Autotransformer Image


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
blueovalbruin commented ·

2 Answers

Autotransformer inverter stacking with non-victron inverters

Hello all. I have a 36v battery pack for my offgrid tiny home. Been surviving on single phase with a 3kw inverter, and I'm wondering if I can purchase another inverter and wire both into an autotransformer to get a split phase connection? The two questions I know I have are.if the autotransformer can align the different phase inputs and also if the lack of the external ground relay(I could open it up and look) is an issue. Thanks for any information in advance

bdale asked
wkirby answered ·

1 Answer

Autotransformer Ground


I have purchased two Autotransformers with the intent to balance loads either on shore or generator. The boat is supplied with 50 AMP (240), a 9KW Generator and an Aims 4K Inverter. Half of the Air Conditioners are 240V, the other are 120V.

The goal is to use two separate autotransformers to power 2 air conditioners (120V) and 120V Battery Chargers. Both autotransformers will have 240V either from shore or generator as the source. (Planning on stepping down 240 to 120V)

Reading through the documentation I am a bit confused on how the ground is setup. Will the autotransformer create a "Fake Ground" thus any fault from an appliance will return to the autotransformer? I am guessing I should not connect the autotransformers ground to the boats central ground. Can someone confirm?

I noticed some information in the documentation recommending I remove the Neutral - Ground bond on the generator. This is not doable in my case since some of the 240V and 120V appliances will not pass through the Autotransformer.


daveinfl asked

0 Answers

AutoTransformer Mount Horizontallly

Hi there.

Limited space on the boat, curious if I can mount the Autotransformer horizontally?


daveinfl asked
Alexandra answered ·

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
dbainbridge answered ·

4 Answers

Split Phase System Configuration Advice

Need some advice on my setup please. The system consist of the following:

2- 48v 3kVA Quatros

50 amp 120/240 Split Phase Shore Power

7,500 Watt 60 Amp 120v Single Phase Generator

Cerbo and a bunch of solar ect...

The system is configured in 120/240 split phase with the shore power L1 going to the master Quatro AC-2 input and L2 going to the slave Quatro AC-2 input. The generator simply goes to AC-1 input on the master Quatro with nothing connected to the slave Quatro AC-1 input. This setup works fine but its a little lacking when running the generator when the batteries are low. I never see much more than 3,000 watts from the generator and the batteries don't see much of a charge when the slave Quatro has a load on it. This causes the generator to run hours on end not charging the batteries. Spending 12K on a new 240v split phase generator is out of the question. We need to keep the split phase for the 240v appliances onboard. Will a Victron auto transformer between the generator and inverters work for me? Or maybe two transformers so I can stack the inverters.. One after the shore power, 240v to 120v to stacked Quatros and then another transformer to get split phase off the Quatros. Any advice would be great thank you.


burnscraft asked
Kevin Windrem answered ·

1 Answer

Voltage for ground relay information wrong in manual ?

I have a Multiplus 24/5000/240 and an Autotransformer. According to the Autotransformer manual the Relay is 12 V, and the output voltage of the Multiplus/Quattro is also 12V regardless of the DC Voltage of the Inverter. Here is what it says in the manual

When the Internal ground relay is not selected in VE Config or Victron Connect, there is 12V on the external terminal of the Multi/Quattro for the ground relay control (on all models 12/24/48V this voltage is 12V).

However if I measure the voltage I get the DC Voltage of my system (in my case 27V) and not 12V. I am afraid this will burn out the coils on the Ground Relay in the Autotransformer.

mfriedel asked
mfriedel answered ·

2 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
blueovalbruin answered ·

2 Answers

Autotransformer to be used to correct voltage drop?

Can the victron autotransformer be used to help correct a voltage drop issue? I am looking for an autotransformer to correct voltage drop over a long power feed to my RV hookup location. Second part to this question is what is the environmental rating for the autotransformer enclosures? NEMA1?

ginosgarage asked
blueovalbruin answered ·

4 Answers

Autotransformer ground relay wiring

I have a non-Victron inverter supplying 240 non-split phase to the AT. There is polarity indicated on the ground relay input (+ & -), so it appears to take more than a jumper. What input is required to close the circuit between output Neutral & Ground?

msandrew asked
jtrobinson131 commented ·

0 Answers

Victron Autotransformer wiring options

Boat currently has 120 30amp service

needs 220v for new ac

1 option ( I’m told) is to pull 120v from a breaker on main panel

to the victron autotransformer and the 220v out to the ac unit

2 option

ac out 1 from Quattro to autotransformer wired to 120/120/220

split then 120 to A side of current panel 120 to B side and the 220 to a sub panel with breaker for the ac unit.

is one way better than the other.?

im concerned about option 1 because I can’t find anything like that described in any victron manual

goboating asked
goboating answered ·

2 Answers

Quattro/autotransformer for off-grid system in US

I am in the process of designing my off-grid power system. PV will be the main source, with a backup generator. I have mostly figured out the PV side, using SmartSolar 150/85 charge controllers. I will have a shop, with a small apartment, and a house will be build a few years later.

I need 240V split-phase to power my shop equipment (welder, plasma cutter and air compressor). Two of them might be running at the same time, so I need quite a bit of surge capacity, as I also will have a 240V well pump. I am looking at the following:

Quattro 48/15000/200-100/100 230V (set 240V/60Hz)

into 100A Autotransformer feeding my main panel in the shop and then eventually feeding a subpanel in the future house.

I'm just trying to run this by a few knowledgeable people before I write the check.

Another question I had, does anyone know how efficient is the autotransformer? What's it power consumption?

dennisuello asked
dennisuello answered ·

2 Answers

Multi+ Duplicating Watts readings on a 230v Split Phase with Autotransformer

Hi Victron,

I live in Central America where we use the US Split phase grid system, I have a ESS system with:

- 1ea Multiplus 48/5K/ 230v

- 48v Lifepo4 Bank 450ah

- SmartSolar MPPT 250/100 rev2

- AutoTransformer 32amps

Note: the system does not feed to the grid.

I have setup my system as per Auto-transformer manual advice for Split Phase systems as below:


I have noticed from the beginning of my setup a drastic Watts measure change when Grid goes out and I already read your article here including the Q6.

But My case is in my opinion more drastic reading difference.

This is a normal Watts reading with Grid power:

- My home consumption says: 1016W

- Battery charge current: 48.6Amps (2452W)


Right after I open or disconnect the Grid:

- Home Power consumption: 480W (Half reading). I confirm No changes in the Real home Load equipment.

- Battery Charge Current: 58.8A (2971W) Yes the MPPT generation increases in that moment 100W but that does not justify the 500W (10Amps) Battery Charge increment. Looks like the increment in charging is due to the decrease in Loads need by the Multi+


The behavior is telling me that for some reason having a 230V Multi connected to 2 Live power lines (L1=120v + L2=120v), the Multi is duplicating the reading in the ACin/ACout side and direct affecting the battery charge performance. Since this 230v Multi+ is designed to connect L1=230v + Neutral. I think this Multi+ is not properly reading 2 live phases L1 + L2 correctly, instead it is duplicating the reading.

I have done other testing with a 3rd party watts reading and the reading is half lower than Multiplus AC Loads reading and that make me think my suspicious is correct. Can Victron staff please confirm my situation here?

I know that an option here is to get the Carlo Gavazzi meter for better reading, but I will like to ask if Victron can do a Firmware adjustment for customers that use their 230v Multis in US market before expending more money.

@mvader (Victron Energy)

Thanks a lot

Yusef Neblett asked
pganguet answered ·

6 Answers

Autotransformer Unbalanced when on shore power

I have been racking my brain over this one. I have this exact setup:

2x Quattros set up in split phase and the Autotransformer after the inverters to balance the 120v loads. When inverting, I am seeing nearly perfect balance between L1 and L2. On shore power it is all over the place. Is there a chance the neutral return is taking a different route via one of the ground wires and somehow bypassing the Autotransformer? Would that cause this? Any ideas where to look? I have used my clamp meter and do show some current flowing over the various ground wires in the RV. If I temporarily remove a ground it does not seem to help though. I am at a loss. I am connected to a shore power that only has a 30 amp limit across each phase and one Inverter always seems to start assisting before the other phase. It would be nice to use the Autotransformer as intended and get the most out of the shore connection we have.


jetwire asked

0 Answers

VictronConnect Does NOT See Solar MPPT 100/50

We have a new Bruder Expedition with a Victron Solar system installed. A couple of weeks ago our system completely shut down. We were able to get it back online but now the MPPT 100/50 does not show in VictronConnect. We've followed ALL of the instructions. Have unintalled the app several times, unpaired from bluetooth and connected from within the app as instructed BUT the MPPT 100/50 still will not show. Just the BMV-712 Smart. The MPTT 100/50 showed up in Victron Connect before the system shut down. We have even turned the system off manually and restarted it several times. We have tried running VictronConnect on an iPhone instead of the Samsung tablet (Galaxy Tab Active Pro, model SM-T547U) and no luck. Really at our wits end. We are not tech illiterate but this one is stumping us.

claminator asked
Thiemo van Engelen (Victron Energy staff) answered ·

4 Answers

RCDs and neutral to ground link with Isolation Transformer -> Multiplus -> Autotransformer

Marine application has shore power coming in to an auto-switching 3600W isolation transformer then going to a Multiplus. The output of the inverter/charger is connected to a panel with some euro-spec single phase 230V outlets.

To accommodate 120V appliances in the US, one of the breakers on that panel now leads to an Autotransformer, with each leg leading to different groups of 120V outlets.

With the isolation transformer we are never directly using the earth to neutral link on shore. Given both the single phase outlets and 120V split phase outlets, where do we need to make these links?

banana asked
michaelhickey60 commented ·

0 Answers

Lynx Shunt VE.Can specs and setup


I am trying to find a datasheet of the Lynx Shunt VE.Can but am not able to.

More specifically I would like to know the resolution and accuracy of the current measurement.

I intend to use this together with some own developed components and interface through CAN, but will I need a CCGX, VGX to set up the Lynx shunt? Or is it possible to set it up through the CAN interface?

candela asked

0 Answers

Multiplus shuts down when trying to use Air Conditioner 24/2000/50

Hey all,

I just setup my Multiplus 24/2000/50 Compact and all seems to be working fine until I tried to turn on my AC.

while leaving the Multiplus in “on” position and plugged into 30amp shore power I turned my AC on and the surge when the compressor turned on made the multi shut down.

I have had my rig parked in the same place for the last 4 months and have had to run my Air con a few times before I setup the Multiplus.

I also tried to run it while my generator was running and that didn’t work either. But I used to run my Air Con off the generator no problem before.

I do have to switch on the “weak AC” setting to get the generator to work but still won’t allow the Air Con to work.

Should I be running the multi on “pass through”? (not sure how to set that yet)

Do I have something wrong in the settings?

does the Victron only allow me to use 2000 watts when I am connected to shore power? (Doesn’t make sense to me)

My generator is 4000 watts and still doesn’t let it happen.

I tried it with everything in the rig off except the Air Con and it still didn’t work.

I am running a 24/2000/50 multiplus compact and a 24 volt 206ah prismatic battery set from LYNX batteries out of Washington state. The battery connections use 4awg wire. Battery is rougly 2 foot away from the multi.

Is the only way to make this happen is to get a soft start for the air con?

journeyoutloud asked
journeyoutloud answered ·

4 Answers

Autotransformer mounting

I have just received my 100A autotransformer and cannot figure out how it is mounted. Bottom has mounting holes but nothing at the top. A metal plate is included but it is not clear how it should be used. I could hang the top of the case to the plate and screw the bottom tab but the case can still rattle. Noting in the manual on that subject.

meteor64 asked
meteor64 answered ·

2 Answers

240V output from QUATTRO 5000W 48V INV/CHARGER 120VAC

My house is originally on grid and I am moving to off grid. I am doing this in phases. I now have the following system implemented which is supplying power to almost 1/2 of my house circuits (via a transfer switch):

2.5 kW PV array


48V battery bank consisting of (4) KiloVault 12V, 300Ah batteries wired in series


I want to add another circuit to this setup supplying power to a 240V house circuit (for a cistern pump).

I found a Victron reference diagram here:

I'm just looking for validation that I'm on the right track here. If I add an Autotransformer and wire it as shown, is this going to give me the 240V split phase that I need for my 240V circuit (I'm in the US)

WRT loads, relative to the rest of the 120V circuits the 240V circuit uses very little power.

Thanks for any feedback that is offered.

FWIW, I love the Victron products and their software. I'm using a Cerbo GX as my communications hub and I love being able to view a snapshot of the system on the VRM portal and well as to have a history of the data that has been collected.

tbratten asked
jmarc answered ·

5 Answers

Phoenix Inverter Smart with Autotransformer

I'm designing an off grid system and I'd potentially like to use a Phoenix Inverter Smart with a Victron Autotransformer. The photo below is what I want to do:


My question is where should I attach the ground relay control (shown above) and is this setup compatible with the Phoenix Inverter smart?

From the Victron Autotransformer manual (page 3), I see that,


From the Phoenix Inverter Smart manual (page 9), I see that,


Since the system is in a vehicle does that mean I simply need to connect the ground relay control wire to the same ground as the inverter?

Thanks for your help and let me know if you need any more details!

Ben Zook asked
Troy Meuninck commented ·

1 Answer

Does the Multiplus act as an autotransformer shore/gen 120v ac input?

I see on the data sheet for the multiplus 24v 3000w inverter/charger that in the "inverter" section it list output as 120VAC +/- 2% and under the "charger" section, the input is 94-140VAC. Does that output apply to inverted loads only, or does it act as an autotransformer and convert (for example) 100VAC shore/gen power up to 120VAC as well? I'm trying to figure out if I should install a separate autotransformer in the RV to account for some RV parks voltage dropping below 110v during periods of high demand. Thanks in advance.

dabean80 asked
dabean80 commented ·

1 Answer

Victron Phoenix 24v/3000/120v and Autotransformer to create split phase 240v for pool pump

I want to purchase a 32amp Autotransformer to create a 240v split phase for the pool pump. I already have the Phoenix inverter 24v/3000/120v. Is it possible? Could I have the wiring instruction please?

lynhnn asked

0 Answers

L2 On Grid showing Negative power (2x Quattros Split Phase + AT)

SOLVED - (See comment below) I am having a strange issue on my new Victron Quattro setup. I am seeing a negative number on my grid current. The AC loads side is also incorrect. I am running 2 Quattros and an Autotransformer wired exactly per this guide:

Any suggestions? I have connected the GND Relay, changed the dip switch and have confirmed it is switching the relay on the AT. Ground Relay is disabled in both Quattros

Everything works perfectly when Inverting. The AT is balancing L1 and L2 perfectly. This strange issue is only showing up on shore power.

The attached photo is with the main breaker off after the AT (No Loads)


jetwire asked
jetwire edited ·

1 Answer

Using a Quattro 48/10000 230V with Autotransformer in US residential 240V split phase

I was originally asking about design consideration between using one large inverter or two smaller inverters. Then got onto a bit of the design using one large inverter, but that wasn't really pertinent to the Subject for tha thread.

So I'm re-asking the one-inverter-autotransformer question here in a dedicated thread. Has anyone set up a 230V Quattro with Autotransformer in a US residential setup ?

I'm envisioning a setup as follows :

  • Main panel : 100A breaker to Quattro AC1-in
  • Main panel : 100A breaker to sub-panel 100A breaker with interlock
  • Quattro AC1-out to Autotransformer
  • Autotransformer AC-out 120-0-120 hot-neutral-hot to sub-panel 100A breaker with interlock

The interlocked breakers are a back-feed setup for the sub-panel. Only ONE breaker can be on, the other must be off. So the sub-panel is fed by EITHER the 100A from the main panel, OR the AC-out from the Autotransformer. For example

In the US, there can be only neutral/ground bonding point, it must in the main service panel. So the GND relay in the Quattro should be disabled, and the GND relay in the Autotransformer should also be disabled. This way, regardless of whether the sub-panel is fed from the main panel or from the Autotransformer, the neutral/ground bond will only be in the main panel.

The created neutral from the Autotransformer is connected to the neutral bar in the sub-panel, which connects to the neutral bar in the main panel, where the final neutral/ground bond is made.

During an outage, power to the Quattro comes from a 240V generator, using only the L1/L2 hot legs. The neutral is not connected, so it acts just like the connection from the main panel.

Does this all make sense ? Is it correct for a US residential install ?


halfwalker asked
henry-cabrera answered ·

3 Answers

Auto transformer tripping

I have an auto transformer ATR 32A connected to a 5KVA inverter, my problem is that sometimes the trafo breaker trips when the inverter switch from battery to line. I’m concerned about the ground relay which is not connected because my inverter is not a Quattro but a MMP and i did not see the technical reason because the solar panel fed from the trafo is a split phase 240/120 volt panel with the neutral grounded. Also the trip occurs sporadically. Should I connect the trafo ground relay to the dry contact on my inverter?

henry-cabrera asked

0 Answers

step up from 120v to 240v split phase to feed in to the grid

i live in US, i have a DC coupled PV system (victron mppt) with 1 quattro setup as ESS thats feeding critical loads, my pv array charges battery in ~2hrs and then all the solar power is wasted, electric company allows feed in (need new meter) but they want balanced split phase 240 and not just feed in on one leg, what do i need to feed in a 240v split phase back to the main panel with 1x 120v quattro?

from my research seems like autotransformer can take 120 and make 240 but manual shows only scenarios downstream from inverter not upstream, will it work upstream as well or do i need something else?


audreez asked
Paul B answered ·

1 Answer

Help look over Multiplus 2 schematic - Reward

Hello everyone,

I need someone, who is very experienced with the Multiplus2, PVs, lithium Ion battery and Grid Connection, to look over my schematic in a zoom Meeting. I will give you 10€ as reward. Someone, who speaks german would be good.

Cansin Sari asked
Matthias Lange - DE answered ·

2 Answers

Auto Transformer split phase, neutral bond question

I have a 230v MP2 feeding an auto transformer for 120/240v split phase to the panel. It is currently connected to the hot legs of 120/240 shore power, shore neutral not connected to anything.

I have a 3200w iso transformer on the way to step up 120v shore power and remove the incoming neutral-ground bond.

In either of the above scenarios I do not take on the shore neutral. Am I correct that I need a N-G bond after the AT 100% of the time, not just when the MP2 is inverting and activates the relay?

Next question:

I noticed that after the AT my legs have different voltages, ~120 and ~126. L1-G reads ~3v higher voltage than L1-N as expected, however L2-N is ~3v higher than L2-G. N-G is ~3v.

Edit to add: As I am passing through shore power with the inverter in charge only mode the internal ground-neutral relay is not functioning. When my ve bus to usb adapter arrives I will disable the relay entirely if my solution of a hardwired bond is acceptable.

To experiment I created a N-G bond with a jumper at the AT output. Now L1-N = L1-G and L2-N = L2-G. N-G = a few mV with the jumper in place. However L2 still 6v higher than L1. Is this normal?

Anyone see any safety issues here? I can not think of any situation where I would not want N-G bonded on board with this setup.

mworl asked
mworl commented ·

2 Answers

Marine Euro 230v to US 120v - isolation + autotranformer or just isolation tranformer

I've read through the portal and have downloaded the PDFs... I can't find a straight answer to the question of if the isolation transformer will convert euro 230v power to us 120v.

On shore power, I'm looking to be able to hook up world-wide (assuming 50/60hz is a non-issue).... or do I want an isolation transformer that feeds an autotransformer?

I'm on a 120v boat with two 5-30s. I'm trying to avoid AC-DC-AC so that I don't have to limit AC usage when connected to shore power.

So, I'm thinking two isolation transformers, one per power inlet... and feed that into a pair of MultiPlus 12/3000/120...

...or do I need the Autotransformer to do the euro 230v to us 120v conversion.

csheldon asked
csheldon answered ·

1 Answer


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