Victron Energy Autotransformer 120/240V-100A: The key to full power in 120/240V split-phase systems
The Victron Energy Autotransformer is a highly specialized power component that solves a fundamental challenge in modern AC systems. It is designed to maximize the performance of power sources such as generators or inverters in 120/240V split-phase networks, which would otherwise be severely limited by unbalanced loads. This device acts as an intelligent power optimizer that significantly improves efficiency and reliability in demanding off-grid, marine, and mobile applications. It is therefore the foundation for robust and highly available energy management.
The heavy circular saw in the workshop starts up while the air conditioning cools the house and the lights are on. Instead of risking a power drop or tripping the circuit breaker, the autotransformer provides invisible, perfect load balancing. You use the full power of your system without compromise and without having to worry about load distribution.
Technical core competence: operating modes and performance values
Three operating modes in one device:
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Step-up (upward transformation): Converts a 120V source into a 240V supply. Ideal for operating powerful 240V consumers such as pumps or tools with only a 120V inverter.
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Step-down (downward transformation): Transforms a 240V source into a stable 120V supply. Enables 120V devices to operate without problems on a 240V generator, as is often found in European configurations.
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Split-phase balancing: This is the core application, where the device balances a 240V source. It creates a new neutral conductor and actively balances uneven 120V loads, ensuring that the power source is always symmetrically loaded.
Performance highlights at a glance:
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Maximum through-current: 100 A with symmetrical 240V load.
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Neutral conductor current: Up to 28 A in continuous operation and 32 A for 30 minutes, which defines the actual balancing and transformation performance.
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Frequency: Supports both 50 Hz and 60 Hz systems.
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Compact design: With dimensions of 425 x 214 x 110 mm and a weight of 13.5 kg, it can be integrated efficiently.
On board your yacht or in your large motorhome, the power supply runs absolutely stable even when fully occupied and with a wide variety of devices in use. The autotransformer confidently manages the unbalanced loads in the background, so that the power of your generator is used efficiently and all systems are reliably supplied.
Intelligent details: Technical features at a glance
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Controllable grounding relay: Features an integrated grounding relay that can be controlled directly from a connected Victron MultiPlus or Quattro. This ensures a standard-compliant and safe N-PE (neutral conductor-protective conductor) connection in stand-alone operation and is a prime example of Victron's deep system integration.
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Thermal protection with manual reset: Overheating protection trips the main circuit breaker, which must be manually reset. This safety feature forces the user to check the cause of an overload instead of masking an underlying problem with an automatic reset.
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High-efficiency toroidal transformer: The core of the device is a toroidal transformer, known for its high efficiency, quiet operation, and minimal magnetic stray fields. This makes it ideal for installation in noise-sensitive living and working areas.
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Robust aluminum housing: The aluminum housing (IP21 protection class) ensures optimal heat dissipation and durability even in demanding environments.
These well-thought-out features create a system you can rely on blindly. The intelligent grounding relay ensures maximum safety in island operation, while the robust construction and thermal protection guarantee reliable and quiet continuous operation even under demanding conditions.
More than a transformer: The strategic advantages of the system
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Maximum power yield: The key advantage is the release of the full rated power of generators or inverters. Active load balancing makes "stranded" power on the unloaded phase usable, which dramatically increases the overall efficiency of the system.
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Superior system architecture: The use of a single 240V inverter with an autotransformer is often more powerful than two stacked 120V inverters. This configuration can handle higher unbalanced load peaks, which is particularly advantageous when starting up large consumers such as air conditioning systems.
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Deep Victron system integration: Seamless cooperation with MultiPlus and Quattro systems, especially through the controllable grounding relay, creates a coherent, safe, and centrally manageable overall system instead of a collection of individual components.
You are not just investing in a component, but in a smarter, more powerful, and safer energy architecture. Your system becomes more robust against load peaks and can be designed more flexibly, giving you more freedom and reliability in the long term.
Versatility in practice: Typical application scenarios
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Off-grid systems: Indispensable for off-grid homes and workshops. Whether with a 240V generator or two stacked 120V inverters, the autotransformer ensures that all the energy generated is available even with unevenly distributed household loads.
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Mobile applications (motorhomes & boats): In large motorhomes (RVs) and yachts with 50A 120/240V service, load balancing prevents circuit breakers from tripping and maximizes the usable power of the on-board generator or inverters for a comfortable and trouble-free journey.
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No galvanic isolation: It is important to understand that an autotransformer does not provide galvanic isolation and is therefore not a substitute for an isolation transformer. An isolation transformer is essential for protection against shore power faults and electrolytic corrosion in marine applications.
Wherever you need reliable power away from the grid, the autotransformer provides freedom and security. It allows you to live and work with all the comforts of home, whether you run a workshop, travel the high seas, or live in your self-sufficient home.
System supplement: Recommended accessories for your autotransformer
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Victron MultiPlus or Quattro: These inverters/chargers are designed to work together seamlessly. They control the autotransformer's grounding relay and form the heart of an integrated system for converting and managing energy.
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Cerbo GX & GX Touch: As a communication hub, the Cerbo GX enables complete monitoring and control of all connected Victron components. You get detailed insights into energy flows and system states, locally or via the Victron Remote Management (VRM) portal.
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Victron Lynx Distributor: A modular DC busbar with slots for fuses. The Lynx Distributor is used for clean, professional, and safe distribution of direct current and greatly simplifies cabling.
Comparison with other models – Making the right choice
The naming of the models "100A" and "32A" often leads to misunderstandings. The actual transformation and compensation power is identical for both models, as the built-in transformer is the same. The only difference is the integrated circuit breaker and the resulting maximum throughput current for purely symmetrical 240V loads.
| Feature |
Autotransformer 120/240V-100A |
Autotransformer 120/240V-32A |
| Max. through current (symmetrical) |
100 A |
32 |
| Integrated circuit breaker |
100 A, 2-pole |
32 A, 2-pole |
| Neutral conductor current (continuous) |
28 |
28 A |
| Neutral conductor current (30 min) |
32 |
32 |
| Transformer capacity |
Identical |
Identical |
Conclusion of the comparison: The 100A model is only necessary if your system is designed for more than 32A (e.g., 50A shore power) and you are simultaneously operating high, purely symmetrical 240V loads. For all pure step-up/down tasks or balancing in systems up to 30A, the 32A model offers exactly the same performance and is the more economical choice.
FAQ – Frequently asked questions from practice
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Can I use the 100A model to transform 100 amps from 120V to 240V?No. This is the most common misunderstanding. The transformation and balancing capacity is limited by the neutral conductor current of approx. 28A (continuous, approx. 3.3 kW). The 100A refers exclusively to the maximum through-current for already symmetrical 240V loads.
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Can I connect the device to a European 230V single-phase shore power supply?No. The autotransformer requires two phases (L1/L2) with 240V voltage between them for balancing or step-up operation, as supplied by a generator or two stacked inverters. It cannot generate split phase from one phase and one neutral conductor.
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Why does my autotransformer get hot even though no load is connected?This can happen in grid-connected systems if the neutral conductor generated by the autotransformer is incorrectly connected to the grid neutral conductor on a permanent basis. This results in high balancing currents. The neutral conductor of the autotransformer must be disconnected from the grid during grid operation.
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Do I have to connect the neutral conductor of the power source (generator/inverter)?No. In balancing mode, only the two hot conductors (L1 and L2) are connected to the autotransformer. This generates its own new neutral conductor at the center tap, which is then used for load distribution. The neutral conductor of the source remains unused.
Conclusion – Your intelligent power optimizer
The Victron Energy Autotransformer 120/240V-100A is a precise tool for system integrators and demanding users that intelligently manages and maximizes the available energy in complex split-phase systems. Its strength lies not in the current rating that gives it its name, but in its ability to take the performance and stability of your entire energy system to a new level.
Contact us for individual advice!
Installation and operation – Important information
Installation should always be carried out by a qualified professional in accordance with local regulations and Victron system diagrams. Some key points are:
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Mounting: Vertical mounting is recommended to ensure optimal heat dissipation through natural convection.
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Wiring for load balancing: Connect the two hot outputs of the source (e.g., L1 from inverter 1, L2 from inverter 2) to the input terminals. The new, clean neutral conductor is taken from the center tap of the autotransformer.
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Grounding: The device housing must be properly connected to the central system ground to ensure safety.
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Dimensioning: The planning of cable cross-sections and fuses must be based on the actual transformation power (max. 32A neutral conductor current) and not on the 100A through-current.
Technical data – Victron Energy Autotransformer 120/240V-100A at a glance
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Part number (MPN): ITR000100101
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Input/output voltage: 120/240V
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Frequency: 50/60 Hz
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Max. 240V through current: 100 A
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Input circuit breaker: 100 A, two-pole
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Neutral conductor current, continuous (@ 40°C): 28 A
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Neutral conductor current, 30 minutes: 32 A (corresponds to approx. 3800 VA compensation power)
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Transformer type: Toroidal
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Housing: aluminum
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Protection class: IP21
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Safety standard: EN 60076
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Weight: 13.5 kg
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Dimensions (H x W x D): 425 x 214 x 110 mm
