Capacity cutoff vs. SOH cutoff

Hi all,

I am currently planning my DIY Powerwall. I am planning to build a 14s140p system using 1.5A cell fuses (the glass ones recommended by AveRage Joe). I will connect the pack to a Sunny Island 6.0H-11 (my existing PV system is all SMA)and incorporate a main 160A fuse. The bus bars will probably we twisted AWG 8 copper wire ormaybe copper tubing.
The packs will be monitored by a Batrium BMS, though I am unsure as of yet if I will get the WM4 or wait for the WM5 (should come out this month). The Batrium BMS will also control a 12V Kilovac EV200 relay to quickly disconnect the packs in case of emergency or maintenance. I know I will bleed about 1.5W of power on the relay continuously, but that is a penalty I am willing to take for added safety.

Now to the main question - cell testing.
I have opened up a couple of packs and the initial voltage measurement on most of the cells looks good, but I have yet to test them as I just started building my testbench.
I am using TP4056s to charge the cells andZB2L3s to discharge andcapacity test the cells. I know that these don't have a constant 1A discharge rate, but since the cells won't have that under normal operation either, I believe they will deliver good results. Right now I am setting up 25xTP4056 and 15x[size=medium]ZB2L3 as my test bench all powered by a 5V 40A LED PS. I will use some of the 1.5A fuses to protect each charger/tester on the testbench.[/size]

[size=medium]Once I get my results I will have to make a decision on which cells to use. I am currently inclined to set the cutoff based on SOH, probably around 80% or so instead of having a cutoff of some fixed mAh number. I believe acell at 1500mAh that was designed for 1600mAh will deliver for better and longer lasting performance than one that was originally designed for 3500mAh. After all, the cells are just current sources in a parallel and will all deliver a slightly different current based on their capacity and the pack's voltage, while the SOC of each cell in the pack should be the same. This also gives me more flexibility to build the closely matching packs required for series connection.[/size]

[size=medium]I am very interested to hear your thoughts.[/size]

CU17 said:

Hi all,
...............Now to the main question - cell testing...........[size=medium][/size]
.........I am very interested to hear your thoughts...........

Click to expand...

Cell testing

Your plan to build a 14s140p pack as you know will require 1960 cells. If you want to speed up the harvest and have good results the first thing you need is a YR1030+ 4wire 1kHz AC IR meter. There are 2 that I recommend out of the 10 I have.

1. https://www.aliexpress.com/item/32817594188.html?spm=a2g0s.9042311.0.0.3da24c4dTiA0FS
2. https://www.18650batterystore.com/V...jtnvxQ0rZdiPhFaPZ5EgT9Q93zmOFFURoCW_UQAvD_BwE

The first one has nice probes and longer wires and a large display. At the moment my favorite
The second one has shorter wires smaller display and different probes. It was my first IR meter so I have an affinity for it.
Both are very accurate. I have tested both with a Voltage reference source and a precision 10m? reference resistor.

The first thing to realize is that all cell manufactures and model numbers have different acceptable IR values of their cells.
After harvesting and recording over 5000 cells there is a definite correlation with IR values and the SOH of a cell.
I have an Excel sheet on my google drive (Click on the link in my signature) called Harvested cell analysis.xlsx that you are more than welcome to look at and download.
Within that sheet you will find a tab on the bottomcalled"IR by part#". It has a list of cells to which I have assigned the optimal IR and marginal IR measurements to. It is still a work in progress as I am fine tuning it and adding notes as I find deviations. All in all though it will give you a 80%+ SOH result for the listed cells especially if you go by the optimal IR criteria.
On a side note any cell over 90m? is not a good candidate period.

On the TP4056s you may find that the do not all charge to 4.2 so be aware of that.
I personally think charging cells ona 20p board with an accurate CC/CV supply set at 4.2v and whatever amperage you want to charge your cells at is a better solution with much more accurate charging results.
I have 11 off the shelfcharger/testers so I trust them to do the grunt work on cells with good IR resultsand have other charging and testing methods for the <2V cells. All cells >2V get charged and tested at 500mA on the off the shelf charger/testers.
All cells <2V get charged onthe 20p board at CC/CV 4.2Vat50mA per cell. I may go as low as 25mA per cell in the future just for testing purposes.
As far as theZB2L3 I have 10 of them but have never put together the board to use them. Something I will do in the near future.
I have used theZHIYU ZB206 the ZB2L3s bigger brother and I like it.It seems to be pretty close to actual capacity and the IR function on it is acceptably accurate but not the best.

Agreed on the SOH of a 95% 1600mAh cell compared to a 75% 3000mAh cell.
Most of the OEM laptop packs will have between 2000mAh to 3000mAh cells in them just look at the Ahs on the pack and you can extrapolate from there what cells are in it. Divide the mAh of the pack by the cells in parallel and you should have an idea what mAhcells you will get out of the pack.

Best of luck in your harvesting

Wolf

With a 160a Main fuse your cell level fuses should be 5a or around... Imagine what happens IF you manage to push 200a... The Main fuse Will run it happily... And you have some cells more happe to deliver current than others. At that rate you are way to Close to the cell levels fuses and you Will end Up with a chain reaction taking down 140fuses....

For your testing board to let everything work properly, incl the tp, you need good power.
One tp must have 1.2a, 30 zb's just need0.800mah.
For discharging at 1 amp you need approx 4 ohm 5w resistors, if you want to be precise buy 1% or lower resistors.

I found out by try and error that the more stable your psu is, that they perform better.
Dont max out your psu, have always some to spare.
When you put in a cell for charging it will ask for a short time more power (a ?surge?)

For every amp calculate a 1000uf and put that capacitor in.
Test all your zb's, they can be pretty far off, like 0.8v plus or minus.
Test also all your tp/tc on there max charging voltage.
Sort them out.

Plus one on wolf, buy also a ir tester.

My two cents, hope this was helpful.
Best

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This board is still under construction.
Still want/must add a other section for "first aid" to low v cells.
And I want to make it in one piece, with some more power.
I can do a 60 cells a day, when working. 90-120 when I am free.
First charge, let them rest for 30 days.
Second, test.
Third, charge them up to 3.45v for storage.

I forgot one thing, the tp's and the tc's will tell you when they are done, with the blue light on.
On the contrary, they are not!
They have a loading program, they stop at a certain voltige, and then continue to fill them up 100%
So when you think that they are done, wait a minimum of 15-30 minutes, they will surprise you with there last load, to finnish them of.

So don't cut off there power or else they will recognize every cell above {tc 4.05} {tp 4.10} (i thought) as full, because you interrupted the program, for when you switch on the power again, they start there program from the beginning, and thus don't finish there program.

My two added cents, best

Ps @Wolf, how do get the light on, on the yr, or a instruction manual in english?

Thanks in advance

100kwh-hunter said:

Ps @Wolf, how do get the light on, on the yr, or a instruction manual in english?

Thanks in advance

Click to expand...

Ouch which one did you order?
I too have several in that hieroglyphic mess of a language.
If you can let me know which one you got I will try to get you the pictures of the english version and how to set it up.

Wolf

100kwh-hunter said:

For your testing board to let everything work properly, incl the tp, you need good power.
One tp must have 1.2a, 30 zb's just need0.800mah.
For discharging at 1 amp you need approx 4 ohm 5w resistors, if you want to be precise buy 1% or lower resistors.

I found out by try and error that the more stable your psu is, that they perform better.
Dont max out your psu, have always some to spare.
When you put in a cell for charging it will ask for a short time more power (a ?surge?)

For every amp calculate a 1000uf and put that capacitor in.
Test all your zb's, they can be pretty far off, like 0.8v plus or minus.
Test also all your tp/tc on there max charging voltage.
Sort them out.

Plus one on wolf, buy also a ir tester.

My two cents, hope this was helpful.
Best

---

This board is still under construction.
Still want/must add a other section for "first aid" to low v cells.
And I want to make it in one piece, with some more power.
I can do a 60 cells a day, when working. 90-120 when I am free.
First charge, let them rest for 30 days.
Second, test.
Third, charge them up to 3.45v for storage.

Click to expand...

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Thanks for the info. I noticed that some cells will charge up to about 4.15Vand others would go up to 4.21V and I thought that was an issue with my connections (my cell holders didn't come in yet, so I built some primitive ones myself.

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daromer said:

With a 160a Main fuse your cell level fuses should be 5a or around... Imagine what happens IF you manage to push 200a... The Main fuse Will run it happily... And you have some cells more happe to deliver current than others. At that rate you are way to Close to the cell levels fuses and you Will end Up with a chain reaction taking down 140fuses....

Click to expand...

Can you elaborate some more?
The fuses will take about 45s to blow at 3A, 85s at 1.5A and of course faster at higher amperage.
The BMS, inverter, and shunt are set up to limit the current to 110A and the inverter comes with a fast-acting 160A fuse (it even requires it). So even if the cells are really imbalanced and push different amps, I don't think the cell fuses will blow before the main fuse.


Should fuses pop during the first load test though, I think I will just double up the fuses per cell to avoid having to deconstruct the whole pack. I don't think it will happen though.

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Here are some photos of test bench #1&#2. #1 Is the lower one and the cell holders are constructed with springs and either the bus bars from the packs or tin foil. Contact is mostly stable and the results appear to be ok, but the wear on the springs makes them come off from time to time.
#2 is the upper one and the cells are held in place either by the friction of wood on wood or rubber bands. These work a lot better.
I will build the same one today for more ZBL's.

The ZBL's show anything from 0.02V-0.08V below the multimeter measured cell voltage (VOC) and sometimes drop to 0.2V below the multimeter measured voltage under load. I believe that happens because some slots on the first bench donot have perfect contact / have some resistance. I hope V2 will solve that problem.

I also have one LiitoKala Lii-500 to measure some reference values for cells from the same pack and they appear to mostly agree with the ZBL's so far.
How accurate is the IR measurement on the Lii-500? I was planning on measuring IR manually with a test resistor and using VOC vs. VLtocalculating it.

Currently, I am testing the cells with 500mA in the Lii-500 and an average of 500mA in the ZBLs. I decided to opt for 500mA instead of 1000mA because the cells will see an average load of 400-600mA.

Again, I am interested to hear your thoughts.

I did a little testing of a zb2l3 with a single cell and found the results to vary quite a bit.
Can you try repeated tests of 1 cell with 1 charger and 1 zb2l3 to see if you get consistent results?

CU17 said:

How accurate is the IR measurement on the Lii-500?

Click to expand...

The IR measurements of the Lii-500 are far from accurate. To prove the point take an IR reading of the same cell 4 or 5 times and you will get a different reading every time. That is because it does a DC IR test and not a manufacturer specified 1Kh AC 4 wire IR test.
Plus the contacts on this and other similar charger/testers are not adequate to measure IR properly.
Please readhttps://hiokiusa.com/wp-content/uploads/pdf/18740-UG_WP_BT4560E1-56E.pdf

I was planning on measuring IR manually with a test resistor and using VOC vs. VLtocalculating it.
Again, I am interested to hear your thoughts.

Click to expand...

Just get yourself a YR1030 IR tester for ~$60 US and be happy. Very accurate and the results are repeatable time and time again.
https://www.aliexpress.com/item/32817594188.html?spm=a2g0s.9042311.0.0.3da24c4dzRjOhI

Wolf

With the tp or tc's they run on sort of a program.
When you think they are done they are not.

Let them sit some longer, they want to finish there charge to get from ~4.15 to ~4.20

100kwh-hunter said:

With the tp or tc's they run on sort of a program.
When you think they are done they are not.

Let them sit some longer, they want to finish there charge to get from ~4.15 to ~4.20

Click to expand...

Have you verified that in any way? I have genuine TPs, and when the light changes colors, they are done. I use the USB input and have verified with a Charger Doctor that when the light changes colors, they no longer draw any current. The most reasonable explanation for the voltage differences is that each TP terminates at a different voltage. Mine range from 4.12V to 4
21V.

I think this is the painful spot, i don't have the genuine tp.
I noticed with mine tc's (22 of them in use) and with the look a like tp's (8 of them in use), that they change the first time from red to blue, that the cells aren't completely full yet, that they wait 5 to 20 minutes and charge a little again, so the LED change color again.
If i take them out and put them back in they think the cell is done, and nothing is happening.
This is why i think they are on some sort of program.

Furthermore, i bought a total of 45 tc's (i thought they where the tp's) the last 10 where tp4056b.
But with every tc/tp i tested with a single testing cell to see the end volt, to make sure they stop at 4.2 and not before

The zb's i tested on volt to see if they where all the same....its a different chapter.

To get good and consistent results you need a good power supply.
If you're power supply is capable of 5 amps at 5 volt you can do 4 tc/tp, if you're psu can give 5 amps at 6v you can do 5 of them.
For the zb, you will have enough of 1 amp to make 40 zb's go to work.

My psu is 30amp at 6v, if i charge more then 35, some of the tc's stop charging, and lower the charge.
One section on my board is only connected to one psu with 30 tc/tp.

I hope my two cents, this answers you're question?
Best

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Supplemental:
I noticed the "finishing" charge, the first time, when i "forgot" them.
Sinds then i give them way more time, and payed more attention, the results were getting better.

Interesting. Mine are red when charging and green when full. I have left mine in for hours after charging and they never go from green to red to top up. Also, I'm not using a separate power supply, I'm just using old USB wall warts from phones and tablets, which is how I can monitor charge with a Charger Doctor. I can even see when the TPs go from CC to CV, as the amp draw goes down, and when they switch from red to green, it reads 0.00A. Obviously the LED is still drawing current, but it's less than 0.005A.

https://www.aliexpress.com/item/32998294312.html?spm=a2g0s.9042311.0.0.400f4c4dSn01Z2
I am going to order 10 of those.
It was on my wish list anyway, i will keep a 5 min time lapse record on excel.
Just to be sure.
Now i have to figure out how i must post a excel, or a part from excel
F***..... me and computer(windows) will never be friends....where is the time of ((gw) (or) (c))basic and dbase?
I am still in the early 80's.

I will put them on my testing board, NOT on my production board.
It was planned anyway.
If i am allowed to give you any advice: take in consideration...please buy a good psu, please.
It will reward you.....

I also ordered two weeks ago some step down converters, for my 12v 60 amp beast...
Because (i think) my6v 30 amp is a little to weak to handle what i am asking for.
Just 30 tp/tc's, its to weak for start up loading fresh harvested 30 cells in one go.
https://www.aliexpress.com/item/32872607362.html?spm=a2g0s.9042311.0.0.19be4c4dgbKM9f
All ready got 3 of them and they don't disapointme.

I hope the links work, best

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mine are red and blue btw