LFP cell test & recovery from Low Volt

Started by Steve_S, May 30, 2022, 08:10:08 AM

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Steve_S

Hello,
I was asked a question within another thread which is off-topic.  Given the nature of the Question, I felt it would be more suitable to start a Thread as I am certain others may encounter similar issues.

The Question as posted by ClassicCrazy.
QuoteQuick question for you Steve. I have some 100ah long  neglected Calb cells that was a 48v pack but a couple cells are bad ( low voltage). The other cells are still showing 3.2v
I would like to put a 24v or 12v bms on some just to see if they will still work .
Do you recommend the jk-bms over something like the Daly bms ?
Oh and when you get ready to try out the pi grafana stuff let me know and maybe I can make an image of mine to share so you don't have to start all from scratch. Unless you want to spend the time doing that !

Larry

So you have 16x Calb 100AH LFP Cells. 
Majority sitting at 3.2xx which is fine, which is well within the static storage voltage range. 
Avoid DALY BMS'!  So many things over time.. They are better now BUT save self pain!
I would strongly urge you to look at a JKBMS B2A24S15P which has a 2A programmable Active Balancer, Bluetooth App and CanBus/RS485 ports for data in/out.  These support 8S(24V) 16S(48V) and above along with various chemistries.  This is a 150A Discharge/75A Charge capable BMS.  (I'm now installing these particular ones on my fleet of packs and the result is outstanding!) LINK:  https://www.aliexpress.com/item/1005003104573871.html

Recovery Instructions: 
Charge each LOW cell, one at a time, starting at 3.000V and around 10A and let it slowly take the charge till it cuts off. Rinse repeat for each cell. They should all take it BUT BE GENTLE & POLITE ! Once they all get to 3.000 then parallel the cells and top them in INCREMENTS, I would suggest 0.100V increments. Yes slow, painful, TEDIOUS but if you want to recover them....

They technically can recover IF they were not frozen or cooked while in a state of discharge, if they have, then do one cell at a time and in a safe box in case it pops & leaks. IF you are lucky, they will recover and maybe you've only lost a percentage of capacity. IF they recover to at least 3.400Vpc, I would run at least 3 good cycles through them (charge/discharge) and then capacity test each cell to ensure the packs integrity, because even if One Cell goes wonky, it will affect the whole pack, as the lowest common denominator rules.

Once you get the cells up to 3.650 (I would stick to 3.600 myself) and fully saturated (meaning taking <2A) and stop charge current. The cells WILL SETTLE which is perfectly normal & expected behaviour. They will likely drop to about 3.500 from 3.600 within 1 hour or so, give or take a bit. They will usually continue to settle till around the 3.400-3.450 mark where it will slow considerably as the LFP Working Voltage range is 3.000-3.400.

Once this is done, I would setup the pack temporarily with the BMS and discharge the battery pack to cutoff, then recharge through the BMS till it reaches full at a respectable Amperage. 100AH Cell can typically take a Max of 0.5C or 50A charge rate. 20-40A Charge rate would be as high as I would go "for now" while determining their condition.

When charging at a higher amperage the cells heat up (normal & expected) and the higher the amps the warmer they get. With ESS cells @ 0.5C it's never crazy ! EV Grade Cells @ 5C Charge Rate = another matter ok. We are dealing with ESS cells here, so staying "in context". You will want to check the cells during Higher Amp charging feel the sides etc, they should be consistent / constant... a Hot Spot = Warning Flag ! You WILL NOT GET THAT with Lo Amp Charging, it has to be at least 0.25C and the temps should be notable within 1/2 hour or so. Be diligent & watchful !

---------
NOTE, some may argue but Real-World Experience verifies that cells CAN be recovered from sitting static @ 1.5V BUT that depends on how long and if they ever got frozen or overheated while at that low voltage.   I have done this myself with EV-Grade LFP cells that dropped to 1.2V due to an Active Balancer Failure while the pack was in storage, and they recovered just fine and now are averaging 0.05mv differential post charge and stick close to that till about 2.750V. at which point they diverge as expected.   These same instructions have been used with Success by others as well.   *The cells must NOT be leaking or highly bloated, if they are, dispose of them according to local regs and DO NOT attempt to recover if leaking in any way.

I hope this helps answer the questions and others who may be facing a similar situation.


ClassicCrazy

Thanks Steve !
I will have to get to it this summer .
Larry
system one
Classic 150 , 5s4p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system two
Classic 150 , Hawkes Bay , 5s 135 watt Kyocero , Jakiper 48v LiFePO4 , Outback VFX 3648 inverter
system three
Midnite KID MPPT 24 DC in to  12 volt AGM batteries

Steve_S

Yesterday I was busy in the Powerhouse and decided to do a Thrash Test on a "Recovered Pack" which consists of EV-Grade LFP not ESS Grade, (these are Yttrium Doped Premium Cells).  The Thrash is to the limit Discharge & High Charge (@.5C) and with the Active Balancing starting at 3.70Vpc.  The Cell Delta's within that pack remained at 0.010mv and lower as programmed.  Rechecked this morning and at 75% the Deta was 0.004mv.   All thanks to the JK-BMS. 

Steve_S

Larry,

I wanted to add this here for further clarity.  The "Failed Pack" of 24V with straight 8S config info from when it failed.  The method above is how I recovered it but look at how low & bad it got.  Pretty scary numbers IMO...

Case in point, I had one LFP Pack collapse because of a Failed QNBBM-8S. No App/No Control/No Alerts-Warnings !
Took the cells down to this:
1.163V 0.37 ir
2.737V 0.40 ir
1.180V 0.38 ir
1.184V 0.39 ir
1.181V 0.37 ir
1.183V 0.35 ir
1.178V 0.42 ir
1.184V 0.36 ir.
I did manage to Recover these Cells and Rebuild the pack, it took two weeks of intense effort and I "Got Lucky" and capacity loss is minimal.

I use a Yaorea YR1035+ Cell tester which provides the cell IR.
Link to Alibaba Site but also available in US from a warehouse there OR for more $$ from Amazon/Ebay. 
https://www.alibaba.com/product-detail/Yaorea-YR1035-Battery-Internal-Resistance-Meter_11000000504328.html

ClassicCrazy

Quote from: Steve_S on June 04, 2022, 10:02:15 AM
Larry,

I wanted to add this here for further clarity.  The "Failed Pack" of 24V with straight 8S config info from when it failed.  The method above is how I recovered it but look at how low & bad it got.  Pretty scary numbers IMO...

Case in point, I had one LFP Pack collapse because of a Failed QNBBM-8S. No App/No Control/No Alerts-Warnings !
Took the cells down to this:
1.163V 0.37 ir
2.737V 0.40 ir
1.180V 0.38 ir
1.184V 0.39 ir
1.181V 0.37 ir
1.183V 0.35 ir
1.178V 0.42 ir
1.184V 0.36 ir.
I did manage to Recover these Cells and Rebuild the pack, it took two weeks of intense effort and I "Got Lucky" and capacity loss is minimal.

I use a Yaorea YR1035+ Cell tester which provides the cell IR.
Link to Alibaba Site but also available in US from a warehouse there OR for more $$ from Amazon/Ebay. 
https://www.alibaba.com/product-detail/Yaorea-YR1035-Battery-Internal-Resistance-Meter_11000000504328.html

That is amazing results compared to what most people would think.
What do you use to single cell charge and discharge them when rejuvenating the cells ?
I will look up that tester.

Larry
system one
Classic 150 , 5s4p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system two
Classic 150 , Hawkes Bay , 5s 135 watt Kyocero , Jakiper 48v LiFePO4 , Outback VFX 3648 inverter
system three
Midnite KID MPPT 24 DC in to  12 volt AGM batteries

Steve_S

Larry, Have a Peek at THIS thread post to see how they are doing now.  174-1 is the recovered pack & 174-2 is as was but with the new JK.  The JK Screen showing deltas etc...
https://diysolarforum.com/threads/jk-4s-200a-bms.38623/post-519587

I use a TekPower TP1540E Bench Supply which can deliver 15V/40A CC/CV and I manually dial it to 3.65 and test with DVOM to verify, then attach to a single cell.   Get all cells back UP to proper voltage and allow them to saturate fully (AH-Capacity * 0.05)  ie 100AH*.05=5A.   Once all the cells have been brought up, set them in Parallel with each and TOP Balance the entire lot to saturation, again that would be 5A if the cells are 100AH.