Posted February 14, 20223 yr Hi all. I have a fairly new PV system installed and was hoping someone could give me some guidance and good advice. My setup consists of 2x 5.5kw Axpert MKSii inverters in parallel, 14 450w panels (7 to each inverter) and 2x 4.8kw lithium batteries in parallel. System settings are as follows: Priority SBU Bulk Charge voltage 51.6v Float voltage 51.5v Low voltage (return grid) 48.2v Low voltage cutoff 46.4v AC charge current 20A Total charge current 30A Battery full voltage 51.0v The system works well, I just want advice on whether my settings are ok? I also have a question regarding the cross over to grid and the return to solar: I understand that at 48.2v (approx 27% SOC in my case) the system will switch over to grid and will stay there charging at 20A until the batteries reach 51.0v. In my case this is around 3.5 hours as it sometimes happens around 5am and there is little load on the system. Is there a way to set the system so that it for example only charges to 75%? Thus using less utility power in the hopes the solar will charge the balance when it starts later on. Also, if the system has reverted to grid and draws 20A to charge from grid, does it also use the solar energy to also charge the batteries (up to the 30A total threshold?), or is the solar lost whilst it is on grid?
February 15, 20223 yr 16 hours ago, brburger said: 5.5kw Axpert MKSii inverters I believe that there is no genuine 5.5kW MKS II model, so yours is probably a clone. 16 hours ago, brburger said: Is there a way to set the system so that it for example only charges to 75%? Is there a setting 13, back to discharge or back to battery setting? The Axperts have this. If it was a genuine Voltronic, you could use a monitoring program like Solar Assistant to talk to the battery's BMS, and switch at exactly 75% SoC, rather than a battery voltage that depends on load and temperature. > does it also use the solar energy to also charge the batteries (up to the 30A total threshold?), or is the solar lost whilst it is on grid? Assuming that they copied the firmware correctly, solar energy will always charge the battery, even in line mode (utility powering the load).
February 15, 20223 yr Author 1 hour ago, Coulomb said: Is there a setting 13, back to discharge or back to battery setting? The Axperts have this. Under menu item 14 it has a "battery full voltage". This I can confirm is the voltage it goes back to grid at. Can this be lowered to say 50.5v to force charging from grid to stop at a lower percentage than full? Then just lastly, my batteries have there own BMS, do the batteries then basically look after themselves?
February 15, 20223 yr 2 hours ago, brburger said: Under menu item 14 it has a "battery full voltage". This I can confirm is the voltage it goes back to grid at. Can this be lowered to say 50.5v to force charging from grid to stop at a lower percentage than full? Then just lastly, my batteries have there own BMS, do the batteries then basically look after themselves? Genuine Voltronics don't have setting 14. The BMS are basically information systems only, except for emergency low voltage cut out. My settings are: Back to utility (12): 47V (48V if load shedding looms); Back to battery mode (13): 50V during night, 49V on daylight; Low battery cut off (29): 42V. My BMS cut out at 40.5V according to data sheet (15 cells LiFePo). Bulk charge (26): 54V; Floating charge (27): 52.5V. Utility charging current (11): 1/10 of battery Ah. The settings depend also on the battery capacity and type you have and the expected consumption during a load shedding at night.
February 15, 20223 yr 4 hours ago, brburger said: Under menu item 14 it has a "battery full voltage". This I can confirm is the voltage it goes back to grid at. Can this be lowered to say 50.5v to force charging from grid to stop at a lower percentage than full? I'd say so; it sounds like Axpert setting 13, except you get more precision (0.1 V compared to 1.0 V). Have you tried it? 4 hours ago, brburger said: my batteries have there own BMS, do the batteries then basically look after themselves? Without a connection to the BMS RS-485 or CAN port, there are limits to what the BMS can do. For example, the BMS can't ask for temporarily less charge current. But as long as the cells stay balanced and you have sensible settings, then effectively the battery does look after itself.
February 15, 20223 yr Author 1 hour ago, Coulomb said: I'd say so; it sounds like Axpert setting 13, except you get more precision (0.1 V compared to 1.0 V). Have you tried it? I have changed the setting on 13 from 51v to 49.8v and will see at what SOC it reverts back to batteries, I am hoping for around 60%, but will have to work with the voltage to get the correct figure corresponding to around 60% SOC. I have also confirmed with supplier that setting 13 can be lowered. 3 hours ago, Beat said: The settings depend also on the battery capacity and type you have and the expected consumption during a load shedding at night. I have my settings as per the recommended settings from battery supplier, I have only now changed the "back to utility" to 48.2 which in my case happens early morning when there is very little load (under 300w) and equates to about 27% SOC on batteries. The batteries have lcd screens which show voltage, SOC, SOH and charging/discharge current, this info is coming from the bms as it is on the actual battery and thus not the inverter making an estimate. I have also now changed the "return to battery" voltage to 49.8v so that the batteries are not charged full from utility, but only to around 60% (this is an estimate and I will work with the voltage figure to get to the 60%) as I have sufficient solar generation between 3 and 4 hours after the batteries have drawn down to "return to grid" at 48.2 volts/ 27% SOC. Edited February 15, 20223 yr by brburger
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