Hi there, just fitted a new 7kw petrol generator to my system and at first everything was fine, but now it charges at 3 kw for about an hour and then it falls to 300w no matter the Soc of the batteries. Anyone have any ideas why?
MultiPlus-II 48/8000/110
3 x dc 5kw lithium batteries
8 600w panels
Mppt ve can 250/100
Please share more information about your system and settings?
Battery / BMS type, and battery voltage during charge cycle ?
Also, Multiplus voltage settings for Abs & Float? Please..
Bms is inbuilt with the Solar Energy 48V DC-5000/LV Lithium DC Battery and absorption voltage 14.2V and float 13.5V-13.6V
Is that a 48V battery or 4 x 12V batteries in series - not a good idea with built in BMS.
What are the inverter voltage settings? (Charger tab) Did you configure the inverter, or are you trying to use is with the default settings?
3 x 5kw 48v batteries, default settings. Is it a good idea to have an external bms to cover these 3 batteries? I am totally new to this and not electrically minded! But I’m learning slowly
OK, so a sort of BMS101:
The BMS SHOULD be able to control charge and discharge of the battery, to do this it needs to measure the voltage of every cell, usually whit milivolt resolution. As the battery charges, the BMS tries to equalise the cell voltages, usually by shunting the higher voltage cells with a resistor. More advanced BMS (active balancing) designs use small dc/dc converters to put the energy into other cells. Should one cell exceed the max permitted voltage, then the BMS will want to shut off the charging. It can do this in 3 ways:
shutting off the battery from charging by the internal switch is a drastic measure - this leaves the DC bus in an unstable condition, and the bus voltage can rise sharply. This depends on how many other battery packs are connected to the bus and what their condition is. This type of control can work where there are numerous packs, but is not good when there are only a few.
Closing a relay contact can tell one other piece of equipment to shut off charging. This is ok when there is only one charge source.
The third option is always the best - but in the case of Victron equipment, it generally requires the BMS to have a CAN connection to the Cerbo, and to have the Victron CAN protocol encoded in it. Victron publish a list of approved battery BMS types, but as you already have your batteries this is not strictly relevant.
Without BMS control of the charger, on needs to program the Battery Absorption and float voltages into the Multiplus inverter. The absorption voltage used should be slightly below the manufacturer’s limiting voltage if this is not specifically given. This reduces the chance of a disconnection.
These voltages also need to be programmed into the MPPT.
You may also need to add a smart shunt to the system, so the Cerbo has a more accurate measurement of battery voltage and battery SOC.
So the question remains for your charging problem,what are the inverter voltage settings, and what are the battery required settings? Look at the battery voltage during charging, the historic graph of this can be obtained from the Advanced widgets page of VRM - to do this the cerbo needs to be connected to the internet, and registered on VRM.
