A couple basic questions about starting with lifepo4

[newhaul]

Originally Posted by wholybee

First, the Lithium batteries in laptops have very different properties from LiFePO4 that we use. So that comparison is meaningless.

And DOD is only one factor. If you limit it to only use 5% DOD (keeping the battery between 95% and 100%) you will greatly shorten the life. Second, how much that shortens the life is tied very closely to temperature. Kept cold, the life isn't reduced much. Over 120F, a fair amount of life is lost. At 75F (kept in the cabin, not near the engine) only a moderate loss in life.

There are also some studies that short cycling an LFP in a small range, (say 70% to 75%) will cause crystallization and form a memory. There isn't much research I have seen on this, but from what I have seen, it is better to use the battery over a wide range than a small range.

The most damage is when the battery is resting at 100%(13.8V resting) or over 100%(14.6V), as is often done to fully charge without needing an absorption phase. But staying just under that, 95% or so, is enough to greatly reduce (but not eliminate) any loss of cycle life. The lower you go, the more diminished the returns. It is still very closely tied to temperature. I have seen NO evidence that going under 20% SOC is any harm at all, as long as you don't go below 0%- and the BMS will prevent that. A prudent user will re-charge well before 0% anyway just to ensure the lights don't go out. But the battery doesn't care.

Not only that, but you MUST charge higher than 80% to keep the cells in balance, or you need to perform an occasional top balance, which most people don't know how to do, and can't be done with a drop-in type of battery without cutting it open. You CANNOT balance cells under about 3.45Vpc, and 3.5Vpc-3.55Vpc is much better. So, if you only charge to 80% you will run into issues. Another user here has a thread on that, and he had to cut open his drop-ins to balance them and fix the issue.

And there is also calendar aging. That an LiFePO4 could last for 1,000,000 cycles (2700+ years under typical usage!) under any circumstances is utter non-sense. They will wear out due to calendar aging long before that. (about 2680 years before that)

The reality is that almost no one will cycle more than once per day. Reality for almost everyone is 2-3 days per cycle, which even with reduced cycles because you are charging over 80% will still last about 20 years, and the battery will be near end of life due to calendar aging by then.

So, with all of that in mind, you can cycle the battery from nearly 0%, to nearly 100%, get a few thousand cycles, and have a 20-year life. My only recommendation is to minimize or prevent them from getting to or especially staying at 100%. More so if you are in the tropics.

Chotu is not wrong to follow manufactures recommendations.


*In regards the laptop batteries. The BIOS doesn't typically limit charge to 80%. Rather, if the laptop is left plugged it 24/7, it will hold the charge at lower than 100%(probably not as low as 80%). But, if the laptop is used on battery power, and you plug it in when it gets low, it will allow a one-time full charge, and only begin to limit it if you leave it plugged in.

Came across this study on calendar aging and seems to mostly apply when in storage where temperature and charge have a great effect on aging .

https://www.researchgate.net/publica...Calendar_Aging

https://www.mdpi.com/1996-1073/14/6/1732

[Joe Okros]

You say "you can cycle the battery from nearly 0% to nearly 100%,". I say,---"Lithium batteries should not be charged past 80% or allowed to discharge to under 20%", in other words, nearly 0 and nearly 100. Seems like semantics to me, factoring in a safety factor and real-world use, I will stick to my 20/80. I believe MOST damage is done when 80% is exceeded and then kept there,-as cruisers like to do with FLA batteries.
You do what you want but I don't know anyone with 20-year-old LIFEPO4 batteries, do you?
Of course, you should do what the manufacturers say (simply for warranty purposes), but let's take a hypothetical scenario where our boats are moored,- you cycle your batteries from 0 to 100, and I go 20 to 80. Covid or some other calamity hits and we go into lockdown unable to access our boats for a year. You left yours at 100 and I left mine at 80. Whose battery will be healthiest when we return a year later?

Passive balancing and active balancing are obviously necessary if your batteries are out of whack, and drop-in battery BMS is not yet up to that level, but all long-time cruisers have a gamut of aging equipment ranging from crappy mppt controllers to KISS wind generators (with no charge control) and as such unexpected events can easily cause your batteries to be overcharged, (don't ask me how I know an unattended KISS can destroy an AGM) so personally I will stick to the 20/80 rule.
YMMV.

[newhaul]

Originally Posted by Joe Okros

.
You do what you want but I don't know anyone with 20-year-old LIFEPO4 batteries, do you?
Of course, you should do what the manufacturers say (simply for warranty purposes), but let's take a hypothetical scenario where our boats are moored,- you cycle your batteries from 0 to 100, and I go 20 to 80. Covid or some other calamity hits and we go into lockdown unable to access our boats for a year. You left yours at 100 and I left mine at 80. Whose battery will be healthiest when we return a year later?

.
YMMV.

Actually yes. Sv third day
Riches lifepo4 are there any still going strong and happy in LA Paz MX

Your hypothetical doesn't really work as people like me have a solar controller set to keep un attended banks at approx 50% mine is set go13.2vdc that is if I'm off the boat for any length of time

[Joe Okros]

What?- How does your controller know you will be off the boat when it's unexpected? Please let me know what controller that is, I also want a psychic controller. Also, would love to know what kind of LifePo4 batteries SV 3rd day bought 20 years ago seeing as in 2014 they still had AGM's https://www.sailblogs.com/member/svthirdday/310807.

It becomes difficult to believe anything you say when its disproven so easily.

If you are going to make claims like that please be aware I also have Google (LOL)

[newhaul]

Originally Posted by Joe Okros

What?- How does your controller know you will be off the boat when it's unexpected? Please let me know what controller that is, I also want a psychic controller. Also, would love to know what kind of LifePo4 batteries SV 3rd day bought 20 years ago seeing as in 2014 they still had AGM's https://www.sailblogs.com/member/svthirdday/310807.

It becomes difficult to believe anything you say when its disproven so easily.

If you are going to make claims like that please be aware I also have Google (LOL)

His cells iirc are Winston's.
BTW he still has AGMs onboard ax well just replaced them last year . Never heard of having more than one chemistry on the boat.?
Also Rod Collins (mainsail) has been running them for 13 or 14 years and at last report still at full capacity .

I have a tracer 3210AN with Ble unit and cloud access to my onboard network from my cell phone .
Not only that but the chances of my being unable to get home for a month is ridiculous.

[Joe Okros]

Ah well, -if we are now regarding "13 or 14 years" to be the same as 20 years, I'll stick to my 20/80,----its, after all really no different than "almost zero or almost 100". In NZ it's quite common for people not to get home for a month when the government decides to lock things down, in fact, some of them got locked out of the country for 2 years, lol.

[SV Confianza]

Originally Posted by Joe Okros

You say "you can cycle the battery from nearly 0% to nearly 100%,". I say,---"Lithium batteries should not be charged past 80% or allowed to discharge to under 20%", in other words, nearly 0 and nearly 100. Seems like semantics to me, factoring in a safety factor and real-world use, I will stick to my 20/80. I believe MOST damage is done when 80% is exceeded and then kept there,-as cruisers like to do with FLA batteries.
You do what you want but I don't know anyone with 20-year-old LIFEPO4 batteries, do you?
Of course, you should do what the manufacturers say (simply for warranty purposes), but let's take a hypothetical scenario where our boats are moored,- you cycle your batteries from 0 to 100, and I go 20 to 80. Covid or some other calamity hits and we go into lockdown unable to access our boats for a year. You left yours at 100 and I left mine at 80. Whose battery will be healthiest when we return a year later?

Passive balancing and active balancing are obviously necessary if your batteries are out of whack, and drop-in battery BMS is not yet up to that level, but all long-time cruisers have a gamut of aging equipment ranging from crappy mppt controllers to KISS wind generators (with no charge control) and as such unexpected events can easily cause your batteries to be overcharged, (don't ask me how I know an unattended KISS can destroy an AGM) so personally I will stick to the 20/80 rule.
YMMV.

As mentioned previously, there are tons of different Lithium battery chemistries, and the rules don't blanket apply across chemistries.

For LiFePO4 batteries, the 80% doesn't apply. Disclaimer: I'm not a battery designer, this is all what I've picked up from research in designing my own LFP system peppered in with a college buddy of mine that's on the team that designs some of Tesla's batteries.

The LI batteries in your phone have a linear charge curve, so the more you charge, the higher the voltage that it requires to charge. Higher voltage is shoving more ions into the cathode faster, causing cracks (degradation). To charge a phone battery, the charger holds the current stable, but increases the voltage as the battery charges.

LFP batteries have a very flat charge curve, so you don't have the same degradation problem. In other words, LFP batteries are at a very similar voltage for most of its charging cycle, and our chargers are set to a single voltage most of the time.

Also, you can't measure LFP batteries accurately by voltage, because the curve is so flat. So our battery monitors have to use an approximation, basically by just counting the amps that go in and out of the battery. We don't normally even get an accurate reading for 80% for LFP from our battery monitors (unless maybe if you're constantly calibrating). So chasing 80% isn't even really an option.

SoC is not really a factor for LFP unless you're overcharging or over discharging, and that's more influenced by improperly set up charging systems or BMS's.

As always, anyone feel free to point out anything I got wrong.

[newhaul]

Originally Posted by Joe Okros

Ah well, -if we are now regarding "13 or 14 years" to be the same as 20 years, I'll stick to my 20/80,----its, after all really no different than "almost zero or almost 100". In NZ it's quite common for people not to get home for a month when the government decides to lock things down, in fact, some of them got locked out of the country for 2 years, lol.

The 13 of 14 years is just another example of the longevity of these batteries . and I trust Mainesail as he is a professional in the industry . he does regular testing and is showing noose or degradation and an aside he is one of the contributors to the ABYC wrt the lifepo4 batteries for industry recommendations
Marinehowto.com
also I don't live in a nanny state I'm on the west coast of the USA at approx 48°N

[Joe Okros]

This discussion is getting tiresome, read this https://cleversolarpower.com/lifepo4-voltage-chart/

Take note of longevity recommendations etc

[newhaul]

Originally Posted by Joe Okros

This discussion is getting tiresome, read this https://cleversolarpower.com/lifepo4-voltage-chart/

Take note of longevity recommendations etc

Perhaps you would do well to do a site search here as we have had all those discussions many times in various other threads .
Best longevity is charge and discharge at .5C or lower don't float charge at 100% its not good best use is slow and shallow say between 60% and 90% no higher unless balancing . Long term storage discharge to approximately 50% and store in cool dry place for up to a year then checking voltage to maintain above 20% . Recharge to 99% upon recomissioning.
Then back to 60/90 at fractional rates . Not faster than .5C charge or discharge

[SV Confianza]

Originally Posted by Joe Okros

This discussion is getting tiresome, read this https://cleversolarpower.com/lifepo4-voltage-chart/

Take note of longevity recommendations etc

I can see that he uses a 90%/10% rule in there, and that’s just not correct (and he doesn’t provide any reason why).

I posted above about how the chemistry doesn’t make sense for his way.

[Chotu]

Originally Posted by SV Confianza

LFP batteries have a very flat charge curve, so you don't have the same degradation problem. In other words, LFP batteries are at a very similar voltage for most of its charging cycle, and our chargers are set to a single voltage most of the time.

Also, you can't measure LFP batteries accurately by voltage, because the curve is so flat. So our battery monitors have to use an approximation, basically by just counting the amps that go in and out of the battery. We don't normally even get an accurate reading for 80% for LFP from our battery monitors (unless maybe if you're constantly calibrating). So chasing 80% isn't even really an option.

SoC is not really a factor for LFP unless you're overcharging or over discharging, and that's more influenced by improperly set up charging systems or BMS's.
.

This is exactly what I have been noticing since starting to use these batteries a couple weeks back.

voltages. They are always 13.x V. Doesn’t matter what you are doing. You can be microwaving. You can be discharged to 20% or some thing. It’s always 13.x and as a matter of fact, after studying the different voltages, I noticed that that’s when you get into trouble. When it’s not 13.x volts.

not a bad rule of thumb.

of course when charging, some of them require different charging parameters. Mine requires going up to 14.4. I think that has to do with balancing the battery now after I have read so many things about it. I could be wrong. however, in real life, it doesn’t end up at 14.4 all the time because you're always discharging and you don't necessarily always get a full charge every day.

as far as the accuracy of battery monitors go, I seem to be having some difficulty with that also. I wish there was a guide on how to set up a battery monitor properly for LFP. I haven’t found one yet. I think there are a lot of things to change. My monitor was quite accurate for the flooded lead acid batteries. I have a Xantrex link light pro battery monitor.

The problem with using the lithium and this monitor is I seem to be showing more energy lost out of the batteries then actually is occurring. I can tell that by the charging Amp acceptance rate. The acceptance rate is lower than I would expect for the percentage of the total battery capacity that is used up in a given day. so I can tell something is off with the battery monitor with these batteries.


I think maybe I have to change the Peukert Exponent setting.


EDIT: interestingly enough, I bought these before lithium batteries were really in use. And I just looked at the documentation online for the battery monitor and they actually mention setting the Peukert Exponent to 1 for lithium in the latest revision of the documentation. That would entirely disable the exponent. I will be doing that right away to see if it corrects the problem. It sounds like it would.

[MVDarlin]

If you need to add more power consumption add an electric water heater. I turn mine on for 1/2 hour each morning when the solar panel fed AGM batteries go to float and they immediately return to bulk charge when the 10 amp /120 v heater kicks on the inverter. The inverter will start to shut down after about 30 min as the voltage drops on my house bank of 6×55 ah Optima AGMs and it will take the rest of the day to recover to float. I plan to convert to a 200 ah Lithium battery in the next few weeks and I have one more solar panel to add to my array.

[newhaul]

Originally Posted by Chotu

This is exactly what I have been noticing since starting to use these batteries a couple weeks back.

voltages. They are always 13.x V. Doesn’t matter what you are doing. You can be microwaving. You can be discharged to 20% or some thing. It’s always 13.x and as a matter of fact, after studying the different voltages, I noticed that that’s when you get into trouble. When it’s not 13.x volts.

not a bad rule of thumb.

of course when charging, some of them require different charging parameters. Mine requires going up to 14.4. I think that has to do with balancing the battery now after I have read so many things about it. I could be wrong. however, in real life, it doesn’t end up at 14.4 all the time because you're always discharging and you don't necessarily always get a full charge every day.

as far as the accuracy of battery monitors go, I seem to be having some difficulty with that also. I wish there was a guide on how to set up a battery monitor properly for LFP. I haven’t found one yet. I think there are a lot of things to change. My monitor was quite accurate for the flooded lead acid batteries. I have a Xantrex link light pro battery monitor.

The problem with using the lithium and this monitor is I seem to be showing more energy lost out of the batteries then actually is occurring. I can tell that by the charging Amp acceptance rate. The acceptance rate is lower than I would expect for the percentage of the total battery capacity that is used up in a given day. so I can tell something is off with the battery monitor with these batteries.


I think maybe I have to change the Peukert Exponent setting.


EDIT: interestingly enough, I bought these before lithium batteries were really in use. And I just looked at the documentation online for the battery monitor and they actually mention setting the Peukert Exponent to 1 for lithium in the latest revision of the documentation. That would entirely disable the exponent. I will be doing that right away to see if it corrects the problem. It sounds like it would.

The Peukert Exponent setting of 1.00 would be correct as there is almost no losses in charging. Lifepo4 are iirc 97% efficient when charging and discharging .

[Chotu]

Originally Posted by MVDarlin

If you need to add more power consumption add an electric water heater. I turn mine on for 1/2 hour each morning when the solar panel fed AGM batteries go to float and they immediately return to bulk charge when the 10 amp /120 v heater kicks on the inverter. The inverter will start to shut down after about 30 min as the voltage drops on my house bank of 6×55 ah Optima AGMs and it will take the rest of the day to recover to float. I plan to convert to a 200 ah Lithium battery in the next few weeks and I have one more solar panel to add to my array.

i’ve definitely been thinking of doing this. As soon as the water maker is up and running, i’ll see where I’m at. It would be nice to be able to do this instead of using the propane water heater that I have.