Can someone explain this strange cell deviation at float?

Balanceandpeace

New Member
Joined
Sep 10, 2021
Messages
4
I recently put together a 12V battery made from 280Ah CALB cells and an Overkill Solar BMS. This is my second pack I've made, but I'm seeing strange cell voltage deviation at float. While charging, Cell 4 tends to be the highest voltage compared to the rest, but fairly close in voltage. But when the charge controller hits a float voltage of 13.8, suddenly the cell voltages begin to deviate from each other. Cell 4 drops rapidly, while Cell 2 & 3 rise together. Rising voltage as the battery continues to absorb some charge is what I would expect, but all together. Cell 1 stays at a fairly consistent voltage. When they discharge, they quickly fall into balance again.

What do you think is going on??

My first guess are mismatched cells. Unfortunately because of a break up, and my ex being the one who ordered the cells, I don't know who the seller was or have contact with them to seek a remedy.

This is the second pack I've made, though the first was with EVE cells, and that one didn't exhibit any strange behaviors like this.

Could it be that they're not effectively top balanced? I was hoping that the BMS would slowly balance them at float like it did with the prior pack.

Would love some thoughts!

Strange Cell Deviation at Float LiFePO4.png
 

grizzzman

Some say "Why" and some say "Why not?"
Joined
Sep 21, 2019
Messages
1,296
You need an active balancer to float. at that voltage.
 

kenryan

Solar Addict
Joined
Jun 29, 2021
Messages
190
Have you checked your battery capacity? Is actual capacity affected by this anomoly. If not, perhaps it is much ado about nothing.
 

RCinFLA

Photon Sorcerer
Joined
Jun 21, 2020
Messages
1,945
Your cells are not balanced, and perhaps are not matched with cell 1 & 4 older batteries. But you need to balance them first to tell if 1 & 4 have an issue.

At 13.75v absorb voltage you are not likely allowing much of any balancing to be done. On BMS set balancing to begin at 3.4v and set absorb to 14.2v to allow some balancing time. With cells this unbalanced you may get some high cell voltage shutdowns by BMS during charging until they get closer balanced.

Once they get balanced then you can check per cell voltage slump with load current to check condition of cells 1 & 4. You first need to burn off any surface charge from charging to 3.55v which only take about 1 amp load for about a minute or two. After surface charge burn off you should have a no load rested cell voltage, after resting for five minutes, of about 3.45v per cell.

You should load initially balanced cells at about 3.4-3.45v with about 60 to 80 amps by inverter load and plot each cell voltage slump verses time out to about 3 minutes of load current.

Poorer cells will have greater voltage slump after 3 minutes of load at this load current range. A new 280 AH cell at 60 amp load should slump about 50-60 mV from starting no load open circuit cell voltage of 3.4-3.45v. A used cell can be up to 5 times this number. Greater than 3x voltage slump is poor cell. Greater then 5x voltage slump is a garbage cell. Matched cells should voltage slump the same amount for same current load even if they are used cells.

If cells are poorly matched with varying amount of terminal voltage slump with same load current it will be more difficult to keep them in balance.

Capacity testing at low discharge rate is pretty much a waste of time. 20 amps discharge rate is absolute minimum, preferrably 40 amp minimum for a 280 AH cell.
 
Last edited:

TomC4306

Solar Obsessive
Joined
Mar 2, 2021
Messages
447
Top balance...
There are reasons why almost EVERYONE says to perform a proper top balance BEFORE serially attaching the cells...
Ignore these entreaties at your own risk and experience what you are experiencing....
Top balance...
 

Steve_S

Offgrid Cabineer, N.E. Ontario, Canada
Joined
Oct 29, 2019
Messages
6,250
Location
Rural NE Ontario Canada
I few notes considering charge processes.
The higher the amperage during charging, the higher likelihood of cell deviations relative to each cells IR.
The higher the Discharge Amperage again will cause cell deviations during the Voltage Sag. Again relative to cell IR.
TYPICALLY, cell deviations will occur @ the Working Voltage Limits (High or Low) where they become more pronounced. LFP standard default working voltage is 3.000-3.400 with Nominal Voltage being 3.200 (this is the accepted industry metric)
-- NB -- Grades, A+, A & A- will provide full "Working Voltage Range" and these cells will A-Typically test out with Gross Capacities exceeding "Label Rating". Example 280AH cells A+ > A- will test no lower than 282Ah but usually closer to 290AH.
-- Grades B and below to Bulk Commodity will have varying IR's and as cells are almost always NOT Properly Matched or batched (very hard to do with commodity cells) they may provide the Full Working Voltage but typically test out at Lower Capacity than Labelled Value. Example: 280AH cells testing between 270-280AH gross capacity.

? Gross Capacity ?
This is calculated from 2.500-3.650 Volts per cell which is the Full Voltage Range but not the "Working Voltage Range" often referred to as "the flat curve" which is 3.000-3.400. "A+, A & A-" test out above rated capacity by a few Percent and will provide a functional working voltage from 2.875-3.475 "usually. NOTE: This can ONLY be determined using a proper Matching & Batching Test process. This process cycles cells from 100% SOC to 0% SOC and back under different Amperage Rates with sample readings taken across the cycle. The point is to MATCH the Cell IR at different voltages so the cells within a pack once assembled act identically. MOST VENDORS DO NOT DO THIS ! They Voltage & IR Match at Static Storage Voltage and provide no Cycle Reports with Cell Serial # & QR Code. IT IS AN EXPENSIVE PROCESS and always results in cells failing grade and becoming Bulk Commodity cells for cheap.

Solutions:
As previously noted, Top Balancing and fully saturating cells is very important. Full Saturation means charging to 3.650 and waiting till amps taken for charge reaches <2A. A Surface charge would go to 3.650V and stop regardless of amps taken, not "topped off"
-!- All LFP settle post charge, this is perfectly normal, It is not uncommon for cells to settle from 3.650 100% to 3.500 +/- a bit within 60 Minutes of charge stopping. Again this relates to Working Voltage Curve.
- If possible test the IR of your cells at Lower Voltage (below 2.800) and again at higher voltage starting at 3.450. Then place your two Strongest Cells as you B1 & B4 with the two weakest as B2 & B3. B1 & B4 (in a 4S config) are the ones who take the hit first or who pushes first, the guys in the middle just struggle with the ends. (I know that doesn't sound good, but it is how it works)
-- Tip IN CASE: Sometimes cells have been stored for a while (New Old Stock), sometimes these will be "sluggish" charging/discharging at first, this can create issues. IF IN DOUBT, one way to make sure they are Fully Active Internally is to cycle them from 10% to 90% and back down up to 3 Times with "Medium Charge/Discharge Rate" IE: 0.5C Charge Rate Max and 0.25C discharge rate


Couple of things that can really muff up BMS Readings and Cell activities... Even a BURR or Ridge on a Bussbar can toss readings off (people are always surprised by that, but do realize, we are dealing with Millivolt & Milliamp Sensitivity). When cells are manufactured & packed, they often have machine oil on the terminals (from taping screw holes) and waxes as well (stop corrosion on Aluminium Surfaces) which need to be wiped off, acetone & rubbing alcohol are your friends. Oxguard / NoAlox is suggested (in very very tiny amounts) if using busbars which are not Tinned Copper or Aluminium to prevent any corrosion.

Balancers can help level up cells in tired packs or slightly mismatched packs BUT they cannot fix/correct defects or cell deficiencies. I myself use QNBBM Active Balancers on my 5 Production Packs and Heltec Capacitive Balancers on my Utility packs. Links Below for your interest. I use the Active Balancers in concert with the Passive Balancing afforded by the Chargery BMS' on my Production Packs.



Bottom Line: These cells will work fine but you need to top balance them - Placing the Strongest cells as B1 & B4 and by possibly using an Active Balancer suitable for the pack. BTW: These is a fair bit of misinformation on this tech, it is not helped by the fact that there are several different types and their behaviours & what they do is different. Also not ALL are compatible with various chemistries, also some will not work in conjunction with a BMS.

Below is my SCC Profile (I run 24V but that's ok) I have Bulk Commodity cells in packs (2x 280AH), as well as Grade A+(1x 280AH) and two packs of used EV LFP (the 175's) in my primary bank... So a good cross section of variations and was tricky to work out... But with the hard Thrash Testing (seriously abusive "to the edge tests") got it sorted nicely.

Settings for \Midnite Classic-200 Charge Controller settings
All equipment MUST BE Voltage Corrected & Calibrated (VERY IMPORTANT) see link in my signature on how to do it.
Divide Values X2 for 12V. Multiply X2 for 48V.
Absorb: 28.2 for 15 minutes (3.525vpc) (some call this boost)
Equalize: OFF
Float 27.9V (3.4875vpc)
MIn Volts: 22.0 (2.750vpc)
Max Volts: 28.7 (3.5875vpc)
Rebulk Voltage: 27.7 (3.4625vpc)
End Amps: 14A (*1)

(*1): End Amps is calculated from the Highest AH Battery Pack in a Bank. IE: 200AH X 0.05 = 10A 280AH X 0.05 = 14A.
NB: Victron Forum discussion says EndAmps = TailCurrent
This get's the bank charged to full with high amps (Constant Current) and then float (Constant Voltage) tops off so the cells are on average between 3.475-3.500. I am running 7/24/365 so float is used up by the Inverter + provides whatever the packs will take to top off.

** Coulumbic Efficiency for LFP is 99%

Hope it helps & Good Luck. Link #2 in my signature is an LFP Battery Assembly Guide which has some other info which may be of help to you, please download that PDF from the resources. Maybe the Voltage Chart in my Sig as well (better one in the LFP Guide though).
 

Capt Bill

Sailing Options
Joined
Mar 18, 2020
Messages
726
Location
Redwood Valley, Cailfornia/ Montezuma, Costa Rica
I few notes considering charge processes.
The higher the amperage during charging, the higher likelihood of cell deviations relative to each cells IR.
The higher the Discharge Amperage again will cause cell deviations during the Voltage Sag. Again relative to cell IR.
TYPICALLY, cell deviations will occur @ the Working Voltage Limits (High or Low) where they become more pronounced. LFP standard default working voltage is 3.000-3.400 with Nominal Voltage being 3.200 (this is the accepted industry metric)
-- NB -- Grades, A+, A & A- will provide full "Working Voltage Range" and these cells will A-Typically test out with Gross Capacities exceeding "Label Rating". Example 280AH cells A+ > A- will test no lower than 282Ah but usually closer to 290AH.
-- Grades B and below to Bulk Commodity will have varying IR's and as cells are almost always NOT Properly Matched or batched (very hard to do with commodity cells) they may provide the Full Working Voltage but typically test out at Lower Capacity than Labelled Value. Example: 280AH cells testing between 270-280AH gross capacity.

? Gross Capacity ?
This is calculated from 2.500-3.650 Volts per cell which is the Full Voltage Range but not the "Working Voltage Range" often referred to as "the flat curve" which is 3.000-3.400. "A+, A & A-" test out above rated capacity by a few Percent and will provide a functional working voltage from 2.875-3.475 "usually. NOTE: This can ONLY be determined using a proper Matching & Batching Test process. This process cycles cells from 100% SOC to 0% SOC and back under different Amperage Rates with sample readings taken across the cycle. The point is to MATCH the Cell IR at different voltages so the cells within a pack once assembled act identically. MOST VENDORS DO NOT DO THIS ! They Voltage & IR Match at Static Storage Voltage and provide no Cycle Reports with Cell Serial # & QR Code. IT IS AN EXPENSIVE PROCESS and always results in cells failing grade and becoming Bulk Commodity cells for cheap.

Solutions:
As previously noted, Top Balancing and fully saturating cells is very important. Full Saturation means charging to 3.650 and waiting till amps taken for charge reaches <2A. A Surface charge would go to 3.650V and stop regardless of amps taken, not "topped off"
-!- All LFP settle post charge, this is perfectly normal, It is not uncommon for cells to settle from 3.650 100% to 3.500 +/- a bit within 60 Minutes of charge stopping. Again this relates to Working Voltage Curve.
- If possible test the IR of your cells at Lower Voltage (below 2.800) and again at higher voltage starting at 3.450. Then place your two Strongest Cells as you B1 & B4 with the two weakest as B2 & B3. B1 & B4 (in a 4S config) are the ones who take the hit first or who pushes first, the guys in the middle just struggle with the ends. (I know that doesn't sound good, but it is how it works)
-- Tip IN CASE: Sometimes cells have been stored for a while (New Old Stock), sometimes these will be "sluggish" charging/discharging at first, this can create issues. IF IN DOUBT, one way to make sure they are Fully Active Internally is to cycle them from 10% to 90% and back down up to 3 Times with "Medium Charge/Discharge Rate" IE: 0.5C Charge Rate Max and 0.25C discharge rate


Couple of things that can really muff up BMS Readings and Cell activities... Even a BURR or Ridge on a Bussbar can toss readings off (people are always surprised by that, but do realize, we are dealing with Millivolt & Milliamp Sensitivity). When cells are manufactured & packed, they often have machine oil on the terminals (from taping screw holes) and waxes as well (stop corrosion on Aluminium Surfaces) which need to be wiped off, acetone & rubbing alcohol are your friends. Oxguard / NoAlox is suggested (in very very tiny amounts) if using busbars which are not Tinned Copper or Aluminium to prevent any corrosion.

Balancers can help level up cells in tired packs or slightly mismatched packs BUT they cannot fix/correct defects or cell deficiencies. I myself use QNBBM Active Balancers on my 5 Production Packs and Heltec Capacitive Balancers on my Utility packs. Links Below for your interest. I use the Active Balancers in concert with the Passive Balancing afforded by the Chargery BMS' on my Production Packs.



Bottom Line: These cells will work fine but you need to top balance them - Placing the Strongest cells as B1 & B4 and by possibly using an Active Balancer suitable for the pack. BTW: These is a fair bit of misinformation on this tech, it is not helped by the fact that there are several different types and their behaviours & what they do is different. Also not ALL are compatible with various chemistries, also some will not work in conjunction with a BMS.

Below is my SCC Profile (I run 24V but that's ok) I have Bulk Commodity cells in packs (2x 280AH), as well as Grade A+(1x 280AH) and two packs of used EV LFP (the 175's) in my primary bank... So a good cross section of variations and was tricky to work out... But with the hard Thrash Testing (seriously abusive "to the edge tests") got it sorted nicely.

Settings for \Midnite Classic-200 Charge Controller settings
All equipment MUST BE Voltage Corrected & Calibrated (VERY IMPORTANT) see link in my signature on how to do it.
Divide Values X2 for 12V. Multiply X2 for 48V.
Absorb: 28.2 for 15 minutes (3.525vpc) (some call this boost)
Equalize: OFF
Float 27.9V (3.4875vpc)
MIn Volts: 22.0 (2.750vpc)
Max Volts: 28.7 (3.5875vpc)
Rebulk Voltage: 27.7 (3.4625vpc)
End Amps: 14A (*1)

(*1): End Amps is calculated from the Highest AH Battery Pack in a Bank. IE: 200AH X 0.05 = 10A 280AH X 0.05 = 14A.
NB: Victron Forum discussion says EndAmps = TailCurrent
This get's the bank charged to full with high amps (Constant Current) and then float (Constant Voltage) tops off so the cells are on average between 3.475-3.500. I am running 7/24/365 so float is used up by the Inverter + provides whatever the packs will take to top off.

** Coulumbic Efficiency for LFP is 99%

Hope it helps & Good Luck. Link #2 in my signature is an LFP Battery Assembly Guide which has some other info which may be of help to you, please download that PDF from the resources. Maybe the Voltage Chart in my Sig as well (better one in the LFP Guide though).
Thanks Steve, ... Just researching options for how to use my below par 280Ah EVE cells that I likely hurt via a low cell volt cycle mistake or two (using BMS discharge trigger to SSR, ... to turn off my Inverter Draws (on 3 networked LV2424) instead of triggering total battery disconnect/ and getting caught off guard via an idle draw mistake). Just ordered a 8S 5A Active balancer ... after taking in a time consuming study of my below par battery cell behavior through charge and discharge cycles. I have now rotating in 6 new cells (ordered from Docan Power, for 5 day delivery time to Calif.) in set of 8, ... to get my hurt pack back to a good looking 24v battery bank; ... I now have two decent 24 v 280Ah battery banks connected up for 560Ahs, w 2 Chargery BS8Ts. Next: I now have some below par cells (some peakers/ runners at high charge volts, others with low Ah volt drop at low volts) that I believe could make up a 3rd 24v battery bank for adding Ahs. Reading this thread is helping me figure out my route. ... I notice your Float Charge setting of 27.9v is higher than the 27.3v I am using on my 4 x MPP LV2424s set up.

Wondering: Can you give me (us readers) any additional pros or reasons to consider upping my Float Voltage from 27.2 or 27.3v ... to 27.9v ? Whatever on that; ... Thanks for your ongoing educational efforts in this forum. :+) Bill
 
Last edited:

Steve_S

Offgrid Cabineer, N.E. Ontario, Canada
Joined
Oct 29, 2019
Messages
6,250
Location
Rural NE Ontario Canada
Well, with my equipment (Midnite Classic, E-Panel, Samlex EVO Inverter/Charger) I calculate in voltage drops to correct. I'm in process of redoing my entire bank of batteries + my utility packs, so I am experimenting again. I bulk Charge to 28.0 for 45 Minutes then float at 27.8V which is bring the current online pack to their max as they settle to 3.410Vpc on average post charge input. Now I am "eagle eyeing" the packs and as such pushed them to their edge. These are NOT A Cell packs, those are being reconfiged now. Now it takes a heap load of BMS fiddling & tweaking and you have to be a tad OCD like me. Because there are multiple packs, I do allow for 1 or 2 to disconnect (BMS forced) within the test bank as it is now.

Regarding possible Borked "below par" cells. Take a deep breath, it's a PITA but can work wonders. Get the cells to lower voltage, 2.750V is peachy, then charge each cell with a respectable charger, preferably in the 30A CC (Constant Current) at 3.650V and let it go into CV (Constant Voltage) and let it go till it's down to taking 2.8A or less (280AH cells). Do all 8 cells similarly, then Top Balance the lot in a string afterwards to 3.650V taking less than 5A. Leave them sit & settle at least 24 hours and they'll likely be sitting in the 3.3xxV range and should be "reasonable". I've recovered LFP that dropped & stayed at 1.100Vpc for months without issue, using this method.

Up till now, I have been using Chargery BMS8T-300's with 300A DCC's couple with a QNBBM-8S Active balancer on each "production" pack (what a dance with settings, sheesh). I am replacing that entire lot with JK-BMS with 2A Active Balancer rs485/Canbus to get everything simplified and uniform with the communications capabilities & better controls. Things can change a lot in a couple of years and sometimes it's costly... 6 Production Packs + 2 Utility Packs, ouch.

Hope it helps, Good Luck.
 

Capt Bill

Sailing Options
Joined
Mar 18, 2020
Messages
726
Location
Redwood Valley, Cailfornia/ Montezuma, Costa Rica
Get the cells to lower voltage, 2.750V is peachy, then charge each cell with a respectable charger, preferably in the 30A CC (Constant Current) at 3.650V and let it go into CV (Constant Voltage) and let it go till it's down to taking 2.8A or less (280AH cells). Do all 8 cells similarly, then Top Balance the lot in a string afterwards to 3.650V taking less than 5A. Leave them sit & settle at least 24 hours and they'll likely be sitting in the 3.3xxV range and should be "reasonable". I've recovered LFP that dropped & stayed at 1.100Vpc for months without issue, using this method.
Thanks for your voice from your detailed hands on experience. I know some lessons like that were time suck learning curves, because I have had my own; ... plus I am willing to go there as part of my "Learning More All the Time Program" (while retired with options). I will try that procedure, and see if I can improve my below par cells to function in a more balanced fashion. I had a few below 2.0 volt brief cell mistake cycles that recharged to 2.5v + withing a couple of couple of minutes of a10 amp bench charger. I hit 1.4v once or twice on some new cells I suspect were also B or B- Grade (those have been acting up). All my low cell volt mistakes came from depending on a Discharge side BMS trigger Cutting Off my Inverter Draws to protect my battery cells. With 3 LV2424 online, my Equipment idles draw at low BMS cell volt triggers hurt my cells by not completely disconnecting my battery (my experiment and mistake lesson). That made it clear a BMS triggered Battery Cut Off is what I needed. I still use BMS Charge side triggers to Cut my Solar In, and then my Full system is still working except for Solar Charge (and cn recover on its own). It would be nice to figure out how to my lesser Ah cells in my Battery Bank expansion. ... So, I am now experimenting with that goal. Thanks for the inspiring ideas :+)

Also Wondering: ... any links for that respectable 30A charger, for 3.650V ? Be way faster than my 10 A Bench Charger for top balancing too.
 
Last edited:

Steve_S

Offgrid Cabineer, N.E. Ontario, Canada
Joined
Oct 29, 2019
Messages
6,250
Location
Rural NE Ontario Canada
I have a TekPower 15V/45A Bench supply but I haven't seen them on sale anywhere for a while. I couldn't recommend a currently available product at this time, everything is a tad messed up.
 

Capt Bill

Sailing Options
Joined
Mar 18, 2020
Messages
726
Location
Redwood Valley, Cailfornia/ Montezuma, Costa Rica
I have a TekPower 15V/45A Bench supply but I haven't seen them on sale anywhere for a while. I couldn't recommend a currently available product at this time, everything is a tad messed up.
I just ordered this one; to try on your cell restore procedure; plus have the ... up to 40 amp charge option my next LiFePO4 Top Balance
 

Steve_S

Offgrid Cabineer, N.E. Ontario, Canada
Joined
Oct 29, 2019
Messages
6,250
Location
Rural NE Ontario Canada
I just ordered this one; to try on your cell restore procedure; plus have the ... up to 40 amp charge option my next LiFePO4 Top Balance
That is the one I have as well.
There is a couple of things to ponder.
1) a thicker wire upgrade than what is provided.
2) Using Ring Terminals as opposed to "clips"
! Preset the Voltage BEFORE connecting to the charging target at the ring terminals, power off & connect to cell(s).
You can do parallel charging of multiple cells but it will slow the overall charging.

When I got mine it would not start, I opened it up to find a connector that came loose, after checking everything it's been perfectly fine. The one connector that did not have a dab of glue, no less.
 

Capt Bill

Sailing Options
Joined
Mar 18, 2020
Messages
726
Location
Redwood Valley, Cailfornia/ Montezuma, Costa Rica
Preset the Voltage BEFORE connecting to the charging target at the ring terminals, power off & connect to cell(s).
Steve, Wonder if you might enlighten me further. I am confused from the way my particular 30v 10a Bench Power Supply functions; I have thought I was supposed to short between the plus and minus terminals to then adjust and set voltage. That has never worked for me on my particular unit. Seemed like I had to turn voltage and current knobs down, connect to battery, and then play with voltage and current knobs to get sort of what I wanted ... and if it behaves how I want toward top end of my charging voltage; ... & then leave it like that (kobs stay exact same) for next cell charging, if I want to charge with same set up. ... Interesting: I also had to re solder a bad terminal connection inside it for a fix.

Question: ... For setting up my new, better, and just delivered TekPower 15 Volt 40 Amp (says) Switching Power Supply: ... for Pre-Setting the Voltage ... Can I do that simply by turning the voltage knob? ...or is it proper procedure to short the + and - terminals ... then turn it on and pre-set the Voltage ... then power off to connect to battery charging target, and then turn on and adjust the current ... ... Your Guidance Info. will be appreciated. Gona try on a procedure you shared in attempt to reconditioned some EVE 280Ah LiFePO4 cells that hit 1. 4v on an overnight cycle or two. (a procedure that worked for you on worse than my mishap ) ... ;+) Bill
 
Last edited:

740GLE

Photon Sorcerer
Joined
Apr 30, 2021
Messages
1,348
Dont short the power supply, just leave ther termials open, then set voltage.

Once turned on and voltage applied to the cells the display will drop the voltage. Dont adjust it up. It’ll be in constant current mode and adjust current to max if you want. The voltage will rise a current starts to fall off and switch over to Constance voltage mode, this point cells are 90-95% full.
 

Steve_S

Offgrid Cabineer, N.E. Ontario, Canada
Joined
Oct 29, 2019
Messages
6,250
Location
Rural NE Ontario Canada
Never short the wires, that seems obvious to me, you are lucky you did not fry the other unit. Which is actually ODD as to why it didn't, it should have popped a fuse or breaker.

I set my voltage at the ring terminals before connecting to a cell or row of cells for Top Balance. Current dialed up to max, I let it go and watch and try to be patient especially in the 3.2xxx through 3.3xx range, oi that takes a while LOL.
 

740GLE

Photon Sorcerer
Joined
Apr 30, 2021
Messages
1,348
Measuring from ring terminals vs cell terminals is always good to compare your lead voltage drops.

With 12awg I had about .3v drop at 10a, with the power supply in CC mode the terminals of the PS still dropped about .3-.5v.

I left the voltage adjuster alone and let it bake and eventually it swapped over to CV mode as current started to drop and cell terminals climbed above 3.48v
 

Capt Bill

Sailing Options
Joined
Mar 18, 2020
Messages
726
Location
Redwood Valley, Cailfornia/ Montezuma, Costa Rica
Regarding possible Borked "below par" cells. Take a deep breath, it's a PITA but can work wonders. Get the cells to lower voltage, 2.750V is peachy, then charge each cell with a respectable charger, preferably in the 30A CC (Constant Current) at 3.650V and let it go into CV (Constant Voltage) and let it go till it's down to taking 2.8A or less (280AH cells). Do all 8 cells similarly, then Top Balance the lot in a string afterwards to 3.650V taking less than 5A. Leave them sit & settle at least 24 hours and they'll likely be sitting in the 3.3xxV range and should be "reasonable". I've recovered LFP that dropped & stayed at 1.100Vpc for months without issue, using this method.
I want to say thanks Steve S. ... and report: I printed your tip and tried it on eight 280Ah cells that had dropped down to 1.4v a couple of times on over night cycles, by my mistakes in BMS protection testing ... on a battery bank that then had peaker cells, especially one runner/peaker near top charge voltage triggering BMS release of battery bank, ... plus 2 other cells that dropped off way early at lower cell voltage. It took some time to drain down to 2.75 v, then charge each cell with 30Amp, then top balance. ... I was kind of surprised plus happy with the results. ;+) ... I have some other challenges to fine tune next. ... and will likely comment about that in a Chargery BMS thread later.
 
Last edited:
Top