v. (3.4v/cell) That range captures almost all of a LFP storage capacity while staying safely away from the cliffs. So little to gain pushing for that last little bit. Testing our CALB cells our capacity is still above the listed nominal 100Ah even with reduced charging parameters. CALB sends data sheets with new cells that confirm their actual capacity is 15-17% higher than their nominal listing. Even with a BMS system why put all your eggs into someones circuit board basket that could fail. By limiting max charging and discharging to a reasonable value you give yourself protection with a very small fraction of operational loss.

 

[b.james]

Can the CALB capacity reports sent with each cell be fudged or just reproduced in any way . Do they serial mark them in any way? I can't see them wasting that time to run a true capacity test on each cell unless you paid for that when you ordered it and even then hmm doubt it.?

 

[b.james]

I would stick to cutting out at 3.0v. From 3.0v to 2.5v, you only get 2-3AH out of these, however you start getting on the steep drop off of the discharge curve and risk stressing the cells to a point of causing damage.

There are "Smart" bms that can send a cutoff signal when a cell drops too low, Will has mentioned them in videos before.

No .If you get and study the charge curves these cells are charged to 3.65V on first charge to lay down an SEI layer then stay under that thereafter. So I would happily charge to 3.4 or even 3.5 if you are confident of your charger .

To stay down at 3V would damage the cells by leaving them discharged for too long . They like to be fully charged from time to time.

$20 BMS's are avilable on ebay and ali and pretty well all work on the same principle. Back to back mosfets and a contol chip that you pick . make sure you get one with a 3.65 high voltage cutoff and a 2.5V low voltage cut off.

These cheap BMS's work well in my experience . You can pay hundreds if you like but they are usually made in the same chinese factories so better to buy cheap and replace if you need to . I have not replaced one in 3 years yet.I have spares ready though in case. Well I can afford to carry spares at that price.

 

[TCgreg]

Can the CALB capacity reports sent with each cell be fudged or just reproduced in any way . Do they serial mark them in any way? I can't see them wasting that time to run a true capacity test on each cell unless you paid for that when you ordered it and even then hmm doubt it.?

The report has corresponding reference numbers labeled on the cells. They do test each cell. On the 24 I ordered they all tested to very close to the same voltage out of the crate aside from one. I contacted the vender, they contacted CALB and had a tech in China get a hold of me to clarify and had the distributer send out a replacement cell right away along with the data info for it as well. They were very concerned that a cell dropped voltage. CALB is a good outfit concerned about quality.

.

 

[b.james]

Thanks for doing that . That looks pretty good. I gather they each had a different bar code on them then also .Thats a good sales point..
I too bought 100Ah cells recently from Ali but they came with no data . When I voltage checked them each cell measured 3.278V also except 2 cells that went 3.276V . I'm wondering if that voltage point is a given from the method of manufacture and chemistry of the plates.

 

[toverb]

How big difference in cell voltage under normal operation is tolerable?

 

[guyman]

b.james bought 100Ah cells recently from Ali

Would you recommend these for a newbie and could you post the link to these please

 

[b.james]

I bought & paid on Ali but they were delivered from Sydney in my country so they are stockpiling it seems .Yeh you can handle it just watch your pos and neg are always right and get an insulated nut screwdriver and cover it with plastic tape because you will drop it and there are lots of terminals and a hell of a lot of energy in there ready to come out instantly.

go here for full details

 

[b.james]

How big difference in cell voltage under normal operation is tolerable?

You will find they mostly stay close unless you are charging and discharging at very high rates then they go out and require balancing. My active cell balancer boards are always connected so on charge and discharge if a cell gets more than 100mV out it turns on and feeds current from the highest voltage cell until it is within 30 mV.

Look at the curves for your cells . For LFP most of a cells capacity life is spent at about 3.2V so if one cell shows 3.1V or 3.3V and the others are at 3.2V then I would get cracking and bring it up or down and do a cell bottom balance as soon as I could .

 

[roleo]

I bought & paid on Ali but they were delivered from Sydney in my country so they are stockpiling it seems .Yeh you can handle it just watch your pos and neg are always right and get an insulated nut screwdriver and cover it with plastic tape because you will drop it and there are lots of terminals and a hell of a lot of energy in there ready to come out instantly.

go here for full details

Are you in Sydney AU?