Variable Auto Transformer (Variac)

Variable Auto Transformer (Variac)

It is very cost effective comparative to that of the other types of transformers since its primary and secondary windings are linked together both electrically and magnetically. Autotransformer subsist of only one single winding which is prevailing to both primary and secondary which also make it distinct then preceding energy transformer.

To facilitate the percentage of primary voltage to to its secondary load the single winding of Autotransformer knocked at very different places along with its height. Thus the autotransformer have normal magnetic core with common winding to both primary and secondary circuits.Thus, the primary and secondary winding in autotransformer are connected in sync electrically and magnetically. This mutual connectivity is mainly advantageous for making the product modest for all the customers and with high efficiency with highest disadvantages is there is no such primary and secondary individual windings available for isolation of a conventional double wound transformer.

It still produces output voltage at specific level beside being fixed or tapped, from a fixed voltage AC supply which can be used to produce a variable AC voltage it is considered as another application to auto transformer.Variac is a type of demo presentation of this type of transformer mostly used in laboratories and science labs in schools and colleges.

variable auto transformers are constructed in a similar manner to that of fixed type. In variable autotransformer around a laminated magnetic core a single primary winding are used to wrap but due to some prearranged tapping point, carbon brush is put around secondary voltage.


  • The output voltage is increased in accordance to the two time of the input voltage.
  • By adjusting the carbon brush it can be obtained any desired voltage within maximum range.
  • Approximately output voltage is shown by calibrate dial at no load.
  • It is possible to move contact arm manually as well by motor.
  • Output voltage is delivered from 0 to above line voltage.
  • 99.9% pure copper is used in the construction of this.
  • High quality of CRGO steel is applied for manufacturing coils.
  • There is rise in low temperature.
  • Large jumble of existing rating 4 Amp. To 1200 Amp.
  • Remaining carbon brushes provided up to 28 Amp.
  • Good quality carbon brush.
  • Strid-less voltage control.
  • Less time overload scope.
  • Maintenance cost.