How many Ah did my cells drift in 1.5 years? And what has the balancer done during this time?
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- เผยแพร่เมื่อ 6 ก.ย. 2023
- I'm trying to find out what the actual cell drift is, since we have installed the battery shelf 1.5 years ago. As announced in the last video, I'm now charging my batteries to a higher voltage to find out, if the batteries would be balanced even with only a passive balancer. So, with that in mind, I'm charging the pack until the first cell hits 3.65V. Now, I'm charging only the cell with the lowest voltage also to 3.65V and measure the Ah necessary to get there. This is the cell drift since installation of the battery, the balancer could not balance. Some simple maths, and we could also calculate the overall cell drift if no balancer would be installed. The result surprised me!
I also had a look in the VRM history and found the days, I had fully charged the battery. A shocking low number, I must admit. And this is maybe the reason why my balancing is a bit... off.
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The normal user with Pylontech etc. doesn't even notice such small things, I think that 90% of users with other systems don't notice such things either, only DIY storage users even pay attention to cell drift etc. The normal battery user only notices that something is wrong when the battery fails and support has to come. Thanks Andy
That is not completely correct. You may use batteryview application specifically developed by Pylontech to monitor and verify the balance of the cells. I have a rack of four us3000c and they are working very well (firmware 1.8). The advantage of those batteries is that the capacity is much lower of magiority of DIY ones (74Ah vs 280/300Ah). Both pylontech and seplos are using a passive balancing system with pretty much same balancing current, become much easier keepping balanced a small battery pack in comparison of bigger one. Anyhow, my EEL Seplos V2.0 10E including CATL 280Ah A grade cells is performing even better than my Pylontech, but only if you set your charging voltage over 3.5/3.55V/cell.
@@peppeper9325 I doubt you are a normal user, I'm talking about people who don't even know the name of the manufacturer of the solar system, let alone the battery, without looking at their app first. There are a lot of them. Those are the people I'm talking about, not people who subscribe to Andy's channel like you and me.😁
Possibly your best video yet..in my opinion. I for one like the clinical analysis.
Thank you very much.
Great work Amdy! Thank you for all the learning and sharing!
I totally expected that (but waited for your results before I posted, heheh). The main reason being that almost all solar-battery systems charge their battery banks at significantly less than 1C rates which means that under normal circumstances the passive balancer should have a lot of time to work with even before the batteries go into absorption.
Your tests are a huge validation of your current settings, thoujgh (which I would normally consider to be a bit on the low side w/regards to charge target). Definitely a thumb up on that!
Remember to set your charging parameters back to normal!
-Matt
Thanks a lot, Matt.
Whenever I fully charged in the past, I could see the deviation going up on all three battery banks. So, I was expecting a bit of drift which the 3.45V was hiding. Charging a bit higher now, makes it far more obvious of course. I'm sure the balancers will all work fine at this higher voltage and if I give them a bit more time.
Is it necessary? Absolutely not! All three battery banks have performed very well since installation and the ~5Ah drift over that period is not important. However, it also shows, that I probably would need to do a 'maintenance' balance every 2-3 years and top balance each bank again. I'm totally happy doing this as it will also show how the cells perform over a longer period of time.
Or maybe we schedule this in every Christmas to gain some data over time...
Wie immer Andy, tolle Recherche. Perfekt. Danke
Thank you. The additional information at the end was very insightful.
Thank you.
Kudos Andy, thanks for all your testing and thorough explanation of the way you test and be frank and open about it. Keep up the good work and enjoy calibrating your SPATs.
Thanks Edward. Happy to share all this here on the channel.
Thank you for all you share, you have helped me exponentially to understand lip04. I too am currently building a system , thanks to your clear and thorough explanations , it has made it a very fun experience. From so cal. Thank you again!
Thanks a lot for your kind feedback. Much appreciated🙏
always a pleasure to see your video andy. due to your channel two weeks ago i started to build my first battery pack for my camper conversion. just a small one compared to your mega setup but still very interesting and i think inthe future i will get my own home battery. Grüße aus den Niederlanden
That's what I wanna hear! Viewers are getting inspired and build their own batteries. Nice work and good luck with your built.
Thanks Andy! I'm really glad I put all JKBMS's in my RV. I only have ~48kw across 4 batteries (16x230Ah Eve Cells). Heh. Yeah, big RV.
Cannot go wrong with a JK.
Hell, yeah, it seems like a big RV!
@@OffGridGarageAustralia Yeah, 40' 5th wheel. Victron split phase inverter setup, charge controllers and 2550 watts of solar goodness. Thanks for all the great testing and keeping us entertained!
Thank you for all the testing and sharing the informations
Thanks, Dirk!
Bloudy ripper once again !! Thanks for the Inspiration !
My pleasure!!
As always- great to see another video from you Andy, love your work and dedication to the task. 👍
Great result, and it all validates our settings.
(I occasionally, maybe every three months or so, isolate one of my batteries, and take the voltage up to about 56v with my power supply to allow the JK to do the balance job to within a few millivolts. There’s usually only maybe an amp hour or less difference between lowest and highest. Just like you Andy, I prefer to charge to a lower voltage on a daily basis to cause less stress to the cells.)
Yes, perfect, Dave. This so called maintenance balance is what I will do as well, taking one bank offline and top balance it again over night. Maybe once a year or even once every 2 years should be enough.
@@OffGridGarageAustralia Yes- sounds good Andy.
The only thing I have to work out is how often I need to do it. (Also- if I spent the money on a NEEY, I would probably never have to do it.)
I do have one cell, in one of the banks, which seems to always be the main offender. I’d MUCH rather have one being a bit of a laggard on the low side compared to the others, (which is what I usually have) rather than one or more topping out at high voltage and thus causing a high voltage disconnect.
@@FutureSystem738I would not worry too much about it. As long as all cells are in line in the voltage range you use them in, let it run.
So I am happy to expect testing, exploring, learning and sharing about the new JK Inverter BMS...
Coming soon... we're still tweaking the software.
Awesome Analysis Andy! AAA!
Thanks!
I really ejoyed the summary Andy. Thank you. I see where this is leading. Well I hope I see where it's leading, because......😉
Thanks for sharing YOUR thoughts and experience as well, my Canadian friend. More testing underway😉
@@OffGridGarageAustralia My pleasure Andy.
I forgot to mention my pack settings I think. You set that at 3.65 and 2.5. This way the pack settings never get in the way of the cell settings.
You were 100% right about your 3.45-3.50V maximum voltage.
LiFePo4 are (contrary to popular belief) VERY sensitive to high voltages.
You can safely leave LiIon at 4.0V/cell, the current consumption during charging then goes to 0A.
But with LiFePo4 you have to charge to 3.50V and then to e.g. hold 3.45V.
Then the cells last extremely long =)
You simply set the balancer so that it only becomes active from 3.45V (regardless of whether passive or active... it just has to be adjustable =).
Another interesting video and exactly matches my experiences.
I think so too and 3.45V seems to be the ideal voltage to charge to. Higher voltage works better for passive balancers though.
I've heard that from time to time it is good to bring LiFePo4 cells to their upper voltage limit (i.e.: 3.60V or even 3.65V) to "reset their chemistry".
Is there any truth in that?
Thank you
@@a-c-g I don't think there is an advantage of that. They don't need a 'reset' or 'equalization' as lead acid does, for example.
Nice work Andy
Thank you.
hilarious Andy! you are so funny! you should be in comedy! im LOL. thanks a lot. excellent results. now it would be nice to find out how much capacity was lost in 1.5 year.
Ciao sono dall'Italia ti guardo sempre BRAVO 👏
Thanks! This is something I definitely was thinking about with my own system but I feel as if I shouldn’t worry. Have a SPAT ON me!
Thanks a lot for your support!
Yeah, don't worry too much about it. She'll be fine!
LoL Andy’s Battery racing who would have thought this shit would be so interesting 🧐 who’s on first , what’s on second and anyone comes last 👍
Haha, a bit like a race every single time. Not sure if the first one wins though😂
10:25 Nice to see your battery getting balanced with the passive balancer well enough that it stopped it from going into OVP.
Give it a few more days like that and watch that deviation fall :).
Yeah, it seems it is getting better over time if charging to 57V now...
Always great job Andy! Perhaps yo ucan assist the guys (such me) who cannot set absorption time. Exemples. I use SOFAR solar inverter. I can only set up the voltage! So I’ve set up 56.5v. But an Andy’s test will be welcome to help the “non Victron owner’s “
56.5V should work. If your cells are not drifting too much at this voltage, increase it to 56.8V or even 57V.
I assume your inverter will just stop charging when it hits this voltage?
13:00 1,5Ah @ 100mA balance current is also 15H of balancing. So I think: For this type of balancer it´s too much to get it down. And this is ONLY 1,5Ah or 0.53% of 280Ah. So this balancer wasn´t able to keep 0.5% pack-inbalance under control. Best selling argument ever for this BMS🤐
But the balancer may work at a higher charge voltage. And this is what this test is about. Charging to 3.55V (instead of 3.45V) may actually work as many say.
But as stated in the video, it could also be the lack of absorption time I gave the BMS in the last 6 months.
Thanks Andy
Thanks Wayne.
You could try a start balancing sooner (3.43v), a longer absoption (1.5hrs?), a higher float and/or charge 12 times per year reaching a pack voltage equiv to 3.5 to 3.55v per cell.
It's obvious the balancer had already fixed some of the drift when you charged >3.50v/cell in the previous video (probably added
Yes, that's exactly what I do right now, higher absorption voltage and time, higher float voltage and more often.
I know it will work but I was curious how much Ah the balancer has to overcome to get from the lowest voltage cell to the highest.
Another great video Andy. Great idea to actually test the capacity difference. I imagin d it would be a lot more, but once I saw all the cells above 3,45v and charging, I could see that the capacity difference should not be that big. Great to watch it and learn even more.
Great teacher you are.
Thanks a lot for your feedback. I was expecting around 5Ah drift over this period of time, so was pretty close...
Hey Andy, I agree with you there has been a lack of top balancing over the last 6 months so you need to stop driving your car and stop all the testing so the batteries get a chance to do a balance. No wait keep driving your car and keep doing testing, we all love that and just get some more solar panels!!!! With the Heltec thing 6 months ago I commented about only the first 10 cells are balancing and I reckon that those 10 are on one connector with the other 6 on another connector, could there be some sort of problem with the second connector. Could you please check that out. Love the show, cheers for now
Thanks Glen, I remember your comment about the balance connectors. The Heltec BMS had issues form the beginning, wrong current, limited settings and now this balance issues.
I have contacted Heltec several times but did not get any info if the BMS is just faulty or what the go is...
Andy. Good result. If you would turn off the balancing the result might be better. ;)
It's good that you explained it
but I perfer not to let my battery fully charge, that normally means lost solar
I live off grid so I plan what needs to be done on sunny days to ensure the solar is still able to keep production
Living off grip without a generator is deffinitly a life style
That is a different lifestyle indeed.
But what do you do with your solar if you don't let your batteries fully charge?
Wouldn't you fully charge them first and use the solar afterwards?
Sorry Andy, I think you missed the problem. If your battery cells go out of top balance, one cell will approach the max voltage point that triggers the BMS over voltage trip sooner than the other cells. The battery will stop charging at that point.
The battery capacity may not be recovered to 100% SOC at that point. If all the cells were top balanced, you could have charged the battery (all of its cells) to its full capacity, That one out of top ballance cell stops battery charging early, The battery potential amp-hour capacity will have been redused from its max amp-hour capacity because the one 'hi' out of balance cell caused an over voltage BMS trip of charging to the battery, not just one cell of the battery.
Not a big deal if your battery is a high amp-hour capacity battery and you seldome use 99.9% of its max capacity before recharging, but becomes more important in a smaller system with perhaps only a 100 AH capacity. Charging the battery to max capacity daily and using that capacity every night is routine for some mobile mobile solar electric syastems.
Watch the video in the description, it is explained in there.
I basically never balanced the pack after the replacement...
Hi Andy, Interesting results. Thanks for trying these things so the rest of us don't have to.
How much of a difference does this top balancing actually make in a full charge/discharge cycle?
As I understand it, top balancing is just aligning the individual cell SoC so that the battery does not stop charging too soon because one cell is full and does not stop deilvering power too soon at night because one cell is already empty.
So in the measured drift of the worst unbalanced battery cell, how much sooner would this battery have stopped delivering power in theory?
Are we talking about very tiny bits in a year, meaning hitting a 1% loss of range only after a couple of years, or is this much worse, even with the passive balancer kicking in sometimes.
Because if it drifts a lot, it might be best practice to put an active balancer in every offgrid system that is oversized for bad weather seasons.
Or alternatively just undersized in case you can fall back on the grid, so the passive balancer gets plenty of time to top balance.
However, if the drifting effect is negligable on a yearly basis (let's say 1% every 3 years), then i would not try to active balance at all, because balancing is also charge/discharge and may cause more wear than it's worth.
But this is all in theory. What do your test numbers say for the imbalance measured? Would the bottom battery have stopped working way sooner or would you have to use a stopwatch to measure the difference?
In laymans terms, did the battery as a whole lose 10% or 0.1% of charge/discharge range and how many days did it take to get there?
P.S. I may just seem a bit lazy not trying to calculate this myself, but it's all a bit hard to put together from a video and a rough timespan.
Yes, you're correct. The difference is tiny as we have seen.
I was kind of expecting a few Ah drift over a year, so this test just confirms it. Out of my 280+280+304Ah in this shelf and if each of the banks drift by 5Ah a year without balancing, that is a very tiny deviation.
The test is now, if I charge to a higher voltage (to make it easier for the balancers), we should see no deviation over a year at all. And we could get away with a maintenance balance every 5 years, taking one bank offline, balance it and do the next one afterwards.
And we already know that this is working... but again, I try things and are not here to 'make it work'.
That is a big deviation, I was expecting 30 amps man!
Thanks!
Thank you, Jim. Your support is much appreciated🙏
@@OffGridGarageAustralia……..thank you… you do a great job with a great attitude..I have learned a huge amount from your channel…
Hello Mr Andy I hope for his own pill of wisdom. According to you I can use balancing cables to load a single cell of a 16s lifepo4 pack. It is true that we have a negative and 16 positives but each positive is also the negative of the cell itself. I hope I have explained myself. I have a battery pack where I don't have access you have individual cell poles
Yes, correct. You have one main negative cable and then the first balance wire goes to battery1 positive, which is also battery2 negative.
Just had a thought about this imbalance issue. Could it be that at the end of winter this problem is bigger and recovers in summer?
1.5 years could give you a big deviation because the passive load balancers only work well on a high SoC. It could have been fine 6 months ago.
And if your battery has no chance to fill up, how much does this imbalance really matter in winter?
Maybe others with a passive balancer have the answer. It's summer here in the Netherlands and Germany, so let's compare that to Australia.
Anyone?
Yes, absolutely. The 'problem' gets worse if the battery is not fully charged for a longer time (winter) and the balancer has no time to do its job.
I expect that the deviation will come down now with the higher voltage and also longer balance time.
As I said before: let the battery absorb until the lowest possible tail current (on the Victron´s) is reached. This should solve the Problem. Yes, it get´s worse the bigger your battery is. couse tail current is a %age of the full capacity, but it should work i think.
That depends on the charge voltage limit you have set. Usually, the manufacturer says if the tail current is at 0.05C, the battery is full.
I would not absorb at 3.65V to 0A but may do this at 3.45V.
hello, often the balance is due to a very small resistive connection problem which causes this connection to heat up a little, part of the energy is dissipated in the connection and is not stored in the cell.
Yes, correct. In my case, I did not do another top balancing when I replaced the cell. I watched my old video back and back then I just replaced it and said it will sort itself out. So, all good. It's in the video description.
Always learn good stuff from your testing. I can get a 200 amp JK BMS is that what you recommend for my battery build?
Thank you.
That totally depends on your battery, load, solar and overall system design if that BMS is right for you🤷♂️
Passive balancers *can* balance at higher amperages (e.g. my REC BMS with 2A) but it seems preferable to use an active balancer anyway to spare the resistors in the BMS (it's pretty expensive).
However, I read in a forum recently that a BMS will briefly stop charging when checking cell voltages. As the active balancer is not controlled by the BMS, this means some cells could be at charge voltages when sampled by the BMS. This doesn't seem ideal either.
The problem is heat, if you balance passive with 2A you might come in the situation where you balance 15 out of 16 cell that would be about 100 watt, of heat you need to get rid of.
@@jonasstahl9826 Exactly, hence not wanting to destroy the resistors of an expensive passive balancer.
We have seen the NEEY active balancer stopping balancing for a brief moment to take voltage measurement. Tested and recorded here on the channel 😉
@@OffGridGarageAustralia That's great for the NEEY, but may mean the BMS is getting varying charge/non-charge voltage readings. I'm not sure what the impact may be, but it may affect optimal charging current and change comms to the inverter etc.
@Andy... today i started my own test.... after 1.5 year with my 304EVE Cell - 3 Packs... First Pack - after Absorption with the Victron Mutliplus-II... Stats: min. 3.360v, max. 3.475v, average 3.450v - delta 0.115v, 178Cycles - Pack was fully Top Ballanced with a old NEEY. After that i disconneced the Neey and used it external for other Packs.
now after Absorption i added a external Power Supply connected and a New Neey... the Stop Watch is running... so when the neey is constantly shifting energy with 4A on 3,45V until the Delta V. is Down to 1mV. after 24h it should be around 0,330 kWh.
lets find out ;-)
You ned to charge to a higher voltage to see the real cell drift. 3.45V is not enough. It seems, the cells are balanced but they are not.
At the end it does not really matter as long as none of the cells runs away when charging.
Great testing! How about if you let the battery absorb at 55.2v for an hour as another test and see how the heltec and overkill bms work over a longer time at lower voltage? Thanks for the videos and info as always!
Yeah, I could try, but honestly they both struggle to balance even when charging to a higher voltage. Update video is coming soon...
What does a battery cycle actually mean with lifepo4?
Years ago, (pre-lithium)when I was looking into a forklift battery for my off grid home the company owner told me a cycle consists of every time the battery is being charged versus discharged, no matter how charged it was. So, on a partly cloudy day, it could cycle each time the sun went behind a cloud if your loads were larger than the solar input....or if on a sunny day your solar input is say 1500 watts but your power tool is using 2000 watts each time you hit the switch......
He said it had nothing to do with a daily total charge.
Simply, a cycle was when the battery went from discharge to charge. So, is that how the lithium battery stats work when the Chinese say "3000" cycles? Has anybody asked?
This is not how battery cycles work in the lithium world. Manufacturer specs for "cycles" always include a SOC range. So a manufacturer might say "5000 cycles 10% to 90%, 3000 cycles 0% to 100%", or something like that. C-rates are also specified (0.2C is the typical benchmark).
Partial cycles in the lithium world do not count as full cycles. If you only cycle 50% of the SOC then you might get 6000 such cycles, for example.
For NMC and NCA lithium chemistries there is added wear when discharging below 10% or charging above 80%, particularly when charging above 80%. For LiFePO4, however, the additional wear is almost irrelevant and it doesn't really matter where in the SOC range your cycling happens. A little, but not a whole lot.
There is no memory effect for lithium either, nor is there any need to equalize or massage the battery state beyond helping the BMS reset its internal SOC tracking. No effect on the physical battery itself.
You assume averge drift over a year. I suspect that it's unbalanced in the winter as the BMS never balances. The battery balances in the summertime as it get to 100% frequently. But like you said You charge to 3.45 and see no imbalance and your test showed negligible capacity loss. So is it an issue at all? The question in my mind is there more longevity charging to 3.55 quickly and then back to resting 3.35. Or absorbing at 3.45 for longer before returning to resting. Or are they the same degradation.
That's a good question. I'm pretty happy to charge to 3.45V only and absorb there for 1h before falling back to 3.35V.
I just need to do it more often and leave it there to give the balancer time. I think this is all it needs...
Maybe not a topic in Australia, but here in Austria we got frost in the winter. Until which temperatures can LiFePo4s be charged? Does JK BMS support heating mats for pre-conditioning before charging?
Please have a talk-video about that topic and solutions.
If i store my sailboat in the winter, do i have to recharge LiFePo4s once every few month or how long do they hold their charge without load?
Thanks in advance!
Hi Olaf, the JK-BMS have a heater option and can be programmed to turn this one.
Lithium batteries should not be charged under 0°C (I would set the cut off to 1-2°C).
Charge the cells to 60% and disconnect for the winter. They will lose around 2-4% every months if nothing is connected.
Another great vid. But I am wondering if you chose that one cell to charge assuming it was the lowest based on lowest voltage, when constantly reminding us that voltage and SOC in LFP cannot be relied upon? Was this one cell the biggest drift? Come-on Andy do this test another 14 times to confirm. ;)
Naaaaah, not doing this test 14 times 😂
From the past video, we know I was lazy and didn't balance this replacement cell in line with the others. So that's the result now..
Andy~!~ Do you think you can do a capacity test on one of your cells for us after the 1.5 years? I was inspired by your build and made one for myself 2 months ago and I am very curious.
Well, I did a test with one of my oldest cells in a past video. Let me find it...
th-cam.com/video/GFuY8MrDAfA/w-d-xo.html
Can you do a video on how heat affects your batteries and what you do in summer to protect them. Is a fan all that is required in the sub tropics?
I have done a few videos last summer about heat and how I deal with it. A fan helps but the AC was better.
I'm working on a better solution now though...
Your values are great, would be nice if you could discharge the highest and lowest and compare capacity.
You only measure the best cell, I know the title is cells drift but we use them for energy so capacity is what mater.
I measured the AH, the balancer needs to overcome to get the lowest cell to the same state as the highest cell. That was the purpose.
Hi Andi greetings from good old northern Germany!
Isnt it that your Balancers start working already at 3,0 volt and try to minimize the deviations ? BR Torsten
My balancers start at 3.45V. Using them below makes no sense as the curve is too flat and does not show any difference in cell voltage.
Lucky you are .... If you had some Litokalaa cells... you would know since a while you need 3-4h and more with a good active balancer to balance everything.... and even like this is not enough. When I see a deltaV of 30mv@56V... for me it's science-fiction :)... I have a minimum x 3 this deltaV and only when I discharged 20-30%of the battery previously... To conclude, your cells are too good to see before such strategy :)
I heard about these Litokala cells before. Are they from AliExpress?
Seems to be a lot of dodgy cells on this platform, used cells with burned terminals, half the stated capacity...
@@OffGridGarageAustralia Yes from AE... My second batch of celles are from Alibaba (much better)... Hope my 3th & 4th batches will be even better ...
this drift could been done by balancer as well. I changed how i balancing few months ago. I am enabling balancing (jkbms) only whet i reach 100% soc (smartshunt tell me when). Not controlled by voltage only. After this change behavior of battery is better. I script this in home assistant
Is the voltage trigger not enough and relatively constant at 100%?
@@OffGridGarageAustralia In my case is problem absorption. Almost whole ABS charging phase is battery voltage already triggering balancing threshold. And cell diff is higher as well. But charging current is still relatively high. So i tried enabling balancer depending on soc. Balancer is now running fraction of time. Super capacitors in jkbms arent immortal :)
👍👍👍👍👍👍👍👍👍👍👍👍
Thanks for answering my same question… go buy some beer….👍
I did 🍺🍺
1.5 AH is the difference between best cell and bad cell
But all the cells losses AH
The real Ah is more than 1.5AH
Please correct me if i'm wrong
I was thinking the same thing. If it is 1.5 Ah for the worst cell, if you used a potential average of 1 Ah per cell, then I think the potential loss for the whole pack would be ~16Ah. (1Ah average x 16 cells)
Isn't that what I explained at the end of the video at around the 17min mark onwards?
I went back and rewatched the video. You did explain that for one “cell” their was more loss over the year than the 2.7 mAh/ day (1.5ah) and the passive balance topped it up by about 5.3 Ah. My comment was more around the loss for the whole battery (all 16 cells). If we look at your whole battery, you would need to top balance the other 14 cells and and it would be more than 1.5 Ah, I think it would be about 16 Ah you are missing in the whole battery pack/shelf. I think that was where It was confusing for me. Not sure when you were talking about one cell and the whole shelf. I do think that the test you are doing is going to prove or disprove the best charging setting which is what I / we are ultimately looking for. Keep up the great work, I never miss a post!!
Need to perhaps take into account the cell drift in the other cells 12, 14 (and others)as they were near the bottom too as you approach 3.65
Yeah, I took the one with the lowest voltage and recharged to 3.65V as the highest was. I wanted to find out how much drift the banks had over that time.
@@OffGridGarageAustralia my thought is the magnitude of "drift" is not truly indicated by the lowest cell or deltaV, but by the sum of the drift of all cells from some reference point. You have done some amazing benchtops testing that has allowed us to understand what goes on to the last mV. Would love to see a head to head comparison of the active balancers where a top balanced pack has one or maybe more cells discharged a set amount and then compare the time taken for each active balancer to get back to the top balance endpoint again.
Stop sending clouds, wind, and rain, Andy. So cold down here, mate😢. What's the go with this cell number 5, I have the same but on my bottom bank. Wait, that is the same. Must double-check that one.
Have you ever tried running without any kind of balancer? It'd be interesting to see the drift after say 6 months with 0 balancing. When I built an e-bike with Li-Ion cells, I didn't have a balancer and would just check it every few months. Since I usually lived in the 20-80% range, it never really showed in regular usage and only when I would top balance or drain to see where things had shifted.
We can certainly try this... good suggestion.
12:45 1.5AH for ~200mv delta (at the top) . . .
At around 7:44 I noticed that your overkill bms does the same thing as mine. Periodically it will lose the voltage readings from cell 8-16 and read as a result it shows deviation of over 3 volts. Any idea why it does that? I thought it was just mine.
I thought it was just mine 😄
Could be a Bluetooth issue, not sure... It does not happen with the XiaoXiang app
Great video. Hopefully you are not coming down with the flu, youre voice was a bit rusty. And whats with the black "mole" on youre right arm in the last couple of videos, should get that checked. 😉
Picked up a bit of a cold the week before. This was just the fallout.. All good again🍺
The mole... it's on my German channel... liquid rubber😉
Do you recommend me to buy Daly active balancer 1amp or Neey active balancer 5amp? I have 16 battery li-ion 200amp 3.2V nominal voltage
Andy, you are wrong, a little. Your balancer do not balance the right cell all the time I found out, as the cells are not always the same who are low or high. It depends on the current and current direction. I have often a high cell while charging, that becomes a low cell during absorption and low current, what causes the low cell take the lead and be balanced down, worsening the issue. Watch ALL cells while charging and discharging and note when the balancers are active. You'll be surprised.
Keep up the great research...
Nick
Thanks Nick. These balancers balance only every second channel for heat disposal purposes. On the app it shows like left and right...
Thanks Andy for the video but isn't it too fast charging 40 amps to 3.65 if you use smaller current you will reach maybe 3-5Ah like absorbe to 5-3Amps. Then disconnect charging.
That is 0,14C for a 280ah cell... Really below the recommended 0,2C charging rate for LiFePO4. That is a lot for a 100ah cell. I also thought the same and had to go do my math...
@ricardomarcelino8388 unless current drops to 0 the voltage will return back to 3.45 or whatever.
Yes, in my experience I think the final imbalance might possibly be a little more Ah by the time you allow absorption, but still no big deal.
I occasionally isolate one of my two batteries and take it to 56v with my power supply for few hours to allow a full balance with the JK BMS down to within a few millivolts. However it’s still no big deal.
Like Andy, I prefer to use a lower voltage on a daily basis to stress (and age) the batteries less.
@@FutureSystem738 I have to disagree there. Of course you would let absorption sink in, but the other cells did not absorb at that same time. It would be a little more, but the goal was to compare similar states of charge. Not to see what would full charge look like. Andy mentions in that in the video, so he was replicating the same charge as the top cell did hit, while charging to the max battery voltage just before going into absorption and then float. So that is when Andy made the lower voltage cell hit 3,65 as the initial cell did. Absorption is not about full/maximum voltage, it's about letting the cells... absorb, away from the highest voltage. High voltage is just usefull to charge faster, so this is for "laboratory experiment purposes only".
If you expect a passive balancer to rebalance in a single cycle then it has to be active & have cells with high enough voltage to work with eg. just above the minimum charge current the BMS can detect & if balancer stays ON after pack reaches 3.65v charge disconnect.
Higher charge currents are fine if the balancer can run several hours per cycle for many cycles (it won't happen overnight but it will happen).
Heya very nice ex[lanation why and how you use your balancers
If you connect 3 ZKETECH in parallel, you can charge and discharge with 120A...
And if you connect 10 in parallel, it will be 400A!!! 😮
That means to me, all passive balancers out and in with the Neeeeeeeeeeeeeeeeeeeeeeeeeeeeyyyy😀
Maybe not if we charge to a higher voltage?
🐸🐸🐸
At the upper end of the charge curve you would not expect much capacity.
No, but this experiment is not about gaining capacity.
We have done all the capacity tests a while back so know exactly how much capacity we have at which voltage.
For Example: th-cam.com/video/pijPu7t-akM/w-d-xo.htmlsi=XIH42ZrMUFEJE_Rj
Don't forget to set you charge controllers back to the original charge specs. Otherwise it's gonna take a long time with the 35A😅
Yes, absolutely🙂
How about configuring the MultiPlus-II to absorb at 58.4V (3.65V), and you manually Top Balance overnight from powerwall V2 for a few hours every couple of weeks?
Looks like it can even schedule it weekly, etc?
Obviously, the MPPTs would still balance daily to 3.45V or 3.55V.
You will never be able to charge to 58.4V. There is always a drift and one of the cells will go over 3.65V and trips your BMS.
I think such a maintenance is only really necessary every 2 years maybe, so can be done manually.
I love my victron.. the only charge controller worth buying
@@robert4027Expensive but very good and I love the VRM and remote access to everything.
Why is the cell voltage deviation 271 mv @ 56.2v battery voltage 14:14 in the previous video and in this video 166mv @ 56.73 battery voltage 10:40. That's a huge inconsistency.
Most likely due to different current - To get consistent results I found you need to wait till the current drops (say 1A) or ideally turn off charge current and wait a bit (5 mins, but make sure load is off). Then 'record' the voltage for comparison. Higher currents for a cell in the 'knee' are almost impossible to compare and can lead to confusing results.
I found that once you simply let the battery settle after charging, you should get very consistent results.
Could u do small difference if u tell bms that cell that is always the lowest has greater balancewire resist than others 🤔
That would make no difference. The benefit would be too small to notice.
Moin Andy, thanks for your fantastic videos. But I think your calculations are wrong. A passive balancer take the energy from the highest cell and change it to heat over a resistor. He don´t transfer it to the lowest cell. That´s only done by active balancers with her big capacitors. Tschüss from the North Sea
Where did I say that? I calculated 53h X 0.1A... has nothing to do with active or passive balancing.
just at the start - having a guess at 1.5ah :) thats all you'll need to add to the lowest cell to balance it.
What a guess!
you could set float to 3.45v/cell - to increase balance time but at a less stressful voltage - especially if its only once a week on average it gets there.
That's what I have done now.
A battery balancer balances cell voltages not cell capacities !!!!
Any battery that is not made up of a series string of perfectly equal cells from a capacity perspective (which is dependant upon manufacturing tollerance, SoH, temperature, and C rate) is going to show an capacity difference, when you fully charge the cells. The strongest (highest dynamic capacity) will always lag in voltage and the weakest (lowest dynamic capacity) will always lead in voltage. The only time you can discharge and return precisely to CVmax at the same capacity is on the first charge after a top balanced discharge. From that point the cells will diverge in the charge, even if they are voltage balanced. This happens pretty slowly in most cells these days because they are high tollerance and well matched and tend, in a static energy storage system that has a low C rate, to age similarly, and because the C rate is low, there is plenty of time for the "slow" cells to catch up to get there electropotential to match there terminal voltage ;-)
I measured the capacity missing from the cell with the lowest voltage to the cell with the highest voltage. That is exact what a balancer would do (just the opposite way).
Great video Andy.
Andy! You like to experiment! You need a data logger for each cell voltage and the current. That would tell you what is going on. If you want graphs I have lots….
My solution to your dilemma: raise float voltage to 3.4V for your solar system. (i.e. 13.6V on 12V system).
You found an imbalance of 1.5AH. Your BMS can (hopefully) provides 100mA passive balancing. So how long would it take to balance this battery? 15 hours as you indicated.
If you had a charger connected (instead) of solar system what would it take to balance this battery? On my 12V system I like to use 13.8V when I balance my batteries. What happens? The voltage will go up to 13.8V and then current will drop. This is where it gets interesting. The current will drop to …. Approx. 100mA … !!! with a 100mA passive balancer. It may take a couple of hours or longer (once battery is full) but the current will drop. It will not go below 100mA until the battery is in balance. Note: if you get HV disconnect you may have to lower voltage or just let it HVD cycle until balance comes into range. The balancer **must** keep running while HVD. (during HVD the current will actually be zero off course).
Note: if it drops below 100mA while still imbalanced- this would tell you the “real” balance current of your passive balancer and it would take longer. Unfortunately, a lot of passive balancers only operate 25% of the time (Daly anyone?) and their actual average current is less than advertised.
What does this mean for your system? Since you want to avoid HV disconnect, you do not want to raise the voltage you want to lower it while you balance (a bit anti intuitive). What I did is I changed my float voltage to 3.4V. That is high enough to keep the balancer active **and** -this is the important part - it gives you max balance time while the sun is still shining! Just rename the float stage on a solar system ‘balance’ stage. 😊
Since ‘full battery time’ on a solar system is precious, and you can only balance with the battery is full, using a float voltage that is in the balance range will maximize balance time.
Some people will say OMG you are using too high a voltage for float. But on a solar system the sun will always set so the time at 3.4V cell voltage will be short anyhow….
Note: If you use an active balancer the current will drop to very approx. 1/5th the balance current. A 1A active balancer, the long term current will drop to about ~100-200mA until the battery is balanced. For a passive balancer the current will drop to the passive balancer rating. Once balanced, the current will drop closer to zero for either (usually to the current consumed by BMS which for example is 7mA for something like the DALY). To see this you need a lot of patience or a data logger…..
Note: I call a battery full when the first (highest) cell is full.
IMHO, in order to determine the rate of degradation of a battery cell, it should be completely disconnected electrically (even with only one end) and run the ENTIRE CYCLE charging - discharging as a reliable result assuming the amount of energy TAKEN from the cell during discharging.
This test is not about degradation though. Just the drift over a year...
@@OffGridGarageAustralia This means that I completely misunderstood the purpose of this test. I also don't understand what the term "drift" means in this specific sense.
Can you explain in two words? English is not my native language and I have to guess some technical terms from the context. PLS! Because the word drift, so far, reminds me of a car skidding in a tight corner. :)
Can I use the ebc -40L battery tester to discharge a 12v 150Ah battery pack
No. The EBC-A40L is only for single cells. You can use the EBC-A20 though.
Links and info here: off-grid-garage.com/battery-management-systems-bms/
should you not have charged with 40A / 16 = 2,5 A as this is a one sell vs 16?
All cells in series are getting the same current. It's a series connection. 10A charging will go through all cells, so each individual cell will see this 10A charge current.
Series connection of batteries one positive goes to the next battery negative, this positive goes to the third battery negative and so on
10A -> +- +- +- +- +- -> 10A
of corse you are right, brane fart. But you could see that it was dropping rapidly after you stop charging, did it rest at the same voltage as the others? @@OffGridGarageAustralia
Hi Andy. Still me, Peppe from Napoli (The guy suggesting you to increase your charging voltage). Most probably you are in a situation where you are damaging your cells even more in comparison of people charging at higher voltage. I'm telling you. In consideration of your almost permanent unbalance for an year or more, you had exposed same cells to higher voltage (3.65V) while the others where at only 3.45V or lower. Doing so, in the long run, you may expose the cells to different degradation levels which is going to increase even more differences between them. I noticed that all your battery sets have higher cell differences of all my battery sets ! Once again, passive balancing system is good enough while charging at least at 3.55V. I olso strongly suggest to limit the charging current at final charging stage, this give even more time to the balancing system to perform his job. Last suggestion, set your cell overvoltage protection to 3.6V. At the end, despite your extreme caring to keep the overall charging voltage low, in the same time you are exposing some particular cells to higher voltage of all my setups ! Kind regards. Peppe from Napoli (Italy).
Hmm. Well, if we look at 8:00, 9:00, and a bit past the 10:27 minute mark in the video... he's at a 3.55V x 16 = 56.8V target already and no single cell is over 3.60V. He actually goes in and increases the charge target to try to get at least one cell to 3.65V.
Personally speaking for general operation I also prefer a 3.55V target instead of a 3.45V target, I do agree with you there. But I think that Andy has proven that his lower 3.45V (I think) target prior to these tests IS top-balancing the cells just fine. At least at the operating temperatures of the packs in his garage.
@@junkerzn7312 please se previous video "something wrong in the battery shelf! Or just 'bad' settings?" and let me know...
@@peppeper9325 Ah, indeed. I missed that he had increased the settings a few days prior to 3.55V. Well, ok, so at least for this test it's a validation that the passive balancer can do the job relatively quickly with a 3.55V target.
But the 3.45V target in the prior video WAS working for two of the packs. The Heltec appeared to be responsible for messing up the balance, and that is a different analysis as to why.
But the other BMS had no problem keeping the other two packs in balance at 3.45V. It isn't a surprise that they couldn't correct the Heltec's imbalance in just a day or two when Andy swapped the BMSs, either, and it also wasn't a surprise that the packs might have seemed to be unbalanced when later charged to 3.55V. That does NOT mean they were unbalanced at 3.45V. In fact they were for the non-heltec packs.
--
3.45V is right on the potential barrier, so small differences in cell chemistry are going to be apparent if you are stabilized there and then later charge the cells up to 3.55V. That doesn't mean they weren't top-balanced though, it just means that Andy hadn't squeezed out the last little bit of capacity available.
So it is not a surprise that the packs would appear to be unbalanced at 3.55V after having appeared to have been balanced at 3.45V. They were balanced and they weren't going to diverge, sans the Heltec.
--
That leaves us with the Heltec. WTF it was doing is still a big question mark to me. But there are any number of settings or algorithmic mess-ups that could have been the cause. There are some possibilities:
* Absolute measurement error of the Heltec. It might think it is balancing to 3.45V but perhaps it was actually balancing to a lower voltage, like 3.42V or something like that.
* Or the other BMSs were balancing slightly higher than 3.45V for the same reason.
* Or some issue with the balancing algorithm of the Heltec.
In anycase, my position in general has always been and still is to charge to 3.55V/cell. Precisely because BMS's are just not accurate to 10mV or anything close to 10mV. The relative accuracy between cells will be very good because they are all being measured through the same ADC circuit. But the absolute accuracy will not be.
Same for the Victron and any other regulator. Absolute accuracy is always an issue, so it is always good to choose voltages that take into account possible measurement errors. Hence why I use 3.55V myself. Think of it like this:
BMS balancer starts: 3.50V
Charge target: 3.55V
BMS cut-off: 3.65V
Absorption time: 2 hours
Parameters like that are chosen to deal with the typical measurement error, temperature ranges, and other issues that occur when multiple pieces of equipment are trying to manage something.
So in that respect, chosing 3.45V is really cutting a fine line in one's assumptions about the accuracy of the charge controllers and the BMS. Which is why I don't.
-Matt
Thanks Matt, great comment again.
Even at 3.45V I saw a bit of unbalanced packs with the Overkill and Heltec of around 100mV. This was caused purely by the Heltec BMS. I had trouble with it from the beginning and the current measurement was like 15% too low (so spot in the app to re-calibrate it).
After I installed the three battery banks and top balanced them, the Overkill had no trouble of keeping the balance for the 304Ah pack at the top. You can see this here right before I swapped the two BMS:
th-cam.com/video/nPFKkIYFt48/w-d-xo.htmlsi=p7EKG24W5KR2e0gg&t=382
I would be interested in your absorption voltage, time and float settings, Matt! Are these the ones you mentioned above? What about float?
@@OffGridGarageAustralia My settings are pretty typical. Absorption voltage is same as bulk, 3.55V/cell (well, Victron, so its just one number anyway). Absorption time is 2 hours (mostly to give balancing time, the actual current tail is usually less than 30 minutes), and my Float is set to 3.375V/cell also very typical when solar load-support is desired.
--
(EDIT: Note, the Victron measurement error is whole-battery, not per-cell, obviously, so it isn't as important as the absolute measurement error a BMS might have... the BMS is measuring per-cell voltages. So for the Victron, in a 48V system, a 0.10V error is 0.006V/cell which is not a big deal. For a BMS with a 0.5% measurement error and a 5V range, however, the cell measurement can be off by (5 * 0.005) = 0.025V). Depending on the BMS it might be less. The cell measurement error of the BMS has two components.. .the absolute offset error, and the ADC resolution. The absolute offset error is the larger problem).
--
I see voltage measurement errors of up to around 0.06V just between what my four Victron controllers report! And I have all four connected to the same bus bars with only a few inches of 10awg wiring! The error increases depending on the solar wattage(s).
I wish Victron had a calibration feature(!). Also I don't have a shunt so I don't have a separate voltage sense wire going to the batteries.
And it is even more significant compared to taking an actual battery terminal reading with a high precision volt-meter. Over 0.08V between what the (worst) charge controller says and what the volt meter says at the battery terminal. Even at 0 charging and 0 load the absolute error is still at least 0.05V.
At higher charging rates or loads, the voltage measurement errors increase.
So for these reasons, I prefer using a target of 3.55V/cell instead of 3.45V/cell. There needs to be enough margin such that measurement errors don't cause issues.
--
Generally speaking, for LiFePO4, the savings grace is that the cell voltage settles down pretty much the instant charging current goes away. Within 15 minutes it will drop below 3.40V/cell. Because of this I do not feel that the cells are getting stressed with the absorption set to 3.55V/cell, even if held for 2 hours. I think it is a non-issue for solar-cyclical operation.
-Matt
I would think the lowest capacity would be in the cell at the highest voltage.
That can be an indication while charging.
Sir i am going to make 60v 42ah LFB BATTERY PACK CAN I USE DALY 19S 1A ACTIVE BALANCER SIR DOES IT BALANCE THE BATTERY PACK
Daly is not great for balancing your battery. Not sure what chemistry you will use, but get a JK-BMS for this battery:
off-grid-garage.com/battery-management-systems-bms/
Why isn't it standard for BMSs to have an active balancer? There must be some reason why even newly developed BMSs still use passive balancers only. I would also think as batteries age it will become harder and harder for a passive balancer to keep the battery in balance.
It shouldn't be harder and harder. Cells might lose capacity slowly but the passive balancer is still top-balancing (resynchronizing) the remaining capacities. The rate of loss from age is generally very low, far lower than the (current x time) that balancer can put out.
Active balancers are almost never necessary, they add complexity and another failure point (as do current limiters, though those can just go into bypass when they fail). And they can hide serious issues with cells that the user should really investigate and replace. When serious issues with cells are hidden by active balancers they can wind up leaking electrolyte or overheating before anyone realizes there is something wrong.
Because it is cheaper and many people build just small batterys for like E-Bike where passive balancing with like 200mA is totaly fine.
I think the future test result will show that passive balancing will work when charged to a higher voltage. Even with such high capacity cells if they had a good top balancing to start with.
Can I do 4P16S (48v) of 3.2v 280AH? I don't want to complicate my build and just use 1 active balancer bms. (less components to fail)
You can but that is a hell of a lot of current if you short your pack. Plus you don't have redundancy in case of a BMS failure, and you can't do maintenance on your pack without completely disconnecting the whole thing. Remember how Andy was able to keep his system operational with the other packs while working on the one he disconnected? That is a very important feature.
You can but you might not have enough balancing current, also one additonal BMS only cost like 2% more for your project and gives you the advantage of redundance. Depends on what you want to use the battery for.
@junkerzn7312 hey, tnx for the tip. Well... i just gotta be super extra careful, not short it then. Anyways, what are the chances of getting a bad battery out of a 4P of 280ah cell? Gonna be charging it up to max 3.45v (55.1v), maybe top bal before I build the pack as well. Honestly, i just want a maintenance-free bat pack, as I'm too lazy or busy to maintain it.
@@jonasstahl9826 be using it as my offgrid setup. Planning on jk bms active bal 200a. Using deye 12k hybrid
@@leotheevinci I'd recommend just buying pre-made packs, e.g. SOK, or EG4, or other brands. Because my take is that you are going to need every single safety feature those things have 🙂
6.8Ah in what total size (in Ah ) of the battery ?
912Ah ? = 0.75% ?
He just measured the lowest cell, so he just wanted to test the drift between the top and bottom. You can't calculate overall Ah drift from that.
@@davidpenfold thank you , i knew that i didnt understand something :)
Nobody don't make us video 3p8s connection.
With 1 bms
I’m thinking of lifetime it’s ok for the next generation 😂 say 20 years and then recheck your records. 😊
What about the inner resistance of cells? When these have changed, it would also impact the cell voltage difference.
Hmm. True, but it might not matter for this test. The voltage differential due to internal resistance is only in effect while current is flowing. As the current tapers off at the end of charging, so to does the voltage differential (due to internal resitance). So it is usually a self-correcting problem.
One does have to wait for the current to taper off while holding the target voltage, though, and Andy might not have. But it probably doesn't matter a whole lot at that point in the charging curve. At any point above around 3.45V any amount of current will more or less hold or raise the cell voltage. Certainly at 3.65V.
@@junkerzn7312 i found that after charging the cells to ovp over volt protection of 3.65v and let them sit for a couple days with no load to see how much the volt drops , one can find the miss matched cells that will effect the over all battery pack. I found that any cell drop to around 3.40v when sitting with no load means that cell will be a stress on the system and will drop to 2.40v uvp under volt protection while the rest will still be at or above 3.00v.
+
I don’t understand how you’re cell went off balance
Because the BMS on that battery has a passive balancer and was not able to compensate for the differences between the cells especially when there is only 1 hour to do so. It is one hour because that is how long he has his solar charge controllers set to stay at the 3.45V absorption voltage.
@@davidb.5544 ohh I was literally like he has a bms and balancer
Andy, after you came back to the video, you sounded a little stuffed up , are you taking care of that stuffy nose? I hope your doing well.
Andy was well calibrated.... ;-)
Jaegermeister for 3 nights in a row took care of it.
Like#1 Woohooo
maybe I should run a cable to you and you can charge with AZ Sunshine! We could be our emergency backup power plants during the night times...
And I'll get a few kWh in return in my winter? Deal!
Also 🥇
@@OffGridGarageAustralia you know it!
1.5ah from the lowest cell. now if every cell that did not hit 3.65 volts could need .2ah x 14 =2.8ah just a guess. so 4.3 or so total AH missing. now that that cell is caught up the whole pack should be around 3ah from the first cell hitting 3.65V
The cells in the bank are in series so the capacity lost is the one of the worst cell, you math is for cells in parallel.
~4.3Ah is the overall capacity missing to fully top balance. This is across 16 cells and the BMS will balance them at the same time.
Hence I took only the lowest and highest and compared.
I don't think you're result is completely accurate as when the bms went in to overvoltage protection the current was around 24A or in any case significantly lower then 40A which you then uesd to charge the singel cell. The volatge of the cell is not only influence by SOC durrong charging but also but the current going through it. So you reached the 3.65V with fewer Ah then the actual imbalance as the current was higher which increase the measured cell voltage more.
The result is not accurate, no, but it gives us a good idea of what drift to expect over a year.
I have made a video a long time ago, exploring exactly the relation between SOC and charging current. There is also a spreadsheet which shows the results: th-cam.com/video/qZg4Jxftw-c/w-d-xo.html
Hope for my Daly yet???😂😂
Which one? The 100A smart BMS? Good luck with that. The rated 20mA(?) is actually 6mA (average) and as a bonus it only balances when the current is above some threshold (1.5A on mine). Here comes the kicker: if you need to balance a 1.5AH imbalance even at 20mA it would take 75 hours (225hours actual). But it will never actually get there because during the 75 (225) hours, the current will drop to near20mA (6ma) and .... turn the balance off during this time.... I managed to get my Daly to balance at 0 current and actually tried this. It will indeed balance but it takes that long.
@@zeropointbalance7366 Yeah I know lol, but I am an optimist and I love an underdog. Mine is a 250A "Smart🤔" BMS, it don't register anything under 2A charge or discharge current and only balances when there is a charge current.
75 to 225 hours is quite comical. 😂
Gary, I should get you an active balancer for your Daly. It will never balance your Litokalaas
@@OffGridGarageAustralia😂 Andy I know the poor thing is hopeless.
I admitted defeat, took your advice and Ordered one off of AliExpress, it is due any day now, yesterday the tracking said it's at customs.
Cheers mate 😃
Luv ya
Gaz
@@garys-half-baked-offgrid-dream Nice! Looking forward to your install videos and seeing Dave again.
34th ;-)
Hello from sunny hot Greece
I disagree about the results of your testing. Charging batteries involves chemical reaction as batteries store chemical energy and the discharging process is the opposite chemistry reaction. The voltage difference measurement between two cells are meaningless. A cell could act like capacitor and could not store real energy. For example if one cell is bad will be charged faster and the voltage will be very fast at top 3.65v. For me after ALL cells hit 3.65v you should do a fully discharge test..... AND then only you should measure between two cells the Ah that the cell with the highest voltage gave more , than the cell that hit the lowest end of voltage accepted value. So you will see the difference in Ah between two cells
Watch the video in the description, it is explained in there.
I basically never balanced the pack after the replacement...
kaputt