question

Maybe. I assume you have 2Kw or 3Kw 120V Multipluses. The Datasheet says you can"stack" two inverters one on each hot leg and provide a 120/240V split phase output. What I cannot find anywhere is confirmation of how well a 120/240V split phase source (Your generator) will perform with pass-through and charging in this stacked arrangement.

I live in the US so I have a great interest in getting a definitive answer.

Pat

In our system, we run two Quattro 12/5000/220-100/100 120V Inverter/Chargers for normally operating on a 50a RV service (240 split phase I believe it's often called). We wired leg 1 to the first inverter, and leg 2 to the second inverter. We then wired the output of each inverter to each 120v leg of our RV.
When on a normal 50a grid service, each inverter/charger operates normally. When on a 30a single phase 120v, split over the 2 legs (both legs on same phase) the first inverter operates normally, and the 2nd inverter rejects the signal and goes into inverter mode drawing from the batteries to make up the other (out of phase) leg. (effectively still maintaining the other phase in its output).

So when adding a 120v generator, when used with an upstream transfer switch, the grid load comes from the 5500w Onan as the same phase (on each leg) and effectively becomes the same thing. The first inverter takes the signal from the generator, the second inverter rejects it and creates its own out of phase leg from the batteries. The first inverter then charges the batteries to make up for the draw from the second inverter.

Its not a perfect solution, but you can read about others with similar experiences here.

https://community.victronenergy.com/questions/122/multiplus-inverters-setup-in-split-phase-to-match.html

In an effort to work around this, we recently commissioned a transformer to be hand-built which should convert the two 120v legs of the Onan into split phase 240 (including creating a new neutral to handle the full load) to feed into the two Quattros allowing them full pass-through operation without having to invert 1 leg. (I've read that the Victron Autoformer would not work very well in this situation due to the amount of potential imbalance of the two legs.)

Their maybe other ways around this and additional discussion can be found in that other thread.

You may also want to check to see if your Onan really offers a true 120v split phase, or if it's simply the same phase split across 2 circuit breakers (as was the case on our unit.)

Good luck and I'm eager to see what others offer as possible solutions here.

Nate

Yes, this is the standard meaning of two “stacked” inverters in split-phase in a North American configuration.

As long as your generator is a 240V generator (that’s what two 120V hots at 180deg phase angle really are), you can do this.

You can also connect them both to the same battery bank. No need to split it up.

When you connect to a shore 120V supply, you will see the “divided” operation that Nate describes in his excellent answer: one will charge/invert/pass-thru like normal, and the other inverter will switch to invert-only off the battery. In practice this doesn’t really change anything and the system will work just like you’d want it to.

You might check with Onan and see if they have a conversion kit to change the 120V output to 120/240 Split Phase. I have a Generac 6KVA generator at my house and they had such a kit. It depends on the generator windings whether this is possible or not.

In my case all I had to do was re-route a few wires and change out the single circuit breaker for a ganged two circuit one. Took about an hour.

Pat