Hi there,
I currently have a 4WD setup with a BMV-712, 130AH AGM rear battery and 1500W inverter. I have standard 4wd type accessories like a 12v fridge, water pump, lights, 12V outlet for phone charging etc connected through individually fused circuits from a central 6 port fuse block. The total load of everything if everything runs at once (except inverter) is around 13A.
The rear battery currently gets charged from the engine alternator through an electronic voltage sensitive relay connecting the two batteries. At the moment all loads are routed through the BMV 712 Shunt, including the inverter (which incidentally only ever gets used for short periods of time for the sole purpose of making toast!)
I am considering fitting a Smartsolar MPPT 100/20 (or 75/15) so I can go off grid for longer without running the engine and I really like the concept of using the load control functionality to protect my rear battery. I would fit all but the inverter to the load connections on the MPPT (through the single +ve cable that currently runs to the fuse block), and the inverter would remain connected direct to the battery. I turn the inverter on and off manually through its own switch.
The problem is when the battery is under load from the inverter (900W to run the toaster through short length 2B&S cables) the voltage often drops below all the MPPT pre set voltage triggers and would therefore to disconnect the load to my fuse block. When the battery is at a low SOC to start with, the load may never actually be reconnected as it may not recover to above the 'reconnect' trigger voltage.
To avoid this I would like to use the BMV-712 SOC setting to trigger the load disconnect signal, rather than the MPPT inbuilt voltage settings.
I have read several posts and understand that that I can easily use the BMV to control a separate high current relay that would disconnect the battery for SOC triggers, but this seems to defeat the purpose of having the 100/20 and its excellent load connection & control abilities.
From my research I understand that the MPPT VE direct port has 4 pins (1 GND, 2 RX, 3 TX, 4 PWR)
I also understand that the VE direct RX port on the MPPT can be set through Victron connect software to act as either a remote on/off (for the MPPT itself), or as a load output on/off (including an inverted mode) to the load connections on the MPPT.
Where I fall down is working out how to actually achieve this.
I have read that the VE direct Rx port is 5V, and I understand the BMV relay has a COM, NC, & NO connections that can also be inverted through the Victron connect software.
So was wondering if I connect a 5V source to the BMV-712 relay COM terminal, can I then connect the BMV relay NO output terminal (which would also be 5V) direct to the MPPT VE Direct Rx port ? I could configure the MPPT such that when the BMV low SOC triggers, voltage at RX on MPPT hits zero and then triggers the load output to off.
Can I do this with my own wiring (ie BMV NO to MPPT RX, plus an earth cable) at the MPPT - or do I have to purchase the VE direct non isolating cable to make this work ?
Or perhaps my understanding from all my research is flawed and this is not actually achievable ?
I know I could just fit the high current relay, just space is at a premium and I am keen to explore the realms of possibility.
