LiFePo4 and Absorption. What I learned from my previous mistakes...
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- เผยแพร่เมื่อ 13 ก.พ. 2021
- So this is a bit of a long story. I had some problems re-charging the battery after the last discharge. When it got fuller, some of the cells peaked and I had to manually discharge them. The more cells peaked, the more I struggled to keep the situation under control. At some point I turned charging off as I could not handle it any more. I'm not sure why the cells were so mis-balanced from the initial top balancing...
Well, I found another method online how to balance the cells without disassembling the whole pack again. So, that's what I did the whole week long. It took a while and I learned a lot about how these cells work and behave. It is all about the voltage and current. I was so wrong by just looking at the voltage...
Will the battery work after this crazy balancing procedure?
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Great work! Appreciate it. Thank you for the opportunity to study together! Best wishes from Ukraine 🇺🇦
Thank you. Take care over there!
Hi Andy. I will give you my opinion. I made a battery with 22 LiFePo4 cells and installed without BMS on a scooter. 2 years after almost daily use I don't see any imbalance. After much reading and watching videos of experts, I opted for the technique of bottom balancing instead of top balancing. The explanation is simple. All cells have a common minimum, but not all can have the same maximum.
I unloaded cell by cell until its minimum tension and left it to rest for 2 days (the tension will naturally rise a little, being necessary to repeat). With all the cells equal at the minimum voltage, I connected them in series and connected the charger until it reached 80% of the maximum capacity. It is my safety margin and I guarantee that all cells are able to balance themselves at this voltage. LiFePo4 chemistry is very stable. It's just my opinion. Good job Andy.
Thanks for sharing. Interesting approach indeed...This method will work as you only charge to 80% capacity, that's correct. How far down do you discharge the cells during operation?
I appreciate your efforts. we are all learning together.
Thank you!
Indeed we are all learning this solar together. But so rewarding ❕❕❕
Thanks Andy 👍🏼👍🏼🌞🌞🌞🌞🌞
Thank you for teaching us as you learn these things yourself.
I have learned so much from your videos! There is so much to learn and you are so good at explaining the key points from your testing. Your channel is the best I have seen to truly make the complicated simple to grasp and you do it with great music and personality!!
Thanks a lot, David. Appreciate your feedback and kind words.
You rotten sod rubbing it in about your lovely weather and how we are freezing and your going in the pool to cool down !
Great episode as always. Lovely to see your frog at the end.... kept thinking of them when I saw your green battery indicator on your phone. Learnt a lot from your channel. Thanks
Thank you 🤗
You can keep your 31 degree weather. I'm going ice fishing. :)
Your explanation of absorption was great, it really helped to visualize that part of the charging process! Where people can visually see there's still so much energy that can be packed into the battery even when you've reached the right voltage.
I've explained absorption before to people that it's like filling a cereal box. You can quickly fill it up to the brim but still not reach the gross weight of a full box until you kind of shake the box and let it settle some. Then you can pour in more. It isn't until you reach the right weight that you can consider the box "full" or "saturated". (The height would be the voltage, while the weight would be the current.) So the "absorption" phase is kind of like shaking the box while you pour in more cereal.
No need to put up the footage from the past 3 days if you feel this video sufficiently explains/educates people on what you learned. It's a wash of whether that could be helpful - on the one hand, people will see the entire process of how you were troubleshooting and learn along with you, but on the other hand it could actually complicate and confuse the message of what ultimately needs to be learned. With the deluge of information people face these days, I tend to think keeping things simple is better, that the value of watching you troubleshoot is negligible since you explained your thinking process pretty well here. So if you're comfortable that there's little to be gained from your footage from the past 3 days, I'd say "spare yourself the effort (and potential embarrassment 😆).
Your cereal box analogy is pretty good but it tends to apply more to flooded lead acid. In the case of lifepo4 that extra energy you're pushing in to the battery is done by fixing the voltage so that the battery cells that are already fully charged cannot accept any more because they resist this voltage but the battery cells that have not caught up yet can accept this voltage. In bulk you were charging based on fixed current but now you're charging fixed voltage. This means that the individual cells that are lower in charge are now going to be able to catch up to the ones that are already charged fully.
Why don't the more fully charged cells also continue to take a charge and end up over charging during this absorbtion stage you may ask? Because you are now keeping voltage fixed and any cell that's fully charged will resist and push back against this voltage. The only way to make them charge more fully would be to increase the voltage.
Why didn't the lower cells take more charge during bulk you ask? Because there are always slight variations between battery cells resistances.
So why can the lower charged cells accept a charge now when they didn't before? The answer is they did, but they just did so at a slower pace.. now you are giving them time to absorb this continous constant voltage over time and bring them up to the same threshold as the other cells at which point they will also start to push back against the voltage.
Think of it like teaching a class of students that vary in intelligence. The bright kids catch on quick and then sit there already educated but learning nothing new whilst you continuously repeat the same information over time untill the slow kids catch up. This repetition of information is analogous to the repetition of applied voltage over time or absorb stage as we call it.
Well i have learned a lot from him, especialy his mistakes.
@@juskarn Thank you!
Always a good day when I see a video from @Off-Grid Garage :)
Glad you enjoy it! Hahaha, thank you :D
I had similar issues, and what worked for me was this: Charge the pack until one cell peaks. I used an 8S charger and did 8 at a time so I could see which cells were topped out at 3.65V, and which were lower. Then individually charge any cell that wasn't topped out. Then charge the pack again as an 8S pack to see which cells were still not peaking, then I charged those independently again, and after 3 rounds of that, all were very well top balanced. You can charge the individual cells with a charger while still in the pack by just using alligator clips for the individual cell. I use a battery charger for the independent cell charging because it measures the AH added, and it shuts down by itself so I don't have to watch it.
Balancers are only for maintenance, you are definitely right on that. You must balance the cells before you can even think about using a balancer, BMS balancers only work when batteries are very close to each other for state of charge. When I had one cell peaking in the 8S banks, the other batteries were anywhere from 6 amp ours, to 84 amp hours lower! I came to the conclusion that adding to the low cells was way more efficient than discharging the high cells, as that is how I started but quickly realized it was a flawed approach.
Wery interesting! Can you explain, what does it mean? I have all the time same three cells, that are higher then others for around 0.010- 0.035 mv when charging, especially higer then 3,5v and in some time after stop charging their voltege goes lower on 0.020- 0.040mv then othe cells. And balencer begins to charge them. I did paralel topbalance befor assemble. I use Daly bms and Neey 4A smart active balancer. I see that during the end of charging, that 3 cells runs up, balencer discharge them, deviation voltage goes from 0.050mv to 0,004mv, charge stops, and after that, when bettery goes in rest, voltege goes down, and that 3 cells become lower than others... They goes much lower ( near 0.080mv) under load 60-90A. Without load, they also steel lower. I set balancer to continue balance after charging to rest to until 3,330v and usually get 0.010 mv diff. But in this case next charging shows bigger then 0.040 mv different, becose other cells gets some deviation between one another. Maybe that is normal behavior? Maybe, I have to charge battary to 3.65v per cell, and then charge that 3 cells individualy with 3,65 v automatic Lifepo4 charger?
Hey! Tried this and it works! My batteries have a complex installation and I really didn't want to take them out of place for servicing. I achieved balanced cells merely by lowering the overvoltage cutoff to 3.45v as you suggested and voila! Thanks!
Dear Andy, love your humor and most practical demo of solar system building.
Just went back to watch your first episode from very beginning. Love it and enjoy it.👍
Wow, thank you!
You been my teacher and I've learned a lot from you.. I'm using sealed wet cell and I know If I took my batteries and disconnect from my system, the solar power of 1000 watts would just take over and maintain my 12 volt / 1000 watts requirement. I really think you very close on solving this.. I live in sunny southern California and my generation has been excellent. If you can master using your batteries banks with the solar system and normal load usages at the same time, then I will upgrade to lithium lifepo4. Thank you for teaching us !!
Great insights there. Thanks for sharing with us! You learn when you jump in the deep end - if you were mucking around with cheaper, lower capacity or fewer cells, you wouldn't worry about these subtleties as much.
So true! It all looks easy when you watch other videos but building a battery yourself is more challenging than expected. Ot at least, it can be...
Excellent detective work there...
It's even harder to build an understanding when you have experience that needs to be forgotten because it no longer applies.
It would be interesting to see what the settled voltages of each cell were, after you carefully saturated each one.
Perhaps they each have a different saturation voltage... This would explain why the voltage based balancers can cause trouble!
Thanks so much!! I have learned more from this and your next video than I have learned from tens of hours of solar/charger/battery videos over the last year or so
No matter how many times I watch your videos I always seem to go back and learn something new YOUR videos never get old my friend
THANKS ALOT 👍🏼🇺🇸❕❕❕
Wow, thanks
Hey, Andy! Great video! The problems that are the most difficult are also the ones that will teach you the most. You already made great progress and learned a lot. I have no doubt you will find the settings for the charge controller and bms that work for what you want. Good luck my friend.
Thank you.
Just wanted to say thank you for showing us the whole process as you learn about charging. I am building a 12v LifePo4 battery right now and am in the same situation and find it all confusing about what settings to use, but watching these video's has helped a lot!
LifePO4 really prefers to take all you can give it. the float charge is for lead-acid batteries. and the absorb is also for lead-acid batties. it wants the bulk charge. that why they disable or have to reprogram the mppt chargers as they are not designed for LiFePO4. study up and you will find the correct information.
Thank you Shawn, much appreciated!
Great Video. I've been experimenting with a Growatt 3000K 24v 8S 3.2 cells. And It is very confusing to get all the parameters rights. Your video has clear many questions regarding CC/CV, voltages and amps. I am still playing around but I think I have found a sweet spot for my setup. Thank you very much for sharing.
hi ANDY there are many teachers in this world, but very view can explain a process that everybody can understand it. u are one of the view exceptions to make ur presentation clear. it was the first time i see the total picture of charging a lifepo4 battery. thank u great job. i am the German guy in Texas and just started up my 30 kw system with a 8 kw solar system. i am using a SOL ARK grid tie inverter that can start a back up generator in case the grid goes down. i will make a you-tube movie the next few month and will send the link to you.
again thanks for all the patience and smarts you have. viel glück Jan
Very insightful, excellent material to ponder. You have hit on an issue that I have been thinking about too. The longevity of the the batteries is greatly diminished by charging to 100%. a combination of voltage and current monitoring must be the answer. The tolerances are so tight as you point out it's so difficult to get it just right. Keep up the good work. Perhaps keep a log of the batteries that are always the highest and lowest to see if their performance deteriorates faster than the others. Keep testing to find the sweet spot! Thanks for your video
I think this was one of the best episodes for learning and conecting things in my brain !
when i test lead acid batterys i have this system, i charge and leave on float for 3 days to let all the energy absorb, i stop the charge then i test the voltage after an hour and then after 24 hours another voltage test and a 50A load test and then i choose the batterys closest to each other to put in a battery bank for solar, it's just the way i do things after years of charging used batterys and resurecting them for solar powerbank use but after watching this vid it clicked, somone else has similar thoughts ! differant chemistry i know but cool to see a similar thought process in somone elses head !I really really enjoyed that one, i love learning alongside you ! keep it up :)
Thanks for the feedback. I've got this effect all the time and step by step things make starting sense... Then I need to test and confirm that new learned, so it all takes time...
Just watched this video. Experiencing the same problem on my golf cart project. I have a 135A 14s LiNMC battery with a JK BMS, a 300W solar panel roof, a Victron 100 20 MPPT, and a Victron 712.
Massive amounts of sunshine here in So. California. Trying to keep the solar power system from triggering the BMS. This video has gone along way to help me understand the MPPT settings. Thanks...
Wow! This was a year ago. How much change from this to today! This was a big one and glad it came up, one does kind of get stuck thinking most about volts and with lifepo4, current is in ways 1st. This vid would be a good one to do again.
Yes, some of the older videos needs to be re-visited and 'upgraded'. But we have covered these topics in other videos already.
Your frustrations make life easy for the rest of us. 🤣. Thanks for your videos. Very informative. In Southern California its sunny always.....until I start experimenting with my solar. ⛅☀️
Thanks Kevin, happy to share everything I find.
I know what you mean, there are always clouds in exactly my area when I want to test something. Blue sky all around but this one cloud ⛅
you're the best ! I literally want to go to Australia specifically to hangout with you 😊. I enjoy learning with you and appreciate your fun attitude to figuring out problems 👍
By the way I am in the middle of this exact issue you encountered here . Just did a single cell to 3.5v taper to < 0.1amp for each cell..I then paralled em and did the same thing.
Waiting for some load testing equipment to re-test. Fingers crossed
Fabulous info and very clear, and thank you for all the effort you put into this, im learning so much from your channel 💯
Good absorption explanation.
This makes a lot of sense versus the common 'just top balance' advice that is usually given
Someone that shares his thoughts and is worth listening too!
what an amazing series learning lots just like you did
You work so hard !
Best video so far. Thumbs up.
And thanks for sharing the new app release.
Thanks John, much appreciate it.
Best videos on solar setup hands down!
This is helping me with my battery so much. Thank you youtube algorithm for leading me to these videos because I have the same bms. I have been having lots of trouble balancing. Before I was trying to balance during charging. I will take the battery to 4.1V/cell average (LMC not LiFePO4) and then balance after because the 200ma balance is so low even for my 68ah battery. Thank you!
Subscribed!
Thank you very much. I'll do another big video about balancing soon. That'll be interesting too. And controversial ;)
Andy please don't annoy me with the wonderful weather.
I have been digging out my panels from inches deep for the last week to be able to charge my batteries.
This video is the most informative you had made so far.
I will pass you from amateur to pro battery builder with a B+
You still need the 10A battery equalizer to help with the lifepo4 algorithm.
Put some voltage on these panels so the snow melts!
I'm probably only a C+ at the moment but came a long way...
NOOOO, no balancer or equalizer. They will just hide the problem. Once I found the issue, maybe, but for now, I need to dig deeper....
@@OffGridGarageAustralia I need more info about the voltage I need to put in the panels. When is freezing rain I have to spend hours scraping the panels.
@@OffGridGarageAustralia I installed version 3.1.1026 but it doesn't work with Samsung DeX. Regular phone is fine.
I'm building a 18s LiFePO4 bank for '48v' Pb replacement. Thanks for the great info!
Fantastic Video. I got lost in exactly the same trouble 1,5 Years later with my cells and that video was THE EYE-OPENER. Where the hell did you get these module FOR FREE in 2021???
Exactly, its the same when you need to really equalise a big battery like an electric motorcycle, you charge with a low current to let the BMS do his job, thanks for the clear explanation 👍
I ask the same question why cant you just make the absorb and float the same voltage? I suspect it may have something to do with What Comment is stated on Emily and Clark's channel, but I dont fully yet understand it.
"""I’m glad you mentioned low current overcharge of LiFePO4. So many people seem to believe that only the charge termination voltage matters, and neglect to notice that the cell manufacturers always stipulate a 0.05C charge termination rate. Charge to that voltage at a lower current and you’re overcharging.""""
Reply from Clark
"""Yes, and that can happen so easily with solar or while using your electrical system during charge.
Honestly I didn't understand this as a problem when I started this project. Solving the low current overcharge is what made this interesting to me."""
Thanks that was a big help. Just starting with my first lifepo. Was scratching my head on what to set my charging parameters
Thanks Mike. There are heaps more videos on how to charge LiFePO4 correctly here on the channel.
If you have a charge controller further away from the battery like I do. I noticed when you set the mppt charge parameters to say charge your battery to say 90 percent (for longevity) you end up undercharging I'm guessing due to voltage drop. It seems the charger sees higher voltages than at the battery while charging. So would I need to increase the parameters to get it closer to 90 percent at the battery terminals?
thank you for doing all this, saving me much brain pain. keep the froggies coming
Will do! Thank you Dirk!
You are doing great things.
Thanks for being you.
🐸
Thanks so much 🐸
Fantastic explanation Thanks for this great video
I am really learning!!!!! ALOT! Thank You!
I'm snowed in but theres a lot of sunshine and its -15c so perfect solar weather
Surprisingly, yes. And the Sun is closer too.
Finally have sun today in SE Colorado after 5 days of clouds , but it’s still -4°F, good for the solar electric panels, but too cold to use the solar water heat collectors. Propane and firewood!
Good call. Just love those sunny/cold winter days.
Not well known that the power produced by solar panels is higher when it's colder due to higher voltage but the current is determined only by the intensity of the light (photons) from the sun (insolation). So for the same intensity of light in summer and winter, you will generate more power in winter.
Great stuff Andy!
Thanks, Dave!
This info really made sense thank you
Mistake makes us to practice.
Practice makes us to perfection.
Perfection makes us fascinate.
And we can't stop thinking so there are some mistakes again... lol
That's a good summary. Success and fail are close together...
I built a 4s pack, and when I first got the cells, I found one which was low and charged it separately for a while. Big mistake. Because I had added several AH to it compared to the other cells, it was always high and the pack cut out before the others balanced.
Even with a 1A balancer board, it would start balancing... and then cut out, charger would shut off and I'd have to manually restart it.
What I ended up doing was taking a small 5A adjustable power supply, and setting it to 14.0/14.1V. Enough to keep the per-cell voltage above the 3.4V needed for balancing, but not high enough that the highest cell would hit 3.65V and cut out. Left it that way for 24 hours as (effectively) the balancer board kept balancing as the supply kept it topped up. Now, it's all nicely balanced, and I disconnected the balancer board and haven't needed it since.
Hallo: Dank deiner Videos habe ich mich inspirieren lassen auch eine LiFePo4 Batterie zu bauen! 8 Zellen 280AH! Genau dieses Thema hat mich auch zum nachdenken gebracht! Ich werde probieren die Obergrenze der Spannung auf 3.65 im BMS zu stellen und den Laderegler die Erhaltungsladung und Normale Max Ladungsspannung auf 3.4 x 8 zu stellen! Dabei sollten sich die Zellen ausbalancieren können solange der Unterschied der Zellen nicht 0,25V überschreiten! Schöne Grüße aus Österreich!
THANKS! From Dallas Texas!
Thanks for watching!
Interesting video. Thanks!
It is a good thing that 2 amp active balancing is built into BMS's now which solves these problems.. Battery construction has also improved..
Thank you sooooo much for a link to the app that actually works on my phone :)
Glad it helped, Michael!
Thank you very much for this crucial info :):):)
Good morning and good job
Thank you so much
Hi Andy! I am a novice at all this. But from my research on the internet this is what I have come up with. It is good to do an initial top balance at a very high voltage such as 3.65 per cell. A charge to this voltage will bring the cell to about 95% of its capacity. Even though you don't want your daily usage to go more than 80% as you have said. This is the way to get them balanced in the beginning. Some commenters have said that wants you achieve this initial balance they should stay in pretty close balance afterwards.
Because of the flat voltage curve you will never be able to get them balanced if you're only going to 3.5 volts.
What do you think? Maybe you could give it a try. Thanks for your videos. I appreciate all your hard work.
If the bus bar contacts are not good, the BMS will never get an accurate cell voltage reading which leads to unbalanced cells.
Oh you are killing me with weather in Australia! ;) great deal on free solar panels!!! i got most of my 18650s for free... i think that your bms is good one, but it should need more balance current like 0.5ma or 1amp ;) i will try to order bluetooth bms for my 18650s. Good luck and have fun! stay healthy and wealthy ;)
Great video! I'm a believer too! Sometimes, I feel like a solar monkey... Thanks for sharing all your trials and tribulations. The experiences and the data - all very helpful. I downloaded the newest XiaoXiang app - Thanks! The Play store only has 1014. Battery balancing is indeed a daunting task. I'm still looking for the sweet-spot where it can all run unmanned. I only have 8 cells in a 2P, 4S, 12V configuration.
Thanks for sharing, Peter. I will probably only charge to 3.35V eventually to stay save and don't charge the cells too high. The balancing and testing takes a long time but that's where I learn the most.
Jeez, you'd think someone named Peter would know it's spelled Monkee. 😜
Just don't over-Tork your bolts!
Great Videos . I took my cc/CV boost converter and set it for the highest cell then charged the lower cells to match , I'm hopping this will work I think there staying on it long enough to get a saturation but then there's the last cell we matched to and don't no where it was in its charge cycle however this seams to work for me until something better comes along .
Great work Dude, thanks.
Yeah yeah rub it in rub it in! :) You have nice weather and we have snow and cold. Really felt that intro :P
Glad you liked it!! 😁
I did. Btw Andy could you perhaps consider getting a po box that we can send stuff to. I was thinking sending some diffrent dc fuses you could test/dissassemble or just send some random stuff.
Anyways really enjoy your channel and your personality. Best regards from northern Sweden.
Why not set float voltage to be the same as the absorption voltage? This will allow the BMS to continuously balance cells as well as allow solar to supply any loads without having to cycle back to bulk and absorption mode again
Yes,, that is how it have to be for grid connected batteries.
Hello. yes, the same here.
Yes, set Absorption = Float. It will be in the next video!
@@OffGridGarageAustralia yeaHHHH waiting for this Video from Spain and ready to get all hardware to copy your experience! we have a lot of sunny days as well in this country.
No, never do this (see my detailed answer elsewhere). Batteries are not capacitors, even if the amps are reading zero there are going to be eddy currents at the potential wall and overcharging above it if the charge controller is left in that state. Setting the float high enough to actually get the BMS to top-balance the cells is also high enough to overcharge the battery or greatly reduce its cycle life.
You want the charge controller to charge the battery high enough for the BMS to be able to top-balance it (e.g. bulk/absorp target minimum 3.45V/cell. 3.5V/cell is better with the absorption time set to 0), and then for both the charge controller and the BMS to both stop messing with the battery until the next charge cycle (e.g. float setting should be no higher than 3.35V or so).
-Matt
Hi, Andy! Great stuff your video, very helpfful. Im not from a technical background, so your video and your drawing as to bulk- , absorption- and float loading made things very clear to me. Thanks a lot for it.
Could you or somebody else from the community please supply the three German terms for me that go with the above mentioned types of loading.
Greetings from Germany and thanks foran entertaining and instructing video.
Dietmar
Thats the knowhow video i was looking for
Great. Absorption time and current varies a lot and depend on many factors. It's all discovered and documented here on the channel.
One thing that may be happening with your cells since some are newer than others is the potential for some variation between manufacturing batches. Another thing I have noticed with my smaller cylindrical LiFePO4 cells that are all new and from the same batch is that they seem to have a wake-up period of a few cycles after being stored for a while (1-3 months) where they don't pull full capacity and then after being cycled a few times they come back. Not sure why that happens but it seems to be a thing. I wonder if since those batteries have such a large internal surface area, it just takes a long time for them to fully saturate.
I have an active balancer on my pack that will balance at 2 amps so I set the float to happen around 2 amps so that the batteries are allowed to balance. I have the balance voltage of the BMS set to 10mv below the setting of the active balancer. When they were out of balance at the beginning I would see balancing happening on the active balancer during bulk and float but now they are usually all fairly well balanced during the absorption stage so the active balancer only comes on when the BMS isn't able to balance which is now fairly rare.
Very true, think of it as if you were filling a drum with foam peanuts. Once full, you tap it a few times more electron settle themselves, and you add more til your full. A good balancer will do this an as you say it takes a few cycles to reach steady state.
Interesting comments. Thanks!
9-12 in of snow yesterday. Had to shovel for the first time this season. More Monday, but may warm up well above freezing enough to melt it down, at least enough to clear the roads.
I cannot imagine this any more, we have pure sunshine all year around.
The full charge voltage is a steep curve, even very slight cell variations will show quite big voltage differences. The remaining capacity of the cells at this point is very small , therefore dont worry about it. When the battery is in a low state of charge, the difference becomes more important as this is more related to differences in cell capacity. I use cells in series parallel to allow cells to be mixed and matched to equalise capacity. Its very easy to over think this, Lifepos really arent all that fussy in real life.
Ich glaub ich werde dein größter Fan!
Great videos! 👍😊 you are the #wernerherzog of off grid power systems!!
I'm enjoying your tech. advice vids from the sometimes sunny west coast of BC Canada, keep up the good work!
Those little DC to DC buck chargers are ideal to charging your batteries and with individual power supplies, they will do your balancing too, after they have been set-up.
having easily replaceable cells after identifying “bad ones” would be a plus
16:16 LOL! :D That video editing is so hilarious! :D
Great info!
Thanks for watching!
very informative thanx.
Thank you.
I had the same problem with my 12v lifep04 battery installed a 5a active balance board. That's sorted the problem took couple of days but it got the job done. The board was like £10 from AliExpress
To me it makes since to charge into the upper voltage peak to get out of the flare zone to know all your batteries have absorbed the bulk of there capacity. It also seems that it’s much easier to balance in that upper voltage peak since it drops quickly to the flat region so quickly. Maybe if you raise charge voltage per cell to 3.45 or 3.5 that will allow the batteries lagging behind time to catch-up in bulk mode and give the BMS a little more room to work. The trick as you have shown, at least on the first go, is that it’s a little tricky to get them balanced at first but maybe this will allow them to stay more balanced. I am learning with you and am waiting for my batteries to arrive, so thank you for all your hard work and then sharing it!! I am also considering using solid copper bars between the batteries, 5mm X 19mm X necessary length.
Thanks for your feedback and kind words.
I was thinking the same at the beginning and hence I chose to charge to 3.4V as this is already in the steeper area of the curve. But yeah, you're right the higher you go the steeper it gets. The problem is that if you have a lot of solar coming in at this point of time it quickly gets out of control as these cells charge very quickly and go over 3.6V in no time. The charge Controller keeps charging as it only sees the overall voltage but not individual cells. I had this twice now and decided to lower the voltage for that reason. There is still a lot to consider and no right or wrong... just a different :) And that's what I'm doing right now, trying different settings and see what consequences they have.
Thank you for the additional information, this is great stuff! I am looking forward to more videos! Keep up the great work!
The BMS will handle any over-charge conditions on individual cells, regardless of what the charge controller is trying to do. But even without a BMS, LiFePO4 cells can tolerate up to 4.2V before the electrolyte starts getting damaged. Nobody ever charges cells above 3.65V so there is actually quite a bit of wiggle room there. You still want a BMS, though, to ensure that no cell is over-volted into damaging territory.
If you are finding individual cells going that far out of balance while all the other cells are perfectly fine, then you have mismatched cells and you need to replace the ones that are going out of balance with new cells. Yes, this does mean that now your new cells will not pop-up as much as the older cells (due to less capacity in the older cells), but that's fine if the older cells represent most of your battery bank. It won't hurt anything and it means you can keep using the battery pack without having to wholesale replace it. Its an economic decision... do you replace the whole thing, or do you replace one or two cells? If the number of cells you'd have to replace gets too high, then you replace the whole thing.
You still absolutely need a BMS for the short protection, low voltage protection, high voltage protection, and to prevent a meltdown if an individual cell goes too far out of spec.
-Matt
Thanks for the video. It all helps :-)
You say that 0.2A balancing current makes "no difference" when they are charging at 18A. That's not quite right.
It won't happen quickly, but over a period of days, some cells would be charging at (example) 18A while others charge at 17.8A and so the balance will slowly improve, all time charging is being balanced.
You may think so, but the practice shows, it is not balancing at all. The 0.2A difference are not enough for high capacity cells.
Maybe if you have a 5Ah battery, this will work over weeks but with the large 100Ah or 280Ah, it does not work at all. For these cells, an active balancer is needed which is being turned on at the right time (or better voltage).
i like learning about the batteries we have AGMS for now but they are not working out for us so we been looking for batter batteries thank for sharing Ryan at midnite solar he good on battery,s
The way they do this at the factory seems to be: Balance to 3.4V, wait for current to drop to insignificant. Balance to 3.5V, wait for current to drop to insignificant. Balance to 3.6-3.65V, wait for current...... . For normal charging later no need to go over 3.5V/cell.
I probably only charge to 3.35V and call it, let them absorb at this stage. This is already over 95% of capacity. Everything higher just stresses me ;)
@@OffGridGarageAustralia Even charging to 3.65 volts, the cells will last well over 4000 cycles to 80% of their original capacity, which is 11 years if you fully discharge to 2.5 volts and charge them back to full every single day. Even then, after 11 years of fully discharging every single day, you still have 80% of the capacity left! You shouldn't be so afraid to charge the batteries to 90 or 95 percent. You will still get 15-20 years of service out of this pack, no problem. In 15 years, I'm sure there will be much better cells you will want to try and they also will be much cheaper to buy at that point. 10 years ago, these cells were $1000 per kwh. Now, you can get cells for close to $100 per kwh. In 10 more years, these cells might be $10 to $20 per kwh. So, don't be so afraid to charge them to 3.5v or so. Its really not going to do very much harm as far as lifespan or capacity over time.
@@catch22frubert yeah, that is probably correct...
What catch22 said. Its not so much how high you charge the cells to as it is how long you hold that high voltage after you have reached it. But yes, the typical charge profile is to charge up to a specific voltage and then immediately stop (absorption time set to 0). Typical voltage targets are 3.45V, 3.50V, 3.55V, or 3.60V (corresponds to 13.8V, 14.0V, 14.2V, or 14.4V for a 4-cell 12V battery). You can go up to 3.65V but there really should be no need. It won't change much other than stress the battery more (though not all that much, really). And the battery will still not be charged above 90%. However, if you charge up to 3.60V or 3.65V and then HOLD that voltage for a time (i.e. non-zero Absorption time setting)... that is what gets the battery all the way to 100% and that is what starts to seriously degrade its cycle life.
And, in fact, holding any voltage above the potential wall can get the battery to nearly 100%, it just might take a long time... as well as overcharge it, or cause other problems due to sloshing currents in the chemistry, which is why the Float should always be set below the low voltage side of the potential wall, never in the wall or above the wall. The low side of the wall is around 3.4V so the float should be below 3.4V (i.e. 3.2V-3.35V. 3.3V is fairly typical).
If you set the float higher than 3.4V you are effectively overcharging the battery by causing the charge controller to constantly go into bulk mode when the battery is ALREADY in a well-charged state, causing the effective charge state to cycle higher and higher. Both the float voltage and the bulk cycling will reduce the cycle life of the battery. You don't want either.
-Matt
For top balancing, I get mine up to 3.7V individually with a RC Charger and then I activate diybms and get them down to 3.55V to have them perfectly top balanced. I made all the experience you've made and it took weeks... :-(. And I fully agree, it doesn't make sense to run cells over 3.35V. There is next to no more capacity and it shows imbalance drastically... even with 800mA balancing current of diybms on my 48V 240Ah you can't manage it.
But no active balancer necessary!
Having -5°C here in Vienna, my PV made 24 kWh today :-)
Thanks for the info. Weeks, eh.....? OK, I just had my first week of head-scratching experience. Even I worked with batteries and charge controllers before, it's so different. I probably let the cells absorb at 3.35 and call it. Everything above makes me nervous.
Gruesse nach Wien!
This is what I have been saying in my comments to you for a while. You need to take the charge up to 3.5v but balance from 3.4 each charge to keep pack in balance. These cheaper cells need a fair amount of balancing. My BMS high volt cut off is 3.6
JD: Wait…what? Are you trying to take credit for that which has been common knowledge for a decade or more and revisited in this video? BTW…your voltages are a bit off, your BMS knows better. Just let it do its job after you top balance when new (and occasionally thereafter if you so desire). Also stating the obvious concerning “cheap cell” balancing issues seems a bit presumptuous from where I sit. Just enjoy the videos and absorb the wisdom.
You're getting so good at these videos!
It's very accurate what you mentioned about every system being individual too. It's the reason I get frustrated at "kits" being sold online with the expectation that you connect A-B C-D etc,and it works, when it's much more detailed than that, at least to get good solid performance, that lasts like it should.
I reviewed a battery kit from a local supplier last week, and found that it was quite easy to balance the cells by leaving the (Lab Power Supply) charger connected overnight with the current limited to a bit under 100mA. The balancer took care of soaking up the excess power to the high cells. The same goes with my Daly, however I have balancing enabled throughout the entire charge procesas, all the way from 3.0v. It's a Hare and Tortoise type scenario, slow and steady is nearly always best.
You cannot build such a battery from a kit without understanding and testing it afterwards.
If you have low capacity cells this method may work but with these 280Ah cells, there is no way the BMS will balance them unless the charger is off and they are already on a high SoC and in the steep part of the curve.
I have learnt a lot about solar batteries from your videos. Im building a 8s , 3,2x120Ahs, 24volt system: The BMS I could lay my hands on is PWOD LiFe Po4 8S 24v BMS. Im kind of lost as I donot know if I can get purformance data from this BMS. Is it worth anything or I should just forget and get a different BMS brand?
god bless brother keep up the great videos iim learning alout thank you
I appreciate that
Another awesome video Andy! keep them coming. I have a great business name for all of your YT channels combined - Green Frog Productions! : ) I have learned so much over the past couple of years playing around with these Lifepo4 batteries. My build is coming along and I should be within a couple of weeks of commissioning my system. I'm on the DIY solar site as DanF if you want to follow my build... Hey, stop rubbing in that awesome sunshine and weather over there! you are making me jealous.. lol Keep up the great work on your system, I get frustrated as well, but it is soooo addicting! Enjoy!
Thank you so much, Dan. I run the business under unpluggedEV.Media at the moment, but the frog thingy is getting bigger with each video 😁 A nuisance at the beginning while making videos, it's now a real mascot 🐸
I'll have a look in the forum... thanks for sharing.
I have a very simple 4 bar led voltage meter on every parallel cell group. This gives me a rough indication of soc. The way the individual meters behave in relation to each other also gives me a rough idea of state of balance. When the cell voltage is at a point of turning off one of the led bars, at that time I can see how long it takes others to follow suit. The longer the difference between meter states, in relation to each other, the bigger the imbalance. They all light/turn off in unison when well balanced.
4 LEDs to show a very flat voltage curve of LFP?
There is always one cell that is lowest and one that is highest :)
God bless you man.....
It's important to test your bms Ballance leads. My bank swung out of balance because of one lead lacking continuity, causing a BMS to shutdown. Had to top Ballance to clear the imbalance.
Just curious, you mentioned previously about a “all in one” unit, charge controller/inverter, would that take care of cell balancing, or would a BMS still be required? Great videos.
Dick, I have an MPP SOLAR LV5048 all-in-one and it provides a TRANSFER SWITCH/BATTERY CHARGER/INVERTER/MPPT CHARGE CONTROLLER in a single package. It's a fantasitc piece of hardware and has been trouble free for over 9 months providing emergency power in my pumphouse.
As far as I know none of the all-in-one's has a full BMS talking to each of the cells in the battery. But they do offer some of the features of a BMS including:
1. Charge rate (maximum current) into the batteries
2. Maximum allowed voltage into the batteries to prevent overcharging
3. Low voltage disconnect to prevent exceeding the low voltage limit of the batteries
Hope that helps. If you need more info just ask.
Yeah, the all in one units are great and I can recommend them highly.
As AI6MK said, you still need to build your battery with BMS but everything else is been taken care of with these units. I probably will get one for testing purposes.
This is one of the limitations when all the components in the charge path are from different suppliers. While they all kind of work they are doing this in isolation. The other issue I have with your system is that having loads connected to the inverter will mess with the charge profiles and balancing. As I said earlier I have a MPP-Pip5048GK and 3 modules of Pylontech lithium battery packs. Each pack is 78 amp hours at 48 volt nominal (16 cells) and each pack has its own BMS. Overall the battery BMS talks to the Pip 5048GK charge controller via RS485 and adjust the charge profile independently for each pack as well as the inverter output requirement. So battery charging is completely separated from inverter power output. So the charge settings I have cannot be change as they are set by the battery pack BMS and are as follows. Float voltage 53.2 volts. Bulk charge voltage 53.2 volts. Battery cutoff voltage is 47 volts. In my system the maximum charge current is 80amps. Hope this helps.
Sorry if I'm confused. But did you come to a final result about how to get these batteries even and all charged up? Is there a summary what to do? I have pretty much the exact same setup as you as far as batteries go I just need to get the other stuff. Looks like BMS is first to be safe. Then Charge Controller and panels. Just finishing assembling a cc, cv, 12A 60V power supply, so geting ready to finally unbox and charge them. In Southern California I will get (a bunch of) PV and an MPPT SCC for PV charging. But I've heard initial charging can avoid many of the issues with them (dis)charging at different rates. I've heard a lot about voltage charging first and then amperage charging at the end. Also some info about letting them rest and then topping them off. So.. did you finally come up with a process for yours or does it change a lot depending on the Sun or what? Love your videos love your attitude thanks for the info.
Thanks Steve. You probably hear and read a lot about this stuff. So, the common sense in this is to top balance the cells before building the battery. All in parallel and slow charge to 3.6V, then let them sit until the current goes to almost 0.
Yes mate you are on your way to be the best BMS, absorption needs time.
for me i do not go for the amps but for the volts for 500 volt that is meaning
10 units from 50 A x 50 V that is a total from 160 cells in serie here a BMS is not working.
they are there but then you have to go for a EV BMS.
YEP!!! a foot+ of snow on the solar panels here!!!
Wow! Stay warm and get this snow off the panels!
In order to top balance you need to be charging at no more than 200ma. So that the balancing circuit can eliminate charging on the highest voltage cell(s) while allowing the rest to charge. With 280AH cells the balancing will take forever.
Hello andy, i've been watching this episode twice, and thats great info, hopefully next video is charging with discharging, lets find out how the scc and bms work during charge/discharge..
My concern on that above seen, if you set abs - 54.4v and float to 54v, means you didn't maximize the whole capacity of battery. Because the top voltage of 16s lifepo4 cell is 57.6 if 3.60v every cell, which is the voltage that reach 100% capacity of the cell. We all know that kind of battery is very sensitive in oc/ uv but since you discuss that topic lets find out what is the stable settings on how to caring that lifepo4 prismatic cell battery,
Thanks 😊😊
Thanks for the comment (and watching it twice).
The purpose it to NOT use the full capacity of the cells. I would rather charge to ~85% only if I exactly knew that point yet. From what I observed, everything above 3.35V is not worth charging as there is very little capacity gained.
I may be jinxing you lol. I seem to run into the same issues as you about a week prior. My SCC and battery charger would not charge to 100%. Turns out it was unbalanced cells. I charged each cell individually to 100% and now it works fine.
However, I don’t know how the cells became unbalanced because they were top balanced and capacity tested prior to use. I look forward to your troubleshooting so I don’t have to 😆
Hahaha, thanks for your feedback. Glad I'm not alone 😁