Two 120/240V inputs, one from the generator and one from shore power, both going to 2 Quattro inverters in split-phase configuration. Is it true that this will result in load balancing, or would an autotransformer be needed?
An auto transformer would be needed to do load balancing. However the 2 inverter solution will still work, but with unbalanced loads. As long as neither phase is overloaded, neither the Gen nor the shore power should object to a moderately unbalanced load.
Would it be correct to say that the inverters only pass through the current; they don’t manipulate it with a transformer in any way, and that’s why they are not balancing the loads?
Secondly, when they are inverting off of batteries providing 120/240 split phase, is it correct that the loads are not balanced in that scenario, either, unless an auto transformer is used?
And in this scenario, will the downstream auto transformer balance the loads across both legs regardless of whether it’s shore power being passed through, generator power being passed through, or power from the inverter when relying on the batteries? The auto transformer does not care what the source of the current is, presumably.
I’m not answering for Mike, but I have some thoughts for you.
In inverter mode, they absolutely use the transformer inside the Quattros. In pass-thru mode, they just pass through the voltage and current (within limits). 120V loads aren’t balanced because there is no common means to do so without an external device such as an autotransformer (AT).
240V loads are inherently balanced because they equally load the inverters. When one inverter is outputting 120V at 0° phase rotation, the other inverter is outputting 120V at 180° phase rotation (exactly opposite) and that’s how you end up with 240V, more or less. The imbalances you speak of are only with 120V loads. A 120V load is satisfied by whichever SINGLE Quattro the load is physically wired to in your breaker panel. You have to ensure that you distribute 120V loads evenly across both inverters. But 240V loads will do it automatically.
You are correct.
It’s important to understand the limitations of the AT. The 100A Victron AT can only balance a difference of about 3000W for a “little while” before overheating. It depends on the ambient temperature of the room and whether or not you actively cool the AT. It is not a magic, unlimited device, so you should do what you can to distribute 120V circuits evenly across the Quattros and use the AT to handle any short-duration imbalances.
The AT has protection circuitry built in to open the breaker when the transformer inside gets too hot. Once it’s cooled down, you can reset the breaker again until another overload occurs. If an overload/overtemp occurs on the AT, then you know your 120V loads are too unevenly distributed across the inverters and you can move a circuit or circuits around to help with that.
I hope this helps.