I am part way through an installation and have come to question some elements of the configuration. I would like to get some expert knowledge on the plan. My apologies for the long question, but this is a kind of complicated scenario and I wanted to describe the situation as clearly as possible.
My original installation as hired out was to install a Victron MultiPlus 12/3000/120, BluePower panel, BMV-702 and six L16 Full River AGM batteries. This worked fine for a couple of years and then I went to upgrade my charging/inverting capacity. I installed a second MultiPlus (same) and Cerbo GX with Touch 70, but due to timing issues installed it as only a charger. This year I embarked on the project to fully install it as a charger/inverter. I wanted the extra charging capacity in addition to the ability to pass-thru greater than 50 amps. My shore power (and genset) is 240V 50A but for much of the year I must bypass the inverter because the transfer relay cannot take the sustained load in the boat, primarily driven by electric heaters. Additional requirements are that I only wanted to use one control device (Cerbo), and take advantage of PowerAssist.
It seemed a reasonably straightforward proposition, but a couple details have come up that make me question my strategy. The plan was to install the two MultiPluses in a parallel, split phase configuration. They would run 240V out and power the entire panel. It’s not reasonable at this time to presume I could run the air conditioners or 240V induction stove and oven from battery (other than for very short bits of time) but I was under the understanding that for PowerAssist to be effective, I had to run things this way to ensure the system was aware of ALL loads, so that it may turn PowerAssist on when needed. There were a few wiring considerations that had to be accounted for, but the biggest question mark just came up with the realization that what I generally consider to be 240V input is actually not. My home marina, where we live aboard, and many of the marinas we stop at during our summer cruising season are 208V which is in fact two legs of a three phase system. (The remainder of our cruising time is spent at anchor, where the genset is the mains supply, and is true 240V split phase with the phases 180°.) The lower voltage is pain in the rear, but not un-survivable, however as part of the grand project I am installing a toroidal isolation transformer with an auto sensing boost capability (14%). This should be mostly a good thing, but now I am considering whether the input phasing of the 208V, which is 120° will cause a problem in my planned environment. I had planned to configure the MultiPluses as 240V split phase (180°) output. I considered that in pass-thru mode the phasing of the 208V input would not cause a problem, it would be just passed through, effectively as it is today. And in pure inverter mode, the MultiPluses would provide 240V split phase (180°?) and all would be happy. BUT, now I am wondering what the situation would be if when running on 208V shore power, what happens if (when actually) PowerAssist gets activated?
To try to sum up and reduce this narrative to a couple simpler questions:
- Can I run two MultiPlus 3000 units in parallel as described above, regardless of whether the source power is 208V with 2 x legs at 120° phasing AND/OR 240V with 2 legs at 180° phasing? And if so, any special configuration options to be chosen?
- If not, how else should this be installed and configured, and is it possible to still have one Cerbo controlling both units?