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LiFePO4 Voltage Chart?

Quite correct, THAT is a BMS to AVOID. Please post a link to it so others know to avoid it.
During my BMS hunt, I was simply not satisfied with any of the "pre-configured" products out there and I certainly did not want to use 100% of capacity limits. I looked at many and decided on Chargery as that suits my use, needs & wants for my installation. There are several configurable/manageable BMS' like ANT, XioaXing and others that people use here with good success.

They claim that I can ask for whatever values I want, that at least the programmable ones can be configured. But at higher $$ of course. I will look at the ones you mention, thanks!
 
They claim that I can ask for whatever values I want, that at least the programmable ones can be configured. But at higher $$ of course. I will look at the ones you mention, thanks!
Who is they?
 
The companies manufacturing the batteries aren't manufacturing the cells inside so they post their recommendations or interpretations of the cell manufacturers data sheet. I think lifepo4 is lifepo4 is lifepo4 and we all should decided what voltage that chemistry likes. There isn't a lot of AH above 13.3 so i don't charge mine over 13.8 but i think that might not be the right choice because the internal bms probably balances the cells by dissipation at a higher set point. What i have chosen is to set the charge limit to 13.8 and then once a month charge to 14.4 to re balance. I think this will give the longest life. The chart you posted is the closest way to guestimate SOC by voltage but you can see that there isn't much capacity above 13.35 so why push above that (other than to balance)? You can actually over charge them at 13.86 if left charging at that voltage long enough.

How is it possible to overcharge LiFePO4 cells at 13.86V (3.465V)?

I have a 10A charger putting out 14.3V )never used yet) and assumed I could leave it connected indefinitely with nothing to worry about (since 3.65V / 14.6V is the specified max charge voltage for the cells).

So how does a proper charger damage cells when charging below the specified maximum voltage?
 
How is it possible to overcharge LiFePO4 cells at 13.86V (3.465V)?

I have a 10A charger putting out 14.3V )never used yet) and assumed I could leave it connected indefinitely with nothing to worry about (since 3.65V / 14.6V is the specified max charge voltage for the cells).

So how does a proper charger damage cells when charging below the specified maximum voltage?

The charger only knows pack voltage ... what you are considering is a perfect scenario where all cells are equal and there is nothing going wrong such as a bad connection developing.
The BMS will be monitoring individual cell voltages and disconnecting if something gets out of line.
 
The charger only knows pack voltage ... what you are considering is a perfect scenario where all cells are equal and there is nothing going wrong such as a bad connection developing.
The BMS will be monitoring individual cell voltages and disconnecting if something gets out of line.

OK, yeah, that’s what I was suspecting - so if the charger is left connected and one ‘higher SOC’ cell hits the cut-off voltage before the others, BMS will disconnect and I don’t need to be concerned about overcharging that cell (or any of the others).

My BMS has an overcharge disconnect voltage of 3.75V and an overcharge release voltage of 3.6V, so I suppose that if one (or several) cell(s) are at a much higher SOC, they could hit 3.75V causing a disconnect and then relax/rebalance to below 3.6V if the other cells are below 3.575V (limit of my charger, assuming equal division onto cells). In that case the BMS May reconnect to resume charging and the cycle will repeat until all of the cells reach 3.575V.

It may take a long time (many cycles) but I believe my BMS+charger combo should eventually get all of my cells to 3.575V if I just leave it connected, right?
 
What BMS do you have? Do you know how much balance current it has?

I have seen recommendations about manually balancing using a resistor if the BMS doesn't have much balance capability. You could probably find that with a search.
 
My BMS has a balance current of 78mA and a balance turn-on voltage of 3.55V.

What I do not know is it’s accuracy.

I just bought a BattGO monitor with balance capability and it clearly states voltage measurement accuracy of +/-5mV and balancing cells accuracy of ‘<5mV’ but it has no specification for the balance current.
 
78 mAmps or 0.078 Amps. Not much if you have a few Amphours to pull out of that cell that wants to be a runner.

Yeah, using the SOC/voltage table at the start of this thread, around 3.55V (where the balanced kicks in), 78mA for a full hour will only shift SOC by 78mAh or 0.087% for my 90Ah cells.

The more expensive ($99) BattGO charger/balancer has a balance current of 2.2A/cell, so I probably need to trade up to something like that if I don’t want to reconfigure the battery and get a 3.2V charger...

At 2.2A, that balanced can shift SOC by more than 2.4% in an hour...
 
What @Ampster said ..... You probably need to look up the manual resistor method.

I’ll try to find it, but any pointers appreciated...

My BMS is going to be next to useless for balancing and significant imbalance, but it should prevent any cells from exceeding 3.75V. If one call is at 3.75V and the neighboring cells are at 3.3V (~70% SOC), that 0.45V of differential should quickly drive the high cell down close to the voltage of the neighboring cells. 10%SOC shared into each adjoining cell should result in all 3 cells being at ~80% SOC.

So again, based on the table at the beginning of this thread, that would mean a ~10mV difference between those three cells at 80% SOC and the adjoining cells at 70% SOC.

Not much current will flow from a 10mV voltage difference, but the entire charge/passive balance cycle can be repeated which should drive another 10-20% SOC from the high cells to their neighbors.

As long as my BMS protects from overcharging any high cells, I feel like I’ve got nothing to lose in trying a few charge - relax-passive balance cycles..,
 
snip- There isn't a lot of AH above 13.3 so i don't charge mine over 13.8 but i think that might not be the right choice because the internal bms probably balances the cells by dissipation at a higher set point. What i have chosen is to set the charge limit to 13.8 and then once a month charge to 14.4 to re balance. I think this will give the longest life.

I'm with you Shane, I'm aiming to set my upper limit to around 13.8v. My Projecta 7 stage battery charger has a power supply mode which stops charging at 13.816v. My BMS is set a little higher, hopefully I can set up solar and DC-DC charger to do the same and not have the BMS cut off charging. I'm just waiting on some cabling to arrive, so I can connect it all up. Still doing lots of research to help me fine tune everything, huge learning curve.

What are your conservative low voltage disconnect settings?
 
Following here because I like to revise my settings in my BMS as I thought I had it figured out until I started looking at it all. Running Chargery BMS
 
Hi, a basic question and apologies for being such a noob.

I have a 19.8v lifepo4 battery pack. 6s3p. I have a BMS attached to it. I have a variable voltage DC charger, so according to the chart if I want to charge to 95% the. The DC voltage I input should be 20.7v is that right? And when my solar arrives that should feed 20.7v too?

Thank you
 
How is it possible to overcharge LiFePO4 cells at 13.86V (3.465V)?

I have a 10A charger putting out 14.3V )never used yet) and assumed I could leave it connected indefinitely with nothing to worry about (since 3.65V / 14.6V is the specified max charge voltage for the cells).

So how does a proper charger damage cells when charging below the specified maximum voltage?
There's a difference between "charge voltage" and "float voltage".

The charging spec for lifepo4 batteries is "charge to 3.65v and then stop charging". It is not "charge to 3.65v and hold at 3.65v".

I haven't seen a manufacturer recommended float voltage. You can search the internet and read a whole bunch of articles to see if a float is a good idea or not, and at what voltage. And the right answer may depend on your use case as well. If I needed a float for some application, I'd set the float voltage to somewhere between 3.35v/cell & 3.4v/cell (13.4v to 13.6v for a 4s pack).

It's certainly not the right answer to hold the batteries at 3.575v for any length of time. You probably won't damage anything, but you will probably significantly decrease the life of the battery that way.
 
Yes, I agree, it is not a good idea to hold Lithium at high voltages for a long time. I agree that setting Float depends on use case. My inverter is always on and there is always load on my pack. Therefore since I only charge from solar my float is set at 3.375 v per cell to keep them topped up slightly above the voltage they would settle at. Most of the days that is only from mid day until solar fades 5 hours later. The float Amperage in my case is also only 10 Amps on a 560 Ahr pack.
 
Hi guys, I was looking through the mobile-solarpower.com website, and on this page I found a battery voltage chart for LiFePO4 batteries.

msf4vpdl-1_14.jpg

But I noticed it wasn't showing the exact voltage ranges that my battery data sheet does.
My data sheet shows 100% charge at 14.6V and 0% charge at 10.0V.

Battery Model100Ah 3.2V
Nominal Voltage3.2V
Standard Charging Current0.5C (50A)
Standard Discharging Current0.5C (50A)
Fast Charging1C (100A)
Charging End Voltage3.65V (14.6V)
Discharge End Voltage2.5V (10.0V)
Charge Temperature Range0 - 55°C
Discharge Temperature Range-20 - 55°C
Max Cont. Discharge Current1C (100A)
Max Burst Discharge Current3C (60sec) (300A)
Impedance<045mΩ
Screw TerminalM6
Weight2.2Kg (8.8Kg)

I thought that maybe I could make my own voltage chart more suited to my battery's specifications, shown below.

Capacity %Pack VoltageCell Voltage
100%14.603.65
99%14.453.61
95%13.873.46
90%13.303.32
80%13.253.31
70%13.203.30
60%13.173.29
50%13.133.28
40%13.103.27
30%13.003.25
20%12.903.22
17%12.803.20
14%12.503.12
9%12.003.00
0%10.002.50

I was wondering if someone could cast their eye over it and let me know if anything needs to be changed. I'm a beginner at this so would like to learn how to be accurate when making the voltage chart.
Thanks.
Just read this whole thread. As a newbie I have to admit it is mostly confusing. Seems like, in this case, we've defeated the purpose of using a forum to gather accurate and meaningful data.

I wish there was a way to separate the wheat from the chaff as you say. Guess I'll have to just keep reading reading reading, experimenting and measuring. I wish I understood this stuff better.

Thanks everyone I know you are trying to help.:)
 
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