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One cell overcharging(EVE lf280k)

Yurtdweller

Solar Enthusiast
Joined
Nov 23, 2020
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305
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USA
I have four sets of 4s lf280k. They are parallel for a 12v system. Recently, one single cell in one pack, cell #4 is overcharging and shutting the pack down. If I leave the pack offline, it eventually evens out(balances), but if I put it back online during solar charging, it immediately(5 minutes) returns to the voltages seen in image. Voltage verified with reliable voltmeter. Note that #4 is the positive end if the pack. The bank is about two years old. 1000020391.jpg
 
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When you leave the pack offline, the voltage may settle back to the same as the other cells but that doesn’t mean it balances. It’s clearly out of balance and until you drain energy out of that cell either via BMS balancing or just connecting an external resistor onto it, it’s going to stay out of balance.
 
Ps… a 3 ohm wirewound resistor with a pair of crocodile clip cables on it is a good thing for any DIY battery builder to have. Clip it across the terminals of your high cell for 20 mins then charge up again and see how the balance is. Way faster than waiting for a 50mA BMS balance circuit to do the job.
 
Ps… a 3 ohm wirewound resistor with a pair of crocodile clip cables on it is a good thing for any DIY battery builder to have
Or use 50 - 100' extension cord shorted on one side or with all 3 conductors connected in series. Just make sure discharge current does not exceed cord max current so you don't melt wire insulation.
 
Ps… a 3 ohm wirewound resistor with a pair of crocodile clip cables on it is a good thing for any DIY battery builder to have. Clip it across the terminals of your high cell for 20 mins then charge up again and see how the balance is. Way faster than waiting for a 50mA BMS balance circuit to do the job.
Yeah. I was going to try an old headlight that O have lying around.
 
Update: last night after sundown, I put that pack back online. I ran my home as usual, and the runner quickly came back into equal voltage as the other cells. This morning, all 16 cells are showing same voltage, and are functioning normally. Charging has not yet begun for the day. Bank will reach full in a few hours, and I will watch that troublemaker. I haven't yet checked all connections other than with ohmmeter, which is not indicating any issues.
 
I have four sets of 4s lf280k. They are parallel for a 12v system. Recently, one single cell in one pack, cell #4 is overcharging and shutting the pack down. If I leave the pack offline, it eventually evens out(balances), but if I put it back online during solar charging, it immediately(5 minutes) returns to the voltages seen in image. Voltage verified with reliable voltmeter. Note that #4 is the positive end if the pack. The bank is about two years old. View attachment 257330
Which supplier? And is it recent enough to ask for a warranty replacement. I just purchased 18 LF280k cells from Docan Battery that are sitting on my living room floor. They look good in terms of equal voltage and flatter sides of my previous EVE 280 ah cells. The two extra are for my possible long term maintenance need (of a cell eventually functioning below par/ IMO: nice to have matched extra cells for that option). Your post here will motivate me to get em top balanced, and test full charge and discharge cycles to see how they perform. Thanks for this type of Heads Up
 
You can adjust to set the Balance charging on a lower volts.
Its now around 3.4volts .
You can set it to 3.375 so it pick it faster up.
You can switch the bms to balance with or with out charging .
Set it on with no charging.

Standard its only balance by Charging and stop if the charging is off.
Til the charge is back on by the bms.
Switch it off and leave it on.
Only if you charge now than it do not balance by Charging but switch off till charge stop and than it do balance it .

This way if you can not open the battery you can Balance the battery more easy.
 
Which supplier? And is it recent enough to ask for a warranty replacement. I just purchased 18 LF280k cells from Docan Battery that are sitting on my living room floor. They look good in terms of equal voltage and flatter sides of my previous EVE 280 ah cells. The two extra are for my possible long term maintenance need (of a cell eventually functioning below par/ IMO: nice to have matched extra cells for that option). Your post here will motivate me to get em top balanced, and test full charge and discharge cycles to see how they perform. Thanks for this type of Heads Up
These are EVE lf280k cells purchased a few years ago from Amy Wan at shenzhen luyaun. They had been working fine until quite recently. I forgot to mention that the bms that runs this one cell set also has the mysterious ability to change its Total Capacity from 280ah to 210ah. I am constantly correcting it, but after a few cycles, I may find that it has reset again:/ I've been very busy with work and have not had a chance to dig into this issue. I will start by cleaning and re-torquing all connections.
 
You can adjust to set the Balance charging on a lower volts.
Its now around 3.4volts .
You can set it to 3.375 so it pick it faster up.
You can switch the bms to balance with or with out charging .
Set it on with no charging.

Standard its only balance by Charging and stop if the charging is off.
Til the charge is back on by the bms.
Switch it off and leave it on.
Only if you charge now than it do not balance by Charging but switch off till charge stop and than it do balance it .

This way if you can not open the battery you can Balance the battery more easy.
I will look into your suggestions. My battery is an assebled-by-me set of cells. I have full access. EVE lf280k prismatic cells. I have 3 other sets that work fine.
 
The very flat voltage curve of LFP cells is both a great feature and a royal pain at the same time. Measuring voltage anywhere from 30% to 80% charged, they will all look very closely balanced, but one cell might be at 70% while the rest are at just 50%. I think this is what you have going on here. When the bank discharges a little, the high cell falls right in line with the rest. When you charge, that cell quickly reaches the upper knee and runs away and the BMS balancer can't keep it in control. As one other reply mentioned, the default setting in the BMS will only pull balance current when it sees charging current. When you stop charging that bank, the balancing also stops, so it is not helping.

The 3 ohm resistor or the headlight are very good options here. Instead of balancing at 60 milliamps, the headlight may pull around 1.5 to 2 amps, the 1 ohm resistor a bit over 1 amp.

Do you have an adjustable bench power supply that can do CC CV? Set the supply voltage at no load to 13.8 volts to start. Set the current limit to just 1 amp. Connect the headlight to the high cell and the power supply to the whole battery. Monitor the cell voltages. The high cell should not climb and may even dip a little while the other 3 climb. Once the other 3 go above the bad cell, then disconnect the headlight. If any cell starts to run above, put the headlight on the running cell. When it get's close to 13.8 volts with all the cells balanced, you can lower the current to say 0.25 amps an raise the voltage to 14.2 volts and let the BMS internal balancer do it's job for a while and the cells should all hit 3.55 volts and nicely top balanced. For a 280 amp battery bank, it can take many hours to get a solid balance with only the BMS balancing. If your other packs also drift out of balance, you might want to invest in a 1 or 2 amp active balancer. I bought a 1 amp smart active balancer from 100Balance. I got the 14S version for my E-Bike batteries. It pulls them into balance in under an hour.

Here it is, you pick the cell count when you order. They sent me the wrong one at first, but got it right the second time with no questions on the return exchange.
You CAN set them to work at a lower cell count, but it is not as straight forward as a JK-BMS to do it. But I did end up making the 16S work on my 14S packs. So an 8S that can do 24 volt batteries SHOULD be able to also be set to do 4S 12 volt batteries. And yes, it is a true smart active balance like the JK where it pulls current from the highest cell and then pushes it to the lowest cell. It uses the same Phone App as the 100Balance BMS.
 
Which supplier? And is it recent enough to ask for a warranty replacement. I just purchased 18 LF280k cells from Docan Battery that are sitting on my living room floor. They look good in terms of equal voltage and flatter sides of my previous EVE 280 ah cells. The two extra are for my possible long term maintenance need (of a cell eventually functioning below par/ IMO: nice to have matched extra cells for that option). Your post here will motivate me to get em top balanced, and test full charge and discharge cycles to see how they perform. Thanks for this type of Heads Up
Just did my first charge and discharge, then re charge cycle on 16 Grade A EVE LF280K v3 cells, after top balancing them. I was expecting to see the voltages difference of each cells be close (like within 0.010 v diff) as the battery cycled down to 20% soc and back up to 100%. 15 of 16 cell remained within 0.004 v diff as measured by my JK BMS through this test; But one cell acted oddly. On first discharge, one cell was 0.031v lower, then 0.061 v lower, then @ 20 % soc had a 0.119 v lower diff.
Then on 30 amps Charge back to full, the same cell was 0.051 v higher diff while all the other cells were within 0.004 v diff. Then with the Charger Off, and No Battery Draw, that one cell matched the others cell as all were within 0.004 v diff. I don't like seeing this in a new battery, and wondering if anyone might have an explanation. I will be contacting Docan to see if I can maybe get this one cell replaced. I will let you know what opinion or policy I get back. Here's some pictures
 

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Just did my first charge and discharge, then re charge cycle on 16 Grade A EVE LF280K v3 cells, after top balancing them. I was expecting to see the voltages difference of each cells be close (like within 0.010 v diff) as the battery cycled down to 20% soc and back up to 100%. 15 of 16 cell remained within 0.004 v diff as measured by my JK BMS through this test; But one cell acted oddly. On first discharge, one cell was 0.031v lower, then 0.061 v lower, then @ 20 % soc had a 0.119 v lower diff.
Then on 30 amps Charge back to full, the same cell was 0.051 v higher diff while all the other cells were within 0.004 v diff. Then with the Charger Off, and No Battery Draw, that one cell matched the others cell as all were within 0.004 v diff. I don't like seeing this in a new battery, and wondering if anyone might have an explanation. I will be contacting Docan to see if I can maybe get this one cell replaced. I will let you know what opinion or policy I get back. Here's some pictures
Lower voltage on discharge and higher cell voltage on charge is a classic sign of a high resistance connection (or higher cell IR). Check tightness of the nuts on the busbar of that cell and even take the busbar off, clean it and the cell terminals and reconnect then try again. Most often it’s a poor connection, but can certainly be a high IR cell.

Taking that cell out of the pack and observing how it behaves when charged individually in comparison to a random other one from the same pack would also be a worthwhile test which would demonstrate if it had a higher IR.
 
I have four sets of 4s lf280k. They are parallel for a 12v system. Recently, one single cell in one pack, cell #4 is overcharging and shutting the pack down. If I leave the pack offline, it eventually evens out(balances), but if I put it back online during solar charging, it immediately(5 minutes) returns to the voltages seen in image. Voltage verified with reliable voltmeter. Note that #4 is the positive end if the pack. The bank is about two years old
I have four sets of 4s lf280k. They are parallel for a 12v system. Recently, one single cell in one pack, cell #4 is overcharging and shutting the pack down. If I leave the pack offline, it eventually evens out(balances), but if I put it back online during solar charging, it immediately(5 minutes) returns to the voltages seen in image. Voltage verified with reliable voltmeter. Note that #4 is the positive end if the pack. The bank is about two years old. View attachment 257330
I just confirmed one of 16 "Grade A" EVE LF280k v3 cells purchased from Docan is spiking early near full charge that my BMS protection cycles off and on. The other 15 cells matched closely within 0.004v diff though discharge down to 20% soc, then recharge back to full. In double checking my cell voltages again my JK BMS values, I also figured out Why my EG4 was cycling off and on ever 60 second on a grid charge near full charge . Also glad I purchased two extra LiFePO4 cells for maintenance down the road. I think it is wise to do a similar test on your LiFePO4 purchases, and maybe especially on these LF280k v3 cells. I will see if Docan can replace my faulty cell (hope so). I am no longer doing ah testing my with that small 20 watt max fan tester cause that is too time consuming. I recommend cycling your cells to low soc, then back up to max (maybe a couple or 3 times) with a BMS that shows individual cell voltages; to see how closely the video large match or Not !!! Such initiating cell is a good way to identify any below par cells you might get have received. My Two Cents :+)
 

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Lower voltage on discharge and higher cell voltage on charge is a classic sign of a high resistance connection (or higher cell IR). Check tightness of the nuts on the busbar of that cell and even take the busbar off, clean it and the cell terminals and reconnect then try again. Most often it’s a poor connection, but can certainly be a high IR cell.

Taking that cell out of the pack and observing how it behaves when charged individually in comparison to a random other one from the same pack would also be a worthwhile test which would demonstrate if it had a higher IR.
I replaced my new oddly behaving EVE LF280k v3 cell with one of the two extras I also purchased as backups with same chemistry for later (which I think is a wise idea, as that exact cell chemistry might not be available later). All cells are now tracking closely at max 0.005 v diff as I test down (60% presently heading to 20% doc, and then back up to 100% ... Happy to see that :+) ... I learned I could match my one replaced LiFePO4 cell voltage to the other 15 cells that were all within 0.005 v diff without top balancing a 2nd time. I did that by charging my replacement cell to just above battery cell voltage with my power supply, and letting it sit a couple of times (last cycle overnight). I then drew down that cell voltage with a momentary load to match my other cells voltages using a DMM that measures 0.000v (0.xxx volts). My follow up test showed that worked perfectly :+)
 
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Issue update follows. I'm gonna admit that I haven't read every response, but I appreciate all contributors.

I think I've gotten it figured out, but we shall see. (Update to ipdate: I don't have it figured out, and cell 4 is still going overvoltage. :( )

The other day I finally had time to get into this, and here's what I found. Opened up my battery crate, and started testing voltages. The cell that goes out of whack is the one on the positive end of the series. My crate does about 5 thousand miles a year in my van between jobs sites, and is never in a climate-controlled environment. I discovered, with my torque wrench, that all terminal nuts were just a tiny bit loose.

I also discovered anomalous resistance in the buss bar connecting cell 2 to cell 3(not the 3-4 connector, which would be more expected, with cell 4 going overvolt) There was basically zero or .oo1 resistance in all other bars, but this bar had around 6 ohms resistance. Pulled it off, cleaned with soap, recleaned with 90% iso alcohol. Cleaned the ring terminal for the bms sensor, even though I had confirmed that the sensor was detecting properly. Reassembled. Again, I retorqued all connections, and all required about 1/8th turn to reach spec torque.

I also went into the bms(jbd) and reset the capacity setting, which had repeatedly lowered itself to 210,000 mah.

Side note: I have noticed that one of my BMSs had increased its capacity to as much as 284,000mah over time, so the bms obviously has the designed ability to alter this number.

I left the errant pack offline for a few days, allowing the balancer, which is set to operate at all times, not just during charging, to do it's thing.

After reintigrating the problem pack, it balanced itself out with the rest of the bank. I've been running it for a few days and even though weather has prevented me reaching 100% soc, the problem pack is now apparently working properly. All cells are remaining in balance, and no fets have triggered any cutoffs. I did notice that the bms did lower it's capacity setting again, but not by much. Sadly, I forgot to note where it reset to, but it was a modest discrepancy. Around 272,000mah, or something. I've reset it to 280,000mah again just now. I expect to reach 100% soc today, so we wait.

So, I had several issues/questions. Here are some preliminary conclusions.

Can the JBD BMS reset its own parameters? Apparently, yes. Apparently this is by design and not a flaw. One of my 4 packs shows 204,000mah capacity.

Can an apparent "runner" be caused by other issues. Again, apparently, yes. A runner is not always a runner.

Is a connection issue usually visible? Not at all. There was no visual indication of resistance-causing corrosion on the nickel plated copper bar that connects my cells together, and even the ohm testing was open to interpretation. Testing from terminal post to terminal post produced variable, inconsistent results, but definitely higher resistance than any of my other buss connections.

I will continue to monitor. Hopefully, when we reach 100%, the bms will register good capacity. One of my other three packs registers above its rating/setting capacity. Pack three shows 284,000mah.

Thanks for all the helpful advice, group. And thanks for being civil. This group is far more friendly than social media groups. I don't know why. I love recommending this group to frustrated social media users. I hope they end up coming onboard.

May the sun always shine on your panels:)
 
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And mayeth thine Lithium always be above freezing!
Funny you should mention that. We had a rare freeze near Houston last night, and several more to come. A side note: my bank cooled from 78°f to 59°f overnight in an unheated space, with temps just hitting 32°f for a few hours. Thermal mass.
 
Follow up: bad news. Bank just hit 100% soc, and that same cell went into overvoltage again:( I guess I will have to swap my BMSs around to see if it is the problem:( and I guess the conclusions I made about the cause of my issues may be wrong. Crap.
 
Follow up: bad news. Bank just hit 100% soc, and that same cell went into overvoltage again:( I guess I will have to swap my BMSs around to see if it is the problem:( and I guess the conclusions I made about the cause of my issues may be wrong. Crap.
It could just still be a little out of balance. This is an issue with how LFP cells work. When you get close to full state of charge, the voltage of the highest charged cells just runs up. Try charging that group at a very low current instead of just leaving it at no current to balance. If you can find the balance current spec for the BMS, charge it at that current. It may be as low as 60 milliamps. This will very slowly charge the other cells, but the runner cell will be stopped and get no net charge as the BMS balancing will bleed off all of it's charge current.
 
Also, charge it to the highest voltage it will allow without tripping any OV alerts and hold that voltage for a couple days. I've written on these forums several times now about how it took me 125 hours of holding at full charge voltage to get a brand new 12V battery fully balanced to within 30mV cell-cell, using the internal BMS's balancer. In your case, it might take that long or longer to bring balance back to The Force. Using an external means to discharge that one cell will take much less time.
 
Update: it's been a week, and for at least the last few days this cell has been behaving itself. Due to bad weather, I have not reached a full SOC during this period, and I probably won't top up today, either, but I'm slowly gaining. My bank is 14.5kwh, currently at 55%. I use about 2kwh/day, and I harvested a PR of 4.7kwh in one recent sunny day, so I probably won't top up for a few more days, then we'll see if that cell goes off the rails again.
 
Update: it's been a week, and for at least the last few days this cell has been behaving itself. Due to bad weather, I have not reached a full SOC during this period, and I probably won't top up today, either, but I'm slowly gaining. My bank is 14.5kwh, currently at 55%. I use about 2kwh/day, and I harvested a PR of 4.7kwh in one recent sunny day, so I probably won't top up for a few more days, then we'll see if that cell goes off the rails again.

Not to be a negative nelly, but if you're not getting to full SoC, and cell voltages are below 3.40V, you don't have evidence it's behaving itself.

Even with a notably imbalanced battery, cell voltages in the ~3.1-3.4V range will be very close to one another.

As an example, my first batch of 280Ah EVE cells all measured 3.29V as received, but they actually were between 28 and 41% SoC.
 

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