Floating at 70%. Why charging LiFePO4 to 3.4V is not enough!
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- เผยแพร่เมื่อ 6 ก.ย. 2021
- I lowered the settings in my solar charge controllers to 3.4V absorption voltage. This did not quite work yesterday but I will try again today to exactly find out what is actually happening at this point and why it is not working. Voltage too low? Amps to high? Both?
Let's find out!
Testing the difference of charging to 3.4V and 3.5V with and without Absorption. • Charging LiFePo4 (LFP)...
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I no longer watch TV, I just wait in anticipation for the next video, seriously, I like this guy his way at looking at problems and his working them out coupled with his happiness all the time, makes for great videos
Thank you so much!
Same sentiment here.
Nothing better than seeing a happy enthusiast presenter share their passion. No matter what it is, but even better when it relates to your own interests.
Me too. I watch Andys channel at EVERY OPPORTUNIY!
I wasn't sure which way to go when I decided to upgrade my solar system until I found Andy and these videos. It is so helpful to watch this gentleman go through the various intricacies of those prismatic batteries. Andy, you definitely inspired me to go further and faster than I would have without you. I enjoy your attitude when you go further just to see what happens. I believe you have inspired many around the world to endeavor to build solar systems.
Adventrue Kings batteries quote in their specs for their 120AH LFP: "... The BMS will also perform cell balancing at 3.5V per cell with 35mA of current... ".
What this means, is that a min of 14v is necessary for battery balancing to occur. These LFP batteries should be charged to 14.2v, and held at 14.2 volts for a minimum of 30mins, (a balancing time of 2hrs is specified by another manufacturer) to give the abalancing circuit time to do the balancing task.
At the lower voltages some youtube comments advocate, the balancing circuit will not function. Balancing is always done at the end of the charge. And no, you do not have to balance charge every time. Charging to >14.2v , and holding that voltage for 30 to 120 mins, every 3 to 5 charges should be enough to keep your 4 cell LFP battery balanced.
At 14.2v, you can watch the balancing currrent operate, with the current slowly falling from, eg, 200ma to 50ma over an hour.
I think it's important to remember that in this scenario your setting isn't really "3.4v" it's actually 54.4v and more importantly: the problem isn't the 3.4v value. It's how you're measuring it. If you're relying on the shunt reading 54.4v you have to remember that is the voltage at the shunt with the resistance of the shunt itself and the internal resistance of the cells. If current is flowing into the battery the voltage at the shunt will read artificially high due to resistance of the cells as well as resistance of the shunt itself and any wiring between the shunt and the battery. If you're pushing 55 amps into the battery and the shunt reads 54.4v, you're not *really* at 3.4v per cell. If you were to disconnect the charger the voltage would *instantly* drop by close to 0.1v per cell because it would no longer be pushed high from the internal resistance. The internal resistance of LFP increases as the cells increase in voltage as well, so the artificially high reading gets even higher the closer you get to 100% SoC.
On my pack 60 amps of charge current at a high SoC results in a cell reading 3.40v when the actual resting voltage would read closer to 3.30v due to IR. So you're going into absorption when the cells are still only at 3.30v. This is why you cannot rely on the voltage reading at the shunt to determine when to switch to absorb/float. On my Orion BMS it actually reports two voltages for each cell: 1.) Actual measured voltage and 2.) "Open cell voltage". Open cell voltage is the calculated voltage of the "open cell", meaning if you disconnected all loads and chargers, what would the voltage of the cell be? It calculates this by watching how the voltage changes as current increases and decreases and it calculates the internal resistance of each cell to come up with this "open cell voltage". So when it's making decisions about when to cut off charging or to cut off loads, it uses the open cell voltage rather than the actual measured voltage.
This inaccurate reading gets worse as you add solar. At 120 amps, for example, a 3.3v cell would read closer to 3.5v. So setting a higher absorption voltage will work for now, but as you add solar you'd have to keep increasing it.
The better way to solve this, in the absence of a BMS that gives you this "open cell voltage", requires that you either: 1.) Set a fairly long absorb time (remember if the voltage drops the absorb timer starts over) or 2) use the "tail current" setting available in the Victron for absorption so continue absorption until the tail current drops to some very small value to ensure that the battery voltage isn't artificially high due to a large number of amps. Using tail current basically tails the charger to ignore the voltage for the purposes of ending absorption until the current falls to a low enough level that it would no longer be causing an artificially high reading. if the voltage stays at 3.4v/cell *and* the current going into the battery drops low enough, *then* you can safely switch to float.
Another option is to just set both absorb and float at 3.4v/cell. You're not going to hurt your cells at 3.4v even if you kept them there 24/7. And since you're only charging from solar the max you could possibly float at 3.4 is just a few hours every day anyway because as soon as the sun starts to go down you won't be maintaining 3.4v/cell anyway.
This comment answers to so many questions. Thank you very much!
I was wondering about exactly this. I was thinking of using a Constant Current / Constant Voltage power supply to charge LiFePO4 batteries to 3.4V per cell, but was wondering if it would age the batteries to keep them constantly floated at 3.4V.
Tiene sentido porque observando el comportamiento de carga cuando está en 3,4v el equilibrio se mantiene sin embargo cuando voy subiendo a 3,42v y así hasta 3,45v este esta disparando la resistencia interna y produce más diferencia entre celdas
I am not sure if someone answered this yet, but I was explained differently when the solar guy installed my first solar system on my first sailboat, I am explaining it in 48v terms, but my setup was a different voltage. The solar guy explained it this way. Float is your target cell voltage x cell count. So let's say you want 3.4v/each cell, that would make your float voltage 54.4v because that is your desired optimal voltage when your batteries are perfectly balanced. Now you need to figure out your charge cell offset, this is how far apart your cells become throughout a full charge. So in my case, the guy set absorption voltage to 54.4v and hooked a load up and discharged my cells to low cut, then he used a charger to charge the battery to full 54.4v. Then with the default 2hr absorption period, we viewed the BMS and noted the cell difference as soon as it went into absorption mode and he timed how long it took the BMS to balance the cells within 0.01v. The cell difference going into absorption is your charge cell offset and the length of time it took the battery bank to balance to within 0.01v during the charger pause period is what we use to adjust the settings. So let's give an example, on the flip from bulk to absorption mode you saw a 0.075v cell difference between your cells because they are poorly matched... well now we would adjust your absorption voltage to Float Voltage (54.4v) + Charge Cell Offset (0.075v) = 54.457 ~ rounded to 54.46v, so this new 54.46v would be your Absorption corrected voltage. In regards to absorption time, this is how long it took your battery BMS to complete the balance, so in regards to my BMS it was only 4 minutes to complete a balance. So the settings would be adjusted as follows based on this scenario: Absorption 54.46v, Absorption Time 0hr:04min, and Float 54.4v. Regarding the bulk voltage offset restart, the guy told me to turn on all my typical constant loads that are expected to be on every single day ex.. frig... and then compare the voltage of your battery bank for a minimum of 1 minute, so if your bank drops less than 0.1v, set it to 0.1v, if it drops to let's say 0.4v after a minute, set it to that.. otherwise, the controller will attempt to maintain the batteries to the float voltage at a lower charge current as needed. The whole point of the absorption cycle is mainly to balance the cells from charging up because they can't balance properly within float mode since the BMS uses voltage bleed for balancing. also.. you need to set your BMS balance start voltage as the FLOAT voltage.
This right here sounds like a great approach. 👍👍
@@firpofutbol I agree!
In just 2 days you have taught me a huge amount about so many things I needed to know to stay up with the times… and the times ,they are a changing ….fast.……Thank you, Jim….in NC ..USA .
Thanks a lot Jim. I had all these questions about the batteries and charging as well and could not find reliable information online. So I started making my own tests and I'm very happy that I can share all this knowledge here on the channel.
I have learned so much from watching your videos. My off grid system performs better based on changes I made from your testing. Thanks so much.
Thank you very much!, Tim!
Thank you Andy!
it's always a pleasure to watch your videos, thank you for your work
Thank you very much!
I learn something new from each video and love your enthusiasm for the subject
Thank you very much, Mark.
The detailed testing and sharing is impressive!!!
Thank you very much!
Il est 23 h et je me régale de ces informations : merci
Continuez.
From France
Every time I watch it load my brain with new information a lot learning from u thanks.
Thank you very much!
I am watching this with great interest Andy. I have a 48 volt LIFEPO4 battery pack in my camper and attempting to optimize charging. I have 1kW of solar installed and have been fighting battery cell balance problems. Keep it up and I will get my system improved also. THANK YOU!!!
Thank you Dave. What I have done so far is a top balancing at 3.65V and then turned off all balancers. I then set the charge voltage to 3.45V (55.2 for 16s) in the solar controllers. So far this works great. I have set the balance voltage to 3.6V in the BMS just in case something goes out of whack.
I guess, the initial top balancing is very important (not that this is surprising or new).
To David Zelkowski Do your bus bars fit properly? I had an odd cell out of balance, but fitting some longer, Heavy Duty bus bars mostly fixed it. The cell still goes high, occasionally, at high state of charge, higher voltage than the level I top balanced to. At that level they maintain near perfect balance. The 200mA BMS balancer kicks in if higher voltage, and sorts it out.
@@michaelbouckley4455 My packs are built from reclaimed 26650 cylindrical cells. They are spot welded together with nickel strips so I don't have any buss bars. I do use a 100 amp bms and am able to monitor each parallel string of cells through bluetooth app. The same app Andy is using.
I don't think anyone is as thorough in going through these ideas and theories. Only been watching you for a few months but I've gone a long ways back and got caught up. Excellent content. And Andy it's appreciated
Thank you very much!
U r great,i like to watch your video every time in detail sir
Thanks Andy
I agree it is good to explore the train of thoughts and see how things work in action even if there is a high chance it wont work its good to see how and why to better understand it.
Thank you.
Fantastic test mate. Keep the videos coming
I will, thank you.
Very interesting Andy! All very useful info thanks!
My pleasure! Thanks.
Thank you so much for the energy and passion that you put in these amazing videos, i'm new to diy with raw cells and i wonder if u find that Eve cells + Victron MPPT solar charger setup is a good combo with both Jk and Daly bms, which one of the two is more reliable for my configuration? thanks again
Thank for your feedback and comment.
I found the Victron solar charge controllers, the EVE LiFePO4 cells and the JK-BMS to be a very good combination. It all works well and reliable together.
The Amiable Andy :) Looks like you have had a lot of fun learning over the past year or so, and sooooo much learned and shared :) Thanks Dude :) Oh the glory of the minutiea :)
Loving the way Andy makes a mockery of the notion that "suppliers know best" with practical examples of where the theory does not meet reality. There is clearly something wrong with bulk/float charging LifePO cells with what is pretty much a voltage based Lead Acid "algorithm". Not that I know what a better algorithm would be - but your experiments are a fantastic way to find out! Keep the things-work-different-in-real-life science coming please!
Thank you very much, Rudie!
Take your time Andy! It is very true and I try my best to keep up in comments as well! Speaking as a content creator as well, I understand the struggle and you can only do what you can do and we understand it's a lot of work :).
Don't over stress! :) take care!
Thank you. It is part of the process to be present in the comments I firmly believe. At least as often as possible 😊
And now everyone changes their settings :)
What i do on my system is read shunt SOC via the raspberry and turn on or off the chargers via a script.
The script also can check the power usage and start the chargers if consumption or SOC is over/under a preset value.
Once every 20-30 days i do a full charge to 3.5/cell to calibrate the shunt and balance.
I did the script in one day after reading the victron VE datasheets, i'm not a programmer but the _frog_ works, don't have to worry anymore about the SOC.
That is indeed a very clever solution! Do you change the charge voltage every 20-30 days to 3.5V manually or is this a script as well?
@@OffGridGarageAustralia That is exactly what i have, i just have 3.5V all time, but stops charging once smartshunt hits 90%.. Then once a week i allow to charge to 100% just to calibrate smart-shunt. But anyway Andy - you are the only youtuber i found who is doing solar/battery science and sharing it. Because what else it is when doing all by try and error? And you really speed up our progress! It is awesome that i do not have to do all the tests because you did them and share them! Great work indeed!
@@OffGridGarageAustralia at the moment i do it manually but it can be scheduled and done automatically.
The charge voltage is always set to 3.5V
I need a 48V LiFePo4 for my sail boat. Motor draws 100A, capacity should be 5-10kWh. One large battery would be to heavy to lift. 4x12V in series would need to be balanced between. Is 2x48V to 4x 48V in parallel a viable solution?
Or would it be best to place single cells into those old 4x AGM compartment and wire them to one fat central BMS and active balancer?
Or do all cells need to be close to the BMS or need equally long balance cables?
What would be your advice?
Before i had 4x260Ah AGMs with 56kg each.
11:25 Victron’s GUI is very colorful!
haha me and my kids watch these videos. i have 2 years old when i interrupt his cartoon he gets pissed and goes away. as soon as he hears the opening music he comes back rushing. no joke this is hilarious, we need more equipment tests and stuff man
Hahaha, that is hilarious!
More test are coming!
Iam really a Fan of you Andy! Why not selling your Offgrid-Garage Shirts, i would buy two of them!😃
Thank you brother for the very informative experiment But when I see problem of multi cell batteries then i think led acid batteries still easy to maintain
On my boat I want to be 95% full at sunset with top balanced mismatched cells. I have found 3.45vpc on absorb, float and bulk is simple and works well. My batteries stay balanced with 3.45 top charge rate and I don’t trust my bms to do the balancing and the bms requires a higher riskier SOC that I want to avoid. Better to just buy more cells than to risk/complicate my life for 5% SOC.
That's a very good point, Danny! I agree, if you need more capacity, get a second battery. There is no capacity gain of charging higher. 3.45V is ~99.3%SOC.
And this is why I'm building a 'supervisor' system on mine which reads the actual state of charge from the shunt and uses this to control the charge controllers.
That's great, you building your own? How do you calibrate the shunt?
@@OffGridGarageAustralia Yes, building my own supervisor system, based on a RPi for now. The shunt is a high precision (+/-1% accuracy) one with an RS485 interface. All the other stuff like the inverter, solar charge controller, and BMS have an RS485 interface and this is already used to log and graph the data, so this will just be the logical next step: make active decisions based on the state of the entire system, and even learned usage patterns. Calibration is just like you would do during a top balance: watch the current go down at 3.6, and then it's full. Since the supervisor has complete overview and control of the state of the system, it can calibrate this shunt automatically, in case it drifts over time.
@@upnorthandpersonal I'm doing same but once a week i'm going to let it charge to 100% and have smartshunt re-calibrated. How are you changing absorbtion voltage on MPPT by RPi? I'm using just SoC from smartshunt to keep battery to 80-90% by disabling MPPT which is programmed to 3.5V and i set smart shut to 3.49V and tail current 1%. MPPT have option to reprogram ve.direct port to enable/disable charging :) that is a nice feature. So on my tiny control "PC" i'm operating relay which disables/enables charging on ve.direct port of MPPT. Now i'm working on keeping battery on bulk full time, but to keep it around 75% i wil connect heater/boiler once SoC hit 80% and disconnecting it when it hit 70%.
@@upnorthandpersonal Wow, that sounds like a fantastic and very interesting project. Keep us in the loop.
@@upnorthandpersonal Yes keep us informed for sure! I got lazy and just bought a solution. 😊
Hey Andy, why you work only with the timeout timer in absorbtion state. I mean in the SOC view the current cut-off during absorbtion is essential. The timeout timer is only a second condition to exit the absorbtion state and go further to floating state if you never hit the cut-off current. So as you know, to say 3.4V meets 99% or something is fussy because voltage alone is a very inaccurate indicator for SOC of a LFP battery.
My settings are bulk until 3.55V, then absorbtion until current drops 1A or 2 hours timeout, then floating at 3.3V with re-bulk if voltage drops under 3.2V
Is it possible to show bench test charging times at different voltages - 3.4, 3.45, 3.5, 3.55, 3.6,.3.65, I know you have done the first 3 and the charge time was around 4 or 5 hours with decreasing absorbtion - the graphical representation was superb. It helps massively to get your head around LIFEPO4 :D
QUESTION? Is it bad for the inverter to run close to your max DC input? Say my inverter is 64v max and my 18 cells comes to 63v at 3.5v each. Thanks in advance. Anythi g you coukd tell me woukd be appriciated.
You don't need to auto-shut off your charging. Just set the max A & V limits & the batts will not overcharge.
So, for example, if you charge to 3.45 V/cell, your system will only charge up to that V limit & your batt will never overcharge because it is well below 3.65 V/cell. There's no need to absorb or float--the cells won't charge above your V limit.
I like your passion in learning solar.
I feel the same. Right now I just need to understand your terminology.
Can you or someone help me with this?
What is Epever terminology for
Absorption?
Bulk?
Float?
I am sure they all are similar but this all new for me. Thanks 😊.
Andy the "MPP-Tracking System" for battery charge settings.
"First I am going to try 3.4V, Then 3.45V, then 3.50 Volts, I think 3.65V is far too high, lets try a lower voltage and adjust the absorbtion time..." just like the MMP tracking systems, searching for the optimal settings.
Great Work Andy, I too always question 'why' when presented with 'conventional settings'. In many industries we see 'this is the way we do it' statements, only later to find the reasons for those methods have changed over time, but no-one bothered to ask 'are these still the best/most appropriate approach, or was this just the best at some time in the past?
With LiFePO4 batteries we see this type of 'old thinking' with the float settings, that was needed for Lead-acid batteries, but serves no purpose with LiFePO4 since the way these batteries perform is completely different.
Always enjoy your logical approach to answering questions and seeking out answers.
55Amps, nice, that’s just one more reason we live in sunny Qld, ay Andy! Good vid, appreciate ur efforts, we know a lot more goes into ur vids than what we see. Agree with all ur logic here (as usual), & yes we can repeat our lab results as you say, but that is it with solar isn’t it, it is in a constant state of change, but we still need the lab results to better understand the chemistry we are dealing with, & in turn helps us to make a quick tweak here n there to compensate for bad weather , etc. Thanks for all ur insights, this is good info, Cheers
Thanks a lot Evan!
I'm not sure about the accuracy of that shunt reading of ~73% at 3.35v/cell. That should be 90+% if not 95% at 3.4v. Am I missing something? Is your shunt resetting SOC to 100% after bulk?
Yeah, it really depends on the controller, and settings. I have a Genasun boost controller that will only do 3.4v, but I think it recognizes the battery is still absorbing current so it will not go float for quite some time. This seems to get the cells to 90% pretty consistently.
Does this have a fixed absorption time or is it monitoring the current and turns off of under a certain value?
@@OffGridGarageAustralia The Genasun controllers are hard coded from the factory so you cannot change parameters, or see what they are. But I kind of suspect monitoring the current is feedback to it's algorithm. That one is for my solar ebike build. My house solar controller is a epever, I let it charge to 3.45v, and float at 3.375v. They call non-float mode "boost" which is called "bulk" on other controllers. I have it set to "return to bulk" at 3.35v. So that lets it charge, then float, and if a load is placed it will return to bulk so I'm pulling power form the solar.
And this is exactly why you set bulk/abs/float to the same voltage 😎
totally but what would Andy play with.
bulk, abs, float are algorithms developed for lead acid chemistry, NOT LiFePO4 !
But all these settings work perfectly for LiFePO4 as well and gives us so much to play with and learn about.
If you set all to the same value, it would either keep the cells on a high voltage so the balance can work or at a lower voltage and the balance does not work efficiently?
I quite like the idea to go higher for balancing purposes and then drop the voltage afterwards to keep the batteries charged.
@@OffGridGarageAustralia AFAIK there’s no evidence that you (for whatever reason) should not “keep” the cells at “high” voltage, eg 3.5v. A lot of hearsay though. In any case the voltage will drop when the sun goes down 🤓
@@andrewseaman7012 Lifepo4 have much the same charge profile as Lead Acid. Most SCC’s do CC (or max available current from solar) then CV charging. Just don’t need equalising at a higher voltage. I contacted Epever support, who recommend Equalise charging at same voltage as Boost (aka Bulk) for Lifepo4 and then you have 2 time periods to adjust. Also have a Victron Smart 100/20 on different panels. The Epever 60 Amp Tracer6415AN Imax (power station model (takes 25mm2 cable, with excellent terminals, and cable clamps) Software is inferior, but ordered an eLOG01, will get ebox TCP02 for wired Ethernet) cost 1/8 of a 60A Victron! Getting a Raspberry Pi 3B+ and Victron VE Direct cable, and wiring that to Ethernet. Later a Victron Smart Shunt, wired to R.Pi, so I can see the battery current. I find the Bluetooth range is poor, through walls.
I know this is off subject
Have you thought of using the victron EV charger to use excess solar after your batteries have charged
Try setting one of your controllers to stop charging at a lower voltage (3.40) than the other charger (3.50). That way, your charging will “slow down” as your voltage climbs. This will allow you to charge and absorb at the same time since you are charging slower once you enter into the curve.
Yes, that works but I would have to unlink both SCC. They are all in the same Victron BT network with the smart shunt to share all info amongst each other.
@@OffGridGarageAustralia Yea I can see how that can be a problem…. So are you ever going to try a “smart BMS” that integrates into the victron equipment? Just curious…
@@Shep5847 Yes, absolutely. That will be the next step. I'm waiting for some to come in.
Even the one I currently have can be connected. There is a Gridhup project for that. It would also show up in the Victron VRM.
Why have you taken your controllers off the GX and out of “external control”?
why do you use absortion at all for lifepo4? i think just CC and CV is required for LifePO4
You can try to set the rebulk offset voltage closer to the float voltage... i did this with my agm batteries. It´s in the advanced settings.
Yeah, I tested this but again if I charge to 3.45V it is already 99.5%SOC, the voltage then drops to 3.35V for float which is 99.3%. There is no benefit to recharge to 3.45V again at some stage.
Might be different with AGM.
I found that Victron Connect disables the Expert mode, each time you start the software.
I have been watching your channel for a long time and learned a lot from it. I recently purchased a PV installation. 10 panels with enphase inverters. Is it possible to connect an enphase iq7 directly to a LiIon battery pack instead of a solar panel. I want to charge the battery during a surplus of solar energy and use the battery as a buffer when there is a shortage of solar energy, taking into account the limited capacity
The Enphase are micro inverters so they connect to the grid only I believe. I don't think you can connect batteries to the input of these inverters.
If I didn't have a father, I'll choose you 🤣
Thank you sooo much for how you explain everything. So many questions... As many answers 💪
Thank you very much! 😊
My multable acp ups I converted to lifepo4 have a constant float of 13.6 while certainly a safe voltage it is not optimal. It works though if you have infrequent outages. Might try a separate charging module and see if that does not set off a battery alarm from the bms.
Can you not limit the amps to 20A using the Victron charge controller? I noticed in a lifepo4 battery I'm looking to buy they recommend 20A although they said it could handle 60A max. Better to configure solar panels to produce more volts than amps? I heard amps but wondered why Victron had a 150v and 250v 60a models.
Amps are what charges the battery.
MPPT solar charge controllers are converting the higher volts and less amps in lower volts with higher amps.
so 100V and 1A from solar will be
12V and 8.3A
So you charge you battery with 8.3A instead of 1A only in this example.
Hi, I think you should use the tail current mesure to stop absorption instead of a fixed duration.
Yes, that would be another option to fine tune the charging.
thank's
You got, we got to chose a end chargé at a voltage that is in the "arise" area.. Or the system can't detect it.
Nice video
Battery cycles, I finally managed to access the historical data on my 8 Pylontech modules, I have 8 installed between Oct 2018 and Mar 2019. SoH on all 8 modules is 100%, the surprising thing was that the lowest charge cycles was 141 and the highest was 191 with other 6 modules spread between 141 and 191 total cycles. Bank has run 24/7 since install charging to circa 3.55 Volts per cell, 15 cells per module, 400 AH capacity. I'm pretty happy at around 1 cycle per week just nice to actually see this info actually stored in the modules, have you any way to interrogate the total cycles on your bank Andy?
Thanks for sharing. That is indeed interesting. I have the smart shunt keeping a record of all cycles. I probably have two cycles a week at the moment but once the second battery bank is going online, it will half. 141 and 191 are Ah or what unit is that? So 191Ah out of 400Ah?
@@OffGridGarageAustralia Sorry my bad description, the Pylontechs are rated for 4,500 cycles from 100% SoC down to 20% SoC so that's 141 - 191 cycles from the 4,500 cycles when the battery was new in 2018-2019. In other words i've got about 80 years left at the current 1 cycle a week.
Not watched yet, but the title says it all. And you may recall that's what I have, and have mentioned. Its funny, your path and learning is just like mine was - but your proving it where as I just guessed and "played". Lets see if my guess of that is correct :)
And yes, but i also use this as a feature when I'm using 3kw.hr a day but could generate 3x that - so as not to float the battery at a high state of charge + no fear of running out
Hahaha, thanks for commenting before watching 😂
@@OffGridGarageAustralia and same again by lowering your (effective) MPPT voltages with the voltage drop ;)
Can't you set absorb time based on amps going into the batteries? I think Victron calls it "tail current" I charge my lead acids like this and Absorb can be 1 hour if lightly discharged or 4 hours after heavy use (midnite classic charge controller)
Yes, I can set the tail current as well. That would be another setting to play with.
55 Amps...nice weather in Australia!
Hell yeah, we're getting there slowly 😁
Why my battery 25.6v 200ah lifepo4 wont charging under 27.2v,mppt going 28.0 then batery is shutig off and inverter can not working,is it bad mppt or bad battery,battery is old fue days,sorry to my bad riding
Try to use the tail current setting combined with fixed time for absorption. I use for my 600 Ah bank 10 amps at tail current and 30 minutes for absorption time. So when the absorbed current drops below 10 amps for more than 1 minute , the chargers change to float mode. For me this happens after 6-7 minutes after the absorption voltage has been reached, in my case 3.5 volts. For you if you use 3.45 volts it might take a little longer, but using tail current you are sure that the battery has absorbed enough and the same power every time.Moreover, in the battery sheet wrote that the charging cycle must end when the absorbed current drops below 0.05C, in my case it would be 30 amps. But the Victron chargers I use do not support more than 10 amps at tail current setting, so I use 10 amps.
I had a tail current set before but found it's not really necessary. At 3.45V, the cells are 99% full, so I can just call it and stop charging after a very short amount of absorption time. I set the 15min usually to give the smart shunt to calibrate to 100% during that 15min window. That's the only reason.
I think tail current settings make more sense when you charge to lower voltages and the absorption time is a lot longer. This depends then on you charge current, if you charge slow the absorption time is far longer at that voltage and a tail current makes sense.
I'll test.
@@OffGridGarageAustralia I charge up to 3.5 volts with tail current at 10 amps and the duration of the absorption sequence varies between 6 and 10 minutes. So the battery bank(600 Ah) reaches 10 amps in maximum 10 minutes and switch to float, which is ok.
@@mihaitaiosub Thank you, that makes sense. At this high voltage, the absorption does not take long regardless how fast or slow you have charged. It's 99.9% full.
I'll test the tail current with my 3.4V and see how this goes. Setting the absorption time to 2h and a 10A tail current. That should get me close to the same result.
@@OffGridGarageAustralia Those 2 hours will only work if the current in the tail current is not reached. If the current in the tail current is reached, the charger can float at any time before those 2 hours.
@@mihaitaiosub it's that's the point. At such low voltage we don't know how saturated the battery already is. So absorption can be anything.
Absorption should be for multiple hours. Basically until current drops significantly, rather than any set length of time. You will figure it out, I used the EBC-A40L with lots of tweaks and repeated tests to come to this conclusion. Use 3.45v/cell to get a lot of amps in quickly, then switch to 3.4v to get the cell saturated. Once current going in drops to one or two amps, you are around 98% full and can switch to float.
This is what LA batteries actually do. For LiFePO4 chemistry just charge to the max charging voltage and wait for the current to drop. No change of voltage. You're done.
John, I love this thought process. Very logical. Wish Andy would have read this.
fifteen minutes of absorption seemed strange to me when I watched the video.
With 3000 plus cycles to 80% we'll all be dead and buried by the time these batteries are dead. I set mine to full 3.6v and have had no problems. If I had class B batteries then maybe I'd be worried. All my batteries are new. Also, if they were AGM then I'd be worried. They don't last long at a full cycle. Also, I'd definitely be setting to full in the winter months. I can't wait until you connect your home to these and become one of us real offgrid. Cut the cord. That's when the real fun begins. You notice every light, every pump etc. Hyper aware of everything you use. Can't wait to see if you cut it or bottle out of the offgrid lifestyle. It's a big commitment.
Thanks, Lee. I'm working with the electrician to get the house connected. It's a bit complicated because of the other solar I have on my house contracted with a high feed-in tariff. We're getting there...
I remember from one of your videos where you used your battery tester that only going to 3.4 would take hours to completely charge the battery, why did you think 15m was enough? From my tests 15m would be more appropriate as an absorption voltage of 3.5.
It was just another test for the whole pack to see what SOC we will hit every day. It brings the same inconsistent result as with the single cell testing we did previously.
So, either charge a bit higher to 3.45V or set the absorption to ~2h.
gyus, need advice about settings for RV battery - victron dc/dc charger, victron mptt solar, victron IP22 charger 230V and JKbms 200A , can anybody help me with this ?
I came to watch one of your previous videos,, the video about compressing those batteries,, at the end of the video you said you'll not be compressing the batteries since you are going to charge it at 80 percent only,, and here we are,, 80 percent charge is not enough,, now,, will you consider compressing your batteries?
I cant confirm you experience because when I start bigger load, voltage drop below float voltage and start bulk stage
I seem to remember another video on this channel which dealt with this a few months ago...
Yeah, there might be one or two more 😌
maybe try upping the volts by 0.01 or 0.02 at a time to find the sweet spot that works for you.
I could do that but I think 3.45V is perfect and gives me 99%SOC already. Let's see if I need to go higher at some point just for balancing purposes.
I got all this figured out in the last few weeks too!
Looks like you're hitting 3.4v during a peak sun patch & flicking to absorption too early. Watch the voltage changes on a cloudy day - they'll vary by 0.5v quite easily on the charge controller.
Have you calibrated your Victron voltage vs your BMS voltages??? is the Victron V accurate?
I have a similar setup - 1600W panels into a 24v battery, and hit charge currents of 40-60A. So we need minimal absorption - as our charge rate is much lower than 0.5C/1C
I set my Victron 100/50 to 28v absorb (3.5v/cell) & float 27.5v (3.4375v/cell). On the BMS the cells hit absorption between 3.47v & 3.49v - they dont actually hit 3.5v as the Victron voltage reads high!!!
The *MAX* absorb time is set to 15min, in reality its been going for 6-11minutes most days before going to float & the voltage drops right off when in absorption.
Pop your voltage up a bit & check what Victron reads compared to the actual Cells & BMS.
Good luck!
Hi Nate B, just curious, how did you manage to install 1.6kw panel if your scc is only 100volts max?
@@noelbondad7423 hey Noel, 4x390w trina panels, theyre 40v 12A each. so 2 pairs in parallel = 80v 24A max
@@nateb3105 thank you very much. From my calculation: battery 7168wh. Panel harvest 7800wh (5 sun-hour). Wow! I love it.
Or 1920w x 5 sun-hour = 9600 wh harvest. Even better mate.
@@noelbondad7423 yeah that was the old config, have 30kw of battery & 10kw of inverters now :)
Oh no, don’t do this to us! I have already set up all my installations at 55.2V bulk and 53.6 float!
When are you going to start on the battery rack again?
Soon, very soon!
if you turn off the absorption and bulk set the float voltage to that of a fully charged battery here your choice would this then act more like a cc/cv charger
That would make no difference, it would just hold the voltage set as long as enough solar is available. It would charge with this constant voltage and the current will taper off. The exact same happens with the absorption/bulk voltage. It's a CV setting as well.
@@OffGridGarageAustralia ah ok I never relay played with lithium a d solar I was lead acid
I’ll make it easy. 👍🤟
Any sense wire on the solar charge controler? Otherwise 3,4V at the charger is not 3,4V an the cell.
I've found trying to catch up means you are behind for a long time on everything.
Instead I like to skip ahead so I do current, and when I finish current then I work on the oldest when i have time. Always current first.
That makes sense!
It's better to get to a high state of charge (pass the elbow on the charge curve) and do a very short absorption and let the voltage drop to in or just before the elbow. This is about the best you could do for battery health - avoiding sustained high voltage. Ideally also then the solar will power any loads because the load will drop battery voltage below the elbow.
The reason for charging to a higher voltage is for balancing purposes?
If you charge to 3.4V only, you would not need to balance as you're still in the flat area of the curve.
plaese show us the voltage of the cells in the BMS when you hit the 3.45 V. Are all cells identically? Beschde Grüße aus der Heimat.
At the beginning, there is around 50mV difference but once the current goes down during absorption, the deviation goes down to under 10mV. So it is still balanced OK.
I would increase the absorption time to 1 hour and determine and program the end amps setting. Voltage is the pressure and current is the flow and when the sponge is full, no more juice will flow.
Yeah, but then again, you could hit that voltage early in the morning and it starts your 1h absorption time. If you have clouds the current is low and it would switch to float right away. You end up with 70-80% SOC only.
@@OffGridGarageAustralia That's not too bad though for LFP to only reach 80% on some days. I'm more concerned with drifting balance over time, and no long periods to keep things balanced. My pack is 7 years old though, so perhaps not a problem with newer cells yet.
@@OffGridGarageAustralia I get that. You’ll probably still get 6000 cycles out of them. 80% SOC is based on theoretical capacity or a 100 cycle measurement of real case measurements of the exact bank? Is there a trend showing loss of capacity? This is getting interesting.
@@OffGridGarageAustralia I don't think this would be the case. If you're charging at 60 amps and that causes your battery to hit 54.4v and go into absorb, as soon as the current drops the voltage would also drop below 54.4 this should cause it tos witch back into bulk mode. So if you had clouds or something during your 1 hour absorb time this would cause voltage to drop below 54.4 because you're no longer pushing 60 amps and this *should* switch you back into bulk mode and start the whole process over again.
The 1 hour timer should means "If I maintain this voltage for 1 hour, then switch to float". if anything causes your amperage to drop, it would also cause the voltage to drop and result in going back to bulk.
I'd also recommend using tail current instead of the timer, because it will give you better control. You can't trust the voltage reading at higher amperage due to the batteries internal resistance so using tail current allows you to say "Don't switch to float unless I maintain this voltage even at a lower amperage" to better account for IR.
@@JeremyAkersInAustin I thought I have seen the Victron MPPTs staying in absorption mode once the voltage has triggered the timer. I cannot recall having seen them falling back to bulk if the voltage drops below absorption voltage. But it's been a while since I paid attention to that.
Yeah, I can set the tail current as well but at 3.45V the cells are 99% full anyway, so there is no real reason to absorb for long unless for balancing purposes.
Wish you would do the same experiment But use a EPEVER controller and use EPEVER language.
why not set the absorbtion time quite high and set the tail current to the current at which you just go into the steep part of the curve? in that way you will switch to float only if the current has dropped below the set value - and more importantly the SOC will be consistent between cycles...
I have just had the same experience and ended up with the same voltages.
i havent heard you mention resting voltage? You can also get a SOC by the measuring the battery resting voltage. In my small test it doesn't matter if i charge to 3.45 or above the battery cell rests at 3.352/50 The total battery voltage is 13.4 which when i googled it said 13.4-13.6 is a 100% charged battery resting voltage. BTW my battery is not in line with a solar setup Just discharging/charging different electrical stuff i have. Like running a small electrical heater or charging other batteries i have that are running my chest freezer.
Determine SOC through resting voltage will only work if the battery is fully charged. In the flat part of the curve, voltage is the same for a span of 30-70%.
@@OffGridGarageAustralia Thank you. Sadly or happily im not sure i need a BMS. I found that while charging the cells were not as balanced as i thought. Discharging there is no problem, for some odd reason im not privy of yet.
Hello how are you plz tell me i have made 12volt 12 amp lithium lifepo4 battery and attached it with my apc 650 plz tell me can it work and give me 2 hour backup my load is 12volt 2 amp dc
I think you could get about 5.1 hours with the APC 650. Total power from pack is 12vdc X 12 amp =144 watts then 144 watts / 24watts(load 12vdc x 2 amps) = 6 hrs less losses in apc 650, say 15% so .85x6hrs=5.1 hours....
Charge the pack up then just run the apc on battery pack until it quits working...just measure the time lapse...
Thanks alot ok plz tell me apc 650 has fully charge and it show 13.55volt plz tell me is it full charged
I'll Pommes you ketchup? Sounds great :-)
I highly appreciate your commenting. But also on your small island, there are only 24 hours available per day ;-)
Maybe the solution is 3.42 V?
Keep going and have fun!
Yeah, ah, nah, no! It will not make a huge difference 😁 The tipping point will be between 3.4V and 3.45V as we now know.
Thank you.
Did I see that right? You finally arrived at 3.45V absorption voltage?! Cool, now the float voltage to 3.375V to optimize solar production:-)
Float is only at 3.5V as this is the natural voltage the full battery goes back anyway. But 50% of people use 3.375V. That's fine too 😂
@@OffGridGarageAustralia true but that is not the reason. The reason is that if your solar can recharge your battery before sundown, it will keep powering your loads after that until sundown, while at lower than 3.375V you start discharging the battery instead of using solar power. At 3.5V float you will overcharge the battery… even at 3.4V float they will overcharge… but often float will only be for a short time until sundown, making it a moot point.
@@DeVerm123 you can only overcharge your batteries if you go higher than 3.65V. Everything below that the current will go to 0 at some point of charging with CV.
@@OffGridGarageAustralia If you CV charge to 3.65V then the cell is fully charged and this is considered to be the finish voltage. The charger should then turn off. If you continue charging in absorption and float modes at 3.65V, the cells will overcharge. You can fully charge the cells by setting the absorption voltage to 3.4V and allowing absorption mode. If you float at 3.4V, you can overcharge according to some, or just not overcharge according to others, but it is considered too high for float voltage by all when considering cycle life. Even 3.375V is a compromise for utilizing solar power, as 3.35V is considered to be the maximum safe float voltage for 24x7 float.
LOL... The Little Island just below Black Forrest right?
Exactly! You know it...!
@@OffGridGarageAustralia HaHa, I do, I dated a girl from that island.
I heard Australia is AKA "Prison Island" is this true? Good video. I mirror your settings in my setup................for the most part.
That is true for some regions here in Australia. Later, settlers came from all kind of countries (like me). They were not prisoners 😉
Don’t reply to this. You are too busy but you are amazing!!! Have fun while you do this,😳. Lol. Don’t Confuse the Electrons!!! That causes Lightening ⚡️⚡️⚡️⚡️.
I wonder what would happen if you left them at 3.45 volts per cell all of the time? The sun would go down every day, so they would not be exposed to that voltage continuously. ;)
No, they would not but the lower the voltage, the healthier it is for the battery.
With LiFePO4, you want to bring the cells out of the flat part of the charge curve to balance them for a while. The the voltage can be reduced to keep them at 100%SOC.
I dont understand why you don’t just roll at 3.6 like they’re designed to be charged ?😃
3.5 is where things kick off
I think 3.4V is enough, but 15m absorbtion time is not. With this low voltage the absorbtion time can be "forever", remember your video where you made these tests with the 100Ah cell, the lower the voltage the longer was the absorbtion time.
Yes, I totally agree. And I was expecting these results but just wanted to test and see if I can confirm that even with a complete pack and not just a single cell charged with CC.
What if you float at 3.4¿?
Sunny hot UK here today (it won't last)
55!!!!!!! 💪💪💪
getting there, ey!?
Great stuff. Some of it is over my head as none technical. Does that mean I should not attempt to build eve cell 50kwh bank in a few years for a new build house in the Caribbean. Should I just buy off the shelf powerwall from Alibaba. Then daisy them up. Bit more expensive but easier to set up and manage maybe??
IMHO, if you have the money and don't enjoy playing with this stuff, buy the powerwalls. If you have the time and want to tinker, and it is fun for you to be a scientist and learn, go with the DIY set up.
@@mfgxl I hear you. I want a little tinker but would need to but a lot of equipment and when the time comes for me to do it I’ll br quite old man so I’m thinking find a way to get thr means to but the powerwalls. But tttttthen there’s always the reliability issue with the cheapest I’d be able to afford. I contacted a company from Shenzhen China. And for 5 pieces of 10kwh rack style (a bit like the Gyll) walls shipped to jamaica was around $12k usa dollors. Plus there’s the Wharf clearance fee which are exorbitant it jamaica. So ad another 1500 to 2k on that. Not cheap at all. But a tonne of power yum.
I have not seen any other testing.
I don't really understand the concept. Wouldn't you just switch from constant current to constant voltage once your desired maximum voltage is reached and then continue charging until the current drops below a fixed threshhold, like 100mA or so? Doing the cut-off simply based on timing seems wrong and may be the reason why it's not working very well.
Yes, that is correct. We can set a tail current in the SCC which would end absorption if the current goes under a certain set limit. that is usually 5-10% of C, so 14-28A for these cells. They are then considered fully charged.
The problem is when you charge slowly or have clouds, there is no CC or CV and you can hit the absorption voltage for a moment. This could already trigger your absorption timer.
Charge it and float it never mind the absorption that's for lead acid my two cents 🤔😁👍🇺🇸
How will you know if you've reached full charge? Even a shunt will not remain accurate. But also absorption is needed for balancing.