Hi. I have a Sunsynk 5kW Hybrid inverter with BSL 5.1 battery.

I am not sure that the inverter is correctly determining SOC as I observe it still feeding power to the battery when its apparently full - I'm seeing over 0.5kW charging when 100% SOC. 

 

I tried AGM V mode for some time and then switched back to Lithium mode. Interestingly, the moment I did that, the SOC displayed dropped from 80% to 60%.

I have checked that I have the latest BSL firmware and Sunsynk firmware. CAN connection seems fine. I gather the float and absorption voltage settings are moot as they're overridden by the BMS when in Lithium mode. I find conflicting recommendation on the float and absorption voltages:

• The BSL Manual v1.0 says (in Victron setup example):
  • - float: 54.8
  • - absorption: 55
• But this page and this thread and my tech support said the opposite (for "Lithium" mode:
  • - float: 55
  • - absorption: 54.8
• And I was advised that for AGM mode it should be:
  • - float: 54.5
  • - absorption: 54.6

 

Any advice, please?

TIA

47 minutes ago, FBJ said:

I tried AGM V mode for some time and then switched back to Lithium mode. Interestingly, the moment I did that, the SOC displayed dropped from 80% to 60%.

AGM batteries are lead and as such have a very linear voltage between 13V full and 10V basically empty i.e. 11.5V is basically half full.

Lithium is very flat till it discharges to 20% and the voltage then drops of a cliff

That is why it is not possible for the inverter to know what the SOC is of a lithium battery without communication to the batteries BMS system. 

Not all BMS's are created the same either. More expensive BMW's have a shunt that measures the amount of power flowing through it and do not use cell voltage for SOC measurement at all. They measure how much power has flowed though it vs the full capacity and work out what the capacity left is and tell the inverter the info via the CANBUS or RS485 connection.

 

Thanks @Sc00bs - it certainly doesn't seem relevant to use the AGM settings as a proxy for Lithium-ion BMS. So then my question is whether I have the correct settings for the BSL when it's in Lithium mode - it doesn't seem like the BMS is talking to the Sunsynk properly.

6 hours ago, FBJ said:

The BSL Manual v1.0 says (in Victron setup example):

• - float: 54.8
• - absorption: 55

I believe these above is the correct setting from BSL manual, but than there is another training video but I cannot remember where I found it that recommended the settings like below for 1 x battery. Batt Type must be Lithium, Batt capacity 125A. Discharge recommended current 90A.

I have set a 8 KW Sunsynk with 3x6.4KWH BSL’s like below and its been going fine since January. 

float - 54.5V

Absorbtion - 55V

equalization - 54V

 

On 2022/08/31 at 2:51 PM, FBJ said:

But this page and this thread and my tech support said the opposite (for "Lithium" mode:

• - float: 55
• - absorption: 54.8

@Gerrieis correct, use the settings he suggested... these ones quoted above are incorrect, your absorption should always be higher than (or at least equal to) the float because the inverter will charge to the absorption voltage first and then go to float.

9 hours ago, jumper said:

your absorption should always be higher than (or at least equal to) the float because the inverter will charge to the absorption voltage first and then go to float.

That's what I thought made most sense - thanks @jumper

On 2022/08/31 at 2:51 PM, FBJ said:

I am not sure that the inverter is correctly determining SOC as I observe it still feeding power to the battery when its apparently full - I'm seeing over 0.5kW charging when 100% SOC. 

if it’s a new installation then that’s correct as the battery cells are equalising