Automatic Phase Changer System



In three-phase applications, if low voltage is available in any one or two phases, and youwant your equipment to work on normal voltage, this circuit will solve your problem. However, a proper-rating fuse needs to be used in the input lines (R, Y and B) of each phase.
The circuit provides correct voltage in the same power supply lines through relays from the other phase where correct voltage is available. Using it you can operate all your equipment even when correct voltage is available on a single phase in the building.The circuit is built around a transformer, comparator, transistor and relay. Three identical sets of this circuit, one each for three phases, are used.
The mains power supply phase Ris stepped down by transformertodeliver 12V,300 mA, which is rectifiedby diode D1 and filtered by capacitorC1 to produce the operatingvoltage for the operational amplifier (IC1).
The voltage at inverting pin 2 ofoperational amplifier IC1 is taken fromthe voltage divider circuit of resistorR1and preset resistor. The reference voltageat non-inverting pin 3 is fixed to5.1V through diode. The phase voltage is compared against the reference voltage and if the phase voltage is low the relay trips and shifts the load to other phase.

Automatic Phase Changer System
S. No. component Name Quantity
1 IC ULN2003 with 16 Pin Base 1
2 On/Off Switch 4
3 Diode 1N4007 5
4 Berg Strip 2 Pin 1
5 Relay (+12v) 4
6 Resistor (1k) 6
7 RM Connector 3 Pin M/F 2
8 LED (White) 2
9 LED (Red) 2
10 LED (Yellow) 2
11 PCB 4×4 inch 1
12 Battery (+9v) with Cap 1
13 DC Socket M/F 1


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