Stormy R. avatar image
Stormy R. asked

Wiring Question: Victron Autotransformer, 2 Multiplus 2, Generator

multi plus 2.pngI am building a system for my RV. I currently am running a 30 amp system. I plan to replace the distribution box and convert to 50amp split phase service. I want to install two Multiplus 2 units and run them in split phase. The 48/5000/70 model.

Multiplus 2 link:

I will be using 48volt EG4 lifepo4 batteries. 200Amp internal BMS

EG4 Lifepo4 link:

I will be using the Westinghouse 12000 running watt 15000 starting watt generator with remote start and auto choke to charge the batteries. (Eventually I will be adding solar panels and only using the generator as a backup, although thats not too relevant to my inquiry here, essentially I’m going to be using the backup system as the main system until I can afford the rest of the equipment).

Westinghouse Generator

And I wanted to also use a 100amp Victron Autotransformer. I want to use it to balance my split phase loads. (sometimes I will want to use it in conjunction with the Multiplus Units running in parallel rather than split phase to accept 30amp shore power but output split phase power for my distribution box. I know this requires a different wiring set up and hope eventually to understand this Autotransformer well enough to craft up a clever design where I only need to flip a switch, or a few, to switch between balancing mode and step up mode. For the purpose of this post you can just focus on my desire to use it for split phase balancing. Thats the wiring I’m trying to currently understand.)

The generator will be wired to the two inverters in split phase, the autotransformer will be wire to the output of the inverters, and the auto transformer output will go into the distribution box. The auto transformer will be used to balance loads when drawing from the battery and inverting the DC to AC. The autotransformer will be used to balance loads when using the generator to charge the batteries and simultaneously powering the RV loads.

My question is about the proper way to wire this. I have read the manuals of the Muliplus 2 and the Autotransformer. In the auto transformer manual in the balancing section there is a diagram for inverter balancing, and there is a diagram for generator balancing. The wiring is different. However the diagram shows the generator connecting directly to the autotransformer with nothing in between. I wont be connecting it this way. The generator goes to the 2 Multiplus 2 units. And the Multiplus units go to the autotransformer.

Auto transformer link:

Do I just wire the system the way that it shows in the inverter balancing diagram? In the generator balancing diagram it shows that the generator neutral is unused. But I think the generator neutral still needs to be wired to the multiplus units the way it shows in the wiring diagram at the end of the Multiplus 2 manual (except there will only be 2 units, and 2 hot legs). And then I think that I would just wire the auto transformer the way it shows in the inverter balancing diagram. Can anyone speak to the accuracy of this? What is the right thing to do with the generator lead?

The other thing that concerns me is that in the generator diagram it says Neutral to ground bind should not be connected in generator. And I don’t fully understand what this means. Whereas in the inverter balancing diagram it says “If needed the neutral to ground bond can be made in the autotransformer by unchecking the ground relay of both multiplus’ in the VE config software or Victron connect app and connecting the positive and negative conductors from the ground relay terminal to the earth relay terminal.

I guess im not sure if these two things are contrary to each other.

Can someone please explain the function and how it works of the ground relay and earth relay? What is it really doing when I wire the two together?

Can someone please explain what the function of wiring the AC 1 neutral output of one inverter to the AC neutral output of the other inverter accomplishes? I thought it was strange to wire output to output. What is happening here? Is this a dangerous connection to make if I am wiring the generator ground into the multiplus units as shown in the multiplus wiring diagram appendix D.

Essentially I am trying to establish the propermulti plus 2.png wiring for the generator and autotransformer when the auto transformer is being used to balance split phase load and when the generator is charging the batteries and passing through the multiplus units power the RV loads.

Thank you for anyone who takes the time to look at this. I am learning more and more each day. Being very cautious to make sure I truly understand before attempting anything in the physical world. I have searched the questions and answers of this community and did not find something that answers my questions. I have tried calling victron dealers but a lot of them are lost the moment I mention the auto transformer and tell me theyve never used one.

auto transformer wiring diagram.jpg

RelayAutotransformersplit phase
multi-plus-2.png (95.3 KiB)
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2 Answers
mvas avatar image
mvas answered ·

Your 1st URL link ...
is for 3-Phase ???

Exactly, which two AT diagrams are you talking about?
There are 5 "standard" diagrams
These two ? ...
AT-4-stacked-inverter-2x120V-to-120-240V-with-2xQuattro-120V-REV-B (pdf)
AT-5-split-phase-240V-to-120-240V-with-Generator-240V (pdf)
The first diagram is for 2 x Multi's plus a generator
The second diagram is for a Generator ONLY.

BOTH diagrams certainly do show the Neutral wire connection.

Here is diagram for 240V/50A or 120V/30A or Generator input ...

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Stormy R. avatar image Stormy R. commented ·

EDIT: Does stacked mean those inverters are configured in split phase or parallel?

Yes, the first link for was for 3-phase. The manual for the 48/5000/70 seems to only have wiring diagrams for 3-phase, and a wiring diagram for 3 units in parallel. I had thought that to connect 2 units in split phase you would use the same wiring scheme minus one inverter and the third hot leg. So I included it because it has been my reference for how to wire 2 of the units in split phase.

The diagrams I was talking about for the auto transformer, i thought i had uploaded as attachments to my post. I see that those links are not functioning correctly for some reason. I will try to re upload them here and in the main post. However, if that doesnt work I am talking about the two diagrams on page 3 of the autotransformer manual (or page 5 depending on how you look at it. it is page 5 of the digital document but the page itself is labeled as page 3).

I have reviewed the diagrams you included. It is the kind of detail and scope I was looking for. I suppose I find it confusing only in that the AC inputs are listed as 240v. It is listed as a balancing setup for 240v to 120/240v. The plug on my generator says 120/240v although it is listed as a single phase generator. Does this make it 240v or 120/240v? Other than that I think this will work if I can figure out how to handle the grounds for the Multiplus 2 units since they dont have those common ground connections like in the quattro.

auto transformer wiring diagram.jpg

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Kevin Windrem avatar image
Kevin Windrem answered ·

Something else to think about: Not all campgrounds will offer 120/240 split phase power. You need to consider having only 30 amp 120 volt shore power. You can't simply connect the one hot leg to the Multi inputs since they won't work with 0 degrees between them. You can connect the single leg shore power to ONE of the Multis and configure then with "switch as a group" turned OFF. The unit connected to shore power will then operate in charger/passthru mode while the other will operate in inverting mode.

The only other way to do this is to use a second autotransformer at the Multi input to make split phase shore power out of a single 120 volt leg.

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Stormy R. avatar image Stormy R. commented ·

In that situation I thought I could run the multiplus 2 units in parallel rather than split phase. Connect the 30amp shore power to the parallel multiplus units, and the multiplus units to the auto transformer in a different wiring configuration to step up 120volt to 120/240volt. And hopefully do this through a series of switches. This guy

Wired his multiplus units in split phase and parallel and uses a transfer switch to select which arrangement. Although he doesn't use an Autotransformer, I had hoped that once I truly understood the wiring I'd be able to design a similar switch arrangement for if I wanted it to balance or step up.

Edit: Upon further review I believe I will just save myself the headache and implement the suggestion of buying a second autotransformer to convert the 30amp 120v leg to split phase.

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Kevin Windrem avatar image Kevin Windrem Stormy R. commented ·

The change from split phase to parallel operation requires reprogramming the Multis, plus the wiring in parallel configuration needs carful attention to lengths. It can be done but ....

It's much easier to deal with single leg shore power as I outlined above. No switching/reprogramming involved.

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