Victron Auto Transformer 100A

The Victron Auto Transformer 120/240V-100A is a heavy-duty toroidal autotransformer designed for step-up, step-down, and split-phase output balancing applications in off-grid, marine, and RV power systems. Rated at 100A feed-through current, it enables the safe and efficient use of 120V and 240V loads from a single power source, and resolves the current imbalance that naturally occurs in split-phase systems where 120V loads are unevenly distributed across the two legs.

The split-phase balancing function is the most powerful capability of the Auto Transformer: when a 240V split-phase supply or stacked inverter output is used to power 120V loads, any current imbalance between the two legs — often 20A or more in real-world installations — is absorbed by the autotransformer windings rather than wasted as lost capacity. This allows the full 100A rating of the supply to be utilised regardless of how unevenly the 120V loads are distributed, dramatically improving system efficiency and preventing individual leg overloads.

A built-in ground relay enables neutral-to-ground bonding within the autotransformer enclosure — essential when operating with a Victron MultiPlus or Quattro inverter/charger in split-phase or stacked inverter configurations where the inverter's internal ground relay is not used. Temperature protection is also built in: a cooling fan activates when the transformer is warm, and a manual-reset MCB (miniature circuit breaker) disconnects the unit in the event of overtemperature or overcurrent.

Constructed with a toroidal core in a robust aluminium enclosure and rated IP21, the Auto Transformer 100A is suitable for fixed indoor and compartment installations in marine, RV, and off-grid applications. It is compatible with both 50Hz and 60Hz systems and carries safety certification to EN 60076.

Features

Step-Up and Step-Down Voltage Conversion

Converts 120VAC to 240VAC (step-up) or 240VAC to 120VAC (step-down) to suit different load and supply voltage requirements. Input current is limited by the built-in 100A two-pole circuit breaker regardless of direction of conversion.

Split-Phase Output Balancing

Absorbs current imbalance between the two 120V legs of a split-phase 120/240V supply, allowing the full 100A rated capacity of the supply to be used even when 120V loads are heavily unbalanced — preventing individual leg overloads and maximising available power from generators or stacked inverter systems.

Built-In Ground Relay for Multi and Quattro Integration

An integrated ground relay provides neutral-to-ground bonding within the autotransformer enclosure, making it suitable for use with Victron MultiPlus or Quattro inverter/chargers in split-phase and stacked inverter configurations where GFCI protection requires a grounded neutral.

Temperature and Overcurrent Protection

An active cooling fan operates when the transformer temperature rises, and a manual-reset miniature circuit breaker (MCB) disconnects the unit automatically in the event of sustained overtemperature or overcurrent — protecting the transformer and connected equipment from damage.

Toroidal Core Construction

The toroidal transformer core provides high efficiency power conversion with minimal losses and low electromagnetic interference compared to conventional E-I laminated core designs — making it well suited to sensitive electronics environments in marine and RV installations.

Aluminium Enclosure with IP21 Protection

The robust aluminium enclosure provides structural strength and corrosion resistance for long-term reliability in marine and vehicle environments. IP21 protection guards against vertical water drip ingress, suitable for indoor and compartment mounting applications.

50/60Hz Compatible

Compatible with both 50Hz and 60Hz electrical systems, making the Auto Transformer 100A suitable for international use across North American and European frequency standards.

Wall or Panel Mountable

Designed for fixed installation with conduit entry options for both 1/2-inch and 3/4-inch NPT conduit fittings, providing a clean and compliant wiring installation in professional and marine electrical panels.

Specifications

Datasheets and Manuals

Datasheet

Product Manual