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Autotransformer output voltage different

I just purchased a 100A Autotransformer, with 240V input from a generator and expecting two equal split phase outputs. Below are my readings (5v difference)


Generator output 235VAC

L1-N is 115VAC

L2-N is 120VAC

Loaded ~226VAC



I have swapped my loads on the output and no help. Also removed PE coming from generator to remove any question of N/PE bonding in the home electrical panel. I see other posts where differences were noticed but none connected to 240 on the input. I can only explain this by the center tap of the transformer is not accurately placed. Any ideas? I have started RMA process.

rick-r asked
shaneyake commented ·

0 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
natebert commented ·

2 Answers

Off Grid with Stand By generator

I have some simple questions that I have not been fully able to flush out in all my research and am hoping that someone will be able to give definitive, simple straightforward answers so I don’t make a costly mistake. (1) Of all the inverters what will be the best option for an off Grid Setup with a back up generator. I can see several options but I am not sure if I should be using a Quattro or and MultiPlus II. I want the generator to back stop the system in case the renewables are not enough to run the system and the batteries are getting low. I will be using a combination of Hydro, Wind and Solar.


  1. Max current out put 300A (200 A house panel and 100 A Shed Panel)
  2. Output Voltage 240V to 120V
  3. Generator activation when batteries hit predetermined low level
  4. Battery Charging from Generator
  5. Battery Bank 48VDC

I have attached my rough design on what I plan to do. The battery bank will be built out of LifePo4 batteries creating a 48VDC system and storing around 9600 ah. The batteries will have an average normal discharge rate 320 A per hour with a peak over 1000a but will need to be under 10 mins.

  1. If the batteries are full and wind/hydro/solar are still producing power
    1. Does the MPPT prevent the extra power from over charging the batteries?
    2. If so what doe the MPPT do with the extra power? I known in some hydro system they have a burn off resister.
  2. Can multiple Autotransformers be placed in parallel? I have seen several references in post about needing multiples, but no one has explicitly said they can be used in parallel. I need to have a 200A circuit of 120V L1, L2 for the house.
  3. Is there any reasons why a Solar Charge Controller could not be used with a wind turbine if properly sized? They hydro turbine I plan to buy have been tested with the Victron MPPT(s) and they even recommend a model to be purchased based on what I buy from them. The wind turn bine has no suggestions from the manufacture.


northboundanddown asked
Mike Dorsett answered ·

1 Answer

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
edgardogarcia answered ·

7 Answers

Way to get two 110v outputs from single inverter/converter from battery power?


I am trying to run a Level 2 car charger off my battery bank; I am currently running a Level 1 off my battery bank using the MultiPlus Compact 24v|2000VA|50A which works fine.


I was looking at the Victron Energy Quattro line of Inverter/Converters; I noticed that Victron makes an Inverter/Converter that can output 208+ as long as both the L1 & L2 are plugged in.

When the battery is the only supply voltage it then chops the voltage down to 110-120v. After reviewing this diagram ( and talking to Nothern Arizona Wind & Sun it sounds like I would have to buy an autotransformer in addition to the Quattro.


- Does this sound like the right approach?

- Does Victron have a device that outputs two phases of 110-115v to form 220v or not?

Thank you for any help!

Jeremiah Landi asked
shaneyake answered ·

1 Answer

Auto Transformer

I have a question regarding the capabilities of the 100A Auto Transformer that Victron make.

I want to make sure my understanding of this unit is correct and this is hopefully a basic question for somebody. I notice that it states that the neutral continuous current capability is 28A AC and from the documentation it implies this is effectively the limit of the imbalance the system can absorb. My two hypothetical questions are:

1. If this transformer was being fed by a 12KVA 240V supply with the output exclusively feeding 120V loads balanced across L1 to N and L2 to N. With the maximum imbalance limitation of 28A would the maximum theoretical UNBALANCED load it could provide on it's outputs be 64A on one leg and 36A on the other?

2. If this same transformer was feeding a system exclusively made up of 120V loads on L1 to N and L2 to N i.e no 240V loads. If absolutely NO loads were present on L2, would the theoretical maximum current on L1 of the transformer be limited by the neutral imbalance limitation of 28A. So this would limit any current to 28A (3.36KVA) on any leg if the opposing leg was 0A?

Appreciate any guidance on this please. Thanks

pmarine asked
pmarine commented ·

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
irwinr answered ·

5 Answers

Split-phase boat power system with MultiPlus-II 2x120 and Autotransformer

TL;DR: I want to build a system that can take in split-phase 120/240VAC, single-phase 120VAC, or 12VDC, and always output split-phase 120/240VAC. I have a potential solution in mind using MultiPlus-II 2x120 + Autotransformer. Will it work? Are there better options?


I have a boat with a split-phase 120/240VAC system. Normally the two phases come from either 120/240VAC shore power, or from a split-phase generator. I'm considering an inverter setup that would allow me to create both legs from the inverter, and am imagining the following system:

Connect a MultiPlus-II 2x120 to the split-phase system. When the generator is on (or split-phase shore power is connected), it will pass through both legs. When single leg shore power is connected, or no input is provided, it will yield only single phase 120VAC.

I want to then connect the output of the MultiPlus to an autotransformer, such that:

  • When the generator or split-phase shore power is being passed through, the autotransformer balanced loads between the two legs.
  • When only single phase 120VAC is available, the autotransformer will convert it split-phase, creating the second leg.

Is such a configuration viable? Is it possible to wire the autotransformer in a way that achieves both of these purposes?

An alternative is just to use an 240VAC inverter with an autotransformers, but that seems to have the problem that it won't work when only single-phase 120VAC is available from shore power. Is there a workaround for that other than installing another transformer?

EDIT: Added diagram for clarity.

resistor asked
Kevin Windrem commented ·

1 Answer

Auto transformer


Victron Autotransformer, 120/240-100A, ITR000100101

How do you wire this transformer? I read the directions, but it was hard to understand and there is no clear markings for hot and neutral wire. The power coming in is from a Honda EU7000IS generator. 2 hot wires, one natural and a ground wire. I need convert the 2 hot wires to 1 hot wire going to the Victron Quattro

ejm asked
Kevin Windrem answered ·

3 Answers

3 Phase Isolation Transformer possible with Victron Isolation Transformers

Hello Guys,

I have a question regarding a 3 phase isolation transformation schematic.

I would like to design a system where in the case of a missing neutral I still have neutral on the boat with the isolation transformers.

Main issue is that in America most shore power system with 3 phases are without neutral on the input and my device behind that needs a neutral.
Voltage and Frequency is clear that it will depend on the input, but that is not an issue in my case.

Question is would that work?




Phil asked
Phil edited ·

0 Answers

Autotransformer step down split phase to single phase

With the 100amp autotransformer, stepping down 240 split phase to single phase… 2 questions… is the single phase output capable of 100amps if the 240 in is 2 legs of 50amp? Also, if I drop a phase (RV setup, say using a 30 amp adapter which only brings in 1 leg of 120) does it effect anything or will it still just put out it’s 1 leg?

whynotrv asked
whynotrv commented ·

1 Answer

IP22 Charger No Lights Not powering up.

IP22 Charger. Have just got back from warranty as was not powering up. They said there is no issue with it and returned it.

Plugged in no load or charging and the lights came on. Unplugged it and back on and no lights. Unplugged and left a while and plugged back in still no lights

Left unplugged overnight and after a couple of unplugs waiting and plugging lights came back on. Did a factory reset, just in case on app.

Unplugged again and now when plugging in no lights.

Anybody got any ideas so I can tech what to look for at Energy Solutions (UK) Ltd ?

deano asked

0 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
pigwet answered ·

3 Answers

220v and 110v hookup autotransformer

I work for a company where we bring a mobile trailer to different job sites everyday. We run two 110v plugs to the trailer. Some of our client only have 220v. I want to be able to easily hookup 110v or 220v depending on what the client has. I think the auto transformer will work for me. I’m unsure if I can wire the autotransformer to switch between 110v and 220v daily. Do you guys think the auto transformer will work?

angryinch asked
Mike Dorsett answered ·

1 Answer

Can two 100A autotransformers be connected in parallel for a 200A split phase output?

Hi VE Experts,
Can two 100A autotransformers be connected in parallel for a 200A split phase output? The system will have two Quattro 15000 240V units. This is for a 240/120V, 50Hz system so we cannot use two 120V Quatto units in parallel as the 120V is only for 60Hz output.



lalith asked
lalith commented ·

1 Answer

Strange Noise from new Mulitplus 2 - Faulty?

So iam a happy new Member to the Victron Family :)

I own 3 MP2 and have them running for three Days now.

Last night this Problem began. My Power went away every then and now with Error "Device Shut off" - i had to manually turn it on via Remote Console.

As I got the Devices running, i was suprised that the "Hum" Sound ist quite loud - But i read here thats quiete normal.

But 2 Hours ago the Multiplus on Phase 2 starts making weird very loud noises.

Is this still normal? Or did I catch a faulty device?


marv21 asked
marv21 commented ·

1 Answer

auto-switching 3600 isolation transformer cycling on/off

I have an auto-switching 3600W isolation transformer which has been working well for a couple of years. Lately it has started to cycle on/off about every 2 seconds when powered up. The green power LED is on, the yellow 120V LED cycles and the red temperature LED is off. Several relays can be heard clicking within the transformer. The transformer is cool (20 degC) and the fans are not running. I’ve checked input shore power and it is stable at 118.4 +/- 0.1 VAC, 60Hz.

When this problem first started, it would happen once/24h, usually around 1AM. At that time our current draw is around 3A. I would simply disconnect shore power and go back to bed. In the morning on power up it would work normally, even with 20+A loads.

Lately, the frequency of the cycling has increased and it could happen at any time of the day with no discernible relation to whatever loads were on or off. It has now reached the point where it begins this cycling behaviour as soon as it is powered up and I have had to bypass it completely.

Any thoughts/suggestions on what the problem might be?

mrcandy asked
Paul B answered ·

1 Answer

CerboGX unable to set two way communication

Local or VRM connection to my CerboGX does not have an option to turn on two way communication in settings. I have spent hours researching and am unable to find out why.

latest updates installed on app and hardware.

joe-h asked
hhau answered ·

1 Answer

Autotransformer 120/240-32 Efficiency

What's the expected efficiency of an Autotranfromer?
I could not find anything in the Datasheet or Users Manual... I wonder why?

I'm considering using it as a 120V/240V step-up to run a Mini-Split.


hookem asked
Mike Dorsett answered ·

1 Answer

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
paul-cotton answered ·

5 Answers

Autotransformer - unusual install - neutral ground bond.

Please take a look at the schematic of this new Leopard Power Cat. It had 2 Pheonix inverters fed by a Centar 100a charger. The owner purchased 2 x multiplus to be able to charge the lithium batteries faster but neglected the fact that the boat did not have a source of 120v besides what was provided by the inverters.

-Shore power is split phase 50a going through an isolation transformer giving 240/60 single phase. Neutral Ground bond at the transformer.

- Selector switch to chose between the IT or generator for source of power.

- Generator wired for single phase 240/60. Neutral ground bond at the generator.

I’ve also included the Victron step down schematic for the autotransformer (disregard hand writing). And if I understand correctly if wired this way the neutral/ground bond would remain through the transformer (since we are not taking a neutral from the center tap?l)

The goal is tapping 120v from a 240 single phase which has N/PE bond at the source. How to best do this and what to do with the N/PE bond at the transformer. I do realize that the max will be 28 amps with this configuration. Considering adding a second transformer to feed each Multi independently. Multi are paralleled.



malolo asked

0 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
malolo answered ·

2 Answers

Wiring diagram for Quattro split phase with autotransformer?

We have an off-grid system with two 48/10000 Quattro inverter/chargers configured for split phase, with a battery bank and solar chargers. We also have a generator feeding the Quattros on AC input 1 when the batteries are low and the sun is not shining. We have a few 110 appliances that consume significant load, causing the legs to become unbalanced.

I'd like to add a 100 amp Victron autotransformer between the Quattros and the breaker panel so that we can balance the legs, especially when the generator is running.

The autotransformer manual has a wiring diagram for balancing two inverters in split phase, but it's not very specific -- it's more conceptual than "connect this to that". The manual also says "split phase output balancing may require some more attention", but never goes into more detail on how to do it. Does anyone have a more specific wiring diagram for balancing two Quattros with the 100 amp autotransformer?

Also, the Quattros open the ground relay when the generator is running. I've wired that up to the autotransformer so that it will drive the autotransformer ground relay. However when the Quattro is powered by the generator the ground relay is opened, which I don't think I want to happen -- the autotransformer ground relay should always be closed, as far as I can tell. Does anyone have any tips for forcing the autotransfomer ground relay to always stay closed?

half-moon-bar-lodge asked
GARY WILLETT commented ·

1 Answer

Autotransformer balancing

Does the autotransformer balance the output and the input 120 lines, or just the output, or just the input? I'm confused!

brianv asked
Mike Dorsett answered ·

1 Answer

Autotransformer wiring for balancing loads, split phase 120/240

My AC source is split phase120/240. It supplies two hot wires and a ground, no neutral. I am using a Victron transformer because I am splitting the two phases into two separate battery chargers for my RV, but I need the loads on the two hot wires to remain balanced. My question is, would it be correct to connect the two hots AND the ground into the autotransformer, and then use the two 120 lines, the new neutral (created by AT), and ground coming from the autotransformer to connect to my loads (battery chargers)? Any potential issues with that set up?

brianv asked
wkirby answered ·

1 Answer

Autotransformer output capacity

I am confused as to what the actual output of the autotransformer 32 and 100 amp is. I see that the neutral caps out at 32 amps on both. So does that mean that the total output of either autotransformers is 3840VA in split phase 120/240? It doesnt make sense because if you are connecting let's say two 120v 5000VA Quattros to the AT to create balanced split phase current, you basically lose a bunch of output capacity. Or is the 100 amp version able to output 100 amps total between the two 120 lines?

brianv asked
wkirby answered ·

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

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


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