Off-Grid Solar Design, Education and Advice

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April 19, 2026 4:48 pm

A big upgrade to my off-grid solar setup today: I upgraded my inverter from the Victron Phoenix 1200W 24V to a huge Victron 24V Multiplus-II 3000W Inverter (with charger feature). The previously-requi... View MoreA big upgrade to my off-grid solar setup today: I upgraded my inverter from the Victron Phoenix 1200W 24V to a huge Victron 24V Multiplus-II 3000W Inverter (with charger feature). The previously-required Bluetooth upgrade dongle got retired. I'm reusing the same set of four 6V marine, lead-acid, deep-cycle batteries as before in series. The earlier setup involved much smaller wiring throughout. The bigger inverter and wiring to my house can now accommodate the larger values. I had to dig a trench and install 10-2 Romex to support the 25A (plus a little more) coming out of the inverter at the maximum output. I had to upgrade the fuse sizes in the premise switch inside the house. I had to upgrade the sizing of the wire between that switch and the circuit breaker box. I had to install the "binding screw" in that panel now that the new inverter provides 120V on just the black wire (the lower-cost Victron provided 60V on black and 60V on white so you can't bind 60V white to ground = very bad). The system is much safer as a result, a tripped circuit breaker before this would have resulted in 60V still being on the return side of all outlets (not very safe). I added a big red wire to connect the breaker box's first hot leg to the second: I don't anticipate ever doing 240VAC in the box so I thought I'd enable the second set of breaker slots for future expansion. The wiring is pretty mondo from the batteries to the inverter, 0/2 gauge. And I upgraded the wiring between the batteries in series as well as the ground side which goes to the BMS shunt. As before, there's a "big black switch" on the ground side of the batteries. The inverter output now has a "big red switch" as well as a large-value inline fuse. I retired the previous Busmann series circuit breaker. I added both temperature and voltage sensors which now connect to the inverter. I added smart connectivity from the new inverter to the existing VenusOS Raspberry Pi computer so that it can manage it as well. It's a dongle with a USB connection. In theory, I can now do some monitoring of the battery temperature in the solar shed in case I need to add the foam insulation back in the winter. I now have programmatic access to the power load on the consumption side of things. I used this as an opportunity to check the fluid levels on all the batteries. They're looking good since they're fairly new.

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