autotransformer current transformer custom transformers AUTOTRANSFORMER An autotransformer is a type of transformer that has the primary winding employed as a secondary winding, or vice versa; This process is also named a compensator or balancing coil. An autotransformer is a simple and inexpensive way to correct problems that arise when a secondary voltage is difficult to obtain or a transformer you have is either too high or too low. A transformer that has a part of its winding included in both the input and output circuit is known as an autotransformer. In a simple autotransformer connection there is a common portion of the winding that has no isolation between the input and output circuits, and there is only one winding. The secondary current rating of an autotransformer must be at least equal to the primary current rating of the subject transformer.  In simple terms, a subject transformer with a primary current draw of 5 amps should be used with an autotransformer with a secondary current rating of 5 amps or more.