3-Phase Auto Changer Circuit

admin June 10, 2010 3 Comments

Circuit Description

The circuit given here is a three phase auto charger circuit. Any modern electrical or electronic device can operate from 230 V ac supply with 15% tolerance in voltage. That is the device will work normally for a voltage range between 195V and 265V. The device may not work properly beyond this range of voltage. To change over to the other phase, the voltage required for can be chosen. Here in this circuit, a step down transformer with a secondary voltage of 15-0-15 volt at 500 mA is used for the operation of 18V relay. Here switching of the relay can be controlled by the resistors R3 and R1 respectively.

Circuit diagram

3-Phase Auto-Changer Circuit

3-Phase Auto-Changer Circuit

Connection diagram

3-Phase Auto changer circuit-Connection Diagram

3-Phase Auto changer circuit-Connection Diagram


  • The circuit given here is designed by Mr.Seetharaman V.S from Chennai.
  • Transformer T1 can be a 15-015 V secondary, 230V primary, 500mA step down transformer.
  • For chatter free operation, use a capacitor of 100μF 40 volts in parallel with relay.
  • Use one mould for each phase.
  • The connection diagram given above gives the relay interconnections.

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