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The Autotransformer:
For Balancing Boost, Step Down, and Split Phases
An autotransformer can be used to balance step up, step down, and split phase outputs. While the step-up and step-down functions are fairly simple, balancing the split-phase output requires a little more attention.
Take a 30A 120/240V split-phase supply as an example.
The supply can be from the mains, a generator, or two coupled inverters.
Some of the connected loads require 240V, others 120V. On any 120V circuit, the load should not exceed 30A. The problem is that the two circuits have different currents as soon as 120 V loads are connected. The reason for this is that the 120V loads on the two circuits will never be balanced. For example, a 120V 1200W hair dryer will draw 10A from one circuit. A 120V washing machine can even draw more than 20A from one circuit. The current difference between the two circuits, also known as current imbalance, is therefore often 20 A or more. This means that the 30 A supply is not fully utilized. Once one circuit is drawing 30A, the other circuit may not be drawing more than 10A. For example, increasing the 240V load will then overload one circuit while the other circuit still has spare capacity.
Theoretically is the total capacity of a 30A, 120/240V power supply = 30 x 240 = 7.2kVA.
In the case of an unbalance of 20A, the practical maximum is 30 x 120 + 10 x120 = 4.8kVA or 67% of the theoretical maximum.
The solution is an autotransformer.
Leaving the neutral of the split-phase supply unused and connecting an autotransformer as the new neutral, as shown in Figure 1, any unbalance in the load will be "absorbed" by the autotransformer.
In the case of a 30A supply, the load can be increased to 7.2kVA. A 20A load imbalance will result in one circuit delivering 40A and the other 20A. The difference of 20 A flows through the neutral wire and the coil of the autotransformer. The current through the two 120V lines of the split-phase supply is 30A.
Grounding relay included for use with Multi or Quattro inverter/chargers
When operating in inverter mode, the inverter/charger neutral must be connected to ground in order to ensure the proper functioning of a GFCI. In the case of a split-phase supply, the neutral must be grounded. For this purpose, a grounding relay is built into the housing of the autotransformer. The relay is controlled by the 230/240V Multi or Quattro. (The internal ground relay of the 230/240 V Multi or Quattro must be deactivated)
Temperature protected
In the event of overheating, the autotransformer is disconnected from the power supply. The reset is manual.
For Balancing Boost, Step Down, and Split Phases
An autotransformer can be used to balance step up, step down, and split phase outputs. While the step-up and step-down functions are fairly simple, balancing the split-phase output requires a little more attention.
Take a 30A 120/240V split-phase supply as an example.
The supply can be from the mains, a generator, or two coupled inverters.
Some of the connected loads require 240V, others 120V. On any 120V circuit, the load should not exceed 30A. The problem is that the two circuits have different currents as soon as 120 V loads are connected. The reason for this is that the 120V loads on the two circuits will never be balanced. For example, a 120V 1200W hair dryer will draw 10A from one circuit. A 120V washing machine can even draw more than 20A from one circuit. The current difference between the two circuits, also known as current imbalance, is therefore often 20 A or more. This means that the 30 A supply is not fully utilized. Once one circuit is drawing 30A, the other circuit may not be drawing more than 10A. For example, increasing the 240V load will then overload one circuit while the other circuit still has spare capacity.
Theoretically is the total capacity of a 30A, 120/240V power supply = 30 x 240 = 7.2kVA.
In the case of an unbalance of 20A, the practical maximum is 30 x 120 + 10 x120 = 4.8kVA or 67% of the theoretical maximum.
The solution is an autotransformer.
Leaving the neutral of the split-phase supply unused and connecting an autotransformer as the new neutral, as shown in Figure 1, any unbalance in the load will be "absorbed" by the autotransformer.
In the case of a 30A supply, the load can be increased to 7.2kVA. A 20A load imbalance will result in one circuit delivering 40A and the other 20A. The difference of 20 A flows through the neutral wire and the coil of the autotransformer. The current through the two 120V lines of the split-phase supply is 30A.
Grounding relay included for use with Multi or Quattro inverter/chargers
When operating in inverter mode, the inverter/charger neutral must be connected to ground in order to ensure the proper functioning of a GFCI. In the case of a split-phase supply, the neutral must be grounded. For this purpose, a grounding relay is built into the housing of the autotransformer. The relay is controlled by the 230/240V Multi or Quattro. (The internal ground relay of the 230/240 V Multi or Quattro must be deactivated)
Temperature protected
In the event of overheating, the autotransformer is disconnected from the power supply. The reset is manual.