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EXTENDING LIFEPO4 BATTERY LIFE

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peterwareing

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Dec 4, 2019
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This may be a silly question. I have a hybrid solar / charge controller / grid tie / 48v LIFEPO4 battery system.
I have used various charge parameters - currently sticking with 55.6v charging and 54.4v float.
I read that when the charging is in float mode the inverter takes the power directly from the solar panels.
If this is the case - this must reduce the charging / discharging losses encountered with batteries.
So is there any benefit in reducing the charging voltage to the same as the float voltage 54.4 (3.4v per cell).
I have read that any voltage above 3.4v is hard to access and provides little benefit?
Any advice gratefully received.
 
55.6V charging is only 3.475V/cell peak, so you're not getting them fully charged.
54.4V is right at 3.4V/cell, generally regarded as safe.

The panel/inverter/float behavior is as you describe.

In order to fully charge LFP, you have to increase voltage beyond what is usable voltage-wise, so simply running up to 3.4V might only get you to 80% or so, and it may continue to accept low current for a long period of time.

Essentially, if your typical battery utilization is notably less than your capacity, increasing cycle life by pulling back from 100% SoC and avoiding deeper discharges can increase cycle life.

If dropping to 3.4V/cell charge leaves the system readily usable, then it's fine. Is there a substantial advantage over your current configuration? I doubt it.
 
Yes I understand the logic behind a more fully charged battery providing more power but to charge the battery and then discharge the battery can result in large conversion losses. My thoughts were that if the battery hits float sooner these losses would be negated by bypassing the battery and subsequently prolong the battery life with regards to lower SOC and less cycling? I am probably talking rubbish so please excuse my ignorance - it is just something that crossed my mind?
 
One thing to watch for when using lower than normal charging voltages is the voltage at which your BMS starts to balance the cells.

Nothing will break as if one or more cells rise up to the cell voltage / cell voltage difference at which the BMS starts balancing the BMS will still try to hold them down while the other cells rise but by limiting the overall battery voltage you can be hobbling the process so that the cells never become balanced. That can have the effect of top and tailing your battery's capacity. It won't be an overnight thing since well matched lithium cells shouldn't drift out of step much over time anyway but it will happen. A periodic, 6 or 12 monthly based upon what seems to be recommended for series connected lifepo4 batteries, higher voltage charge will allow the BMS to bring the cells into line again if this actually becomes a problem.

If it's a prebuilt battery rather than a DIY with your own BMS you'll probably not be able to get any good information about the circumstances in which the BMS balances the cells.
 
peterwareing said:
Yes I understand the logic behind a more fully charged battery providing more power but to charge the battery and then discharge the battery can result in large conversion losses. My thoughts were that if the battery hits float sooner these losses would be negated by bypassing the battery and subsequently prolong the battery life with regards to lower SOC and less cycling? I am probably talking rubbish so please excuse my ignorance - it is just something that crossed my mind?
Click to expand...
Snoobler nailed it. ;)
You might be over thinking this. I did for a long time myself as well. :)
 
So from memory - the recommendations I have seen / heard linked to Will's videos / information I have:

55.6v (this may have been from elswhere? 55.6v charge and 55.6 float - Lion?)
56.4v (Victron/Prowse)
58.0v (Battleborn/Prowse/Relion)

I have a passive BMS that balances above 56v - my thoughts had been to play it safe with 55.6v and any run away cells would hit 56v and the BMS would start to restrict charge. Am I being too conservative? Should I slowly increase the charge voltage over time or just increase to 56.4 perhaps? The pack is 150ah by the way. Any thoughts or advice?
 
peterwareing said:
So from memory - the recommendations I have seen / heard linked to Will's videos / information I have:

55.6v (this may have been from elswhere? 55.6v charge and 55.6 float - Lion?)
56.4v (Victron/Prowse)
58.0v (Battleborn/Prowse/Relion)

I have a passive BMS that balances above 56v - my thoughts had been to play it safe with 55.6v and any run away cells would hit 56v and the BMS would start to restrict charge. Am I being too conservative? Should I slowly increase the charge voltage over time or just increase to 56.4 perhaps? The pack is 150ah by the way. Any thoughts or advice?
Click to expand...
This might be helpful.
Voltage vs capacity of Lifepo batteries.jpg
Many do not do a full charge after having done a top balance on lifepo battery cells.
Instead many [like myself] charge to a top of 90% and only go down to 10%. Or better top at 80% and bottom to 20 %. This will effectively double the life of the batteries. :)

Hopefully this helps you. :)
 
Thank you for the help - the chart is the 'loaded' chart for LIFEPO4. Can I ask how much of a load this refers to? My system runs 24/7 and always has some power being inputted or extracted - that is until LVD on the inverter switches everything back to grid. There is always an approx 200w draw from the fridge and freezer. Also how much over the required capacity voltage do I need to input into the SCC to achieve the target voltage and does it speed things up if I input 58v instead of 56.4v or even 55.6v. Sorry if the questions are basic / stupid but there is so much differing information I think I end up being too conservative.
 
Interesting - same idea and very close to the voltage of the Lion suggestion (I read somewhere?)
I was worried about the float being too high compared to the generally accepted 54.4v (3.4v) but they say 3.475v and you use 3.5v.
Thinking I may give 55.6v charge and float a try and keep a watchful eye on the cells then step up to 56v if all goes well.
I suppose its all about monitoring the cells at the top of their charge cycle and looking out for any run aways - everything appears comfortably balanced mid voltage with a little variation at the bottom (hence LVD 48.5v)
 
peterwareing said:
Thank you for the help - the chart is the 'loaded' chart for LIFEPO4. Can I ask how much of a load this refers to? My system runs 24/7 and always has some power being inputted or extracted - that is until LVD on the inverter switches everything back to grid. There is always an approx 200w draw from the fridge and freezer. Also how much over the required capacity voltage do I need to input into the SCC to achieve the target voltage and does it speed things up if I input 58v instead of 56.4v or even 55.6v. Sorry if the questions are basic / stupid but there is so much differing information I think I end up being too conservative.
Click to expand...
Look at the cell voltages, not the overall voltage.
When you see what you want as a percentage of your total [even 100%] then multiply that number by the number of cells you have. THAT is the number you aim for when charging your battery.
It confused me for some reason as well.
I think we over complicate these things.

But do not OVER charge a lithium battery of any kind as it can go to thermal runaway and then you have a problem.
There is so little difference in SOC [state of charge] between 3.4 nd 3.65 that many here ignore it and only charge to 3.4 volt per cell.
Also it is MUCH safer as well.

Is this what you were looking for?
 
SherylinRM said:
Look at the cell voltages, not the overall voltage.
When you see what you want as a percentage of your total [even 100%] then multiply that number by the number of cells you have. THAT is the number you aim for when charging your battery.
It confused me for some reason as well.
I think we over complicate these things.

But do not OVER charge a lithium battery of any kind as it can go to thermal runaway and then you have a problem.
There is so little difference in SOC [state of charge] between 3.4 nd 3.65 that many here ignore it and only charge to 3.4 volt per cell.
Also it is MUCH safer as well.

Is this what you were looking for?
Click to expand...
Well it sort of brings me back around to wehere I started I think? If I go with 3.4v for safety then thats 54.4v which is generally considered float voltage. Going back to the initial post it sounds like 54.4v charge and and 54.4v float may be suitable?
Sorry - I don't know about frying my batteries but my brain is certainly fried :D
 
Ok, the title of this thread i "extending Lifepo battery life".
And so based on this I recommend not going to 3.65 volts per cell.
3.65 is certainly good for bragging right. But once you do a top balance once [and you do not have to do one at 3.65 volts] then you are good to go for 6 month to a year.

However, if you want your batteries to last longer then protect them from heat [anything over 45 Celsius kill them]. Charge and discharge to 80 % and you can almost double the life of your lifepo batteries.
Is that "extended" enough? :)

Lastly, lithium batteries do not like to be floated. So lowering the top end and "floating" it there is a good idea. I plan on going no higher than 80 percent. Maybe 90 percent occasionally. But I don't need it that high.

And I hope to not go below 20%. This way I can charge the batteries 300 days a year and they will last me 20 years as a result. No I am not kidding.
 
SherylinRM said:
Ok, the title of this thread i "extending Lifepo battery life".
And so based on this I recommend not going to 3.65 volts per cell.
3.65 is certainly good for bragging right. But once you do a top balance once [and you do not have to do one at 3.65 volts] then you are good to go for 6 month to a year.

However, if you want your batteries to last longer then protect them from heat [anything over 45 Celsius kill them]. Charge and discharge to 80 % and you can almost double the life of your lifepo batteries.
Is that "extended" enough? :)

Lastly, lithium batteries do not like to be floated. So lowering the top end and "floating" it there is a good idea. I plan on going no higher than 80 percent. Maybe 90 percent occasionally. But I don't need it that high.

And I hope to not go below 20%. This way I can charge the batteries 300 days a year and they will last me 20 years as a result. No I am not kidding.
Click to expand...
Thank you for your help - and yes I do over complicate things!
Kind regards
peter
 
peterwareing said:
Thank you for your help - and yes I do over complicate things!
Kind regards
peter
Click to expand...
We all do at first I think because there is so much to learn.
After a while though it becomes second nature. :)
So you are not alone there. :)
 
So if I’m reading this correctly, it has not been healthy to charge and float my batteries at 56v?
I’ve been doing this for the past 4-5 months, they seem happy, but I guess I wouldn’t notice the damage.
So instead I need to set the absorb at 56 and float at 54.4? ?‍♂️ I guess I need to watch a video to understand these two terms lol
 
I've had my 220ah lifepo4 for 3 years, I charge everyday to 3.65 per cell. Hasn't damaged the battery, So you charging to 3.50 per cell should be good. I demand max performance from my battery, I paid for 220ah, I expect to get it thats why I charge to the max. With solar its rare I ever reach the max. As far as float, get it as low as possible so the battery stops charging when full.
 
jony101 said:
I've had my 220ah lifepo4 for 3 years, I charge everyday to 3.65 per cell. Hasn't damaged the battery, So you charging to 3.50 per cell should be good. I demand max performance from my battery, I paid for 220ah, I expect to get it thats why I charge to the max. With solar its rare I ever reach the max. As far as float, get it as low as possible so the battery stops charging when full.
Click to expand...

So say I’m wanting to do 80% soc... that would be 53v...

So I need to do 56 absorption and 53 float? Or you’re saying set it as low as possible so, my cc will allow me to float it 48v. So do that? ?‍♂️ I’m really over thinking this at this point I believe lol
 
Brandon8792 said:
So say I’m wanting to do 80% soc... that would be 53v...

So I need to do 56 absorption and 53 float? Or you’re saying set it as low as possible so, my cc will allow me to float it 48v. So do that? ?‍♂️ I’m really over thinking this at this point I believe lol
Click to expand...
The basics for a long life as I know them are.
Mild compression. Mostly just stop them from expanding when at full charge.
80% charge and discharge.
So stay away from the top 10% and bottom 10%.
Keep below 35C or 45C maximum.
Heat will kill these cells.
Never charge below 0 Celsius [32 F]. And if you have to charge that low then only charge at 5% until the cells get to 20 Celsius.

Doing all of these [but not being anal about it] will increase the cycle life to as much as 6,000 cycles.

I hope this helps. :)
 
SherylinRM said:
The basics for a long life as I know them are.
Mild compression. Mostly just stop them from expanding when at full charge.
80% charge and discharge.
So stay away from the top 10% and bottom 10%.
Keep below 35C or 45C maximum.
Heat will kill these cells.
Never charge below 0 Celsius [32 F]. And if you have to charge that low then only charge at 5% until the cells get to 20 Celsius.

Doing all of these [but not being anal about it] will increase the cycle life to as much as 6,000 cycles.

I hope this helps. :)
Click to expand...
So I should probably just stick with my bulk and float staying the same then.
3.5vpc seems to be doing me good lol

from everything I’ve read that’s really close to 80% (really 3.375. When I tried to charge any lower my batteries wouldn’t get to 4 bars on the charge gauge.

And then 3.65 is the full charge.
I’ve read you can go down to 2v and as high as 3.9 before any perm damage occurs to the cells.

im mainly trying to find the 20-80% range, which I’ve found, but now I’m more concerned with my bulk and float being set the same is a problem.
 
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