We are aware that when the line voltage becomes more than 250 volts and less than 160 volts, it can damage our TV sets, refrigerators, etc. Hence, we use voltage stabilizers which are costly. The circuit Automatic Cut-off Power Supply described here is low-cost. The assembling cost comes to around $1 only. If the voltage exceeds the mentioned range it automatically cuts off the supply so that the life of the TV set and other devices can be extended.
Circuit Description of Automatic Cut off Power Supply
The common point of the relay is connected to the phase line and from the normal point, it is connected to the device. The neutral will have a direct line from the main supply.
To adjust VR1 and VR2, you have to take the help of a manual voltage stabilizer. First, adjust the manual voltage stabilizer so that its output gives 160 volts. Then adjust VR1 so that the relay goes to the exciting position. Now adjust the manual voltage stabilizer to give an output of 250 volts. Then adjust VR2 so that the relay just goes to the exciting position.
This circuit requires nearly 75mA current at 12 volts. You may not get a transformer of this range in the market. Therefore, take a 6-volt, 300 mA center-tapped transformer which is easily available in the market. Now obtain 12 volts from the transformer using a full-wave rectifier from the two endpoints of the secondary winding.
Check out other voltage stabilizer and protector circuit posted on bestengineeringprojects.com
- Auto Cut Circuit for Over and Under Voltage
- Auto Cut for Manual Stabilisers using 741 IC
- Versatile Auto Cut-Off Unit
- Single Phase Preventer with Under/Over Voltage Cutout
PARTS LIST AUTOMATIC CUT OFF POWER SUPPLY
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Resistors (all ¼-watt, ± 5% Carbon unless stated otherwise) |
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R1, R5 = 47 KΩ R2, R3, R6, R7 = 150 Ω R4 = 100 Ω, 0.5W VR1, VR2 = 68 KΩ |
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Semiconductors |
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T1, T3 = BC158 (General Purpose silicon PNP transistor) T2, T4 = BC148 (General Purpose silicon PNP transistor) D1 – D4 = 1N4148 (Small Signal Diode) D4 = 1N4007 (Rectifier Diode) ZD1 = 9V, 1W |
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Miscellaneous |
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RL1= 6V, 300 Ω Relay |