The Autotransformer: for step up, step down and split phase balancing

An autotransformer can be used for step up, step and split-phase output balancing purposes. While the step-up and step down functions are fairly straightforward, split-phase output balancing may require some more attention.

Ground relay for use with Multi or Quattro Inverter/Chargers included

When operating in inverter mode, the neutral output of the inverter/charger must be connected to the ground to guarantee 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 in the autotransformer’s enclosure. The relay is controlled by the 230/240V Multi or Quattro. (The internal grounding relay in the 230/240V Multi or Quattro must be disabled)

Temperature protected

In case of overheating, the Autotransformer is disconnected from the supply. Reset is manual.

An alternative to stacked inverters

The alternative to stacking two 120V inverters to provide a 120/240V split phase supply is a 240V inverter with an additional Autotransformer.

Two stacked 120V 3kVA inverters will supply up to 25A to each 120V leg. If the load on one leg is less than 25A, the maximum load on the other leg is still limited to 25A.

One 240V 5kVA inverter with a 32A Autotransformer will supply up to 21A of balanced load to each 120V leg.

Fewer loads on one leg will however result in more power being available on the other leg, with a maximum unbalance of 32A. Therefore the load can be up to 38,5A on one leg if the load is not more than 3,5A on the other leg (maximum unbalance: 38,5 – 3,5 = 35A). If load unbalance is to be expected, a lower power 240V inverter with autotransformer will therefore be preferable to the stacked inverter solution.