Best LifePo4 charge controller settings known to man for Maximum Service life and Minimum battery stress!!! 5,000-10,000+ cycles?

[Goboatingnow]

All devices would have easily accessible programmable function, in my dream world. eg switch between Lead Acid and Lithium mode, option to terminate after CV phase, etc. however in the absence of programmability, I agree many chargers optimized for Lead Acid profile will be suboptimal for LFP etc.

A Li charger should have the option to terminate charging not revert to some lead acid “ float mode “

Accentuates the need for programmable option to terminate charging after CC or CV phase.

If you know of any papers that explore the difference between LFP charging with termination after CV phase vs using "float" ie Lower Voltage CV phase, please share. I want to read them and learn. It is an under-explored concept afaik.

I’ll root through and dig out some links

Disabling float may waste a bit of solar yield, but also makes sense that the cells would spend more time at a lower voltage, which may reduce absolute degradation.

It doesn’t really because load sharing doesn’t happen in mppt set to low “ float numbers “

Temperature seems to play a huge role too. Charging LFP when the cell material is over 30-35 Celsius seems to result in much more rapid degradation.

Agreed many factors degrade Li

How to achieve lower DOD, should I use CV termination sync and coulomb counting, or perhaps purely voltage thresholds? Maybe voltage combined with ampere/C-rate to account for droop? Honestly trying to learn. Victron shunt uses CV termination sync and coulomb counting as far as I can tell to estimate SOC.

CC , to CV setpoint , then terminate on 0.05C current threshold. CV setpoint is an article of “ faith” I aim low

Slow charging (near 0.05C or less) being more degrading than just terminating charge and restarting when SOC goes below some threshold, is a relatively new concept to me,

SEI layer growth mainly occurs in charge cycles , hence the shorter charge time the better. This means either fast charge ( low DoD ) or high current charge. Trickle being the worst , float voltages encourages trickle charging right at 100% when Li is particularly susceptible.

Restarting charging should be based on discharge having occurred whatever metric you use. This is not the scheme used in Lead acid as these batteries can tolerate continuous charging at 100%

and I'm trying to integrate it into diy energy storage projects to maximize service. Victron solar charge controllers do have an option for delaying CC phase until voltage drops below a certain amount relative to CV termination voltage, they call it "Re-bulk voltage offset"
View attachment 110326

Does this refer to the need to charge at slower rate when fully discharged? eg "Normal" C rate at 0% SOC can damage LFP

Re bulk is an attempt to determine when to recharge. It’s not great for LFP as small voltage changes mean big SOC changes. Personally I think coulomb counting is better. This needs external logic , like Cerbo Gx running DVCC etc

If you run a Li to 0% ( which should never happen with a BMS ) you have to trickle charge to approx 15 or 20 % then envoke Full CC , it’s not something most people have to deal with.

? some tout that LFP is "not at all like other lithium chemistry" but I recognize that there are fundamental similarities that are important to understand (for those who are curious)

The difference in LFP largely relate to the safety of the electrolyte , it’s gaseous output and lack of thermal runaway. Other then that it’s essentially identical to other Li ion tech.

it's ok to link here! ?

This is how I want to do it. When is the best time to allow charging again? Purely by voltage drop from CV termination voltage? Trying to learn ?

Again voltage drop is easy but not very accurate columb counting by the bms would be better

Yes!! BMS should ideally instruct charger. Sadly very few affordable options seem to exist. The BMS should know everything about the cells, and Instruct the Charger, this would be ideal to me.

Yes the industry is full of “ transition “ products or trying to convince people it’s just “ drop in “ technology and it’s all a few settings change. It’s not

May I ask, what threshold do you use? I wish to do this, the CC CV terminate wait until discharge algorithm in practice with my cells.

I tend to be conservative and charge to 90 %

CAN bus control being standard on all charge controllers would send me over the moon (happy)?

I too hope everything moves in the direction of charge controllers that have a data control interface that is directed by a BMS that understands the chemistry properly.

Yes I’m currently building a BMS that’s like the REC BMS and talkS VE.CAN. This is actually a marine CAB bus standard that recently added charge control data commands. It offers a way forward but we need mppt controllers that listen to it etc

Whew, sorry for the wall of text.

Thank you for your time and contributions!!

 

[Mattb4]

This is one of those situations where, while yes, the research shows you can get more cycle life if you limit DoD - it doesn't mean anything in practical applications like solar. For example, take a cell which is specc'd to 4k cycles 100% DoD. If you were to cycle them fully once a day, you would reach its end of life after 10 years. If you were to do this, the impact of calendar aging as more of an impact than DoD. Now consider that rarely anyone cycles their pack on a daily basis. It could be weekly, or not at all in summer. The impact of DoD in these applications is insignificant compared to calendar aging of the cells.

And yes, you could make a better charging system, and not float, and... but in the end, the effects of this on cycle life in particular with LiFePO4 in solar applications will be minimal. Suppose you have a system that now does 10k cycles compared to the 4k I originally started with. That's close to 30 years. But over that time, you never get to use the capacity you paid for because you limit to low DoD (and you had to buy more cells just to make sure you don't go low DoD, and charge them back up asap - sounds like lead acid again), and calendar aging will kill your cells, likely well before those 30 years are up.

So in the end, yes, technically, you can increase cycle life and there are better ways of doing things then we have available now. But does it really matter and is it at all practical, let alone more cost effective?

I would like to thank everyone for their posts in this Thread. Provided much food for thought.

It is obvious after my short time using a solar off grid inverter setup, with at first lead acid, and now LiFePO4 batteries that there are competing goals at work that require a degree of compromise solutions.

 

[Sojourner1]

There are some that have hands on experience with white papers and implementing there interpretation into a system that works for them when using it and others that live off of their system day in and day out.

Certainly have to decide what will work for you with daily need demands.

Can't imagine turning off the solar system so batteries can be depleted just to be charged again if the sun is still able to do so before evening no solar hours.

 

[Goboatingnow]

There are some that have hands on experience with white papers and implementing there interpretation into a system that works for them when using it and others that live off of their system day in and day out.

Certainly have to decide what will work for you with daily need demands.

Can't imagine turning off the solar system so batteries can be depleted just to be charged again if the sun is still able to do so before evening no solar hours.

Then don’t use Li , simple. Li is not great in a float style situation where the solar is covering the load because you may be subjecting the li to a trickle charge as well.

Of course you can rig load diverters that are powered by the panels directly , this leaves the Li just sitting there.

But people have been ruining lead acids for decades with poor practices , no doubt Li will be the same

 

[Sojourner1]

If you mean not using "float" in a longterm no load situation then I agree.

For a daily use system like mine when it hits "float", which might be for a couple hours the solar is carrying the loads and batteries are taking no charge other than sitting at 13.6v unless there is a high draw that the solar can't cover then solar tops the batteries off again if needed.

I'm not going to argue or debate the white papers with you, I've read them and implemented what works for my lifestyle. Weighing pros and con or power needs/ wants verse longevity/ batteries aging out.

Are you preching or implementing in a longterm day in day out living off of said regiment?

 

[Steve_S]

Oivey, this turned into a "PILE" and pointless...
REPORTED ! There is nothing helpful in this last pile of twaddle.
Li - a GENERALIZATION

It is important to note that the six types of lithium-ion batteries are compared relative to one another.

Lithium-ion battery Types	SP	SE	SF	LS	CS	PF
Lithium Cobalt Oxide	L	H	L	L	L	M
Lithium Manganese Oxide	M	M	M	L	L	L
Lithium Nickel Manganese Cobalt Oxide	M	H	M	M	L	M
Lithium Iron Phosphate	H	L	H	H	L	M
Lithium Nickel Cobalt Aluminum Oxide	M	H	L	M	M	M
Lithium Titanate	M	L	H	H	H	H

• SP stands for specific power
• SE stands for specific energy
• SF stands for safety
• LS stands for lifespan
• CS stands for cost
• PF stands for performance
• L stands for low
• M stands for moderate
• H stands for high

HERE with our ESS ( Energy Storage Systems) {DIY or Otherwise} WE DEAL WITH LFP / LiFePo4 / Lithium Iron Phosphate

ALWAYS REFER TO MANUFACTURER SPECS & RECOMMENDATIONS (Not Vendors, Marketers or Polyester clad Sales Shmucks)

 

[Goboatingnow]

Well the person that said I agree with you but good luck changing people minds was right

Clearly the truth is anything you believe

 

[Goboatingnow]

If you mean not using "float" in a longterm no load situation then I agree.

For a daily use system like mine when it hits "float", which might be for a couple hours the solar is carrying the loads and batteries are taking no charge other than sitting at 13.6v unless there is a high draw that the solar can't cover then solar tops the batteries off again if needed.

I'm not going to argue or debate the white papers with you, I've read them and implemented what works for my lifestyle. Weighing pros and con or power needs/ wants verse longevity/ batteries aging out.

Are you preching or implementing in a longterm day in day out living off of said regiment?

Yes the test system I rigged has my own Ardunio based bms. No floating is involved

The system is being redesigned and upgraded to be installed next winter, my setup is a boat so it’s more complicated then domestic as i have three charge sources To control

But again float is a nonsense in Li. It’s called trickle charging and it’s not a good idea . If you can avoid it do so. If you can’t or don’t , well see the OP for a new thread title

 

[Horsefly]

Clearly the truth is anything you believe

Not sure if you are referring to yourself or someone else.

But again float is a nonsense in Li.

You said earlier you would post or link to some supporting material for this statement. I for one would like to see it, if it exists.

 

[Goboatingnow]

Oivey, this turned into a "PILE" and pointless...
REPORTED ! There is nothing helpful in this last pile of twaddle.
Li - a GENERALIZATION

Lithium-ion battery Types	SP	SE	SF	LS	CS	PF
Lithium Cobalt Oxide	L	H	L	L	L	M
Lithium Manganese Oxide	M	M	M	L	L	L
Lithium Nickel Manganese Cobalt Oxide	M	H	M	M	L	M
Lithium Iron Phosphate	H	L	H	H	L	M
Lithium Nickel Cobalt Aluminum Oxide	M	H	L	M	M	M
Lithium Titanate	M	L	H	H	H	H

• SP stands for specific power
• SE stands for specific energy
• SF stands for safety
• LS stands for lifespan
• CS stands for cost
• PF stands for performance
• L stands for low
• M stands for moderate
• H stands for high

HERE with our ESS ( Energy Storage Systems) {DIY or Otherwise} WE DEAL WITH LFP / LiFePo4 / Lithium Iron Phosphate

ALWAYS REFER TO MANUFACTURER SPECS & RECOMMENDATIONS (Not Vendors, Marketers or Polyester clad Sales Shmucks)

View attachment 110340

Most of those comparisons are meaningless , we are not talking about safety here. We are dealing with what the OP asked for “ maximum life “ and “ minimum stress “

You do what you like with your cells god knows 1000s of lead acids are ruined every year by similar ideas.

 

[Horsefly]

Here is a paper that examined what things most impacted the cycle life of LiFePO4 cells. The conclusion is that "The effects of test parameters (time, temperature, DOD, rate) were investigated and described. The results show that the capacity loss is strongly affected by time and temperature, while the effect of DOD is less important". I think that is what I said some number of posts ago, but it won't stop @Goboatingnow.

I think @Steve_S is right. This discussion is not helpful.

 

[Cheap 4-life]

Then don’t use Li , simple. Li is not great in a float style situation where the solar is covering the load because you may be subjecting the li to a trickle charge as well.

Of course you can rig load diverters that are powered by the panels directly , this leaves the Li just sitting there.

But people have been ruining lead acids for decades with poor practices , no doubt Li will be the same

Saying “then don’t use Li” should not be said.. as Upcloseandpersonal explained (or how i understood what he said) it’s basically not worth worrying about most of what your saying due to calendar aging when Lifepo4 is used for a home solar setup.

 

[Cheap 4-life]

Yes the test system I rigged has my own Ardunio based bms. No floating is involved

The system is being redesigned and upgraded to be installed next winter, my setup is a boat so it’s more complicated then domestic as i have three charge sources To control

But again float is a nonsense in Li. It’s called trickle charging and it’s not a good idea . If you can avoid it do so. If you can’t or don’t , well see the OP for a new thread title

It’s been my experience that float doesn’t trickle charge Li. Unlike lead acid, Lithium’s voltage stays constant without needing to be trickle charged to maintain that voltage.

 

[Sojourner1]

Most of those comparisons are meaningless , we are not talking about safety here. We are dealing with what the OP asked for “ maximum life “ and “ minimum stress “

You do what you like with your cells god knows 1000s of lead acids are ruined every year by similar ideas.

You have a "test system" whatever that means which you'll implement next winter.
Yet, Steve & I & others live off of a "float" or a low "CV" for short periods during the day while power other loads for many years and thousands of partial cycles. Is it shortening the longevity so many seem to be hung up on instead of powering daily needs/ wants only time will tell. Pick your poison.

I believe alot of people will kill these lfp batteries before their righful life by taking short cuts, by cheap components or just hen pecking. Many threads already on the forum of situations mentioned.

 

[shot428]

ALWAYS REFER TO MANUFACTURER SPECS & RECOMMENDATIONS

This thread has been an interesting read and I appreciate those with years of experience chiming in

I have 2 questions (not tryin to beat the horse)

When you guys talk .05c, 1c, 2c etc I admit I'm lost, terms I never encountered in my years of electronic repair
The manufacturer of my battery says to charge at 20amps not to exceed 100a. The recommendation seems to be related to temps/heat, I have set my inverter to 10a with a 20a max (I don't have solar yet) and I see several here charging with much higher amps. I read in this thread that trickle charge is bad ,,,,, my question, is 10a considered trickle with regard to solar ? (my head says 2a is trickle)

And to stay with the op's topic, At what charge current would potential temp increases become detrimental ?

Second question, I have a Growatt 6000T and it does this daily dance where it discharges and charges the batteries, I read on this and other forums that this is normal behavior for Growatts, one member described it as being like the float valve in a toilet making up for the wattage that the inverter uses. I decided not to worry about it but after reading this thread my question is

Would this daily action constitute a cycle ? and how might it affect battery life ?

I have seen some say it does it more than once a day and some say higher discharge rates then I am seeing, mine discharges bout a half volt then trickles (1 to 2 amps) it back up to float (I don't yet have software to output a graph) here is an example post

https://diysolarforum.com/threads/why-are-my-batteries-charging-daily.33894/

 

[Goboatingnow]

You have a "test system" whatever that means which you'll implement next winter.
Yet, Steve & I & others live off of a "float" or a low "CV" for short periods during the day while power other loads for many years and thousands of partial cycles. Is it shortening the longevity so many seem to be hung up on instead of powering daily needs/ wants only time will tell. Pick your poison.

I believe alot of people will kill these lfp batteries before their righful life by taking short cuts, by cheap components or just hen pecking. Many threads already on the forum of situations mentioned.

My test system is just that a highly instrumented system be used as a development for my own systems . I’m not running down your system.

I’m merely responding to the OPs thread title. If you don’t accept scientific principles based on good research that’s fine.

 

[Goboatingnow]

It’s been my experience that float doesn’t trickle charge Li. Unlike lead acid, Lithium’s voltage stays constant without needing to be trickle charged to maintain that voltage.

How do you “ know “ it’s not trickle charging

 

[Goboatingnow]

Here is a paper that examined what things most impacted the cycle life of LiFePO4 cells. The conclusion is that "The effects of test parameters (time, temperature, DOD, rate) were investigated and described. The results show that the capacity loss is strongly affected by time and temperature, while the effect of DOD is less important". I think that is what I said some number of posts ago, but it won't stop @Goboatingnow.

I think @Steve_S is right. This discussion is not helpful.

Everyone can point to research

“This is explained by the well-known observation that cycling at higher SOC leads to more pronounced SEI generation compared to lower SOC cycling [32, 37, 38]. The cycling at 50% DOD leads to a longer duration at high SOC ranges (compared to 100% DOD) of the cells with more electrolyte and salt decomposition. Furthermore, an important difference between the 50% DOD cycling and the 100% DOD cycling is the number of charge–discharge cycles. One cycle for the 50% DOD cells represents 1.25 Ah cycle−1, leading to roughly 1600 cycles until EOL, while for the 100% DOD cells (2.5 Ah cycle−1) only about 800 cycles are performed until EOL is reached
“

Influence of cycling profile, depth of discharge and temperature on commercial LFP/C cell ageing: post-mortem material analysis of structure, morphology and chemical composition - Journal of Applied Electrochemistry

Abstract The paper presents post-mortem analysis of commercial LiFePO4 battery cells, which are aged at 55 °C and − 20 °C using dynamic current profiles and different depth of discharges (DOD). Post-mortem analysis focuses on the structure of the electrodes using atomic force microscopy (AFM)...

link.springer.com

 

[Goboatingnow]

This thread has been an interesting read and I appreciate those with years of experience chiming in

I have 2 questions (not tryin to beat the horse)

When you guys talk .05c, 1c, 2c etc I admit I'm lost, terms I never encountered in my years of electronic repair
The manufacturer of my battery says to charge at 20amps not to exceed 100a. The recommendation seems to be related to temps/heat, I have set my inverter to 10a with a 20a max (I don't have solar yet) and I see several here charging with much higher amps. I read in this thread that trickle charge is bad ,,,,, my question, is 10a considered trickle with regard to solar ? (my head says 2a is trickle)

And to stay with the op's topic, At what charge current would potential temp increases become detrimental ?

Second question, I have a Growatt 6000T and it does this daily dance where it discharges and charges the batteries, I read on this and other forums that this is normal behavior for Growatts, one member described it as being like the float valve in a toilet making up for the wattage that the inverter uses. I decided not to worry about it but after reading this thread my question is

Would this daily action constitute a cycle ? and how might it affect battery life ?

I have seen some say it does it more than once a day and some say higher discharge rates then I am seeing, mine discharges bout a half volt then trickles (1 to 2 amps) it back up to float (I don't yet have software to output a graph) here is an example post

https://diysolarforum.com/threads/why-are-my-batteries-charging-daily.33894/

c is the capacity of the battery so a C =100Ah , charging at .1C would be 10A

 

[Goboatingnow]

You have a "test system" whatever that means which you'll implement next winter.
Yet, Steve & I & others live off of a "float" or a low "CV" for short periods during the day while power other loads for many years and thousands of partial cycles. Is it shortening the longevity so many seem to be hung up on instead of powering daily needs/ wants only time will tell. Pick your poison.

I fully agree , all systems are a compromise but that’s not what the OP of this thread asked for

I believe alot of people will kill these lfp batteries before their righful life by taking short cuts, by cheap components or just hen pecking. Many threads already on the forum of situations mentioned.