Update Old Inverter to Charge Lithium-ion batteries

[ABarbarian]

I have a 10 year old Steca Xtender XTM 4000-48 inverter used with lead acids, wanting to move to lithium-ion and was updating settings to try and allow the inverter to charge batteries from grid, but am scared its charge method will damage the batteries.

Many sources of information state lithium-ion should only be charged by a lithium-ion charger, I will be using a lithium-ion specific solar charger, but for grid charging it would be nice to use the inverter.

I am concerned about CCCV charging, that the old inverter wont do this, and perhaps other things not considered. Documentation for the inverter does not mention lithium-ion.

Additional info:
- Batteries: Lithium NMC 48v 120Ah 145Ah (limited manufacturer detail)

Settings I was looking at adjusting include:
- Battery charge current {1138}: 31 A
- Floating voltage {1140}: 53.6 V
- Absorption phase allowed {1155}: No
- Equalization allowed {1163}: No
- Reduced floating allowed {1170}: No
- Periodic absorption allowed {1173}: No
- Battery undervoltage level without load {1108}: 47 V
- Battery overvoltage level {1121}: 59 V

 

[sunshine_eggo]

You can't formulate a charging scheme for a battery without giving battery data.

"48V" NMC is not a sufficient designation.

How many cells in series? NMC "48V" may be 12-14 cells in series, and it's critical to know your cell count.

 

[ABarbarian]

1

You can't formulate a charging scheme for a battery without giving battery data.

"48V" NMC is not a sufficient designation.

How many cells in series? NMC "48V" may be 12-14 cells in series, and it's critical to know your cell count.

14 cells

 

[sunshine_eggo]

I have a custom 14S NMC battery.

You need to pick a target cell voltage based on desired cycle life:

3.92V = maximum cycle life (75% SoC)
4.05V = balanced cycle life
4.15-4.20V = minimum cycle life

If this is for UPS operation, I would not encourage storing them at full charge.

Set absorption to 14X desired cell voltage and allow absorption to fill the battery.
Float 0.1V below absorption.

3.5V cut off is 20% SoC

Yes 20-75% SoC is pretty limited, but you can get tens of thousands of cycles. This is my normal operating range. I will extend it at both ends depending on conditions. If I see bad weather headed our way, I may charge to max voltage to give me more margin, and I will go below 3.5V if needed.

Expert 1139 Temperature compensation 0 mV/°C/cell (you don't want this)
Expert 1140 Floating voltage 0.1V below absorption
Expert 1155 Absorption phase allowed Yes
Expert 1156 Absorption voltage (set to your desired cell voltage * 14)
Expert 1157 Absorption duration 4 hours
Expert 1158 End of absorption triggered with current Yes
Expert 1159 Current limit to quit the absorption phase 1 Adc

 

[ABarbarian]

Expert 1139 Temperature compensation 0 mV/°C/cell (you don't want this)
Expert 1140 Floating voltage 0.1V below absorption
Expert 1155 Absorption phase allowed Yes
Expert 1156 Absorption voltage (set to your desired cell voltage * 14)
Expert 1157 Absorption duration 4 hours
Expert 1158 End of absorption triggered with current Yes
Expert 1159 Current limit to quit the absorption phase 1 Adc

Thank you for going into the specs and referencing the settings, that is very appreciated.

I understand your answer to my main question "can this old-timer inverter charge lithium-ion/NMC without damaging the battery cycle life?" is yes it can.

I have attached a common charge profile for lithium-ion batteries, your suggested settings I understand create this result:
- the inverters bulk phase which operates up to setting {1140} matches the images "Constant current charge" stage
- there will be a short inverter floating phase between settings {1140} and {1156} which kind of matches the images "time=1" to "end of Stage 1" markers
- the inverters absorption phase is used to match the images "Saturation charge" stage

I assume these settings:
- Equalization allowed {1163}: No
- Reduced floating allowed {1170}: No
- Periodic absorption allowed {1173}: No
- Softstart duration {1599}: 0.0
- Smart-Boost allowed {1126}: Yes

By my reading, your suggestions do create results that match the suggested lithium-ion charge profile, I was concerned there were other things the inverter does that do not fit the profile, as the inverter appears to be made before lithium-ion was in use and many sources say only use lithium-ion chargers on lithium-ion batteries.


-- Additional information, not important to my core concerns above --

I am planning the system with these requirements:
- use with battery as primary source
- switch to grid when reach low-voltage
- optionally top the batteries up with grid when I believe a power cut is coming

To achieve this I am planning to:
- set "Batteries priority as energy source {1296}" to No
- have a manual cutoff switch between grid and inverter that must be engaged manually when battery source reduces below "Battery undervoltage level without load {1108}" (alarm will sound)
- use the manual cutoff switch to top up batteries preemptively when a power cut is coming

Not perfect but I will have no access to inverter settings once setup and can't see a better way to achieve requirements, we had a similar setup for 10 years and are used to the manual intervention on low battery.