Best LifePo4 charge controller settings known to man for Maximum Service life and Minimum battery stress!!! 5,000-10,000+ cycles?

[Go2Guy]

---ORIGINAL TITLE----​

Best charge controller settings to achieve 10%-90% usage on lifepo4 ?​

EDIT-UPDATE and the ANSWER to this question. . . This post is a accumulation of all the great and wonderful information given to me by all the great people on this thread. I consolidated all of this into this post and is the result of many hours of research and consulting with the people of this forum. Again thanks every body!!!!! This would not be possible with out you guys. if you believe i missed something or want to amend something please comment on this thread but please do so in a way that can be consolidated and added to this post , . . this is really not my post per say but an accumulation of the knowledge of the people of this forum and thread. .



BEST SOLAR SETTINGS [SO FAR] FOR MAXIMUM LIFE 5,000-10,000+ cycle life

PREFACE The Best settings possible are actually to run from 14%-90% SOC and this has little to due with voltage [besides staying out of the high and low voltage knee] however this is not possible with out a columb meter,or even better a charge controller that operates off of this principle. . Most charge controllers are designed for lead acid and being that the case we have to enter in voltage numbers numbers, so even tho this is not the ideal way to go about it, its the only way for most of us with cheaper and/or older charge controllers. . Here best voltage numbers possible known by the great contributors of this group to achieve the maximum service life possible and put the batteries under as little stress as possible.

BULK/ADSORB 3.45-3.52 [heavily debated] but universally agreed no higher than 3.52 for max service life [3.52 is what victron recommends for max service life
[lower voltage= slower charge times IE [C rate] which is Good but potentially longer in absorb phase which is Bad]
[Higher voltage=faster charge times which is more stressful on cells, BUT less time in absorb phase which is good ] 3.5v-3.52 seems to be a good compromise fast and slow charge times NOTE: Lower voltages means charge rate will be reduced at high SOC and it will be harder to reach 100%. which is great if your shooting for less than 90% state of charge. !!!IMPORTANT NOTE: While the above mentioned data is recommended for minimum stress on the cells it is important that the voltage you set activates your BMS, to keep your cells balanced, if not your BMS becomes useless and will never actually balance , most BMS activate around 3.4 VERIFY at what voltage your BMS activates at . if you are not sure, it just may be better to higher voltage to ensure that its activated[Will Prowse goes all the way to 3.6v OR another option is to keep an eye on it and make sure the cells stay balanced.

FLOAT 3.35
3.35 volts is a good float voltage for high reserve capacity and minimal cell
degradation [3.35 is not really debated if maximum service life is the goal 3.4 if you want a little bit more reserve. Also 3.4 is recommended by many OEMS, however according to some data at 3.35 the cell is not really in a state of stress while anything higher than this it is. . your choice a little bit more conservative or a little bit more reserve ]

CUT OFF 3.1V [but a more ideal verifying the cut off voltage is is to run down battery pack under average load you will be running and then take note of what cell voltage drops off first, once the first cell drops off in voltage , measure the total pack voltage and set low cut off voltage to that measured total pack voltage.
NOTE: In certain high load situations you may get get voltage drop causing the system to "cut off" and shut down under high load even if its not necessarily towards the end of your desired capacity. . , if this is the cause. you may have to set the cut off lower voltage. . 3.1 is a conservative number 3.0-2.9 is recommended for high load situations, but remember this post is all about having the data to make educated choices if your goal is maximum service life and achieving a balance between functionality and maximum service life

OTHER NOTES:
TEMPERATURE-"""storage at high State of charge and high temperatures promoted such severe losses that the cells in question were unable to recapture capacity that they had lost reversibly""".DO NOT STORE IN HIGH SOC especially in HIGH HEAT, i dont have all the data yet but it seems operating under 32F or over 100F could/will causes damage[especially under 32] as a good precaution in short if your not comfortable the batteries are not comfortable, [this is a super generic but a safe conservative recommendation] As solutions to this conundrum people will run thermostat controlled heat pads and heat blankets for the winter [search the forum] and use water tanks/pads or ac for high temp operation [search the forum] .

Why temperature of lithium cells is important

Temperature is an important parameter that influences the aging of a lithium battery. At 35°C a lithium cell ages twice as fast as it does at 15°C. So if the battery’s useful life is 15 years at 15°C, it will be 7.5 years at 35°C. I summarize...

diysolarforum.com

The Degradation Behavior of LiFePO4/C Batteries during Long-Term Calendar Aging

Abstract: With widespread applications for lithium-ion batteries in energy storage systems, the performance degradation of the battery attracts more and more attention. Understanding the battery’s long-term aging characteristics is essential for...

diysolarforum.com

VOLTAGE LOSS Every connector in your system as well as wire length attributes to a certain amount of resistance and which results in voltage loss. in other words If you set the charge controller to 3.5 volts the battery may only see 3.2 due to this voltage loss You have to adjust the controller to compensate for the loss. you may also have different losses for different components in your system depending on where there located for example inverter is on a longer length of cable than where the charge controller is located.

HOW TO RESOLVE use a good quality meter . . .measure the terminals at the battery pack , measure the terminals at the controller or inverter, subtract the difference and add this difference to your charge controller or inverters settings. [when testing for charger controller you want to be under charge, for inverter you would want to be under discharge]. measure and test again to ensure this was sufficient compensation

STORAGE, batteries should be stored at about 40% SOC if going to be in storage for long periods of time. . high SOC storage causes premature cell degradation

DON'T BE AFRAID to use the battery at 100% if needed, calendar aging [definition, loss of capacity due to time alone] [thanks will for this input] also plays a role in long term degradation so if even if you baby these cells to the max, with old age you will still loose capacity. .so these numbers above are to baby the cells, but it is perfectly okay to use full 100% soc when you need it , when taken into consideration that the effect that calendar aging has on the battery. Its is a balance between the battery is loosing capacity on its own due to aging and you babying or not babying the cells , because of calendar aging some say who cares and just use it at 100% at all times , however that defeats the purpose of this post of attempting achieve maximum service life. . but it definitely doesn't hurt to use it when you really need it. .
Balance--(run batteries to a high SOC to trigger a good balance on your BMS 4 months or so, -as a maintenance. think of as a equalization ]

A great read by Joey on taking care of your cells https://diysolarforum.com/resources/how-charging-works-in-the-context-of-lfp-batteries.233/download
END POST


______________________________________________________________________________
ORIGINAL OPENING POST

i have spent about 6 hours reading thru google and and almost every relevant search result this website has as well as youtube. . and and my brain is on information over load. . I have a simple question, but i can only seem to find complicated answers and debates between people. I have several charge controllers and all in one units i will be setting up soon for family members and im looking to find what are the best settings to achieve a usage of between 10%-90% SOC on lifepo4 batteries. . . from everything i read it seems this is the safest for long term reliabilty [10-15 years or more if possible] . . but cant find info how to set the settings to achieve this .. . . . as we all know almost all charge controllers are designed for lead acid, so we are stuck with programming such parameters and have to make do with float and absorption settings. . what im looking for is the approximate voltages settings on a per cell basis for the following

bulk
absorption
float
low voltage cut off


also any other settings you recommended changing for lifepo4. .
should these numbers be different when under load?
any other considerations when using mpp units ?

the most straight forward answer i found was wills on his site, [ https://www.mobile-solarpower.com/diy-lifepo4-solar-battery.html ]
however his recommendations were based on 100% SOC which i prefer not to use since were looking for extra long life with this batteries ,so i prefer to stick to 80% however his post was the most straight forward answer of the 6 hours i have been searching online . . essentially looking for same answer but with 80% in mind. .

 

[BentleyJ]

I would recommend you go over to YouTube, Off Grid Garage and watch the video series where he did all sorts of charge/discharge testing. Its very informative, real world stuff.

 

[sunshine_eggo]

i have spent about 6 hours reading thru google and and almost every relevant search result this website has as well as youtube. . and and my brain is on information over load. . I have a simple question, but i can only seem to find complicated answers and debates between people. I have several charge controllers and all in one units i will be setting up soon for family members and im looking to find what are the best settings to achieve a usage of between 10%-90% SOC on lifepo4 batteries. . . from everything i read it seems this is the safest for long term reliabilty [10-15 years or more if possible] . . but cant find info how to set the settings to achieve this .. . . . as we all know almost all charge controllers are designed for lead acid, so we are stuck with programming such parameters and have to make do with float and absorption settings. . what im looking for is the approximate voltages settings on a per cell basis for the following

bulk
absorption
float
low voltage cut off


also any other settings you recommended changing for lifepo4. .
should these numbers be different when under load?
any other considerations when using mpp units ?

the most straight forward answer i found was wills on his site, [ https://www.mobile-solarpower.com/diy-lifepo4-solar-battery.html ]
however his recommendations were based on 100% SOC which i prefer not to use since were looking for extra long life with this batteries ,so i prefer to stick to 80% however his post was the most straight forward answer of the 6 hours i have been searching online . . essentially looking for same answer but with 80% in mind. .

You can't do what the subject requests on a pure voltage basis. Here are your options:

Fast charging to full: 3.55-3.65V/cell - 30 minute absorption time.
Slow charging/longer cycle life (98%+ charge): 3.45V/cell - 4+ hour absorption time.
Float (95%+): 3.4V/cell

The slow charging method is less stressful to the cells and should improve cycle life while still attaining near 100% charge.

Depending on the load, you want to disconnect around 3.1V/cell to stay in the 10-20% range.

The only real way to accomplish a 10-90% operating range is to get a quality battery monitor and synchronize it to 100% charge.

Discharge until it indicates 10% - that's your low voltage threshold.

Charge until it indicates 90% - that's your absorption voltage AND your tail current, i.e., you terminate charging once it's attained that voltage and current has dropped below the observed value - your charging hardware must be programmed accordingly.

 

[Go2Guy]

I would recommend you go over to YouTube, Off Grid Garage and watch the video series where he did all sorts of charge/discharge testing. Its very informative, real world stuff.

actually watched a bunch of his vids to day, but still overloaded with info, when im really just looking at what voltages to set these charge controllers, i love data but to much data makes it dificult to know what actually set the charge controller at. .

 

[Maintenance guy]

GO 2 GUY;
The basic parameters to get long life of your LiFePo4 chemistry is to stay out of the top and bottom knee of the curve as the above member has indicated. it is called the knee of the curve where it drops very fast at the end of the discharge cycle and the top charge cycle where it rises fast in voltage. staying out of these knees will get you the longest life possible and staying in the .5c charge discharge parameters of your cells.

 

[Maintenance guy]

Here is the knee curves.

 

[Go2Guy]

You can't do what the subject requests on a pure voltage basis. Here are your options:

Fast charging to full: 3.55-3.65V/cell - 30 minute absorption time.
Slow charging/longer cycle life (98%+ charge): 3.45V/cell - 4+ hour absorption time.
Float (95%+): 3.4V/cell

The slow charging method is less stressful to the cells and should improve cycle life while still attaining near 100% charge.

Depending on the load, you want to disconnect around 3.1V/cell to stay in the 10-20% range.

The only real way to accomplish a 10-90% operating range is to get a quality battery monitor and synchronize it to 100% charge.

Discharge until it indicates 10% - that's your low voltage threshold.

Charge until it indicates 90% - that's your absorption voltage AND your tail current, i.e., you terminate charging once it's attained that voltage and current has dropped below the observed value - your charging hardware must be programmed accordingly.

so to convert what you said into settings for longeveity would it be "
bulk 3.45v per cell 13.8----27.6----55.2
float 3.4 ____ ---- 13.6----27.2----54.4
absorption [what would you recomended] [ i know this is not needed but required for most charge controllers [lead acid based]
low voltage cut off 12.4----24.8----49.6

as far as im aware there is not time settings on mpp units[not certain of this ] but it doesnt seem to be. .

 

[Go2Guy]

GO 2 GUY;
The basic parameters to get long life of your LiFePo4 chemistry is to stay out of the top and bottom knee of the curve as the above member has indicated. it is called the knee of the curve where it drops very fast at the end of the discharge cycle and the top where it rises fast in voltage. staying out of these knees will get you the longest life possible and staying in the .5c charge discharge parameters of your sells.

EDIT . . Sorry, just saw your other post . . .

 

[Go2Guy]

Maintence, guy the other thing i get confused on is , for these number are those settings you put into your charge controller OR are they resting voltage numbers, thats the other major hurdle is determing what voltage since, loaded voltage and under charge voltage numbers can be drasticly different from resting voltage numbers

 

[John Frum]

Maintence, guy the other thing i get confused on is , for these number are those settings you put into your charge controller OR are they resting voltage numbers, thats the other major hurdle is determing whats since, loaded number and under charge numbers can be drasticly different from resting voltage numbers

If you have commodity cells like most of us do you need to charge into the high knee regularly so that your bms can maintain top balance.
Try 3.55 volts per and if your BMS disconnects titrate between 3.45 and 3.55 until you get a charge voltage in the high knee that does not trip the bms.
As for low voltage disconnect that depends on your battery.
To find out where to set your low voltage disconnect discharge your battery at a current that is representative of your use case and make note of the voltage at which the first cell starts to nose dive.
The point at which it nose dives is your low voltage disconnect voltage.
Hope that is clear.
Setting an appropriate low voltage disconnect will aid your bms in maintaining the top balance.

 

[Maintenance guy]

No float charge. that is the third in the cycle. set it below absorption levels. the inverter manufacturers are killing everyones LiFePo4 cells prematurely using lead acid parameters.
Bulk, absorption only. Bulk is CC absorption is CV.
you can also lower your balance levels to coincide with the above parameters.

 

[Go2Guy]

Thank you every one for your respones, so to summarzize I should set charge program settings to the following


CC bulk----------- 3.45v per cell------13.8v----27.6v----55.2v [ upto 3.55v if you have balance issues but lower for longevity]

CV absorption---- 3.40v per cell------13.6v----27.2v----54.4v

Float [not needed but mandatory for most controllers [ So set to lower than absorption Would 3.3 Be Good???]

low voltage cut off-3.1v per cell 12.4v----24.8v----49.6v BUT better to test under load until weakest cell hits knee and then set cut off voltage at total system voltage of were the knee drop off occurs. .


in regards CC bulk times if there no charge timer is this an issue are then any work arrounds to this issue ?
Did i get anything wrong??

 

[John Frum]

Thank you every one for your respones, so to summarzize I should set charge program settings to the following


CC bulk----------- 3.45v per cell------13.8v----27.6v----55.2v [ upto 3.55v if you have balance issues but lower for longevity]

CV absorption---- 3.40v per cell------13.6v----27.2v----54.4v

CC and CV should be the same voltage.

How charging works in the context of LFP batteries

How charging works in the context of LFP batteries

diysolarforum.com

Float [not needed but mandatory for most controllers [ So set to lower than absorption Would 3.3 Be Good???]

3.3 would be fine.

low voltage cut off-3.1v per cell 12.4v----24.8v----49.6v BUT better to test under load until weakest cell hits knee and then set cut off voltage at total system voltage of were the knee drop off occurs. .

Yep you got it.

in regards CC bulk times if there no charge timer is this an issue are then any work arrounds to this issue ?
Did i get anything wrong??

 

[mikefitz]

when im really just looking at what voltages to set these charge controllers,

The charge current also has an effect on battery life, so keeping under 0.5 C is desirable, under 0.25C even more so. In general, regardless of charge voltage you need to keep the absorption time, ( the charge phase where the voltage is held constant) as low as possible, even zero time is suitable in most situations if there is no need to fully charge the cells.

Its been reported, and my tests gave similar results, where charging to a target volts of 3.5 and 3.4 volts per cell.

A charge target volts of 3.5 volts per cell, 14 volts for a 4 cell battery, with no absorption time and a charge current of 0.2C, gave charge to over 97% of capacity.
A lower target volts of 3.4 volts per cell, 13.6 volts for a 4 cell battery, again with no absorption period at the same charge current, will charge to around 85 to 90%.

For most applications where long service life is requited, 3.50 volts per cell, no absorption and with a charge current of 0.25C or lower, is in my view a practical method.

If the charger has a float mode then using the rest voltage, typically 3.35 volts per cell is my approach.

Whilst using a battery monitor, like the well regarded Victron BMV range, will report state of charge and can via its control relay control system charging. However there will be small errors that will accumulate over time requiring manual sync at intervals.

There are two factors that may require charging at higher voltages than above and require some absorption time.

Cell balancing is normally activated by the BMS when the cell volts is greater than 3.40 volts.

Memory effect may occur if the cell is 'short cycled' leading to temporary capacity loss. This is removed by a full charge to 100% .

The limit on discharge is easy to determine as there is a increasing voltage drop at low SOC.
The actual voltage will depend on load but 3.2 to 3.0 volts per cell should be regarded as a limit.

It would seem that two factors that may reduce service life are high temperature and having the battery at a high SOC for long periods.

Mike

 

[sunshine_eggo]

EDIT . . Sorry, just saw your other post . . .

Thank you every one for your respones, so to summarzize I should set charge program settings to the following


CC bulk----------- 3.45v per cell------13.8v----27.6v----55.2v [ upto 3.55v if you have balance issues but lower for longevity]

CV absorption---- 3.40v per cell------13.6v----27.2v----54.4v

Bulk and absorption are the same voltage. I recommend 3.45.

Float [not needed but mandatory for most controllers [ So set to lower than absorption Would 3.3 Be Good???]

It is needed if you're using the batteries in a cyclic power system. Otherwise, you'll stop getting solar and cycle your batteries unnecessarily.

I recommend 3.4V. 3.4V will allow the battery to discharge slightly by a few percent and hold. 3.3V will take you a little farther. You can experiment for yourself.

low voltage cut off-3.1v per cell 12.4v----24.8v----49.6v BUT better to test under load until weakest cell hits knee and then set cut off voltage at total system voltage of were the knee drop off occurs. .

Yep.

in regards CC bulk times if there no charge timer is this an issue are then any work arrounds to this issue ?

CC bulk isn't what matters. It's the CV portion that's a concern if run for too long.

 

[sunshine_eggo]

The charge current also has an effect on battery life, so keeping under 0.5 C is desirable, under 0.25C even more so. In general, regardless of charge voltage you need to keep the absorption time, ( the charge phase where the voltage is held constant) as low as possible, even zero time is suitable in most situations if there is no need to fully charge the cells.

Not sure how, but you quoted something I didn't say.

Vigorously agreed.

Its been reported, and my tests gave similar results, where charging to a target volts of 3.5 and 3.4 volts per cell.

In contrast to your above statement, charging to 3.4V requires a long absorption period.

A charge target volts of 3.5 volts per cell, 14 volts for a 4 cell battery, with no absorption time and a charge current of 0.2C, gave charge to over 97% of capacity.
A lower target volts of 3.4 volts per cell, 13.6 volts for a 4 cell battery, again with no absorption period at the same charge current, will charge to around 85 to 90%.

My results were MUCH lower:



Eve 280Ah cells: 0.07C from empty to 3.44V, 180Ah vs. 280Ah was deposited: 64% SoC

For most applications where long service life is requited, 3.50 volts per cell, no absorption and with a charge current of 0.25C or lower, is in my view a practical method.

I would agree.

If the charger has a float mode then using the rest voltage, typically 3.35 volts per cell is my approach.

I don't disagree, but I like 3.4V better for more reserves.

Whilst using a battery monitor, like the well regarded Victron BMV range, will report state of charge and can via its control relay control system charging. However there will be small errors that will accumulate over time requiring manual sync at intervals.

Agree.

There are two factors that may require charging at higher voltages than above and require some absorption time.

Cell balancing is normally activated by the BMS when the cell volts is greater than 3.40 volts.

Memory effect may occur if the cell is 'short cycled' leading to temporary capacity loss. This is removed by a full charge to 100% .

This is over-emphasized. It's not necessarily a loss of capacity, but a shift in operating voltage vs. SoC downwards. It is only meaningful on systems that utilize voltage in SoC computations (EV).

The limit on discharge is easy to determine as there is a increasing voltage drop at low SOC.
The actual voltage will depend on load but 3.2 to 3.0 volts per cell should be regarded as a limit.

It would seem that two factors that may reduce service life are high temperature and having the battery at a high SOC for long periods.

Vigorously agree.

 

[curiouscarbon]

Not sure how, but you quoted something I didn't say.

after pressing quote, you can still just edit the text

Not sure how, but you quoted something I didn't say. waffles are cool

sorry if this example is unwelcome, happy to remove. just to clarify forum functionality.

also waffles are cool ​

 

[Go2Guy]

sunshine_eggo said:Eve 280Ah cells: 0.07C from empty to 3.44V, 180Ah vs. 280Ah was deposited: 64% SoC

so would 3.45 not hit 90% i noticed you said with your 280ah cells. you only got to 64% SOC.
were running 120ah cells

our goal really is maximum service life and we over sized the system accordingly The total is 6.3kw but with the 80% goal in mind it gives us 5kw which is exactly what we planned for [120ah 8s2p] max charge will be between .12c and .20c . What CC CV voltage would you recommend for this to reach 90% but will keeping max service life[we'd like to get 15+ years out of them . . rumors have are you can get 20+ years if you baby them which is our goal] Eventually we will get a columb meter but right now we dont have that as we are just now setting them setting them up for the first time. .

it seems according to your guys comments [thanks by the way] that having lower CC CV voltage while altho good, will keep it in absorption mode longer which is bad [, while having a higher voltage which is bad for max service life but will keep it in absorption shorter which is good for max service life [doesnt seem to be a choice to shut off absorption in the mpps]

. . . good, ol dammed if you do dammed if dont situation. lol . ?

what would you guys recomend for max service life 3.4 3.45 or 3.5v per cell while allowing enough voltage to reach 90% SOC with in typical 5.5 FL sun day [we have between 1.5 and 2k coming in [depending on our system[were making multiple] which is a total of 8.2kw and 11kw with a average consumption during sun time of 500w so minus are consumption exactly we will have exactly 5kw of sun to charge the 5kw pack. in the alotted 5-6 of Fl sun hours and we can always cut back consumption during sun hours to allow more power to make into the batteries. .


Again i really really appreciate all the great advice, I learn more in the couples since starting this thread than the last 6 previous our searching online. . . lol now that think about its been a total of 12 hours seaching for these answers. . lol

 

[Sojourner1]

6 years of daily use. 14.1 absorb which last about 6 min., float 13.6. Over 1,800 partial DOD of 35-45%, SOC use from 25%-100% depending on the season and solar conditions. 99% of the time solar charges unless I need to fire up the eu2200i generator for a small hold over charge. Gone as long as 40 days in a partail SOC between 25-85%.

Some of you folks are over thinking it. ?

 

[Go2Guy]

6 years of daily use. 14.1 absorb which last about 6 min., float 13.6. Over 1,800 partial DOD of 35-45%, SOC use from 25%-100% depending on the season and solar conditions. 99% of the time solar charges unless I need to fire up the eu2200i generator for a small hold over charge. Gone as long as 40 days in a partail SOC between 25-85%.

Some of you folks are over thinking it. ?

that's pretty cool . . .so your running 3.52 for the bulk/absorb and then 3.4 for the float , thats awesome they have lasted so long. . . . . . my goal is to set it up right the first time and not make mistakes with a very expensive battery pack ., or as they say "Set it and Forget It" . .these batteries cost my family alot of money and unlike most we cant afford to drop several thousand evey couple years, not only that but some say these batteries could last potentially last for ever if set up precisely and if there very well taken care with the only age related issue of diminishing capacity. . Our goal is 15-20year service if that's even possible, . . . to achieve this we are taking a extreme amount precaution and digging for the most perfect parameters known to man aka "over thinking it" . . . . . I am extremely great-full for the contributors to this thread to helping us achieve this goal . . i know lifepo are very durable and in reality you could just beat the piss out of them, and even get a way with running them with out a bms but that would defeat our goal of potentially making this a once in a lifetime purchase . Not only that once i have found these exact parameters im going to re post them in a simplified fashion for others to find and use so they dont have to do the 12 hours of research that i have done

 

[sunshine_eggo]

so would 3.45 not hit 90% i noticed you said with your 280ah cells. you only got to 64% SOC.
were running 120ah cells

I have always indicated an extended absorption time for 3.40/3.45. I was illustrating the difference between having an absorption phase vs. not.

it seems according to your guys comments [thanks by the way] that having lower CC CV voltage while altho good, will keep it in absorption mode longer which is bad [, while having a higher voltage which is bad for max service life but will keep it in absorption shorter which is good for max service life [doesnt seem to be a choice to shut off absorption in the mpps]

. . . good, ol dammed if you do dammed if dont situation. lol . ?

No. Absorption at peak voltage (3.55-3.65) for extended periods is unnecessary/bad. Getting to near full at 3.40-3.45, absorption is necessary and also occurs at a lower current - lower voltage + lower current = better.

what would you guys recomend for max service life 3.4 3.45 or 3.5v per cell while allowing enough voltage to reach 90% SOC with in typical 5.5 FL sun day [we have between 1.5 and 2k coming in [depending on our system[were making multiple] which is a total of 8.2kw and 11kw with a average consumption during sun time of 500w so minus are consumption exactly we will have exactly 5kw of sun to charge the 5kw pack. in the alotted 5-6 of Fl sun hours and we can always cut back consumption during sun hours to allow more power to make into the batteries. .

Fast charge with generator: 3.55-3.65
Slow charge with solar/grid: 3.45
Float: 3.40

The reality is that if you have good quality cells, you don't abuse them, and make an effort to use them will within their ratings, you should expect good service life - likely longer than spec.

 

[Horsefly]

You can't do what the subject requests on a pure voltage basis. Here are your options:

Fast charging to full: 3.55-3.65V/cell - 30 minute absorption time.
Slow charging/longer cycle life (98%+ charge): 3.45V/cell - 4+ hour absorption time.
Float (95%+): 3.4V/cell

The slow charging method is less stressful to the cells and should improve cycle life while still attaining near 100% charge.

Depending on the load, you want to disconnect around 3.1V/cell to stay in the 10-20% range.

The only real way to accomplish a 10-90% operating range is to get a quality battery monitor and synchronize it to 100% charge.

Discharge until it indicates 10% - that's your low voltage threshold.

Charge until it indicates 90% - that's your absorption voltage AND your tail current, i.e., you terminate charging once it's attained that voltage and current has dropped below the observed value - your charging hardware must be programmed accordingly.

Although there is absolutely nothing wrong with what @sunshine_eggo has suggested, I'll just throw in a slight change to the charge profile I've arrived at: Bulk/Absorption to 3.5V/cell (kinda between his fast and slow charging), 30-60 minute absorption time. Truth is the current drops to almost nothing before that time. Then float at 3.35V/cell. I like the SoC way of getting to a voltage on the high end and low end, but the voltages can vary significantly for charge, discharge, and resting. Makes it hard to find the perfect spot, but the goal does have merit.

Here is the knee curves.
View attachment 82268

I kinda wish people would not keep posting these curves and the SoC table. It is easy to trust it too much. The thing that needs to be said is that these voltages in the graphs and in the table appear to be resting voltages, i.e. some hour or more after any charging or discharging, and with nothing going into our out of the cells. If the pack is being charged at even a relatively small current (0.2C or more) the voltages will be higher, and if it is being discharged it will be lower. I appreciate @Maintenance guy is trying to help, but it is easy for someone new to this to put too much faith into these voltages, when they shouldn't.

 

[Sojourner1]

I'll bet 6 years ago lfp cell/ batteries cost more than what you guys are paying now so if you think I wouldn't like longevity,, I do but at the same time I want to live off them not coddle them. I believe with my use pattern I'll still get 10 plus years with everyday use. I don't coddle my bank either, it will pull loads of 75 -225a from a few minutes to hours depending what I'm using.
It's amusing to see "rumors" of longevity of 20 years. I've read of a few lfp off grid setup going on 10-12+ years now.

My system has been a set it and forget. Just amazing to see lfp at 25% SOC and still use microwave (150a) for 5 minutes and still not hit low volt disconnect from the inverter which is set at 12.0v. ?

 

[Go2Guy]

Although there is absolutely nothing wrong with what @sunshine_eggo has suggested, I'll just throw in a slight change to the charge profile I've arrived at: Bulk/Absorption to 3.5V/cell (kinda between his fast and slow charging), 30-60 minute absorption time. Truth is the current drops to almost nothing before that time. Then float at 3.35V/cell. I like the SoC way of getting to a voltage on the high end and low end, but the voltages can vary significantly for charge, discharge, and resting. Makes it hard to find the perfect spot, but the goal does have merit.


I kinda wish people would not keep posting these curves and the SoC table. It is easy to trust it too much. The thing that needs to be said is that these voltages in the graphs and in the table appear to be resting voltages, i.e. some hour or more after any charging or discharging, and with nothing going into our out of the cells. If the pack is being charged at even a relatively small current (0.2C or more) the voltages will be higher, and if it is being discharged it will be lower. I appreciate @Maintenance guy is trying to help, but it is easy for someone new to this to put too much faith into these voltages, when they shouldn't.

I guess the big issue, is we as a solar community have no choice BUT to set these numbers on these controllers,. . .
Bulk/Absorb
Float
Low voltage cut off

. . .. I know its not the ideal way to manage it BUT its the only way that 90% of currently available and affordable charge controllers handle these battery packs. Eventually i would like to get a columb meter, BUT it seems even if i get one ,it will give me SOC numbers which is great . But IT still not control the system since its the above settings handled by the charge controllers that controller the pack charges , I know its not the ideal way to do it BUT its the only way most of have, so my reall goal is to have the best humanely possible numbers that i can plug into these settings to get this battery to last as long as physically possible. what you mentioned about resting voltages is also a huge issue even with lead acid[ been dealing with this for years] , if your using a battery back there is no way of actually telling what the pack is at. . since loaded and charging number are always so different from resting numbers. . but even when i was just setting up the mpp i had no choice but to set such "in load" and "in charge" numbers when it ask what voltage like like when to connect to grid when battery gets to low and what voltage to connect back to battery, with out a SOC table how would one even go about setting this number, is the number i even put right when under load or charge??? I dont even know I set to switch to grid when at 25.5 roughly 20% according to a SOC table it back to go back to battery @ 26.5 roughly 70% according to a table is this ideal ???? not even sure but i have no choice to but to set these numbers if i want to use this feature SBU[solar battery utitility] SMH lol

 

[Will Prowse]

Really good discussion, but at 20 years, calendar aging will probably be what kills lifepo4. Cycle bandwidth modification probably won't help much. Solar cycling is typically at very low C rates and typically does not hang out at high SOC, so you should get 7,000-10,000 daily cycles without issue.

But keep in mind you can still use the batteries at this point, they will just be at a reduced capacity. Batteries are getting cheaper though, so I wouldn't stress it. Charge to 100% and down to 0%. Use the full capacity before you lose it to calendar aging regardless.

You can reduce calendar aging rate by keeping your batteries in a cool environment.