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Automatic Load Sensing Power Switch


Part- Total Qty.- Description 
C1, C3 -2- 10uF 35V Electrolytic Capacitor 
C2 -1- 1uF 35V Electrolytic Capacitor 
R1 -1- 0.1 Ohm 10W Resistor 
R2 -1- 27K 1/2W Resistor 
R3, R4 -1- 1K 1/4W Resistor 
R5 -1- 470K 1/4W Resistor 
R6 -1- 4.7K 1/2W Resistor 
R7 -1- 10K 1/4W Resistor 
D1, D2, D4 -3- 1N4004 Rectifier Diode 
D3 -1- 1N4744 15V 1 Watt Zener Diode 
U1 -1- LM358N Dual Op Amp IC 
Q1 -1- 2N3904 NPN Transistor 
K1 -1- Relay, 12VDC Coil, 120VAC 10A Contacts 
S1 -1- SPST Switch 120AVC, 10A 
MISC -1- Board, Wire, Socket For U1, Case, Mains Plug, Socket 
Notes 
This circuit is designed for 120V operation. For 240V operation, resistors R2 and R6 will need to be changed. 
A maximum of 5A can be used as the master unless the wattage of R1 is increased 
S1 provides a manual bypass switch. 
THis circuit is not isolated from the mains supply. Because of this, you must exercise extreme caution when working around the circuit if it is plugged in. 
Source: aaroncake.net

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