LiFePO4 charge, float, and absorb voltages for different brands of batteries

[ewilhelm]

What charge settings are optimal for my setup?

I have a 48V 100AH LiFePower4 Battery by EG4 and a JK48V100 100 AH LiFePO4 Jakiper Battery that I plan to run with 2 kW of solar and a MidNite Solar MN3548DIY Inverter/Charger. The Jakiper arrived first and has been operating for a week (replacing flooded lead acids that ran fine for months), and I plan to add the LiFePower4 in parallel shortly.

I read the following thread about float charge for LiFePO4:

Float LiFePO4 or not??

Can someone give a definitive answer if you should turn off float stage in charge controller for LiFePO4 cells? I see conflicting information in messages here. Most of the information I see says Float should be disabled completely. cc: @Steve_S

diysolarforum.com

and am asking a similar question to ensure I understand/see if I've missed anything.

The LiFePower4's spec sheet reports:
CHARGING VOLTAGE REC. 58 V
REC. BULK VOLTAGE 57 V
REC. FLOAT VOLTAGE 56.5 V
REC. ABSORB VOLTAGE 56.5 V

The Jakiper manual states:
Recommend Charge Voltage: 58.4 V

I've set the inverter/charger to:
Battery Type: L16
Battery Absorption charge voltage: 58.4 V
Battery Absorption charge time: 120 minutes
Battery float charge voltage: 56.4 V

The system runs my fridges and freezers in solar-only charging and inverter priority (failing to the mains if the battery level drop too far). Since there is a constant load on the battery, perhaps I'm going OCD and the float voltage and differences between the batteries' recommended charge voltages doesn't really matter? What would you set the charge voltage to?

Thanks,

Eric

 

[Mr-Sandman]

The information in Signature Solar's specification sheet and the EG4 manuals contradict each other a bit. Different voltages listed on things. I was going to provide links to the manual, but it says access denied when I click on the link on their website right now.

I have the EG4 LL batteries which Signature Solar says share the same cells, the charge profile and voltages should match.

I've been researching this topic to try to determine the best charge profile for my Schneider MPPT controller so that I can sell to grid when the batteries are full without floating the batteries too high. I wanted to make sure I didn't charge my batteries too high daily, especially since they rarely get discharged, mostly for backup.

What I've learnt:

1. For maximum life of the batteries do not charge batteries all the way full nor discharge all the way down to cut offs. They call this 10%-90% cycling. Try to keep your batteries inside that window for max life. If you NEED the full capacity then this rule might not be ideal for you situation, but if you can stay mostly inside this windows, then your batteries will last longer doing this.

2. Bulk/Absorption can be the same, NO equalize. For Bulk/Absorption I use 54.5 volts which seem to give me near 100% SOC on batteries without needing to push the voltage on up. You will need to make sure your absorption timer is set to allow the batteries to fully charge without timing out. If that's an issue, you might have to set the Bulk setting .2 to .5 higher just to delay the start of the absorption timer.

3. My EG4 batteries rest fully charged at about 53.3 volts. Float voltage on these batteries shouldn't be much above your fully charged rest voltage. No need to float a LifePo4 battery higher than that. I use 54.5 volt also for my float, only because my Schneider XW Pro 6848 will pull it down .5 volts below my float setting while selling to grid, so my batteries see a 53.8 to 54 volt while in float and I'm selling to grid. 54 volts would be a good target for float.

4. I'm using a 48v low voltage cut off. The batteries are almost empty at this point, no need to suck that voltage down any farther.

I would think the Jakiper batteries would work well with the same settings, they are same configuration and size of cells, just different makes.

Hope that helps some.

 

[SandyMcC]

Thanks for your insights. It's hard to reconcile the various recommendations on the web.
Everyone seems to agree that 10%-90% cycling is desirable for long-life, but the exact voltage is fuzzy
I have been gradually pushing up my Absorption voltage (and float voltage) to 55.6v.
Once charging stops, the battery voltage drops back to 53.7v and eventually to 53.3v.
According to one write-up I saw, this equates to about 95% full. Is this what you reckon?

My inverter manual has 56.4v as it's default cut-off voltage and the default float voltage as 54.0v.
I see on the DIYsolarforum site there is another recommendation to use 56.4 for long-life:

"5,000+ Charge Cycle Absorption Recommendation​

If you want your LiFePO4 cells to last a long time, you can set your absorption to Victron's custom LiFePO4 charge profile recommendation: 48V Battery: 56.4V"​

I am using LiFePO4 cells rated at 320AH from BLMPOW.
At present I have not put a data link between the Growatt and the Daly

 

[Mr-Sandman]

I have recently bumped my Bulk/Absorption from 54.5 to 55v and extended the absorption time out timer. Reason being it give the cells more time to balance using the BMS after a cycle, before entering float. Float is still 54v.

 

[Steve_S]

We often talk about pack/cell voltages and tend to use cell volts in general, so that makes searches a bit tough. Please see teh voltage chart attached, you likely should download & store it for reference.

Essentially, anything above 3.425Vpc (Vpc = Volts per cell) 54.8V per 48V Pack is pointless.
The Working Voltage Curve is what delivers ###AH and NOT the Entire Voltage Range.
Working Range is 3.000-3.400, with A+ cells that can goto 2.900-3.450.
The Entire Voltage range is 2.500-3.650, From 2.50-3.00 AND 3.400-3.650 only represents about 5-7% of GROSS Capacity. NET Capacity is from the Working Range.

EndAmps / TailCurrent is calculated for (48V 100AH) as 100AH*0.05= 5A. The largest battery pack in the bank is used to determine this because it will be the last to hit 0% during discharge and last to hit 100% during charge. This is used to determine when to switch from Bulk to Float which allows the cells to settle up & level out and balance. When the system can take no more than 5A due to internal resistance, it should switch to FLOAT.
Bulk/Boost = Constant Current Max Amps. Charges LFP to 90% using CC.
Float = Constant Voltage / Variable Current. Charge the final 10% using CV.

NOTES ON MIXED PACKS !
At present you have two packs with ?? cells within them. They are both 100AH so that makes stuff a HEAP LOAD SIMPLER ! Packs of different capacity preset other issues / quirks. IE, putting 100AH & 150AH together not much issue but do 100AH + 200AH pack and problems WILL happen. They can be dealt with but things get weird. More than 100AH difference = BAD - plain & simple, you do NOT want to go there.

Every Packs will have it's own "personality" more or less. The fine details & settings within the BMS', the cells and their conditions etc... Even having packs at different temps affects their behaviour. YES, even 1 Degree Celsius difference can be noticeable ! Therefore when dealing with a "BANK" of Batteries the laws of Averages is applied and that means a little compromise for the greater benefit.

IF you can Monitor what is going on inside the packs with the cells, then with observation overtime you can fine-tune and tweak out settings that will give you full charge to Your Designated 100% SOC and provide you with trouble free operation. Your Designated 100% means that YOU set what is full, so for example if you decide that 3.400Vpc (54.4V) is your 100% then the shunts/coulomb counters can work within that.

! WARNING !
Be aware of Line Losses & System Calibration. There are ALWAYS Line losses, for every connector, shunt, switch, fuse it ALL adds line losses in both Voltage & Amperage ! During Charge by SCC it HAS to be correct, Check the Voltage Drop between SCC & Battery Pack Terminals and correct it by increasing/decreasing voltage settings so when the Battery Terminals says 54.000 that the SCC likely will see 53.9 then you have to correct for it.. YES even 1 Volt can cause headaches. During Discharge the INVERTER also has to be corrected for line loss... When Inverting the line loss is NOT the same as when Charging, it does present differently. Again check at Battery Terminals and at Inverter Terminals and correct the numbers to compensate. If you want to cutoff at 2.750 (44.0V) the Battery Terminal Voltage is what you want to gauge by, if you have a 1V loss then the Inverter would cut off @ 45.0V. You need a Good DMM/DVOM to do this. PLEASE, THIS IS IMPORTANT ! Too many ignore it or fudge it and get themselves into all sorts of bad adventures and often end up blaming the cells, bms etc but NOT themselves of course.

Hope it Helps, Good Luck.

 

[jberger]

I'll vote this one "Post of the Week"
Great summation and presentation.

 

[Bluedog225]

Seconded!

 

[Browneye]

Thirded. Thanks @Steve_S
Printed and saved.

 

[cliffgrimes]

I have recently bumped my Bulk/Absorption from 54.5 to 55v and extended the absorption time out timer. Reason being it give the cells more time to balance using the BMS after a cycle, before entering float. Float is still 54v.

Just curious - what did you set your time out to?

 

[SandyMcC]

Essentially, anything above 3.425Vpc (Vpc = Volts per cell) 54.8V per 48V Pack is pointless.

Am I correct in thinking your limit of 54.8v is the highest cut-off voltage when charging?
I monitor the voltages 'at rest' and 'under load' which tend to be more like 53.x volts at the start of my discharge cycles.
Can you say how long the 'rest' period would be in the tables you shared on Jan 28 2022?
My Inverter says I am charging up to 55.8v and this drops down to 53.4v over the subsequent 2 hours of resting.
However, a volt meter connected to the battery terminals (while charging at 90A) indicates a voltage more like 54.8v.
I'm hoping the 54.8v that you recommend is the same as the 54.8v that I measure at the battery terminals when charging stops.

 

[Usangira]

The information in Signature Solar's specification sheet and the EG4 manuals contradict each other a bit. Different voltages listed on things. I was going to provide links to the manual, but it says access denied when I click on the link on their website right now.

I have the EG4 LL batteries which Signature Solar says share the same cells, the charge profile and voltages should match.

I've been researching this topic to try to determine the best charge profile for my Schneider MPPT controller so that I can sell to grid when the batteries are full without floating the batteries too high. I wanted to make sure I didn't charge my batteries too high daily, especially since they rarely get discharged, mostly for backup.

What I've learnt:

1. For maximum life of the batteries do not charge batteries all the way full nor discharge all the way down to cut offs. They call this 10%-90% cycling. Try to keep your batteries inside that window for max life. If you NEED the full capacity then this rule might not be ideal for you situation, but if you can stay mostly inside this windows, then your batteries will last longer doing this.

2. Bulk/Absorption can be the same, NO equalize. For Bulk/Absorption I use 54.5 volts which seem to give me near 100% SOC on batteries without needing to push the voltage on up. You will need to make sure your absorption timer is set to allow the batteries to fully charge without timing out. If that's an issue, you might have to set the Bulk setting .2 to .5 higher just to delay the start of the absorption timer.

3. My EG4 batteries rest fully charged at about 53.3 volts. Float voltage on these batteries shouldn't be much above your fully charged rest voltage. No need to float a LifePo4 battery higher than that. I use 54.5 volt also for my float, only because my Schneider XW Pro 6848 will pull it down .5 volts below my float setting while selling to grid, so my batteries see a 53.8 to 54 volt while in float and I'm selling to grid. 54 volts would be a good target for float.

4. I'm using a 48v low voltage cut off. The batteries are almost empty at this point, no need to suck that voltage down any farther.

I would think the Jakiper batteries would work well with the same settings, they are same configuration and size of cells, just different makes.

Hope that helps some.

Moreover.....

As float voltage = bulk voltage....
This saves alot of battery cycles as once the battery bank is full.... Even if it is 9am, the remainder of the day will be consuming PV power directly instead of charge/discharge cycles to get to a float voltage.

I guess to my case this saves almost half of cycles....As my power bank is always full by mid day.... and there after I keep consuming all the afternoon directly from PV

 

[Steve_S]

My FINAL Tweaked out settings, NOTE this is for 24V system, Using a Midnite Classic 200 and JKBMS Settings & Delta Screens.
Written up as a Full Proper Thread

Steve_S-Tech: My Final Config for Midnite Classic SCC & JKBMS' w/ Large Bank (works amazingly well) Includes Charge Profile & BMS Config

INTRO: I have debated posting this for a while until I got everything tweaked in and working as best as possible. The End Result is Gobsmackingly Good ! I cannot speak for other SCC and such as each is different & unique in their own ways BUT this may likely be a Good Reference. Civility &...

diysolarforum.com

Hope it helps, Good Luck.

 

[upnorthandpersonal]

As float voltage = bulk voltage....
This saves alot of battery cycles as once the battery bank is full.... Even if it is 9am, the remainder of the day will be consuming PV power directly instead of charge/discharge cycles to get to a float voltage.

Except it's not a good idea to keep your battery at 3.6V per cell. LiFePO4 wants and needs to settle. Keeping it at high voltage can lead to overcharging and other issues.

 

[Ampster]

Except it's not a good idea to keep your battery at 3.6V per cell. LiFePO4 wants and needs to settle. Keeping it at high voltage can lead to overcharging and other issues.

I agree so instead of having Float be the same as Bulk I use a value near resting voltage. In my case I only charge to 3.45 volts per cell and set the Float to 3.35 volts per cell. The Float is only from solar so the longest it could be on would be six hours after batteries are charged. Also I have loads during the day that often exceed the current from the Float charge so the only thing I accomplish is a few Watt hours on some days.

 

[Capt Bill]

Essentially, anything above 3.425Vpc (Vpc = Volts per cell) 54.8V per 48V Pack is pointless.

Steve, ... Wondering for my 280Ah grade B -ish cells. When you use 3.425Vpc (Vpc = Volts per cell) for the Bulk/Absorption Charge voltage (54.8v on 48v LiFePO4 Pack; or 27.4v on a 24v Pack); ... What do you set your Float Charge Voltage to? Same 54.8 volts, or a bit less ? Curious from past post of yours, without fully understanding what I read ;+) ... while always learning more.

I have 3 x 24v sets of the EVE 280Ah cells integrated together now; with Bulk Charge (from my MPP LV2424s (x 4 now) ... set to 28.0 volts/ and Float Charge set to 27.2 volts. When I first charge tested my 280 Ah EVE cells, they all were able to take a 29.0v bulk charge (except one defect that got replaced by Xuba); ... but that is no longer possible with some age on my B Grade cells (wonder if A Grades would still take a 29.0v charge?) ... At my 28.0v set Bulk Charge setting, ...two of my three 24v battery banks are getting 130mV - 180 mV Diff between lowest and highest cells, (... on account of one runner cell in each bank Peaking to higher cell voltage) when my full 24v battery banks reach about 27.6 v -27.8 volts before shifting into Float Charge at my lesser 27.2 volt setting. ... So I am looking at my options, to get my set up automated, for smooth operation without BMS triggers ... and now considering adjusting my Bulk Charge Downward.

Side Topic: ... I am also learning from my BMS info. as battery cell reach near full charge. I have learned my Chargery BMS8T (x3) puts a 1.2 Amp resistance on peaker cells (in its' effort to keep cells balanced), and I can see when that is happening on one of the Chargery BMS (LCD) info. pages. ... and that stops happening when the BMS body get warmed up to about 31.5 degrees C. ... I now have all my BMS8T bodies mounted for full air flow over all sides, plus now putting small fans on the top side blowing downward (automating fan turn on at high battery voltage w a timer) ... to keep the balancing function working more full time, at high battery voltage in best way I can achieve w what I have ... (experimenting to see if that makes any differences) ... I do notice when my Chargery BMS8Ts do stop balancing cells when I would like em to / on account of shutting down the balance mode for heat protection. ... This might be a little to much info for this thread, but I wanted to share my experiment somewhere, along with my above question. ... Thanks in Advance, Bill

 

[Steve_S]

Steve, ... Wondering for my 280Ah grade B -ish cells. When you use 3.425Vpc (Vpc = Volts per cell) for the Bulk/Absorption Charge voltage (54.8v on 48v LiFePO4 Pack; or 27.4v on a 24v Pack); ... What do you set your Float Charge Voltage to? Same 54.8 volts, or a bit less ? Curious from past post of yours, without fully understanding what I read ;+) ... while always learning more.

I have 3 x 24v sets of the EVE 280Ah cells integrated together now; with Bulk Charge (from my MPP LV2424s (x 4 now) ... set to 28.0 volts/ and Float Charge set to 27.2 volts. When I first charge tested my 280 Ah EVE cells, they all were able to take a 29.0v bulk charge (except one defect that got replaced by Xuba); ... but that is no longer possible with some age on my B Grade cells (wonder if A Grades would still take a 29.0v charge?) ... At my 28.0v set Bulk Charge setting, ...two of my three 24v battery banks are getting 130mV - 180 mV Diff between lowest and highest cells, (... on account of one runner cell in each bank Peaking to higher cell voltage) when my full 24v battery banks reach about 27.6 v -27.8 volts before shifting into Float Charge at my lesser 27.2 volt setting. ... So I am looking at my options, to get my set up automated, for smooth operation without BMS triggers ... and now considering adjusting my Bulk Charge Downward.

Side Topic: ... I am also learning from my BMS info. as battery cell reach near full charge. I have learned my Chargery BMS8T (x3) puts a 1.2 Amp resistance on peaker cells (in its' effort to keep cells balanced), and I can see when that is happening on one of the Chargery BMS (LCD) info. pages. ... and that stops happening when the BMS body get warmed up to about 31.5 degrees C. ... I now have all my BMS8T bodies mounted for full air flow over all sides, plus now putting small fans on the top side blowing downward (automating fan turn on at high battery voltage w a timer) ... to keep the balancing function working more full time, at high battery voltage in best way I can achieve w what I have ... (experimenting to see if that makes any differences) ... I do notice when my Chargery BMS8Ts do stop balancing cells when I would like em to / on account of shutting down the balance mode for heat protection. ... This might be a little to much info for this thread, but I wanted to share my experiment somewhere, along with my above question. ... Thanks in Advance, Bill

Please Review This Posting. It should help clarify many of your questions.
I may be able to answer more tomorrow depending on how I am feeling, I am not doing very well (health), so I can help only minimally with stuff now.

Steve