Hi Guys,
Got a bit of a curly one although there are some real knowledgeable folks on here so I'm sure someone will know some info that might help.
I have purchased all the Victron gear for a stand-alone off grid system to be installed on a shed on a country property.
I purchased the following Victron units:
Quattro 15000VA/48V Inverter/Charger
BMV-712 Battery Monitor
2x 250/100 Smartsolar MPPT Solar Chargers
Cerbox GX and Touchpad
The system will be two sub arrays of 16 panels each, configured 4 panels in series per string, 4 strings in parallel. System will be DC coupled as no mains available and I want black start functionality.
Batteries will be Drypower 200AH solar deep cycle units, 4 batteries per string to make 48V, 3 parallel strings to give me 600AH total capacity.
Here is the million dollar question... What is the best way (if any) of detecting a blown fuse (or faulty battery) in the battery bank to trigger the solar chargers (and Quattro inverter charger if on genset backup) to limit the charging current to the bank ? Note: battery bank will have separate fuses for each string to limit fault current to meet Aust standards.
As it stands, I will need to set the solar controllers down to 90A each to give me 180A total so that each string only gets 60A which is the max charge rate of the batteries. I want the system to pick up on a blown string fuse and drop the max charge current down accordingly. .i.e One blown string max current is 60A per controller, two blown strings 30A max per controller. I know its an unlikely event but this system will be unattended 95% of the time and I don't want to cook my entire battery bank due to one blown fuse or string fault.
Now the trick is how to detect blown fuses ? Due to parallel strings a voltage drop across an individual blown fuse will not be system voltage. Current sensing is expensive and will need a smart device to interpret the results due to different conditions during charging and discharging events.
My thinking is there should be a small volt drop across the blown fuse, equivalent to the difference between the system nominal voltage (48V) and the bulk charging voltage of around 57.6V. If I'm correct in my assumption I might be able to use a 3V or 4V solid state relay to close a dry contact wired to a digital input on the Cerbo GX. If my assumptions are correct, what are my options with the Cerbo GX to make changes to the DVCC parameter to adjust max charging current on all chargers ?
Sorry for the long explanation but I figured its better to put all the info out there rather than people wishing to help having to ask questions. I am a sparky but this is my first foray into solar and I have no experience with the advanced features of the Victron control gear. I am prepared to tackle it though so feel free to make suggestions.
Any help or suggestions appreciated.
Cheers
