Autotransformer Image


Unexpected grid feedback from Quattro 15000

I have a newly installed Quattro 48/15000 connected with an autotransformer to my house. I brought the grid to the AC in 2 terminals from the meter panel. The autotransformer feeds our house through a panel which has two feeds to sub panels. I also have a battery bank (30KWH EG4 batteries) and an MPPT 450/200 that has 10KW or panels attached.

The inverter has a loud buzzing noise that comes and goes as well as some noise on the AC waveform but this question is about the grid tie. When I throw the breaker enabling the grid connection I hear the relay click and the sound from the unit changes, all expected. What isn’t expected is that the cerbo display shows the grid connection at 50W or so but an additional 3KW of load that is not coming from the house. External measurements have shown this to be exported to the grid but the cerbo knows nothing about this. This even happens if there is no solar and all of the power is coming from the batteries. I have the grid set point at 50w and have turned off export from the dc and ac connected solar chargers in the ESS settings so I’m at at loss to explain what is happening. I can’t leave it connected to the grid when it exports against configuration. This means that if my batteries get too low I will be without power.

Maybe I have something misconfigured? Any ideas about how to fix this would be appreciated.

mkbrandt asked
rickc edited ·

3 Answers

Ground wiring question about specific system with Autotransformer

Link to my hand drawn wiring diagram:


This is not a perfect or complete diagram, I am still figuring some things out like breaker placement, the auto start relay, and the temperature sensor. However it should be enough information to be able to answer my question. The busbars are those small unlabeled rectangles, the circles are where I have been debating if breakers should go. And I have crossed out some things.

I am using two Multiplus 2 units 48/5000, I am connecting a DC battery bank (1 battery at first that will be expanded to 4). I will be using the Multipluses in split phase. I will have generator hooked up to an automatic transfer switch, and a 30 amp shore power cord will run through a 32 amp autotransformer to be converted to split phase and the output of the autotransformer will also run into the automatic transfer switch. The output of the automatic transfer switch will go to the 2 Multiplus units (I have not at this time added a bypass switch but plan to, here). The multiplus units go to a 100amp autotranformer that will be used for balancing. The output of that autotransformer will go to my distribution panel.

Wiring Diagram of Distribution Box from manual:


Ground Diagrams From Wiring Unlimited:



My question is: Where do I connect the main ground of the 32 amp autotransformer to? Is it okay to connect it to the negative DC busbar with everything else?

Does my main ground on my distribution box go directly to the RV chasis? Or does it need to go to the negative DC busbar with everything else?

Also, it looks like the 30 amp shore power needs a wire splitting off from the ground that goes to that same negative DC busbar, do I do that before the 30amp auto transformer or after it before the automatic transfer switch.

I have included all the diagrams I have been using as a wiring references.

I have included links to all the components of this system.

So all of the diagrams say that the inverter/chargers should be grounded to the central negative DC busbar. And it says that the autotransformer should be grounded there too – however in the diagrams where it says this the autotransformer is always after the inverter/chargers. The one I don’t know where to send the ground to is before the inverter/chargers. I do plan to charge the battery bank from the 30 amp shore power and to supplement loads from the battery bank when pulling from 30 amp shore. Don’t know if that makes a difference.

Also, the diagrams in Wiring Unlimited, show connecting a ground wire to the negative battery terminal and connecting that wire to a ground bus bar where all the grounds I was going to put directly on the negative busbar go to. And that bus bar actually goes to the main grounding point. Is this acceptable in my system? Can I do this instead? It just seems like a cleaner wiring design. I though that electrically speaking its the exact same setup as grounding at the negative bus bar, but don’t want to misunderstand something. This looks so much cleaner and I want to know if its okay to wire my system this way. See attached photos or Wiring Unlimited.

Stacked Inverter Balancing with Generator - Autotransformer

120 to 120/240 split phase


Multiplus 2



Go Power Auto Transfer Switch

EG4 Battery

Distribution Box

Stormy R. asked

0 Answers

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

Stormy R. asked
Kevin Windrem commented ·

2 Answers

Does the Victron Autotransformer balance and step up simultaneously?

Or is it one or the other?

This product is for balancing, step down, or step up.

But does it only do one at a time. Obviously it is not going to step up and step down simultaneously.

I mean if it is going to be used to step up 120v to 120/240v split phase will it also balance those legs?

Consider a 30amp 120v shore connection. Am I going to be stuck with 15amp on either leg. Or will the auto transformer also do what it does when it is in balancing mode while stepping up allowing 30 120v shore power to become 120/240v where 30amps could be pulled on either leg (so long as the combined simultaneous load of either leg does not exceed 30amp)?

Link to autotransformer:

Application: to determine if a system build will require more than one autotransformer. It's is my desire to design a flexible system for my RV so that I may power a 50amp service distribution box, with either 50amp shore power, 50amp service from my generator, my battery bank or 30amp 120v single phase from shore power. I am already intending to use an Autotransformer to balance the legs when using the batteries, the generator, or the 50amp shore power. The theory was that when needing to access 30amp shore power, I could connect my dual Multiplus 2 set up in parallel rather than split phase, feed in the 30amp 120v shore power, and feed the 120v output of the inverters into the same autotransformer I was using for balancing, have it instead step 120v up to 120/240v, send that along to my distribution box, and problem solved. At long last. Maximum flexibility. But if the auto transformer won't balance and step up this is not going to serve me too well. Being limited to 15amps on either leg won't do much good.

I do know the wiring to the auto transformer is different when you are stepping up 120v to 120/240v than when you are balancing a split phase input.

And that the wiring is different when running Multiplus 2 units in parallel than it is when running them in split phase.

The idea is hopefully to use a series of switches to switch between the two wiring configurations rather than having to spring for a second auto transformer.

Stormy R. asked
snoobler answered ·

2 Answers

220v feed to 110v Multiplus ?

Hi All. Awkward one. I have a 120v yacht which is being fed through lithium batteries to 2 x Multiplus inverters (120v) . When in Europe and connected to shore power the incoming 220v supplies the battery charger ( Skyla TG 24/100) only and then the power to the yacht both 120v and 220v are supplied by the Multiplus and a Auto transformer for the 220v. The owner has asked my to try and change the system so that when plugged into 220v the multiplus inverters can be fed directly from the incoming mains. Obviously the solution is a transformer to drop the incoming down to 120 but the largest Isolating transformer is 3600. Can another autotransformer such as the 120/240 - 100 be used as a standard transformer? I didn't design this system and it is a bit of a puzzle. Mik

mik-poore asked
Alexandra answered ·

1 Answer

Should I install an Autotransformer on my Sailboat

I am working on refit my electrical system for an around the world journey starting in 2024. I have 2x Multiplus II charger / inverters that I plan on wiring in Split Phase since my 120v 50a shore power connection supports it.

Reading some literature I am coming to the conclusion that it would be in my best interest to install a autotransformer. My reasoning is my generator, current split phase shore power and solar controllers would be feed into the autotransformer and the output would be a stable and balanced split phase 120V input to my Multiplus II charger / Inverter.

Is my reasoning justified in spending the money to install an autotransformer?

bluelagoon asked
snoobler commented ·

4 Answers

Autotransformer to convert shore 230v shorepower to two 120v/120v

I have read several posts on this topic and I am still confused. I have a sailboat with US shore power inlet (2 x 120v). I am adding an european 230v shore power inlet for when I go to an european 230v 50hz marina. I would like to step down the 230v inlet to 2 x 120v (L1 & L2). My question is: having already a galvanic isolator installed for the ground wire, and assuming frequency (50 or 60hz) is not an issue for me, can the Victron Autotransformer accomplish this?

luigi-miranda asked
Kevin Windrem edited ·

4 Answers

Autotransformer: 120/240VAC variable input (single-phase); always 240VAC output (single-phase).

Hi everyone,

I have a sailboat that is entirely wired for 220VAC (single phase), including all appliances aboard. I am currently in Europe.

In January I will cross the Atlantic and I want to be able to accept 110VAC (single phase) from the shore and step it up to 240VAC (single phase) for use aboard. Hence, I'm looking at an Autotransformer.

I'm trying to understand exactly how this device works.

(1) can I give it any voltage (110VAC or 220VAC) and have it always gracefully output 240VAC regardless of input voltage?


(2) do I need to implement a transfer switch, so that when I am in a country with 240VAC I bypass the Autotransformer entirely?

I have studied the manual and believe it's the latter, but as we're talking about mains voltage I would appreciate the confirmation. Option two would be much less convenient because I also have a 220VAC generator and so I will regularly switch input voltages from 110VAC to 220VAC and back, and at some point I am sure to make a mistake and forget to operate the transfer switch...

Thank you!


whistler asked
rickc edited ·

3 Answers

Victron Autotransformer 3ph 208v to spilt ph 120/240

I want to use the 100a victron autotransformer to solve a 208v problem I have with a mobile solar solution. My solar setup connects to 3ph 208v using only two legs of 120v....So L1=120v L2=120 but L1-L2=208v. 50% of the time my mobile connects to split phase 240v.

My users are completely ignorant of the difference. They think 120+120=240 which is never the case in 3ph.

My inverter supports both case but must be set in the config to do such.

What happens is they connect 208v when its configured for 240v and it blow a circuit board.

I need 50a to run my mobile solution so here is my question.

Is it possible to run one or two victron auto transformers to use the 120v legs to 240v?

I've done this with single 120v to split ph 240 but that was 30a max required.

Can one victron use 2 legs of 120 to output split phase 240v?

If not, can I use two victrons to grid combine breaker the outputs then send 240v split to my mains breaker?

Insights welcomed.

mfrederick asked
mvas edited ·

1 Answer

Autotransformer voltage outputs are different

I am having an issue with the Autotransformer output voltages - 114V on L1 and 120V on L2 (with no load)

120V current is supplied by a Quattro 48V / 10000 / 140-100/100 to the 100A Autotransformer. I'm using the AT to provide a split-phase 120/240v supply to the 50A main break panel in my RV

I have wired the AT connections according to the diagram #3 shown on the system schematics page from the Victron website: (

The Ground Relay in the Quattro is set to ON and is correctly grounding the Neutral to earth.

Here are the voltages I read at the terminals:


The problem I have with this is that the voltage on L1 decreases a lot with load, and when occurs equipment will pull more current to compensate for the lower voltage.

Here is a pic of my RV control panel, showing the disparity in voltage between L1 and L2. Even though there are 2 air conditioners on Line2 it has only dropped 2 volts - Line1 dropped from 114v to 105v. This can't be good.


Questions: 1) - Is this method of wiring correct, and 2) what is causing the voltage discrepancy?


Aug-31: Editing this in an attempt to make the question visible again. I'm thinking of sending this AutoTransformer back to Victron as it is not performing to expectations. I have seen voltages as low as 96 volts on L1, at which point my UPS shuts down my computer, and various other circuits shut down. Not happy...

I'd appreciate a comment from anyone who has had experience with an AutoTransformer.


Pete MacLachlan asked
gutzpowers commented ·

6 Answers

Autotransformer output not 120v

Hello. Is my brand new 100a autotransformer defective?! It is putting out 120v and 114v on each leg.

Can I fix this? What do I do?

georgev asked
sinyyl edited ·

5 Answers

Auto Transformer - 240 single phase to split Phase?

By looking at the terminals and instructions I am led to believe that you can feed the autotransformer single phase 240 and generate 120/240 split phase. However that is not the results we are getting. Defective unit or misunderstood ?!?

As you can see by the circled leads you see the following;

120v-0v-120v 240v-0v

By having connected single phase 240 we get the following;

On the terminal labeled 120v-0v-120v

phase to ground we get 240v-120v-0v

is it only possible to drop the voltage on a single phase? Victron seems to advertise that you can use this auto transformer off a 230v inverter to creat split phase 120/240 VS using two inverters. Victron 230v inverters are 240v phase to neutral/ground. Hence my confusion.

Thanks for your help.


malolo asked
sharpener commented ·

4 Answers

Using AutoTransformer to create 120v/240v split phase from single phase 120v input

I have a use-case for the AutoTransformer that is different from what I see generally discussed. I want to use it in my RV to take in 120v 60 Hz from either my Onan Generator (2 separate 120v legs that are SAME phase) or the shore power inlet (30/15 Amp which are 120v 60Hz single phase). I have those 2 inputs going to an automatic transfer switch so whichever one is "on" will pass through to the AutoTransformer. I would like for the AutoTransformer to step up the voltage from 120v single phase to 120v/240v split phase. I will then pass that split phase into the input side of my dual inverters (one inverter for each 120v leg) so that when I have a single leg input, I still get both inverters charging instead of one side passing through voltage and the other rejecting the phase and inverting to make the "correct" phase.

So, my question is, how should this be wired up to the inverter. It has labeled "input" and "output" sides but the "input" side only has 240v Line and Neutral labeled connectors. The "output" side has 120v Line 1, Neutral, 120v Line 2 connectors.

My intuition tells me to disregard the input/output labeling and connect my source 120v power with:

source 120v Line > AutoTransformer "output" Neutral

source Neutral > AutoTransformer "output" 120v Line 1

Then my output would be the 240v wave form stepped up via transformer as measured between the "input" Neutral and "input 240v Line connectors. I would need to carry over the neutral from the other side to provide 120v/240v split phase.

It is this last part I am unsure of and need some guidance on.


Diagram attached of my planned whole system that hopefully makes clear what I am trying to achieve.


cookinwitdiesel asked
jjbond answered ·

4 Answers

How many Victron Autotransformers can be connected to a single Multiplus II?

If I have a single Multiplus II 230V supplying single phase power to several different locations on my property, how many Autotransformers can I have at each location to split the power into individual breakers given that a relay is required from inverter to Autotransformer? Can other relays from the Cerbo GX or MPPT RS in the system provide the relay to the Ground Relay of additional Victron AutoTransformers?

alaskannoob asked
alaskannoob edited ·

1 Answer

Autotransformer on each 240 output of 48/15000/200

Can 2 autotransformers be used , 1 on each 240 output to provide split phase 120/240 on each from a single Quatro 48/240/15000?

palmeris asked
alaskannoob answered ·

1 Answer


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