Floating at 70%. Why charging LiFePO4 to 3.4V is not enough! 

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

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.

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 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.

I dont understand why you don’t just roll at 3.6 like they’re designed to be charged ?😃

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.

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.

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.

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.

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.

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.

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.

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 💪

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

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.

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.

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!

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 .

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.

Iam really a Fan of you Andy! Why not selling your Offgrid-Garage Shirts, i would buy two of them!😃

I have 16s with float 54v and absorb 55v ,with float time 2hrs,11kwh....in qld and seems to work fine.....I had it higher and it tripped my system.

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?

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

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 ?

1 one of my cells will not charge over 3.4v were others will head up to 3.5v , i going put claim in to supplier , works perfictly under load , cells blance out as i draw amps ,got me stuffed why cell number 4 it will not charge over 3,4v other cells over take it head to 3.5

Some of these "old" videos keep popping up in my feed, and I'm still learning a lot from these "old" videos. Great! Always looking forward to these videos from the Off-Grid Garage :)

I've been watching your video series and another very knowledgeable RU-vidr while building my new lifepo4 bank in my RV. You made a comment in this video about absorption time vs. voltage to maintain full recharge. I think the stock Victron settings are 15 minute absorption, but as I understand it, that time is per 100ah of battery in your bank. So, a 500ah lifepo4 bank would require 135 minutes of absorption time at 3.4 volts. I just completed a 480ah bank yesterday and this is the basic formula I am running today. I am excited to see my results this week after the system cycles a few times. My weather forecast for the week is very sunny, so I expect to see best possible results. Your video series has helped me very much and I would like to thank you for all your hard work.

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

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!

Hello, Thank you for your help. I have 4 12 volt lithium batteries connected in series at 48 volts. however, I have a large voltage variation between the batteries. In the morning I see a battery with closed bms and during the day I see one at 15 to 15.8 volts. the other three are between 12.7 and 13.2 can you tell me what could be wrong?

La cosa che più mi rende pazzo è che ogni azienda che produce batterie, caricatori, inverter ecc ti dice che bisogna caricarle a 3,65 poi interrompere la carica . Allora .. o tutte le aziende vogliono che le nostre preziose batterie si rovinano o stiamo sbagliando qualcosa tutti noi!!!!! Se si ascolta 10 RU-vidr si ha 10 parametri diversi o ognuno ha le proprie ragioni. Quindi dov’ è la verità???

Sunny hot UK here today (it won't last)

Isn't this a good thing. I thought lithium should be kept between 25% and 80%. For a much longer life.

Purtroppo dopo 2 anni di fotovoltaico e esperimenti vari sono giunto alla conclusione che non esistono dei parametri giusti x ogni stagione. Anzi neppure quasi per ogni settimana. Io se le previsioni danno bel tempo almeno per 3 gg metto 54.4 per restare al 90% massimo .Se è variabile o le previsioni danno brutto tempo per alcuni giorni metto 55.2 per caricare il più possibile. Anche gli Ampere di carica cerco di distribuirli sull intero giorno se è bello. E’ inutile che arrivo pieno alle 2 di pomeriggio avendo buttato 50 Ah in batteria per niente. Lo metto a 30 Ampere anche per salvaguardare il più possibile le batterie.

Why don't you do a vid on ups conversion from sla to lfp? I'm digging out all my EE school books and working on a circuit that addresses over/under charge and discharge. would like to share my design with others and get their thoughts.

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

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

why do you use absortion at all for lifepo4? i think just CC and CV is required for LifePO4

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.

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?

it's always a pleasure to watch your videos, thank you for your work

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.

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!!!

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.

maybe try upping the volts by 0.01 or 0.02 at a time to find the sweet spot that works for you.

Lifepo4 doesn't need float or absorption. Set 3.6v per cell and leave it.

LOL... The Little Island just below Black Forrest right?

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 :)

i found 3.48 to 3.52 was good

Charging lower than 0,5C not needed absorption.

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!

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.

When are you going to start on the battery rack again?

Hi, I think you should use the tail current mesure to stop absorption instead of a fixed duration.

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

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

U r great,i like to watch your video every time in detail sir

I checked the most (all?) videos... did i overlook a "Replace a single LiFePo4 cell out of a battery pack"?

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

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

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. ;)

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)

And this is exactly why you set bulk/abs/float to the same voltage 😎

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.

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 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.

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.

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 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.

1 Acronym: TAIL-CURRENT!!! For the comments: Make a 1 week answering. If you publish this to the people, you have "just" to read the comments of the last videos of 7 days.

Oh no, don’t do this to us! I have already set up all my installations at 55.2V bulk and 53.6 float!

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.

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.

You know did really good job great work

Your channel is great This information is invaluable and so very practical Thankyou

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 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 😊.

Just admit it… you’re in Antarctica :-)

I charge my to 3.525 v

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.

I seem to remember another video on this channel which dealt with this a few months ago...

Very interesting Andy! All very useful info thanks!

Why have you taken your controllers off the GX and out of “external control”?

Every time I watch it load my brain with new information a lot learning from u thanks.

Wish you would do the same experiment But use a EPEVER controller and use EPEVER language.

55 Amps...nice weather in Australia!

I know this is off subject Have you thought of using the victron EV charger to use excess solar after your batteries have charged

I’ll make it easy. 👍🤟

I learn something new from each video and love your enthusiasm for the subject

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:-)

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.

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 :)

I have not seen any other testing.

Any sense wire on the solar charge controler? Otherwise 3,4V at the charger is not 3,4V an the cell.

The detailed testing and sharing is impressive!!!

Nice try. How about show folks what happen when you cut off at 3.1V

Just charge to whatever voltage you want and keep it there. done.

I heard Australia is AKA "Prison Island" is this true? Good video. I mirror your settings in my setup................for the most part.

I charge to 3.475 per cell. No absorption.