Float of LFP

[sailorboy1]

You read it all time that it is bad to float a LFP battery.

Anyone have an actural link to paper on an actural test to support this? Not just a statement from "X" (even if a supplier), but an actural test.

I couldn't.

[SaltEnjoyer]

If you mean floating at 70% or 80% state of charge to store energy (charging lithiums to 100% is a different topic), there is no problem with that. The LFP battery will recharge up to that voltage and remain there.

e: here is an interesting read on LFP aging, which is tangential since you'd be keeping it at a % SOC https://iopscience.iop.org/article/1...0411609jes/pdf

[wholybee]

What is important to understand is what "float" actually means. "float" is charging at a low current, when the battery is fully charged. For lead-acid, the counters self-discharge, and helps prevent or reduce sulfation.

LFP to not self-discharge, and do not sulfate, so floating is not needed. Moreover, if you continue to charge an LFP after it is 100% charged, you will damage it, and that is well documented.

The confusion is that when you set the "float" voltage in a charger at some voltage below fully charged, you technically are not float charging the battery. For LFP fully charged is considered 3.4Vpc. That is why the recommendation is to set float to less than 13.6V. At 13.6V or higher you risk overcharge. When you do this, you are not float charging. What really happens is that charging stops entirely, until the battery discharges to whatever the float voltage is set to.

[sailorboy1]

Moreover, if you continue to charge an LFP after it is 100% charged, you will damage it, and that is well documented.

/QUOTE]

Is it? That is the question, post a link to a testing study

[wholybee]

Originally Posted by sailorboy1

Moreover, if you continue to charge an LFP after it is 100% charged, you will damage it, and that is well documented.

/QUOTE]

Is it? That is the question, post a link to a testing study

https://www.google.com/search?q=over...+dendrite#ip=1

[sailorboy1]

Originally Posted by wholybee

https://www.google.com/search?q=over...+dendrite#ip=1

I read through a few of those and don't feel they answered the question. Some mentioned "overcharge" but didn't define what that was/is.

[sailorboy1]

Someone on another forum posted a link that is close so I am going to add it here also:

https://iopscience.iop.org/article/1...0411609jes/pdf

The study was about aging capacity loss due to storage at various state of charge (SOC). I feel one can argue that a float voltage corresponding to a given SOC is reasonable to assume.

So from page A1874 of the page and the chart for the LFP battery stored for 9 months, and using the 25C

stored SOC between 80-100% the capacity was 94% relative (a 6% loss of capacity)

stored SOC between 40-80% the capacity was 97% relative (a 3% loss of capacity)

To me this suggests the "don't float at full" is almost meaningless loss compared to other SOC.

So overall to me this says float doesn't mean anything for LFP. Assuming of course you aren't holding a voltage above 100% SOC, which is a different subject.

[Nicholson58]

Great link. Knock yourself out.

https://marinehowto.com/lifepo4-batteries-on-boats/

I have all my programmable charge devices float set to about 95% full charge. Overcharging Lithium will wreck them. While on the hard for hurricane season, 6 months, setting is 65%.

[wholybee]

Originally Posted by sailorboy1

Someone on another forum posted a link that is close so I am going to add it here also:

https://iopscience.iop.org/article/1...0411609jes/pdf

The study was about aging capacity loss due to storage at various state of charge (SOC). I feel one can argue that a float voltage corresponding to a given SOC is reasonable to assume.

So from page A1874 of the page and the chart for the LFP battery stored for 9 months, and using the 25C

stored SOC between 80-100% the capacity was 94% relative (a 6% loss of capacity)

stored SOC between 40-80% the capacity was 97% relative (a 3% loss of capacity)

To me this suggests the "don't float at full" is almost meaningless loss compared to other SOC.

So overall to me this says float doesn't mean anything for LFP. Assuming of course you aren't holding a voltage above 100% SOC, which is a different subject.

Setting a float voltage less than 100% (3.4Vpc for LFP) is not floating. Thats storage. To float, the voltage must be greater than the full charge voltage. For example, lead is fully charged at 12.7V. But float is over 13V.

And that is what's bad. Setting a lower float voltage isn't float charging, and is fine.

[sailorboy1]

Originally Posted by wholybee

Setting a float voltage less than 100% (3.4Vpc for LFP) is not floating. Thats storage. To float, the voltage must be greater than the full charge voltage. For example, lead is fully charged at 12.7V. But float is over 13V.

And that is what's bad. Setting a lower float voltage isn't float charging, and is fine.

if that is how you feel you win it is OK with me

meanwhile my non lithium battery charger has 2 different fixed profile setting with float of less than 13.6

[rslifkin]

Originally Posted by sailorboy1

if that is how you feel you win it is OK with me

meanwhile my non lithium battery charger has 2 different fixed profile setting with float of less than 13.6

I think the distinction being made is that depending on what voltage the "float" mode in the charger is set to, it may or may not serve the function of a float charge from the battery's perspective. Having it set lower than the 100% SoC resting voltage of the battery will allow the "float" mode of the charger to carry loads instead of discharging the battery below a point, but it won't serve as a float charge for the battery (and therefore won't make sure the battery stays 100% full).

[CaptainRivet]

Originally Posted by sailorboy1

You read it all time that it is bad to float a LFP battery.

Anyone have an actural link to paper on an actural test to support this? Not just a statement from "X" (even if a supplier), but an actural test.

I couldn't.

https://nordkyndesign.com/charging-marine-lithium-battery-banks/
Best description i know and not from therory from armchair but practical knowledge.
Not only about float. But he even describes how you can overcharge an LFP with floating it.

My bms ends charge if a cell hits 3,53V

[Captain Bill]

I have one program I use for underway an one for dockside. Underway I charge to 14.2 and float at 13.3. At the dockside I charge to 13 and float at 12.99. My charger does not like the float and absorption to be the same. The batteries power the house load from full until the voltage drops below the float and then charges back to the float voltage. The battery monitor tells me it really drops to about 12.98 when at the dock the cycles to about 13. Underway I usually get to full at about midday on solar and the voltage is down to float by 1600 or so in summer the solar will hold the voltage at float until evening when the voltage again begins to drop. The batteries are only about 20 months old and I haven't noted any obvious change in capacity, but I can't really say what the long term effect will be.

[CaptainRivet]

Originally Posted by Captain Bill

I have one program I use for underway an one for dockside. Underway I charge to 14.2 and float at 13.3. At the dockside I charge to 13 and float at 12.99. My charger does not like the float and absorption to be the same. The batteries power the house load from full until the voltage drops below the float and then charges back to the float voltage. The battery monitor tells me it really drops to about 12.98 when at the dock the cycles to about 13. Underway I usually get to full at about midday on solar and the voltage is down to float by 1600 or so in summer the solar will hold the voltage at float until evening when the voltage again begins to drop. The batteries are only about 20 months old and I haven't noted any obvious change in capacity, but I can't really say what the long term effect will be.

Total voltage is fake security, at 14.2V one cell can have 3,75V while all other 3.3V or even worse.
Charging must be done on cell level, that why its best the BMS manages the battery and charging and not the charge sources.
Flaot at 13.2V makes no sense with a LFP, if it gets into the knee it reduces the current it takes by itself. An LFP needs no float at all,.you can but it is unnecessary.
A friend of mine i charging his LIfepo4 Calb cells since 17 years with a power supply with 13,85V, BMS cuts off of a cell hits 3,5V. Calbs have still 92% of their original capacity.
I would put 13.8 and 14.2V if you only can on total voltage but add a BMV 712 and use the midbank voltage of the 2nd measurement input to check voltage devation of cell 1+2 versus 3+4. So if devation rasises you avoid overcharging a cell.

[sailorboy1]

we are talking LFP "float" which is no higher than 100% SOC voltage

I got my answer and am moving on as I can see thread drift is about to set in.