Limit state of charge of GBLI 6532

[radiomean]

Hi, I have a SPH 5000 hybrid inverter, GBLI 6532 battery (6 kWh) and have added two 'Chinese' 3.5 kWh batteries myself - thus doubling the storage capacity of the system from the original 6 to around 12.5 kWh.

Monitoring of the 'Chinese' batteries is not connected to to the invertor, but I have a mini-PC monitoring these using the RS485 port.
This generally works pretty well, and when I charge the batteries from AC mains (at cheap rate overnight) I use the Growatt invertor settings to limit charge to 96%, which ensures the batteries don't get overcharged (I know their own BMS will manage this but I don't want to stress them).

However, I can't find any setting in the invertor to limit the state of charge to the GBLI 6532 and Chinese batteries when charged from the PV panels? (There is a clear setting to limit SoC when charged from AC). Does anyone have any thoughts as to how to achieve this?

Cheers!

 

[sunshine_eggo]

The BMS is controlling the inverter specifying charge voltage and maximum charge current. These values will supersede your AC charging setting if a limit is triggered, e.g., if a single cell hits OVP, it will cut charge to 0A even if it hasn't reached your 96%.

There is no reason to limit upper SoC. LFP batteries require regular charges to full to:

1) ensure SoC remains accurate.
2) ensure cell remain top balanced.

 

[radiomean]

Hi, thanks for the reply.

However, I deliberately want to stop the inverter charging the two Chinese batteries, as they do not communicate with the invertor. The GBLI 6532 battery talks to the invertor, but the Chinese batteries are not connected and they reach full charge before the GBLI 6532 charging is stopped - so I want to manually stop charging at 96% to be doubly sure these separately connected batteries are not overcharged...

 

[sunshine_eggo]

Hi, thanks for the reply.

However, I deliberately want to stop the inverter charging the two Chinese batteries, as they do not communicate with the invertor.

They should be at the exact same voltage as the other battery, so they will be at essentially the exact same SoC when nearing full.

The GBLI 6532 battery talks to the invertor, but the Chinese batteries are not connected and they reach full charge before the GBLI 6532 charging is stopped

Are they imbalanced? If so, this is a battery issue, not a control issue. What do the cell voltages read when "full" is indicated?

- so I want to manually stop charging at 96% to be doubly sure these separately connected batteries are not overcharged...

The BMS is in total control of the system. Either you need to reprogram the BMS to change the way it operates (I'm not certain this is even an option with the tools available), or you need to disconnect comms, set battery type to USE and set absorption/float manually. You will lose all SoC data, and you will have to base all your management on voltages.