First off - Thanks in advance for all help with my question.
As you can see in the subject line I have a 50A RV here in the U.S. I’m designing my system and have decided to run dual inverter/chargers. By mistake I already have (1) 24V 3000 MultiPlus-II. I ordered a 24V 3000 MultiPlus-II 2X120V and was shipped the regular MultiPlus-II. I caught this mistake after the return period.
So, do I build off of what I already own? Add another MultiPlus-II and an Autotransformer to balance the loads on each leg, or should I sell the MultiPlus-II and go with two 2X120’s? I’m not sweating losing a little money on the MultiPlus-II if need be. I just can’t seem to find a clear answer as to any advantage of one setup over the other. I’ve studied Victron’s manuals, watched many videos, and pieced together info from multiple threads, but am still unsure. It seems like they will both net the same result. Hoping some one here can shed some light on this.
The great advantage of the 2x120V models for RVs is the internal relay switching to handle single-phase 30A, single phase 50A, or split-phase 50A shore power without rewiring.
Note the at the 2x120V models pass split-phase when split-phase shore power is connected, but only do single-phase 120V when inverting. So no 240V loads from a single Multiplus 2x120V when inverting.
If you only care about 50A split-phase shore power, two standard multiplus-ii are fine.
Do you have 240V loads?
The autotransformer is a major pain to use, but it will balance the loads.
If you are stacking two units, they need to be the same model.
No 240V loads. But I do want to power both sides of the AC breaker panel when inverting. Never know when a family member may randomly toss a snack in the microwave while an A/C unit is running.
Already plan to run two identical units.
And to your point, 50A split-phase shore power is not always available. I have a myriad of “dog bone” adapters to combine shore power from multiple outlets, but the internal relays of the 2X120’s would be an advantage when 50A split-phase is not available.
Good to know about the Autotransformer being a pain to use. I don’t mind a little extra effort or cost during the the install. What’s most important to me is that things work seamlessly once it’s all together.
If you don’t have any 240V loads, you can use a single Multiplus-II or a single Multiplus-Ii 2x120V to serve your needs. Or buy a second for more power by running in parallel. You do not need an autotransformer if you do not have any 240V loads.
Case 1: For a single standard Multiplus-II, you would have to wire its AC-out to both sides of the breaker panel (L1 and L2). You would have to use only L1 from your 50A inlet, which is severely limiting. Not recommended but feasible.
Case 2: Two Multiplus-II 3000 kVA in parallel. AC-out of the first goes to L1 in your panel, AC-out of the second goes to L2. This is not a split-phase configuration, this is a parallel single-phase configuration. There is 0V between L1 and L2, so no 240V loads. The AC inputs go to your inlet L1 and L2. No autotransformer needed. Dogbone needed for 30A shore power. Recommended configuration, plenty of power.
Case 3: Same as Case 2, except configure the two Multiplus-Iis in split-phase. Similar wiring as Case 2 (neutrals are different), but L1 to L2 measures 240V. Your breaker panel will work the same, except you will have the option to add a 240V load later. This configuration is tricky to get to work with 30A single-phase shore power, but it is feasible. Not recommended but feasible.
Case 4: Same as Case 3, except insert an autotransformer between the ACOuts and the breaker panel. Feasible, but grounding and neutral isolation gets very tricky and frustrating when on shore power. Will balance the inverters to provide maximum power output regardless of which side of the breaker panel is pulling more power. Recommended only if you really need that balancing, e.g., to run multiple microwaves and hair dryers from the same leg. You only need the autotransformer if you want split-phase 120/240V power when inverting.
Case 5: Get a Multiplus-II 2x120V model. Or get two if you need the wattage, running in parallel. Handles the 30A single-phase and 50A split-phase configurations with its internal relays, much easier for your application.
Most recommended option.
If your RV has a generator, then usually it drives the selection. If it’s a 120V only generator, then two 2x-120 in parallel is a better choice because both chargers will be engaged. If it’s a 120/240 generator, then check to see if the generator can output its full rated capacity at 120V. If so, use two 2x-120’s. If it only produces its full rated capacity into 240V, then two regular 120V’s in split-phase would be better.
If you don’t have a generator, or it’s very small, then I’d recommend two 2x-120V in parallel as Rick suggested.
Your answers support my original plan to use (2) 2X120’s. Clearly will be the best setup for how I plan to use it. Now it’s time to put together a parts list!