Auto Transformers

Auto Transformers

 

An auto transformer has a single tapped winding with a direct electrical connection between the input and the output. When an AC voltage is applied to a section of the winding, a voltage is produced across another section of the same winding. For example, if the transformer has a tap at the centre of the winding and 230V is applied across the entire winding, 115V could be measured between one end and the tap. The transformer can also, at least in theory be reversed so if 115V is applied between one end and the tap, 230V could be measured across the entire winding, however losses mean that in practice, slightly less voltage will be obtained. Auto transformers are usually smaller, lighter and cheaper than the more commonly found isolating transformer which has two physically separated windings, giving high resistance between them, even though they are closely coupled magnetically.