Top Balancing "How to"

Steve_S

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I have 2x 02YCB66110000H & 2X 02YCB66710000J 280AH cells that I am doing now.
Last one just finished capacity test, they are all coming in 276-278AH. the "H" version at 276, the "J" at 278. starting from 3.60V, they do drop fast from there to 3.450-3.500 and go into the long flat curve from there on. So now charging 1 cell at a time from 2.60+/- to 3.60 for final.
 

Capt Bill

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Invite to Troubleshoot with me: ... on my 5th Morning of Top Balancing Attempt on 8 x 280Ah EVE cells; Charging at 10A (w some 7A cycles) on 8 LiFePO4 cells wired in Parallel; Stuck at 3.365 Volt top for last 24 + hours; while wanting the Full 3.650 Volts Top Balance Charge !!! . This is my second set of LiFePO4s which I intend to add my 1st DIY 24v 280Ah set to get a 24 volt 560 Ah battery bank; for my 3 x MPP LV2424s with 6000 Watts of PV input. I recently received this second set of 8 EVE cells from China via sea freight to USA measuring 3.304 v - 3.305 volts. I think: I may have one below par cell(s) holding me back from achieving my full 3.650 Volt Top Balance Charge ???

Studying a few recent Threads here related to top balancing, after my earlier 1st DIY LiFePO4 and Top Balance lessons; has been helpful. I documented one below par cell on my first DIY LiFePO4 build set here in this forum, and got that one cell replaced for free by Xuba (took time of documenting the problem, then the sea freight shipping). Further testing of that one below par cell (now on my shelf) revealed it getting only 225 Ahs (max as measure on that 200 watt fan heater unit Will P has turned us on to; ... originally estimated to be 170 Ah via my earliest Chargery BMS info. that it bottomed out early) ... out of its' 280 Ah Rating. That same cell also shows it is below par by NOT being able to take a full charge to 3.600v or 3.650v; had higher internal resistance than the other good cells, and it will only charge up to a 3.360 volt MAX (its' max top charge voltage). That history is why I currently think I may have one below par cell holding me back from getting a Full Top Balance Charge on this second set ???

REFERENCES # 1: I did some math calculations to estimate how long it might take me to get to 3.650 Volts on a Top Balance effort; and estimated about 67.2 hours = 2.8 days from this math: 280 Ahs x 8 cells in parallel = 2,240 Ahs; ... & my 3.305 volts starting point = about 70% SOC; so charging 30% of 2,240 Ah worth of my LiFePO4s to full 3.650 Volts, to 100% SOC @ 10 Amps Charge; Math: 2,240 Ah x 30% = 672 Ah / divided by 10 Amps (charging) = 67.2 hours = 2.8 days. I realize this is not perfect/ might have other factors involved. After 96 + hours of charging at 10 Amps (with a few cycles of 7 A charging when adjusting Power supply voltage downward/ closer to 3.650 V ); I have been stuck at 3.360 to 3.650v for that last day and half (@ about 3.365v for last 24 hours) !!! ... I just turned my power supply charging off, and my new 8 cell battery banks drops to 3.350 v within an hour/ and is 3.348 v two hours later (might be normal). ... After 1 + day at same voltage/ with no climb; Does anyone think I would benefit from more parallel charging?

REFERENCES # 2: I copied some comments from recent forum threads to register my lessons (thank you to the authors): While this is may be redundant; these posts below speaks to my lesson junction; ... from folks w similar 8 or 16 new 280 Ah LiFePO4 sets:

one post: ... So after days and days of slowly charging my battery bank and getting everything top balanced I was finally able to fully assemble my battery today. The 4 groups of parallel cells all showed either 3.600 or 3.601 prior to making the series connections. ... Once the cells get past 3.5V they should start filling up a lot faster (my comment: I notice that too, good to be watching past 3.5v, to avoid, then easily overcharging/ I did that once!) ... 10A is fine.... but can take a long time if the cells start in a low state of charge. Even at 10 amps your are only getting 10A * 3.65V = 36.5W.

a GOOD IDEA : I would do this next time for the larger Ah LifePO4s/ *** quotes (mixed w my comments)
*** What I do is first wire the cells into the 24 V bank (with the BMS) and then charge to 29.2V till one of the cells hits 3.65. This allows me to push 29.2V * 10A = 292 watts. However, even this can take quite a while if the cells are in a very low state of charge. Note: Initially the charge will be limited by the 10 amp limit of the supply ... Once the cells are mostly charged, take the bank apart and re-wire them all in parallel and then charge them to 3.65V till the current drops to near zero.

(MY NOTE: ... or I could much more quickly charge and discharge via one, or up to three of my currently wired up and working MPP Lv2424s All In Ones for up to 0.5C / 140 Amps or more, to get close to my full charge (w view of cell balancing act), ... & then reconfigure battery bank for its' full top balance / then go for my 580 Ah battery bank. )

REFERENCE # 3: Picture Attached shows 2 DMMs; one w a DC amp clamp confirming my 30V /10A rated Bench Power Supply putting out Amps to my 8 batteries for my top balance effort. I had question about if my $60 Power Supply might be malfunctioning, as it does not allow me to dial my desired voltage when 1st turned on, until I hook it to battery (wish I had spent an extra $20+ for a better model). My DMM with DC Amp Clamp Meter has also confirmed 10 Amps IN to battery when I dial up the voltage (max).

**********
Troubleshoot Options: I think any of these ideas will lead me to a below par battery.
... I will see by proceeding one step at a time.

Option #1: Disconnect batteries and charge one cell at a time for one hour: Look at which ones gets to higher voltage, and which one(s) might not. I have a timer switch to easily do one hour cycles. If I find one cell that will not charge like the others, I will Ah test that cell's Ah Capacity (1st) with the 200 Watt fan heater unit I have here. While I wish I had an Ah tester w good cut off voltage option that could draw more watts (amps), that 200 watt fan heater allows me to set a low voltage cut off to stop its' smallish current draw when battery hits < 2.5v volts. That its' plus !!!

Option # 2: I could also hook my new 8 cells in series w my 2nd Chargery BMS, and connect BMS charge side trigger to a battery cut off relay; and charge with my 30v/10A rated Bench Power Supply to see what the BMS info shows for individual cell voltages.

Option # 3: I could replace my current 24v LiFePO4 set with these new ones have have been top balance to only 3.365v (vs 3.650v ), and put them through some charge and discharge cycles at up to 140A (0.5C) to see what my Chargery BMS8T information shows. ...

If I find a below par cell, I wonder if a few full charge and discharge cycles at various amps up to 140 Amps in and out could help it???

Open to comments while hoping for the best. Currently Attracted to Option #1 while going to posting this first :+) Bill
 

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DJSmiley

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I'd go for the series charge. Charge with 29.2V (8x3.65V) at 10A or whatever your supply can deliver.

That will speed up the charging by 8 times compared to parallel charging.

Set the BMS to disconnect at 3.65V. Since the cells aren't topbalanced yet, eventually a single cell will hit HVD and stop charging

Reconnect in parallel and finish the topbalancing at 3.65V. That will take much less time, since you only have to charge the cells for the last bit (the difference between the cells compared to the fully charged one). Assuming they aren't too much off balance it will take a short time to finish.
 

snoobler

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@Capt Bill

Yours is the umpteenth post like this. What you are seeing is normal. The vast majority of the charging process occurs between 3.3 and 3.4V at these very low currents. It is not at all uncommon to see voltage hold almost constant for very long periods of time, especially with such low charge currents (these could be charged at up to 1120A in this configuration).

8 * 280 = 2240Ah - likely at least 1/2 is required on as-received, possibly more.

1120/10 = 112 hours @ 10A

If you decide to change course, the only sensible option is to series charge with the BMS.
 

FilterGuy

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Invite to Troubleshoot with me: ... on my 5th Morning of Top Balancing Attempt on 8 x 280Ah EVE cells; Charging at 10A (w some 7A cycles) on 8 LiFePO4 cells wired in Parallel; Stuck at 3.365 Volt top for last 24 + hours; while wanting the Full 3.650 Volts Top Balance Charge !!! . This is my second set of LiFePO4s which I intend to add my 1st DIY 24v 280Ah set to get a 24 volt 560 Ah battery bank; for my 3 x MPP LV2424s with 6000 Watts of PV input. I recently received this second set of 8 EVE cells from China via sea freight to USA measuring 3.304 v - 3.305 volts. I think: I may have one below par cell(s) holding me back from achieving my full 3.650 Volt Top Balance Charge ???

Studying a few recent Threads here related to top balancing, after my earlier 1st DIY LiFePO4 and Top Balance lessons; has been helpful. I documented one below par cell on my first DIY LiFePO4 build set here in this forum, and got that one cell replaced for free by Xuba (took time of documenting the problem, then the sea freight shipping). Further testing of that one below par cell (now on my shelf) revealed it getting only 225 Ahs (max as measure on that 200 watt fan heater unit Will P has turned us on to; ... originally estimated to be 170 Ah via my earliest Chargery BMS info. that it bottomed out early) ... out of its' 280 Ah Rating. That same cell also shows it is below par by NOT being able to take a full charge to 3.600v or 3.650v; had higher internal resistance than the other good cells, and it will only charge up to a 3.360 volt MAX (its' max top charge voltage). That history is why I currently think I may have one below par cell holding me back from getting a Full Top Balance Charge on this second set ???

REFERENCES # 1: I did some math calculations to estimate how long it might take me to get to 3.650 Volts on a Top Balance effort; and estimated about 67.2 hours = 2.8 days from this math: 280 Ahs x 8 cells in parallel = 2,240 Ahs; ... & my 3.305 volts starting point = about 70% SOC; so charging 30% of 2,240 Ah worth of my LiFePO4s to full 3.650 Volts, to 100% SOC @ 10 Amps Charge; Math: 2,240 Ah x 30% = 672 Ah / divided by 10 Amps (charging) = 67.2 hours = 2.8 days. I realize this is not perfect/ might have other factors involved. After 96 + hours of charging at 10 Amps (with a few cycles of 7 A charging when adjusting Power supply voltage downward/ closer to 3.650 V ); I have been stuck at 3.360 to 3.650v for that last day and half (@ about 3.365v for last 24 hours) !!! ... I just turned my power supply charging off, and my new 8 cell battery banks drops to 3.350 v within an hour/ and is 3.348 v two hours later (might be normal). ... After 1 + day at same voltage/ with no climb; Does anyone think I would benefit from more parallel charging?

REFERENCES # 2: I copied some comments from recent forum threads to register my lessons (thank you to the authors): While this is may be redundant; these posts below speaks to my lesson junction; ... from folks w similar 8 or 16 new 280 Ah LiFePO4 sets:

one post: ... So after days and days of slowly charging my battery bank and getting everything top balanced I was finally able to fully assemble my battery today. The 4 groups of parallel cells all showed either 3.600 or 3.601 prior to making the series connections. ... Once the cells get past 3.5V they should start filling up a lot faster (my comment: I notice that too, good to be watching past 3.5v, to avoid, then easily overcharging/ I did that once!) ... 10A is fine.... but can take a long time if the cells start in a low state of charge. Even at 10 amps your are only getting 10A * 3.65V = 36.5W.

a GOOD IDEA : I would do this next time for the larger Ah LifePO4s/ *** quotes (mixed w my comments)
*** What I do is first wire the cells into the 24 V bank (with the BMS) and then charge to 29.2V till one of the cells hits 3.65. This allows me to push 29.2V * 10A = 292 watts. However, even this can take quite a while if the cells are in a very low state of charge. Note: Initially the charge will be limited by the 10 amp limit of the supply ... Once the cells are mostly charged, take the bank apart and re-wire them all in parallel and then charge them to 3.65V till the current drops to near zero.

(MY NOTE: ... or I could much more quickly charge and discharge via one, or up to three of my currently wired up and working MPP Lv2424s All In Ones for up to 0.5C / 140 Amps or more, to get close to my full charge (w view of cell balancing act), ... & then reconfigure battery bank for its' full top balance / then go for my 580 Ah battery bank. )

REFERENCE # 3: Picture Attached shows 2 DMMs; one w a DC amp clamp confirming my 30V /10A rated Bench Power Supply putting out Amps to my 8 batteries for my top balance effort. I had question about if my $60 Power Supply might be malfunctioning, as it does not allow me to dial my desired voltage when 1st turned on, until I hook it to battery (wish I had spent an extra $20+ for a better model). My DMM with DC Amp Clamp Meter has also confirmed 10 Amps IN to battery when I dial up the voltage (max).

**********
Troubleshoot Options: I think any of these ideas will lead me to a below par battery.
... I will see by proceeding one step at a time.

Option #1: Disconnect batteries and charge one cell at a time for one hour: Look at which ones gets to higher voltage, and which one(s) might not. I have a timer switch to easily do one hour cycles. If I find one cell that will not charge like the others, I will Ah test that cell's Ah Capacity (1st) with the 200 Watt fan heater unit I have here. While I wish I had an Ah tester w good cut off voltage option that could draw more watts (amps), that 200 watt fan heater allows me to set a low voltage cut off to stop its' smallish current draw when battery hits < 2.5v volts. That its' plus !!!

Option # 2: I could also hook my new 8 cells in series w my 2nd Chargery BMS, and connect BMS charge side trigger to a battery cut off relay; and charge with my 30v/10A rated Bench Power Supply to see what the BMS info shows for individual cell voltages.

Option # 3: I could replace my current 24v LiFePO4 set with these new ones have have been top balance to only 3.365v (vs 3.650v ), and put them through some charge and discharge cycles at up to 140A (0.5C) to see what my Chargery BMS8T information shows. ...

If I find a below par cell, I wonder if a few full charge and discharge cycles at various amps up to 140 Amps in and out could help it???

Open to comments while hoping for the best. Currently Attracted to Option #1 while going to posting this first :+) Bill
Check out this resource:

https://diysolarforum.com/resources...ls-using-a-low-cost-benchtop-power-supply.65/
 

Steve_S

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I am as noted above charging 280's from 2.60V to 3.65 with a 0-15 Volt / 0-40A Bench charger. Starting at 38A CC it takes about 12 hours. Between 3.2 & 3.4 takes forever, as the Amps drop and the charger transitions to CV is when you will actually see the cell voltage climb. Remember a 280AH cell can take 140A.

As Snoobler pointed out 112 hours @ 10A but you won't even get 10A as you already said 8-9A. And worse, you have 8 cells in parallel, talk about watering it down. TBH, You should invest into a charger that can do more amperage at "cell voltage" and preferably at "battery pack" voltage too. Don't mean to be abrupt, but you're fighting a 5 Alarm Tower Fire with a Garden Hose while standing on the hose.
 

Capt Bill

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@Capt Bill

Yours is the umpteenth post like this. What you are seeing is normal. The vast majority of the charging process occurs between 3.3 and 3.4V at these very low currents. It is not at all uncommon to see voltage hold almost constant for very long periods of time, especially with such low charge currents (these could be charged at up to 1120A in this configuration).

8 * 280 = 2240Ah - likely at least 1/2 is required on as-received, possibly more.

1120/10 = 112 hours @ 10A

If you decide to change course, the only sensible option is to series charge with the BMS.
Reading your: ... "Yours is the umpteenth post like this. What you are seeing is normal." ... has the me back to the parallel charging. The 8 cells in parallel had dropped to 3.350 v after an hour of disconnect; and is back up to 3.360v within 20 minutes w Bench Power Supply dialed to 3.85v to get 9.67 amps In (closer to power supply max of 10.2 amps); I will leave my set up like this for 24 hours or more, and see what happens. I will make sure to dial voltage downward to near 3.65v when I measure 3.5v on my battery bank w a DMM. ... I really Appreciate this Support Forum for DIYers and newbies. ... THANKS to all for the feedback :+) ... I would be doing series charging first w a BMS, if I started this over from scratch, and/or with my next set of LiFePO4s in the larger 280Ah arena. If I start helping friends get into these LiFePO4s, I will invest in a 3.2 v cell charger w a higher amperage output ... I'd say Yes to that option :+)
 
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Steve_S

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Bench Power Supply dialed to 3.85v to get 9.67 amps In (closer to power supply max of 10.2 amps)
You can get away with doing this without an issue BUT. Take your DMM, check the voltage coming off the supply, then check the actual voltage at the cell. The cell will still be down at 3.3whatever while sucking in the amperage. The "but" is as the cell starts to get full, the voltages will climb faster, especially after 3.5V it starts to pick up pace. Then you will have to dial down the voltage on the charger, to not exceed max volts.
 

Capt Bill

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You can get away with doing this without an issue BUT. Take your DMM, check the voltage coming off the supply, then check the actual voltage at the cell. The cell will still be down at 3.3whatever while sucking in the amperage. The "but" is as the cell starts to get full, the voltages will climb faster, especially after 3.5V it starts to pick up pace. Then you will have to dial down the voltage on the charger, to not exceed max volts.
I just went with your check on contrast of voltage / power supply vs battery ...suggestion. I have those banana plugs at power supply; and remembering posters in other threads (Ghostwriter 1st, then another saying he upgraded to 12awg / ...10awg would be better) ... saying those wires and banana plugs are weak links for amperage transfer; and via my DMM, ... I just measured 3.772 volts at the power supply, on the metal of those banana plugs; and 3.367v at cells nearest my clip ons to battery, and 3.366v at ends cells farthest away for where I clip to battery bank (a 0.406v difference). ... I think I might see some improvement if I put cable end terminals on those wires for the power supply connects. I will investigate to see if that makes any difference. Dialing in my hands on lessons with this forum help; has me thinking I am/ we are / learning via YouTube University, and possibilities are endless

... Added NOTE 20 minutes later: I Got a much better connection with shift to number 8 AWG wire I had laying around here (overkill) and copper eyelet type terminals (click picture to expand and see power supply). I am now getting 3.368v at battery, with 3.410v at power supply (a 0.042 v difference) ; my Bench Power Supply acted differently with this wire upgrade, and my battery voltage has already climbed a knotch to 3.369v (45 minutes later). Yes to this wire upgrade. Those banana plugs spin on their connectors. and replacing just those shifted voltage difference to 0.387v. I now say yes: I recommend replacing the banana plugs and upgrading the wire size too. :+) Bill
 

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snoobler

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you're done. Stop charging. Now.

EDIT: I realize the lack of exclamation marks may suggest a lack of urgency.

OMG! STOP CHARGING RIGHT THE EFF NOW!!!!

...Is more indicative of my emotional state.
 
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FilterGuy

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Folks,
It does not matter if there is a voltage drop across the leads. As long as the voltage at the CV/CC Power Supply is not above your target voltage things will be OK.

When the current is high, there will be a voltage drop to the cells.... but that is ok. Don't worry about it! As cells charge and the current drops, so will the voltage drop across the leads. When the current gets to zero, the voltage drop will also be zero. Consequently, when the current goes to zero, the voltage at the cells and at the power supply will be the same (and the cells will be fully charged).

Do not set the power supply to a higher voltage than your target voltage.
If you set the power supply above the target voltage to 'speed things up', our friend Murphy guarantees you will forget to turn it down and the cells will end up at too high of a voltage. Remember what everyone has been saying, "at the end of the charge things start happening quickly". If your power supply is set too high, the voltage at the cells can go from OK to too high in a fairly short time.

Getting better leads for the power supply will help speed thing up *slightly* because less energy will be wasted heating up the leads. However, the difference will be minimal. Also, you would probably get the most improvement by replacing the alligator clips with lugs to make a better connection to the cells.
 

FilterGuy

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One more thing: When the cells are in parallel during the top balancing, don't worry about voltage differences between the cells. Just like with the power supply leads, as the cells charge the voltage drop between cells will drop. When all the cells quit taking current, all the voltage drops will be zero and all the cells will be charged to the target voltage. Yes, some of the cells will charge slightly faster than others. Yes those cells will stop charging first.... but that is OK. The end goal is to get them all to stop taking current at the target voltage and it does not matter if some of the cells get there first.

However.... this only applies to top balancing where the cells will all get to the same state. In normal use, voltage difference between parallel cells must be minimized or the cells will wear unevenly. (The higher voltage cell will wear faster than the lower voltage cell)

Edit: Changed wording from 'top charging' to 'top balancing' for clarity.
 
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Capt Bill

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If your power supply is set too high, the voltage at the cells can go from OK to too high in a fairly short time.
Yes to FilterGuys's (and others') WARNING: I know this is a true great heads up warning because I made a mistake and once overcharged my 1st LiFePO4 set; ( ... and the picture I share might led a newbie to same kind of mistake). I have sometimes set my bench power supply voltage setting up higher than my 3.650v battery cell full target to get higher Chargering Amp (some aim for just 3.6v, as in 3.600v) on a top balance; I have set my voltage up higher because with8 battery cells in parallel near 3.4v, setting my power supply voltage to 3.6v reduces my amp charge down to only 5 or 6 amps out of the power supply's 10Amp max. ... I got that idea of dialing in a higher voltage setting to get more charging amps from Will Prowse's Top Balancing LiFePO4s video (I think his main video lesson on top balancing linked to recent threads). Will said something like ... come back and check on it every couple of hours, ... if I am remembering correctly. (and set it back down lower when closer to 3.65v/ I would set it to 3.65v top at bench power supply when battery is about 3.5v ). When I go up higher than 3.65v on that setting to get a higher amp charge, I then dial my voltage knob and setting back downward to see the amp figures on power supply just start heading downward (... to think there is some kind of volts top limit vs maybe none, as that setting number can shift upwards as the battery voltage rises when the knob is dialed anywhere !!!

... My bench power supply does act differently now with my wire upgrade. ... In setting its' voltage top limit, it now only goes up to a 3.5v top max (won't dial higher/ will dial lower); to get the max 10.18 Amp charge. I imagine I will be able to dial my bench power supply top/ stop the charge current @ voltage setting up to 3.65v, ... when (or if) my 8 battery cells get above 3.5v. I am at presently @ 3.368v aiming for 3.650v. ... YES to FilterGuy's Warning: ... I personally will make sure to be watching closely @ 3.5volts +, because I know from my past hands on mistake lesson, on top of repeated good advise and info in this forum: (in FilterGuy's words): "cells can go from OK to too high in a fairly short time."

Re: My previous Invite to Troubleshoot with me:
... added note: I still think I may have one below par cell because my voltage went up from 3.365v to 3.368v after my wire upgrade; and has since dropped back down an hour late to 3.365v ??? (NOT the" 3.650v Battery Cell - FULL Charge Target I am aiming for/... which kind of looks the same but is less ... 3.365v vs 3.650v as in 3.6v on some lesser DMM). I will leave my top balance charging set up going as is, and see what is going on tomorrow. ... Proceeding ... One Step at Time.
 
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Capt Bill

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Ah... somebody edited their typos... not 3.66 and 3.67.
RE: Over Charging Battery Damage: I previous corrected some typos in some voltages I mentioned. My over charge mistake lesson on my first DIY 24v 280 Ah build came after I was trying to charge up that one separated defective cell I still have that just would not (& will not) not charge to over 3.365v !!! ... Since it was taking so long on just one single cell, ... I was kind of sleeping on the top balance I did for mixing its' new replacement cell to my 24v set. While top balancing a second time, I also somehow mixed up my 3.365 v numbers w that 3.65 v full charge number, and before I knew what happened, I got up to 4.1v on my cells (*&%$#@?!!! Scary; Dammmm it) ... I brought my cell voltages back down to 3.65v in about 10 or 15 minutes with that 200 watt fan heater - Ah measuring unit. ... I think I am lucky, as I did not get puffed up cells. I also have not noticed damage, but have to admit that I have not Ah tested since then. My 8 cells charge and discharge evenly; while I have limited my LV2424s bulk charge (absorptions) setting to 28.4v, as I notice this limits my cells getting out of balance (they can spike differently at higher voltages), plus believe that 28.4 or 28.2 bulk charge will help em last longer in charge cycles. ... In my reading since my over charge mistake, I discovered LiFePO4s used to be charged up to 4.0 volts or possibly a little more, mostly in the Electric Vehicle world (I think); and read that is currently old school. In studying this forum; I copied some info. from Florst in Thailand ... This is a Florst Lesson from another thread (for whatever it might be worth / and I know folks here have various, sometimes contrasting opinions:

from Florst >>> It's within specifications to go up to 4.2v without real damage. Charging is supposed to stop at 3.65 to prevent damage. Even at 3.65, stop charging the cell will go to rest mode and after time it's about 3.375 - 3.450v (0.5% SOC difference) At 3.4 a cell that haven't been used a few days you can consider it fully charged. .. 4.1v isn't always bad. If you are charging at high current it's "normal"... BUT BAD ... If you are charging at low current and just pass the 3.65 safety level to see if you can charge more than 100%.... Then it is bad, really bad, as in can = getting bloated cells bad. ... (as in) Bloating is delaminating sheets ... <<< ... (& thus losing Ah Capacity) ... My note: I think he knows from personal hands on experience type lessons, as one of his stories is about puffed up cell (s). I am lucky I did not get bloat cells from my personal mistake lesson. Reminds me of that saying: If you never make a mistake, you are being like sheep and missing out. Living Life involves taking risks ... When folks I know have wrecked their valued equipment in water sports (like windsurfing in a wave zone), that is sometimes called "getting initiated" :+)
 
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Capt Bill

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I just went with your check on contrast of voltage / power supply vs battery ...suggestion. I have those banana plugs at power supply; and remembering posters in other threads (Ghostwriter 1st, then another saying he upgraded to 12awg / ...10awg would be better) ... saying those wires and banana plugs are weak links for amperage transfer; and via my DMM, ... I just measured 3.772 volts at the power supply, on the metal of those banana plugs; and 3.367v at cells nearest my clip ons to battery, and 3.366v at ends cells farthest away for where I clip to battery bank (a 0.406v difference). ... I think I might see some improvement if I put cable end terminals on those wires for the power supply connects. I will investigate to see if that makes any difference. Dialing in my hands on lessons with this forum help; has me thinking I am/ we are / learning via YouTube University, and possibilities are endless

... Added NOTE 20 minutes later: I Got a much better connection with shift to number 8 AWG wire I had laying around here (overkill) and copper eyelet type terminals (click picture to expand and see power supply). I am now getting 3.368v at battery, with 3.410v at power supply (a 0.042 v difference) ; my Bench Power Supply acted differently with this wire upgrade, and my battery voltage has already climbed a knotch to 3.369v (45 minutes later). Yes to this wire upgrade. Those banana plugs spin on their connectors. and replacing just those shifted voltage difference to 0.387v. I now say yes: I recommend replacing the banana plugs and upgrading the wire size too. :+) Bill
Update: My Wire Upgrade helped. I saw my voltage start climbing in my parallel bank of 8 280Ah cells within hours ... I switched my battery configuration to series charging to get fuller watts out of my 30V /10A rated Bench Power Supply. Now think it was short sighted to parallel charge 8 x 280Ah cell starting out at 3.04v. I did not connect my BMS with disconnect (not recommended), but I monitor my cells closely w my DMM. The end battery went up in voltage faster than others (kind of surprised at cell voltages differences I saw as I charged without a BMS) ... I took off the individual batteries cells hitting slightly above full, one at a time as they sometimes quickly poked above 3.65v; ... and then readjust my power supply to charge the rest. This was an ongoing process for me after the first cell required me taking it off line. I could see that series charging I used, without a BMS or HCV battery cell disconnect could easily hurt a cell or several cell if left unattended (I attended my charging w regular DMM checks of all individual cells being charged. ... getting each and all my cells up to near 3.6v each; I have since top balanced em in parellel / and presently checking the Ah Capacity of the cell the hit full charge first/ presently checking the Ah Capacity of the cell the took the longest to reach full charge via that 180 W fan heater tester ... So far looking good while still wondering. I will Top Balance a 2nd time after I confirm a few of their Ah Capacities ... Got a battery rack idea to work on too.
 

fafrd

Photon Sorcerer
Joined
Aug 11, 2020
Messages
2,251
Just to toss a monkey wrench into the works.

I've just received 4x EVE 280's to build a 12V pack. Before doing so, I figured on top charging each cell and doing a capacity test on them, curiosity got the better of me. I'm only using one of those 180W / 20A load testers, so it's 14 hours run per cell... talk about tedious. Charging though is why I'm popping in.

I've been charging these 280's with a TekPower 1540E power supply and doing one cell at a time. Starting with 3.60V/30A CC which eventually flips to CV mode and slowly the amps decrease as the impedance changes. The DOCS say 0.05 of the C-Rate which is 14A is fine but as I am doing per cell, cutting off at 1.5A taken. That sets the cells to 3.650. and they settle out to 3.62-3.63 within an hour. At one point I allowed the cells to sit a couple of days after that charge level and they independently settled between 3.51-3.56 "Without Paralleling". The Capacity tests are showing between 276 & 278AH but I am cutting off at 2.65V and starting from 3.60V after being charged & rested for an hour. A Side benefit of doing this, is being able to charge each cell from 2.65V with the same CC-CV charge, helps get things balanced up.

An observation: While it may be a PITA to do a single cell charge (not so bad with 4 but) it is quite a bit faster per cell. It's also easier to top that single cell down to 1-2A taken. Once I've completed my current charge run per cell, I'll tie them together in parallel, let sit a few hours (overnight) and then apply a topping charge to 3.60 to the parallel set until the Amps drop down to 4 or so. Then it's reconfigure & BMS Time.

Remember, the cells can take 0.5C Charge rate, the more amps you can put behind the charge the faster the cells will top off.
You seem very knowledgeable about the damage that can result from mistreating / mischarging these LiFePO4 cells, so I hope this is the appropriate place to ask you my question.

I charged a new 280Ah cell to 3.65V last night and at the time I cut-off charging, charge current was down to 0.47A.

I monitored voltage as the cell settled over the subsequent hour and it dropped to:

0’ 3.650
15’ 3.616 (-34mV)
30’ 3.595 (-21mV)
45’ 3.582 (-13mV)
60’ 3.571 (-11mV)

I let the cell continue to settle overnight and by the next day 16 hours after charging had ceased, the cell had settled to 3.346V.

I decided to top-off charging before beginning a capacity test and the cell charged up from 3.346V to 3.650V in about the same time it took the first time, and final charge current at 3.650V cut-off was also identical at 0.47A.

During the one-hour test following charge cut-off, however, the cell settled less quickly than it had the night before:

0’ 3.650V (vs 3.650V)
15’ 3.630V (vs 3.616V or -20mV vs -34mV)
30’ 3.622V (vs 3.595V or -8mV vs -21mV)
45’ 3.617V (vs 3.582V or -5mV vs -13mV)
60’ 3.611V (vs 3.571V or -6mV vs -11mV)

So it appears that my cell ended up at a higher SOC after this second top-up and is settling more slowly and to a higher voltage.

My question for you is whether there is any downside to repeated charge cycles to 3.65V without any active discharge cycles in between? (passive settling only).

I believe I saw you post somewhere that it is a bad idea to ‘hold’ LuFePO4 cells at 3.65V for an extended time because of some damage/degradation that can result and I’m interested to understand whether ‘tipping-up’ charge to 3.65V is a bad idea for the same reason.

And in a related note, EVE specifies charging until an 0.05C (14A) current cut-off, but we are all obviously charging with currents far below that level (at least during top-balance & cell characterization).

Is there any downside as far as cell health when it comes to Lowe charge-current?

My supposition when charging at lower currents is that you will be ‘overcharging’ the cell compared to EVEs specification and so you will be inflating capacity and measuring a higher number of Ah than you are likely to get when charging at higher current levels.

So other than inflating the number of Amp Hours measured in EVE’s favor, is there any downside to charging at 3.65V until charge current drops close to 0A (<10mA with my charger/supply)?

Thanks for your insight.
 

Steve_S

Offgrid Cabineer, N.E. Ontario, Canada
Joined
Oct 29, 2019
Messages
5,429
Location
Rural NE Ontario Canada
I am no expert, just a critical observer.
There is far too much over concern about LFP cells sitting at "FULL" SOC. 3.65V and lower will NOT hurt the cells and over time they will self-discharge albeit quite slowly. The cells never sit there as they will always settle, typically to 3.5** Volts. Where keeping Voltage Hi is a problem, is with people "FLOATING" cells to Hi State. The other problems are also if there is a runner or lazy cell playing games in the battery pack. If FLOAT has to be in the equation due to charger type then it should be set to lower than max charge value, typically around 3.4V per cell equivalent.

EVE says 0.05C Rate for their cutoff for 14A on a 280AH cell. I have force charged, trickle charged and it seems I cannot get below 1.7A... Just had cells Topping for 12 hours and they ARE full but 1.7A was the lowest, they are actually now sitting in parallel just cell leveling. Each cell was Top Charged to 3.62V and allowed to reduce to 1.8A and allowed to settle, after 24 hours they all settled to 3.55 +/-10mv, then set in parallel and Top Charged as a set till amps taken dropped to 1.8A. These are "H" & "J" Series EVE 280's. @ 14A I can absolutely tell you that the cells are NOT at 3.65V, that it more in line with 3.500 +/-50mv zone.

A NOTE:
You can start to charge cells at 10, 20, 40A but as they charge the amps taken will reduce down to 2.0A +/- at which point the cell is saturated. It does not matter if you start with 5A or 20A, just the lower the amperage the longer it will take. !! The higher the amps, the faster the charge, a maintained "forced" Hi Amp charge will heat up the cells. NO Solar or Inverter will or can "force" that !

Using End-Amps / Cut-Off Amp with battery packs can be quite problematic, especially with Un-Matched cells.
An SCC or Charger will do normal charging using Constant Current & Constant Voltage CC-CV and will reduce amperage relative to the impedance, which is as it should be. BUT it's a FOOLEY in part! Because of the number of cells in the pack, it's an aggregate value of all the cells. If the cells are UNMATCHED, they will have different Internal Resistance & Impedance values at differing charge levels. This can be observed at the cell level as you cycle the battery pack, as the cells deviate through their cycle of charge/discharge.
  • For End-Amps to work, all cells would have to reach the same threshold at the same time.
  • If you have more than One Battery Pack in a bank, they would all have to reach the same point at the same time AND would have to assume you are charging each battery pack to 100% SOC... which 99.9% of folks do not do.
  • Reality is that typically, because of runners or by design, packs don't usually get charged above 90%, usually more often to 85% SOC. At 90% or 80% the End-Amp value will not be 14A.
The Main Voltage / Power curve for LFP is from 3.450 to 2.900 (Edge to Edge). Nominal is 3.200V.
Above 3.45V only represents a few AH as it is a cliff climb. Below 2.950 to 2.50 is also only a few AH... probably no more than 14AH worth on both ends.

Hope it helps.
 

fafrd

Photon Sorcerer
Joined
Aug 11, 2020
Messages
2,251
I am no expert, just a critical observer.
There is far too much over concern about LFP cells sitting at "FULL" SOC. 3.65V and lower will NOT hurt the cells and over time they will self-discharge albeit quite slowly. The cells never sit there as they will always settle, typically to 3.5** Volts. Where keeping Voltage Hi is a problem, is with people "FLOATING" cells to Hi State. The other problems are also if there is a runner or lazy cell playing games in the battery pack. If FLOAT has to be in the equation due to charger type then it should be set to lower than max charge value, typically around 3.4V per cell equivalent.

EVE says 0.05C Rate for their cutoff for 14A on a 280AH cell. I have force charged, trickle charged and it seems I cannot get below 1.7A... Just had cells Topping for 12 hours and they ARE full but 1.7A was the lowest, they are actually now sitting in parallel just cell leveling. Each cell was Top Charged to 3.62V and allowed to reduce to 1.8A and allowed to settle, after 24 hours they all settled to 3.55 +/-10mv, then set in parallel and Top Charged as a set till amps taken dropped to 1.8A. These are "H" & "J" Series EVE 280's. @ 14A I can absolutely tell you that the cells are NOT at 3.65V, that it more in line with 3.500 +/-50mv zone.

A NOTE:
You can start to charge cells at 10, 20, 40A but as they charge the amps taken will reduce down to 2.0A +/- at which point the cell is saturated. It does not matter if you start with 5A or 20A, just the lower the amperage the longer it will take. !! The higher the amps, the faster the charge, a maintained "forced" Hi Amp charge will heat up the cells. NO Solar or Inverter will or can "force" that !

Using End-Amps / Cut-Off Amp with battery packs can be quite problematic, especially with Un-Matched cells.
An SCC or Charger will do normal charging using Constant Current & Constant Voltage CC-CV and will reduce amperage relative to the impedance, which is as it should be. BUT it's a FOOLEY in part! Because of the number of cells in the pack, it's an aggregate value of all the cells. If the cells are UNMATCHED, they will have different Internal Resistance & Impedance values at differing charge levels. This can be observed at the cell level as you cycle the battery pack, as the cells deviate through their cycle of charge/discharge.
  • For End-Amps to work, all cells would have to reach the same threshold at the same time.
  • If you have more than One Battery Pack in a bank, they would all have to reach the same point at the same time AND would have to assume you are charging each battery pack to 100% SOC... which 99.9% of folks do not do.
  • Reality is that typically, because of runners or by design, packs don't usually get charged above 90%, usually more often to 85% SOC. At 90% or 80% the End-Amp value will not be 14A.
The Main Voltage / Power curve for LFP is from 3.450 to 2.900 (Edge to Edge). Nominal is 3.200V.
Above 3.45V only represents a few AH as it is a cliff climb. Below 2.950 to 2.50 is also only a few AH... probably no more than 14AH worth on both ends.

Hope it helps.
Thanks for the helpful post.

So it sounds like you don’t know of any reason repeated top-off cycles to 3.65V are anything to be worried about

I understand your warning about ‘Float’ but can only understand that warning in the case of packs (where battery voltage cannot accurately translate to cell voltage).

Do you see any problem with ‘floating’ a single LiFePO4 cell at 3.65V? (Obviously with properly-calibrated equipment, otherwise back-off to 3.60V, 3.55V, or 3.5V).

There are two things you did not mention: cell internal settling transients and self-discharge. A newly charged-up cell takes time for newly-added charge to evenly distribute internally, and that internal redistribution is a lot of what is going on when ‘settling’.

After settling, topping off repeats the process and the fact that my cell settled to a higher voltage (after similar time) means that there was less ‘room’ for newly-added charge and the cell is more ‘full’ after the top-off charge than it was after the initial charge to 3.65 (by about 1Ah in my case).

If additional top-off charge cycles were performed, the cell would likely be filled even higher and would settle to higher voltages after equivalent time (closer to 3.65V).

This is ‘overfilling’ a cell versus EVEs charging spec of 3.65V at 0.05C (14A) cut-off. It’s that overfilling that caused me concern and caused me to reach out to you but it sounds like in and of itself, you don’t know of any reason to be concerned.

With cell swelling greatest above the knee and cycle lifetime limited by mechanical deformation, there is probably a reason you don’t want to get carried away with topping-off / overfilling, but I’ll save that discussion for another thread.

The other reason cels settle is self-discharge. Once you top-off and the cell settled to the same voltages after the same amount of time, the charge added by topping-off is merely compensating for the charge that has been lost through self-discharge over the settling time and the battery is not being filled to any higher intrinsic charge level.

I believe ‘float’ cycles are intended exactly to compensate for self-discharge and at the single cell level, I can’t understand why it should be a problem to float at 3.65V (especially if topping off to 3.65V repeatedly is not a problem).

And I absolutely agree about charging to 3.65V at lower currents overfilling a cell compared to EVEs specified 0.5C charge / 0.05C cut-off. All of us gently charging up to 3.65V at currents dropping to ~2A or less and then capacity testing are adding a few extra Amp-Hours which won’t be achieved through normal use.

What really matters is how many Ahs your cells deliver when charged with whatever charger you will be using...
 
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