LiFePO4 Voltage Chart?

[John Frum]

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.

 

[HJHH]

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]

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%?

 

[John Frum]

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%.

 

[John Frum]

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%.

The 100% voltage doesn't really matter after we have found the 90% voltage.

 

[HJHH]

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 ??

 

[John Frum]

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.

 

[MisterSandals]

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]

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.

 

[reg]

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:

 

[Ampster]

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.

 

[reg]

I suspect you mean 13.8

Yes, 13.8V, as the Valence document that I appended says. I've corrected my post, where I missed the "1" and said 3.8V.

 

[HJHH]

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 .

 

[John Frum]

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]

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

 

[Ampster]

I charge my cells to 3.4 volts and think I have charged them to 90% or 95%. I agree with @smoothJoey that those numbers look way off. There is no loss of capacity from a full charge at 3.65 volts to a resting voltage of 3.35. The chart implies that there is 25% loss. Also when my pack gets to 3.0 volts per cell I think I have 10% left and that chart implies 45% capacity. It is one thing to have the lights go out because one thinks there is some capacity to get through the night. I would not want to be driving an EV that said I had 45 miles left and then be stranded on the side of the road 10 miles later. I agree with the majority of the other charts published so far in this thread.
As a practical matter I rely more on my Coulomb counter to tell me how much I have consume since I last charged my pack.

 

[cyclen]

Thanks for sharing, the chart of the battery is very useful for reference, and your avatar is very interesting ~ thanks

 

[OnTheRoadAgain]

With such a huge change (70-30%) over just a 0.2V range you're really not getting a very good idea of the actual SOC by using voltage. IMHO using a shunt/hall sensor is really the best way to tell how much power is left in your pack.

So tell me,
in all seriousity......

If I was to put my LiFePO4 at 13.10 volts, would I not be "close enough" to storage state (40%) to sleep comfortably?

I mean, would I really need to dilly with a shunt, hall sensor and all that?

Are you telling me that if I use a good VOM and the terminals say 13.10v I can't use that and be assured I'm pretty darn close?

 

[MisterSandals]

If I was to put my LiFePO4 at 13.10 volts, would I not be "close enough" to storage state (40%) to sleep comfortably?

Yes. Good night.

 

[time2roll]

I would sleep just fine with the battery at 3.10 and no chance of being depleted.

 

[MisterSandals]

I mean, would I really need to dilly with a shunt, hall sensor and all that?

If you can measure your battery voltage, you can live by this chart unless you're living on the edge of squeezing every amp hour out of your battery. I live between 13.0 ("getting low") and 13.3 ("looks pretty full").
Don't overthink it.

 

[OnTheRoadAgain]

With such a huge change (70-30%) over just a 0.2V range you're really not getting a very good idea of the actual SOC by using voltage. IMHO using a shunt/hall sensor is really the best way to tell how much power is left in your pack.

CMM

 

[Michaelz850]

I think JASONHC is correct ...

Charging LiFePO4 is a two step process … FIRST step uses constant current (CC) to reach about 60% State of Charge (SOC); And then STEP 2 kicks in until the charge voltage reaches 3.65V per cell. Turning from constant current (CC) to constant voltage (CV) means that the charge current is limited by what the battery will accept at that voltage, so the charging current tapers down asymptotically.

If you had to time the process – STEP ONE (60% SOC) needs about one hour and the STEP 2 (40% SOC) needs another two hours .. I have seen it that way ever since I started working with LiFePO4

Ghostwritter66

Yes, I do believe this is correct or at least it’s correct on how my lifepo4 batteries charge. I have a 200ah Calb battery bank that charges each cell to 3.33 volts fairly quick but after that it takes twice as long to reach 3.40 or 3.50

my personal opinion is that I do not charge my cells past 3.60 / 3.65 simply to extend the life of them based off everything I’ve researched and personally tried out myself. Now my cells won’t charge above 3.4 and or I don’t push them above that and I’m happy with that because I still get 210-215ah when I did a capacity test a year later!

 

[Michaelz850]

If you can measure your battery voltage, you can live by this chart unless you're living on the edge of squeezing every amp hour out of your battery. I live between 13.0 ("getting low") and 13.3 ("looks pretty full").
Don't overthink it.

MisterSandals

I would say you are spot on with those numbers! 13.3 or 13.4 on the high end is where I keep my battery bank at and it works flawlessly! I’m happy knowing I still pull full capacity on my Calb 200ah lifepo4 12v system well over a year later! Especially since I’m fairly new to all this technology!

I’ve recently upgraded my backup power system to a 24v set up to save money on the wires. As we all know 62mm or 2/0 gauge welding cables are expensive!! Not to mention a pain in the A$$ to maneuver through boxes and boards, etc. and like you said don’t over think it! If your getting dam near the capacity or even a little under than what you paid, be happy! Just because a car says it will go 200mph don’t mean ya should test the max limits! LOL ?

 

[JohnnyOcotillo]

That makes no sense. Couloumbic charge efficiency of LiFePO is about 100%. If you are charging with a constant current from 0% to 100% the last 20% (from 80% to 100%) takes exactly 20% of the time.

If you are trying to define your point of 80% charge from your table of voltages above, you are just fooling yourself. If you are not in the top or bottom "knees" of the curve, you need to have the cell resting for many hours before you can get any idea of charge state from voltage. Even then, it's extremely blunt.

The big word you used doesn't work like you think it does. The Couloumbic efficiency of a LiFePo is indeed 99%. . . . at a moderate charge and cool ambient temperatures. Unfortunately, full batteries like to heat up, dropping that efficiency. While I agree the 3x the time claimed for the final 20% charge does seem a lot for a LiFePo since it isnt bothered by the stadium effect as much, it is not immune to it.

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