A couple basic questions about starting with lifepo4

[mlydon]

I use lipo’s for airplane propulsion - Generally speaking, lithi7m batteries will ‘take’ whatever current you can throw at them, up to 1c (200amp for a 200amphr pack), or whatever the manufacturer specifies. A good charger will dial down the current as they approach full. They do NOT like to be fully charged - if we don’t use a fully charged pack, we discharge to 50% soc for storage. LiFE is more tolerant of a full charge, but in general, you’re better off filling to what you need than going to FULL and partially discharging - it’s basically the opposite of lead acid….

Matt

[Be Free]

Originally Posted by Chotu

It’s much appreciated. But I think I was just confused because the batteries were so empty upon arrival. That’s not how flooded lead acid batteries arrive.

I guess in order to ship them, they have to keep them pretty empty.

I’ll just keep an eye on things. I still have to integrate the second battery anyway. This is just one battery out of two of them.

Chotu,
IIRC Lithium batteries can only be shipped by air if they are not charged above 30%. That's probably the source of your difference.

[Chotu]

Originally Posted by Be Free

Chotu,
IIRC Lithium batteries can only be shipped by air if they are not charged above 30%. That's probably the source of your difference.

That is correct. They were all the way down like that. In shipping mode.

Just the other day. Yesterday? I think? The days are running together.

Just the other day, I was getting 40 something amps into them with that same big charger. So they are functioning properly.

[CaptainRivet]

Originally Posted by Chotu

It’s much appreciated. But I think I was just confused because the batteries were so empty upon arrival. That’s not how flooded lead acid batteries arrive.

I guess in order to ship them, they have to keep them pretty empty.

I’ll just keep an eye on things. I still have to integrate the second battery anyway. This is just one battery out of two of them.

Most likely you got old stock that was sitting very long at the storage

[Chotu]

Originally Posted by CaptainRivet

Most likely you got old stock that was sitting very long at the storage

actually, they can’t fly them here and ship them to me unless they are pretty much empty. So they deliver them all empty.

they working like a champ.

I have been seeing higher charging rates when appropriate. I’m just not used to the charging and discharging profiles of these batteries yet so it was confusing me.

[Grigory]

any guidance from the LIFEPO for pros?

You can see this: https://marinehowto.com/lifepo4-batteries-on-boats/

NO 14.4V any case. LiFePO have very low internl resistance (much lower than Pb), 13.6 V is quite enough.

[newhaul]

Originally Posted by Grigory

You can see this: https://marinehowto.com/lifepo4-batteries-on-boats/

NO 14.4V any case. LiFePO have very low internl resistance (much lower than Pb), 13.6 V is quite enough.

Except for one thing . Many BMS's active ( or passive ) top balancing don't start to do their job untill 14.4vdc to begin with . 13.6 is proper full when lifepo4 is resting . Most of us don't see banks ever at rest for any significant period. They cycle daily to some extent.
My own mppt set to charge to 14.4vdc and stop. Restart charging when bank is down to 13.2vdc . Have not needed balanced in 4 years .

[Chotu]

Originally Posted by newhaul

Except for one thing . Many BMS's active ( or passive ) top balancing don't start to do their job untill 14.4vdc to begin with . 13.6 is proper full when lifepo4 is resting . Most of us don't see banks ever at rest for any significant period. They cycle daily to some extent.
My own mppt set to charge to 14.4vdc and stop. Restart charging when bank is down to 13.2vdc . Have not needed balanced in 4 years .

Exactly.

Plus I will stick with what the manufacturer says over anything I read on the Internet. They know what voltages are needed for their batteries.

[Joe Okros]

Lithium batteries should not be charged past 80% or allowed to discharge to under 20%. If you can adhere to those parameters they should last 20 years.

[newhaul]

Originally Posted by Joe Okros

Lithium batteries should not be charged past 80% or allowed to discharge to under 20%. If you can adhere to those parameters they should last 20 years.

And you get thi information where?
I agree with the not below 20% but I regularly charge to 14.4vdc which is fully charged and I am sure I will have them for 20+ years.

There is a difference between charging to and using daily and keeping charged with little to no usage

[Joe Okros]

I can quote many sources but I'm sure you have access to Google like I do,---suffice to say most reputable laptop manufacturers now allow BIOS control over laptop battery charging, and its normally limited to 79%. Cycle life of Lithium batteries increases to incredible amounts if you use them to only 50% DOD

[Joe Okros]

[wholybee]

Originally Posted by Joe Okros

I can quote many sources but I'm sure you have access to Google like I do,---suffice to say most reputable laptop manufacturers now allow BIOS control over laptop battery charging, and its normally limited to 79%. Cycle life of Lithium batteries increases to incredible amounts if you use them to only 50% DOD

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.

[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.

One thing I have heard from manufacturers is that the calendar life applies to storage time mainly before commissioning.

[rslifkin]

Originally Posted by newhaul

One thing I have heard from manufacturers is that the calendar life applies to storage time mainly before commissioning.

In many applications, that's effectively true, although batteries still age while in use. Many use cases will wear them out or destroy them before they ever get a chance to age out.