Charging LiFePo4 (LFP) to 3.4V and 3.5V with and without Absorption. What a difference!

i think a higher rate of charge reflecting the high charge currents that solar can do and equivalence on discharge say at least 50amps and also 100amps. extrapolating that out at "48volts" is a kettle and / or a toaster load. Cheers for your vids!

That's really some eye-opening results from the tests you did. Thanks very much for sharing. I'm interested in discharged capacity with the cut-off voltage at 2.6 or 2.7v. How much would the capacity be reduced. I'm guessing that's similar to shallow depth of charge, but not sure how shallow or deep that is. Thanks again

Great test. I always wondered if a battery will charge to full capacity with a lower voltage using absorption. Question is answered 👍

I have a brand new tester and my max cutoff amperage is 9A. I cannot set 19A.

Very good video! It expains a lot! I always charge my cells to 3.469V (55.5 / 16). This is for my setup the best voltage to minimize deviation of cells to each other and absorb this voltage till the sun goes down! In summertime for 3 or 4 hours... so I can be sure the battery is fully charged!

Best greetings from sunny Germany! 😊

i was wondering all the time "what is absorption?" "do i need absorption with my lifepo4 box?".
All my doubts are gone!
i dont have words to thank you Andy!

Sorry but what ive seen on his videos I wouldn't put much faith into his advice.

Isn't "absorption" actually where the BMS balances the cells?

BMS

I use a 100 amp 24v battery for a wheelchair, I charge it to 3.45v per cell and discharge it to 3.2, 3.1 per cell. Is that good for the cells themselves?

Ciao avendo un inverter ibrido, bulk e float come vanno impostato? Grazie per eventuale risposta

You did it the wrong way. Measure capacity first, then discharge to 3,3. Then test charging to whatever, compute, charge to 100%,discharge to 3,3, do another test. Would take you half the time.

Even at home, there is no float/absorbtion time. I don't want to charge from grid, solar charge time can be 20minutes 2hours or 12hours a day. If soc is ready, i let it discharge to a set point. No more magic allowed.

Info about those 20A-30A Aliexpress chargers with cooling fins and fan in the middle: you can order them with custom voltage, e.g. 55.4V (=3.4625V).
The alternative: most of the chargers (even cheapo €30 4A chargers) you can open them (at your own risk) and find the tiny potentiometer which is for fineadjusting. But in many cases it is +/- 0.8V. - so i ordered a LiIon 13S charger at 54.6V and could adjust it to 55.3V which is 3.46V per cell. The closer the base-voltage to 3.45-3.5V the better.

Thanks to all your experiments and sharing/education I charge to 3.46V. But at which voltage should i enable active balancing? 3.42? 3.43? Or really late at 3.46V?

Excellent! Would it then be ok to keep a lifepo4 constantly on a 3.35v cv w/o overcharging? If so, using a cheap buck cc cv where cc is set to a reasonable max current, and cv to 3.35v would be a perfect lifepo4 charger (provided I do not need to recharge in a rush)?

Hey Andy, thank you very much for this. Very informative!
I have just installed a yixiang diy box with 304 Ah EVE cells and is learning lots as I integrate it with my Victron / Fronius AC coupled off grid system in the north of New Zealand.

Do you think it would be useful to have a low cell voltage start balancing setting in the JK BMS?

Question: what is the best way to limit final charge voltage???? When using normal charger. With the BMS or charger??? I thing BMS just cut charging after reaching set voltage. Charger after reaching set voltage will finish with decreasing current. Am I right?? Anyone Something????

Добрый день. ваши видео интересны, спасибо. только начал изучать эту тему, у меня нет приборов, делая тесты я смотрел на показания БМС заметил что инвертор начинает снижение тока заряда примерно в 3,8v или чуть выше, тогда основная емкость еще не получена, а ток уже снижается, что естественно увеличивает время заряда, так как ток заряда меньше. но это более щадящий режим заряда.
я хотел поговорить вот о чем, если сравнивать свинцовые батареи, то там были такие параметры как основной заряд, поддерживающий заряд и выравнивающий заряд.
если БМС подключается с ручными настройками, то это тоже можно организовать чтоб основной заряд был 3,55, поддерживающий еще его называют плавающий 3,4 и раз в 10 дней включался выравнивающий заряд батарея используется как UPS в буферном режиме.
А как ведет себя инвертор когда подключен к БМС по CAN или RS485, но используется в буферном режиме, его надо взбадривать до 3,55 или он может спокойно находится в 3,4 долгое время.

Excellent work, i have learned many things from you thanks.
Sir, I have a small setup 4 cell lifepo4 100ain series (12v) battery pack my load is small like 30a i am using that load around 2 hours once a week
So i am thinking of unplug battery charger because it is waste of electricity in my area where i live electricty is expansive.
1. can i unplug my battery charger for a week or 10 days after charge the battery till i take some energy from battery then recharge and unplug can i do it this way ?
2. it will effect my battery life ?
3. it will effect my battery pack ?
i need your expert openion and if possible guide me some tips for make my battery pack long run and energy saving.
if possible make a short video on that topic because many peoples are using small setup and want to save electricity it will help lot of people they are thinking about it or not when they see the video they will think and they got benefits from your knowledge.
Regards

Sir this is really amazing keep it up and i learned lot of from you thanks

Seems like the absorption would be important though to top balance the cells.

Will you damage or reduce the lifespan of a cell if you only constantly charge at 3.4v without absorption, so only taking it to approx 89% instead of 100%. I also normally stop discharging when there is around 15% SOC left so not to stain the battery. I have heard that not fully charging a cell can drastically increase the lifespan of the cell.

Where should I set the FLOAT on my 48v bank?

Realistically the only way to really limit the level of charge of a lifepo4 is counting ah in. 🤷🏻‍♂️

You save us all a lot of time and energy!!! Thank you!

Does 3.65 volts mean 100% charge and 3.4 volts will charge the cell to 80%?

Or are 3.65, 3.5, or 3.4 volts the charging speed of the cell?

Id be very curious to see the test repeated for 3.45V - this way a 12V pack can be charged to 13.8V (standard float voltage for gel batteries).

Brilliant information. Thank you for putting your time and effort into making this video.

Have you make a video of next lower steps of voltage?

Hello. How are you doing for use the vertical and horizontal rules displaying the points values on the graph in the EB software?

Yes .
I life on a boat.
And my mppt are set on 14volt so that is 3.5volt on a cell.
On the port with wall power i use only charger if i need it .
But that us set on 13.2 volt means 3.3volt on a cell
Reason is that you have to pay for power on the port .( 0.60 cent for 1kwh)
With a lower volt for the night it will only charge if the battery is part discharge.
So if the sun go up the mppt thake over by charging with a higher volt and charger will shutdown.
Only charger wil be use if days with bad sunlight (rain)
Normal i use about 10/15% on a night discharge for run the systeem on board.

I can always charge with the dc to dc charger by the alternator with a max of 20a and 14.2 volt if i'm on the sea and the solar power can not charge .

Hi Andy, complete beginner here. Love your videos and your humour. There's a lot of info there to try to get my head around. But in a nutshell are you saying that its best to only charge each cell to 3.4v rather than the 3.65v that seems to a common figure used. I want my batteries (when built) to last as long as possible. Appreciate your thoughts maybe. Thanks

I also have a mitor yacht I spends 4-5 months at a time on in the Bahamas and Florida. Mostly when I am at anchor, I set the charge controller to 14 volts, or 3.5 volts per cell and absorbtion time to 6 hours. I use about 10-20% per night depending on how much cooking we do out of the 1500 amp bank. One night I did turn on the front AC for better sleeping and woke up at 25%. This ks not normal though as it takes several days to get the batteries back up. My large bank is also there because I can be 3-5 days of little sunshine. When charging we'll, it ussually supplies 50-70 amps for a large portion of the day amounting from 2-7 kw a day from solar. When I move locations, the engines will supply about 200 amps more for 1-8 hours depending on the trip. These have vehicle alternators that I have changed the regulators in to stop at 14.0volts instead of the 14.3 volts they shipped with and with temperature compensation to not kill the prematurely. When I am at dock not using the batteries, I change to 13.5 volts, 3.25 per cell just keeping them on standby. This is where I let them remain until I am under way again, sometimes a month later. I could not tell you how this affects my batteries, but it is what makes me comfortable after watching your and other videos. Thanks for all the good work.

Does it really make a difference a tenth of a volt...

Great info...thanks for sharing ❤❤

Actually, the cells are within the battery and prismatic batteries use internal folded membrane cells known as a prismatic cell configuration. Thus your battery consists of many prismatic cells and your battery bank, consists of many batteries.
You are testing a parallel grouping of cells called a battery. You aren't testing a single cell, you would have to carefully take the battery apart in a controlled environment to test one of the cells within the battery if you wanted to test a cell.

Thank you.

I use a elejoy charge controller 600 w . i set the voltage 14 v and it stops why spend more money on a change controller

The other thing to remember is that new battery will have retained its charge but when the battery gets old many half life the equalizing will be a better way to charge also when the cels are in series equalizing/absorption is preferred.

You check battery capacity without discharging. You can measure the internal impedance of the battery instead. The lower the internal impedance the higher is the capacity.

Very good information. At my home I am using a 12V LiFePO4 6ah battery as a DC backup for my home network. I have a simple power supply to both run the network equipment and float charge the battery and had been trying to determine what would be the best voltage setting to keep the battery fully charged but also not damage the battery. There are many articles which state that you should never float charge an LiFePO4 battery. However, a PowerSonic article stated that you can use 13.8V (equivalent to a cell voltage of 3.45V). Your testing shows that I should be fine by setting at 3.4V per cell (13.6V for the battery), so that's what I am now using. Excellent info! Thanks

I'm confuse. What is absorption

at what percent of 100% do you use your system in everyday use. Do you charge to 100% every time you use your solar ? I'm thinking about battery life.

Very interesting indeed! I am using an 8 cell Eve battery of 305Ah per cell for a boat. Lately for being in port I adapted to charging only to about 3.3 vdc this because in port while on shore power charging at a higher voltage could lead to overcharging. At first I was charging to 3,5, and found that one cell usually went up to 3,65v causing the bms to switch off the battery. Now I only charge to 3,45v per cell the day before we plan to sail. Same story when running on engine for long periods. Also then a lowered charge voltage should be prefered I feel. I am interested to hear your opinion about this idea.

In a typical battery, you charge the cells in a series. Cells tend to have different self-discharge rates, which is the only reason for voltage balancing. Charging to a lower finishing voltage protects cells from over-charging, while others may not come up as soon. it also requires a longer absorption charge, giving the voltage balancing system more time to equalize the states of charge, of the individual cells. Voltage balancing should only be done, during absorption. The battery should be discharged and bulk charged coulombically, meaning NO balancing during use. This helps keep the states of charge of the individual cells in the battery as close as possible. There are 3 variables in a battery. Self discharge rates, equivalent series resistance, and capacity. All three of these conditions are completely independent. During load, cells with higher resistance will show a slightly higher voltage during charge, or lower, during discharge. Capacity will show different states of charge after discharge, but will often re-equalize as the battery charges back up. Self discharge rate causes unbalance over time, no matter how the battery is used. Voltage balancing during absorption becomes more critical, as the battery ages. Proper balancing goes a long way, towards getting as much cycle life out of a battery, as you can get out of a single cell.

This is a very good and valuable test! It shows a LFP cell can already be overcharged at 3.4V if you charge too long and with too little current. If you charge only to 3.4 and let it absorb its probably less stress for the cell. If you charge to 3.5 with a cutoff current high enough (about 0.02C) the cell will be fine but if you keep charging until 0.00xC you will most likely overcharge and damage the cell already a bit. A Voc (open circuit voltage) of 3.5 is already massive overcharging for one cell! You are more on the safe side with 3.4 or even 3.35V with absorption.

Respected sir
Salute to your deep knowledge ❤❤

Sir. I request you to speak English. A little slow speed .....
That's why we can understand. Your video more. Deeply ...,
Please. Spake little slow English ....for future videos ❤❤❤