LiFePO4 Voltage Chart?

x4dow

Solar Enthusiast
because of the lifepo4 being so linear, I'm actually setting up my voltimeters (that show capacity in a linear way) as 0% on 25.5V and 100% on 26.8V. even though that technically is 20 to 90%. because if i set it as 20v to 29.2v the battery would display "50-60%" across 90% of its capacity. I rather have it showing "0%" on 0-20% and "100%" on 90-100% and have a better "estimate" of capacity across the 10-90% displayed capacity
 
I question the voltage results on the chart.. 3.65v = Max, 2.5v = Min, Cell voltage useable range = 1.15v / 100 = .015v per %
1617472463978.png
Please let me know if someone would.. I am planning to use 56.5v max and 42.0v min which is fine.
It's a minor issue but mostly wondering how the voltages were determined? Total AH / 100 * 80% = xyz voltages? Don't know?
Thanks Prospector Tripp
 

dRdoS7

Solar Enthusiast
Hi,

I question the voltage results on the chart.. 3.65v = Max, 2.5v = Min, Cell voltage useable range = 1.15v / 100 = .015v per %
View attachment 43654
Please let me know if someone would.. I am planning to use 56.5v max and 42.0v min which is fine.
It's a minor issue but mostly wondering how the voltages were determined? Total AH / 100 * 80% = xyz voltages? Don't know?
Thanks Prospector Tripp

It really has no meaning except for relationship between various cell voltages, and what that would equal for the different pack voltages. Someone probably divided up between 2.5V minimum, and the 3.65V maximum for LFP. Looking at a graph for LFP, you'll see that 3V is around 9% SOC, but in that table it's 40%.

dRdoS7
 

HJHH

New Member
Hi .. I have EVE batteries 280Ah 8 cells 24V .. I want to use 80% so that they last long .. What is the highest voltage and lowest voltage for charging and discharging that I will program the BMS and inverter with to give 80%?
 

smoothJoey

Scary!
Hi .. I have EVE batteries 280Ah 8 cells 24V .. I want to use 80% so that they last long .. What is the highest voltage and lowest voltage for charging and discharging that I will program the BMS and inverter with to give 80%?
Assuming you have a shunt based battery monitor or bms with similar instrumentation.
Do a capacity test from as close to 3.65 volts per cell as you can get.
Then discharge the pack at a rate commensurate with your typical load until the first cell hits 2.5 volts and triggers the bms to disconnect.
Note the voltage where the bms disconnected.
The charge the pack at your normal rate of charge until you get you have put 15% of the capacity back into the battery.
Then discharge at the rate equal to your typical usage model until you are at 10%, not that voltage.
The is the voltage for the low voltage disconnect of your inverter.
Now charge again until you have put 90% of the capacity back in the battery.
Note the voltage.
That is your charge voltage.
Bo's yer uncle.
 

HJHH

New Member
Alternatively you can try 3.375 for your charge voltage and 3.0 for you low voltage disconnect.
See if that satisfies your use case.
This is easier .. But I want to ask about the preferred capacity 80%, which starts from .. 100% - 20%? Or from 80% - 0%, or from 90% -10%, or even from 95% - 15% ??
 

MisterSandals

Participation Medalist
or from 90% -10%
If your preferred capacity is for cell longevity this would be my guess.
If your preferred capacity is to keep cells from going out of balance, then my answer would revolve around what voltages (high and low) they begin to significantly diverge.

Similarly, what voltage to you consider 100%? 0%?
 

smoothJoey

Scary!
If your preferred capacity is for cell longevity this would be my guess.
If your preferred capacity is to keep cells from going out of balance, then my answer would revolve around what voltages (high and low) they begin to significantly diverge.

Similarly, what voltage to you consider 100%? 0%?
Charge the cells as high as you can without tripping the bms and then let them settle.
That is 100%
When the first cell hits 2.5 volts that is 0%.
 

HJHH

New Member
If your preferred capacity is for cell longevity this would be my guess.
If your preferred capacity is to keep cells from going out of balance, then my answer would revolve around what voltages (high and low) they begin to significantly diverge.

Similarly, what voltage to you consider 100%? 0%?
You mean that 80% starts from 90% - 10%? This means 3.54 - 2.62 volts .. Is this correct ??
 

smoothJoey

Scary!
You mean that 80% starts from 90% - 10%? This means 3.54 - 2.62 volts .. Is this correct ??
80% of starts at 90% and goes to 10%.
3.375 volts to 3.0 volts.
To get a better answer than that follow the steps I laid out in a previous post.
Those values are just estimates because we don't know how hard you charge or discharge, the capacity of your battery bank, or how good your top balance is etc.
 
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MisterSandals

Participation Medalist
This means 3.54
Where do your cells settle in an hour? That is when the surface charge (nearly 0 capacity) bleeds off. That is what I consider 100%; my cells settle to 3.35v fairly quickly.
2.62v seems like an aggressively low number for 10% SoC. where did you get that number?
 

Gazoo

Dumb Dumb
Hi .. I have EVE batteries 280Ah 8 cells 24V .. I want to use 80% so that they last long .. What is the highest voltage and lowest voltage for charging and discharging that I will program the BMS and inverter with to give 80%?
You want to program your BMS HVD and LVD at 3.65 volts and 2.50 volts respectively. The BMS is to be used for the last line of defense in case there is a malfunction with another device in the system...like your inverter. I am attaching a file that may help you. Keep in mind there can be slight variations because every cell is slightly different. But this is in the right ball park.
 

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reg

Winter: New York City Summer: Atlantic Canada
I haven't seen a manufacturer recommended float voltage.

I'm responding to an old comment, but thought I'd note that Lithium Werks recommends a float voltage of 13.8V for its U1-12RT, and perhaps other Valence batteries. See the screen capture below from its 2015 data sheet:

Screenshot 2021-04-10 at 4.37.51 PM.jpg
 
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Ampster

Renewable Energy Hobbyist
Lithium Werks recommends a float voltage of 3.8V for its U1-12RT
I suspect you mean 13.8 which is 3.45 v per cell. That works for them in the context of using 14.6 volts for charge setting. That is 3.65 volts per cell and I think they warranty their batteries. I have no warranty on my EVE cells so I only charge to 3.4 volts per cell and float for a few hours from solar at 3.35 volts. This thread is full of seven pages of opinions on the subject.
 

HJHH

New Member
Where do your cells settle in an hour? That is when the surface charge (nearly 0 capacity) bleeds off. That is what I consider 100%; my cells settle to 3.35v fairly quickly.
2.62v seems like an aggressively low number for 10% SoC. where did you get that number?

I am charging at C 0.14 = 40 Ah , while the discharged at C 0.25 = 70Ah .
 

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smoothJoey

Scary!
I am charging at C 0.14 = 40 Ah , while the discharged at C 0.25 = 70Ah .
Where did you get those numbers?
Do you have a shunt or bms with similar function to map amp hours to voltage?
Those numbers just look way off compared to any charge or discharge curve I have seen.
 

HJHH

New Member
Where did you get those numbers?
Do you have a shunt or bms with similar function to map amp hours to voltage?
Those numbers just look way off compared to any charge or discharge curve I have seen.
This is my daily use .. The charging speed was determined by the solar inverter.
yes I have BMS 8S 150A
 
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