LiFePO4 Voltage Chart?

Ampster

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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

https://www.lifepo4battery-factory.com/
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Thanks for sharing, the chart of the battery is very useful for reference, and your avatar is very interesting ~ thanks
 

OnTheRoadAgain

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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?
 

time2roll

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

MisterSandals

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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.
 

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Michaelz850

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Jun 27, 2020
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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

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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

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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.

 

firemen

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Oct 2, 2020
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I am charging with grid-tied solar, so basically grid power. I have off-grid about ready to get installed in the next few weeks. I plan to set up the MPP Solar LV5048 to charge only from solar. I expect it is more than enough to charge the batteries, my end game is to go entirely off-grid with about 8 kWp.

I have been bulk charging at 56.5V@16amps which is 3.53V@0.25amp per cell. (16s4p) Since these are very used cells, mine self-discharge, so I float them at 52.9V.
Hi Jason, 56.5 v @ 16 amp will give more 3.53v@4 amp par cell for 16s4p array.

My best regards
 

jasonhc73

Cat herder, and dog toy tosser.
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No that's not the way it works. If you have a 16S pack, and you put 16A into it, *ALL* the cells in the pack are seeing 16A go through them. Like @BiduleOhm said, your 16s4p has 16A split across four parallel sets of 16, so each cell should be seeing 16/4 = 4A.
I see the monkey wrench now.

I am 4p16s. or 4 batteries in 16S.
 

nifty-stuff.com

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Long thread, lots of interesting discussion but this sounds pretty solid and dead-simple to me, so I'm sticking with it! :D
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.
 

Capt Bill

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I wrote down: between 25.35v to 27.2 volt (as sweet spot voltage on 24v set from one respected opinion) for a 24v LiFePO4 battery bank; which equals 3.168v to 3.4v per cell; & for a 12v battery bank would = 13.4v to 13.6 / .. a little bit of contrast to your view "13.0 ("getting low") and 13.3 ("looks pretty full"). I think if you get equalizing cell voltage on charges above 3.325 v per cell, one could safely go up to 13.6 v on a 12v LifePO4 battery bank. If solar is available for that higher charge, why not go there is ... my two cents way of thinking :+) ... (from just glancing at this tread)
 
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