Float of LFP

[s/v Jedi]

Originally Posted by nfbr

The BMV requires a charge to 100% approx weekly to maintain SOC calobration. Charging LiFePO4 via SOC will rapidly drift into meaningless
You have to charge by voltage and find the knee (voltage rise) point to calibrate the SoC
Hey, this Jedi, you do good posts, you know all this

Yes, unless it is a very dark day, we recharge to “full” daily. We define “full” as the absorption voltage we selected and program the BMV setting “charged voltage” a little lower conform what the manual recommends. This works perfectly.

For storage mode, cycling between 50% and 60% SOC is fine as well. It will take years before the accuracy becomes so bad that the cycles are too deep or recharge too high.

[T1 Terry]

Float charging damaging lithium batteries refers to batteries that do not monitor cell voltages, only the terminal voltage of all the cells collectively.
Setting the stop charge cell voltage @ 3.4v or 3.45v will result in a not fully charged battery, setting the stop charge voltage @ 3.6v and using an active cell balancer and a timer that restarts the charging 1 min or more after the high cell drops below 3.6v, then a two stage or three stage charger will allow the battery to fast charge to around 98% SoC and then slow the charging till it is fully charged.
Charging at 14.1v and dropping to 13.8v for float will keep the battery charged while under load, but leaving the battery on a float charge for long periods will often result in one cell going high voltage and one cell going low voltage, yet the total of all 4 cells will still equal 13.8v .... so, unless the charger drops to a low maintenance charge at float of maybe *0.5 amps, yet can return to full charging once the battery drops below 13.5v and runs through the charging cycle again, I'd recommend not leaving a lithium battery on a constant float charge.

T1 Terry

* The 0.5 amps is intended to be low enough for the active balancer to holds all the cells close to the same voltage and thereby avoiding cell voltage run away

[sailorboy1]

Alright, lots of people writing like what they write are proven facts. But no source is given for a study that supports it. Let's remember that just because it is on the internet or you read it somewhere doesn't make it true unless there is test/study documentation that backs it up. Just being able to retype what you read doesn't cut it.

[CaptainRivet]

Originally Posted by sailorboy1

Alright, lots of people writing like what they write are proven facts. But no source is given for a study that supports it. Let's remember that just because it is on the internet or you read it somewhere doesn't make it true unless there is test/study documentation that backs it up. Just being able to retype what you read doesn't cut it.

Read eric bertscher' s article i linked from Nordkyn Design. Thats full of sources and proven study, you obviously didn't read it otherwise you wouldn't state that.
With your low budget drop in Lifepo4 and basic BMS you cannot do much anyhow then stay away from floating as what you can gain versus f... up poential and resulting damage means total loss or cut open is not worth it.

[sailorboy1]

Originally Posted by CaptainRivet

Read eric bertscher' s article i linked from Nordkyn Design..

don't see any link, and ift need to be a study/test, not an article

[CaptainRivet]

Originally Posted by sailorboy1

don't see any link, and ift need to be a study/test, not an article

https://nordkyndesign.com/charging-marine-lithium-battery-banks/

I highly recomend reading all his articles, a really eye opener for many incl. me.

[sailorboy1]

Originally Posted by CaptainRivet

https://nordkyndesign.com/charging-marine-lithium-battery-banks/

I highly recomend reading all his articles, a really eye opener for many incl. me.

That is called an article, which is NOT a study or testing.

[CaptainRivet]

Originally Posted by sailorboy1

That is called an article, which is NOT a study or testing.

no we are not repeating the internet. I deal with Lithium since over 20 years...so from experience like Eric or TerryT1 or Jedi. And yes we learn too.
And not from one boat installation, i installed in cars,RV,Boats, house...my DIY installation on my cat is rated for 600A continiuos and certified, so i may know what i talk about. yes with LFP there are different ways to achieve the same.


So much comes from the lead thinking and missunderstanding LFP.
Jedi's post above shows that clearly.

So understanding how this chemstry works is key to understand how to deal with it and not a study...
study are mostly to proof a fact by statistical data, well I don't believe a statistic i didn't manipulated myself or has the output i like.
want a study ask the big LFP manufacturers...

[nfbr]

Part of the problem is the history of LiFePO4. Due to their history they were ignored by the west and patented / produced in china until recently. We have now 20 years of Lithium experience and <4 years of international LiFePO4 manufacturing.
It will take time.
People still argue about how to treat Lead Acid for best life.

[sailorboy1]

Originally Posted by CaptainRivet

no we are not repeating the internet. ...

Sorry, but 100% of that was about following group think. All you really know is what you believe because you have read other believers say so.

I already posted a STUDY that showed that storing a LFP at 80-100% has little difference from storing at 40-80%, so while the STORY of needing to store at 60 % and not 100% has some basis, it is just really a 3 % difference from a STUDY. So in the context of what I asked at beginning of this thread means "floating" at 100 % probably makes difference and other factors of use probably are more

[CaptainRivet]

Originally Posted by sailorboy1

Sorry, but 100% of that was about following group think. All you really know is what you believe because you have read other believers say so.

I already posted a STUDY that showed that storing a LFP at 80-100% has little difference from storing at 40-80%, so while the STORY of needing to store at 60 % and not 100% has some basis, it is just really a 3 % difference from a STUDY. So in the context of what I asked at beginning of this thread means "floating" at 100 % probably makes difference and other factors of use probably are more

Well then let the group think...

Floating at 100% makes a 1-2% difference =1-2AH on a 100AH battery but carries a lot of risks as you have a lot potential to screw it up and have dead or heavly compromised drop ins...so not worth it for drop ins. Floating is lead thinking...
Thats why there is no study as it makes no sense.
Much easier to slightly overspec the cells at 105AH and keep it at 98% and have 100AH battery...thats what most manufacturer actually do.

2nd lifepo4 are also evolving in production and quality means the earlier times Lifepo4 that most like contained in study where more sensitive for storage and top end then todays production.
Then it depends if you have top noth Winston, CALB or EVE or grade b/fail to meet specs that get delivered to a lot of this cheap chinese budget battery company...some match them quite well, some don't...
So what is true in the study for a Winston maybe not true for your 100A EVE grade b cell in your budget dropin.

So instead try to get the last 1-2% focus on your overall install and keep it running nicely within the specs and avoid extreme cases.

As i wrote i know an installation where the bank is 17 years old charged with a fixed power supply to 14,2V till 1A, then shut off. This bank never had a float or absorption charge in its life and has still 94% of its original capacity and used heavily.
On the other side several they tried to squeeze last bid and constantly optimized that f.. the bank up in 5 years.

[s/v Jedi]

Originally Posted by sailorboy1

Sorry, but 100% of that was about following group think. All you really know is what you believe because you have read other believers say so.

I already posted a STUDY that showed that storing a LFP at 80-100% has little difference from storing at 40-80%, so while the STORY of needing to store at 60 % and not 100% has some basis, it is just really a 3 % difference from a STUDY. So in the context of what I asked at beginning of this thread means "floating" at 100 % probably makes difference and other factors of use probably are more

If you have a study that says that storing a LFP cell at 100% instead of at 40% is only a 3% penalty on lifespan then that study came from idiots. First of all the important factor of how long it was stored isn’t included, which is disqualifying right there. Maybe their definition of storage was one day?!
Second, throwing around ranges like 80-100% which includes an extreme is a big red flag and totally flawed.

Maybe, when you play the ranges out to fit your agenda, they took 80-100% vs 40-80% ranges as comparing 80% vs 80%. Yes, then a 3% difference in lifespan can be observed, which is just a variation from cell to cell. Idiots.

[patja]

I have an all-Victron installation, installed in Jan 2021. I go primarily by what the manufacturer says is required, taking what I read on the internet with a grain of salt. Agree that there is a paucity of hard data on damage due to storing these batteries at 13.5v.


Victron requires a full charge for balancing once a month. I can't be bothered to do the level of micro-management of remembering to futz with this on a monthly basis.


Can't say I've done a disciplined capacity test, but that seems like a good idea to gather some real world data on whether my approach of leaving it on "float" at 13.5v year round has caused damage.


https://www.victronenergy.com/media/...operation.html

[s/v Jedi]

Originally Posted by patja

I have an all-Victron installation, installed in Jan 2021. I go primarily by what the manufacturer says is required, taking what I read on the internet with a grain of salt. Agree that there is a paucity of hard data on damage due to storing these batteries at 13.5v.


Victron requires a full charge for balancing once a month. I can't be bothered to do the level of micro-management of remembering to futz with this on a monthly basis.


Can't say I've done a disciplined capacity test, but that seems like a good idea to gather some real world data on whether my approach of leaving it on "float" at 13.5v year round has caused damage.


https://www.victronenergy.com/media/...operation.html

How can you leave it on float year round? Is the boat stored year round?

[patja]

Originally Posted by s/v Jedi

How can you leave it on float year round? Is the boat stored year round?

OK it is not literally year round. I do use the boat 30 - 40 days per year, and during that time the charge level is up and down as you would expect. But other than that it is at its slip plugged into shore power.