Battery bank, stop charging at 90%

[Cuemaker]

One final question (I hope), think I have finally figured it out.
How do I stop charging at 90%?
Right now I have a couple disconnects to turn off strings of panels.
There must be a way to do it automatic but can't find it.
Thanks for all your help!!!!

 

[timselectric]

Why do you want to stop charging at 90%?

 

[Cuemaker]

Why do you want to stop charging at 90%?

That is Will's parameters to get the most life out of the cells.
Discharge no less than 10% & charge no higher than 90%.
This will extend the life of the cells a lot!

 

[timselectric]

That is Will's parameters to get the most life out of the cells.
Discharge no less than 10% & charge no higher than 90%.
This will extend the life of the cells a lot!

If it's being used for EV propulsion, yes.
But since you are in this forum, I will assume that it's for solar storage.
So, use the full capacity. Calendar aging will degrade your battery before anything else.

 

[Cuemaker]

If it's being used for EV propulsion, yes.
But since you are in this forum, I will assume that it's for solar storage.
So, use the full capacity. Calendar aging will degrade your battery before anything else.

It's for an off-grid solar system.
I may have misunderstood but I know Will said 10% to 90% would make the cells last longer.
I just assumed it was for electric system to run a house.
Would like to get as much life out of the cells as possible.

 

[Robbert]

If 'saving' your batteries is your objective, you could choose to charge to a lower voltage.
High voltages cause more stress on the cells.

I for example charge to 55.4v with 1 hour absorption.

 

[timselectric]

It's for an off-grid solar system.
I may have misunderstood but I know Will said 10% to 90% would make the cells last longer.
I just assumed it was for electric system to run a house.
Would like to get as much life out of the cells as possible.

It's possible that he said that, in an older video.
This is from two weeks ago.

 

[Eber]

It's possible that he said that, in an older video.
This is from two weeks ago.

Interesting video. Based on the video, float at what then?
My 48V system i have been floating at 55V

 

[timselectric]

Interesting video. Based on the video, float at what then?
My 48V system i have been floating at 55V

I float at 56v.
But anything above 3.45v per cell (55.2v) is good enough for balancing.

 

[Cuemaker]

It's possible that he said that, in an older video.
This is from two weeks ago.

Yes it was an older video, I think about 3 or 4 years ago.

 

[Steve_S]

Bulk/Absorb to 55.2V (3.450) to a max of 56V (3.500) NOTE Absorb should be set to 1 Hour runtime.
Float @ 54.8V (3.425) to a max of 55.0V (3.437)
EndAmps/TailCurrent = Largest Battery Packs (AH X 0.05) IE (100AH X 0.05) = 5A, (280AHX0.05)=14A
This is when batteries are taking only the EndAmp Value of ##A to transition from absorb/bulk to Float Mode.

LFP can Happily be charged to 100% (which is 3.400 Volts per Cell). We charge slightly above with float because LFP settles (Natural & Normal).
The 10% to 90% "SHTICK" is NOT RELATED TO LFP ! is it not NCM/NCA Chemistries!

Do not disconnect your Solar Panels let the solar controller deal with it, that is its job !

Please Understand that LFP like most other chemistries has TWO VOLTAGE RANGES and unfortunately many make assumptions and do not realize... The ASSumption rule applies here, even if it is because of misunderstanding.
The ALLOWABLE Voltage is from 2.500 -> 3.650. IS the Range the cells can be used within without ANY Harm or Damage !
The WORKING Voltage is from 3.000->3.400 (Nominal / 50% SOC is 3.200V). YES only 0.400 Volt Flat Voltage Curve. This is the range the cells are tested at and is responsible for delivering the specified Cell Amp Hours. A-Grade Cells will deliver their specified AH from this range, B-Cells will fall just short in AH.

SPECIAL NOTE: You CAN safely use from 2.800-3.400 without issue BUT ensure that your Low Voltage Disconnect is no lower than 2.700V per cell, to ensure that the BMS will have enough power to stay "awake" and allow for incoming charge. This also allows for a deep surge (which causes voltage sag) when the battery pack is low. (Think of a Fridge start surge)

EXTREMELY IMPORTANT - This is NOT Lead Acid Brute Force Tech ! ALL Lithium Chemistries ARE MilliVolt & MilliAmp sensitive !
DURING CHARGE:
Use a Digital MultiMeter and check voltage coming out of SCC @ SCC Terminals and then at the Battery Pack Terminals and note the difference down to 0.00 accuracy. This is your Charging Offset ! NOTE THIS ! Also if you have an External Charger or an Inverter/Charger that is used for Charging... Check when charging and note the offset as above.
DURING DISCHARGE ONLY (No Solar Input at all, after sundown is best):
Check the voltage again @ SCC, Inverter and Battery Pack Terminals you WILL see a different offset (bias)
The offsets MUST be corrected for and most importantly for CHARGING because you do not want to be outside of the voltages you want... Most Tier-1 Products have OFFSET Values that can be entered to correct for this. Otherwise you have to manually correct for it in your settings as applicable to the SCC & Inverter/Charger.

 

[Madcodger]

Much good information already posted here. About all I can add is:

Check out your battery mfr's recommendations. They know the battery they produced.

Check out videos on YouTube from Off Grid Garage (Andy, down in sunny, hot Australia)). He's done much research and experimentation on this exact issue and has evolved his thinking a bit over time. Much good background and great explanations on this topic in his videos, if you're willing to spend the time watching and learning.

Personally, I've settled on charging my 24V system to 28.4 V, and charging to 100% whenever possible. I, too, thought stopping charge at 85-90% would be beneficial, but it proved to be both difficult to manage and, possibly, harmful in the long run because the batteries/cells couldn't "top balance". So, I now charge to 28.4 V (3.55 V per cell), float at 27 V (3.375 V per call) and call it a day. I may play with the float V a bit, but otherwise I find this is working well for me, and I suspect calendar age will get to my batteries long before the effects of this charging approach.

 

[Cuemaker]

Bulk/Absorb to 55.2V (3.450) to a max of 56V (3.500) NOTE Absorb should be set to 1 Hour runtime.
Float @ 54.8V (3.425) to a max of 55.0V (3.437)
EndAmps/TailCurrent = Largest Battery Packs (AH X 0.05) IE (100AH X 0.05) = 5A, (280AHX0.05)=14A
This is when batteries are taking only the EndAmp Value of ##A to transition from absorb/bulk to Float Mode.

LFP can Happily be charged to 100% (which is 3.400 Volts per Cell). We charge slightly above with float because LFP settles (Natural & Normal).
The 10% to 90% "SHTICK" is NOT RELATED TO LFP ! is it not NCM/NCA Chemistries!

Do not disconnect your Solar Panels let the solar controller deal with it, that is its job !

Please Understand that LFP like most other chemistries has TWO VOLTAGE RANGES and unfortunately many make assumptions and do not realize... The ASSumption rule applies here, even if it is because of misunderstanding.
The ALLOWABLE Voltage is from 2.500 -> 3.650. IS the Range the cells can be used within without ANY Harm or Damage !
The WORKING Voltage is from 3.000->3.400 (Nominal / 50% SOC is 3.200V). YES only 0.400 Volt Flat Voltage Curve. This is the range the cells are tested at and is responsible for delivering the specified Cell Amp Hours. A-Grade Cells will deliver their specified AH from this range, B-Cells will fall just short in AH.

SPECIAL NOTE: You CAN safely use from 2.800-3.400 without issue BUT ensure that your Low Voltage Disconnect is no lower than 2.700V per cell, to ensure that the BMS will have enough power to stay "awake" and allow for incoming charge. This also allows for a deep surge (which causes voltage sag) when the battery pack is low. (Think of a Fridge start surge)

EXTREMELY IMPORTANT - This is NOT Lead Acid Brute Force Tech ! ALL Lithium Chemistries ARE MilliVolt & MilliAmp sensitive !
DURING CHARGE:
Use a Digital MultiMeter and check voltage coming out of SCC @ SCC Terminals and then at the Battery Pack Terminals and note the difference down to 0.00 accuracy. This is your Charging Offset ! NOTE THIS ! Also if you have an External Charger or an Inverter/Charger that is used for Charging... Check when charging and note the offset as above.
DURING DISCHARGE ONLY (No Solar Input at all, after sundown is best):
Check the voltage again @ SCC, Inverter and Battery Pack Terminals you WILL see a different offset (bias)
The offsets MUST be corrected for and most importantly for CHARGING because you do not want to be outside of the voltages you want... Most Tier-1 Products have OFFSET Values that can be entered to correct for this. Otherwise you have to manually correct for it in your settings as applicable to the SCC & Inverter/Charger.

Great info, this explains a lot.
No doubt I messed up, had a setting wrong that took voltage down to low.
Top balancing the cells now & corrected the setting.
Will set it up to run between 3.000-3.4000 & see what happens.
Thanks for all the info!