Wiring circuit

For making adjustments, first remove C2 from the circuit to avoid delay which will confuse the matter unnecessarily. Set potentiometer VRI to get monitor voltage VM of 7V with nominal 220V supply. VR2 controls the lower limit and VR3 controls the higher limit. Initially keep VR2 in the lowermost position so that voltage at pin number 3 is minimum, and keep VR3 in the uppermost position so that voltage at pin number 6 is maximum. In this condition the window limits are wide open and the relay should operate. Nominal operating limits are between I80V and 250V. s lf the monitoring voltage is 7V with nominal 220V AC supply, then set VR2 to give 5V at pin number 3 and VR3 to give 8 V at pin number 6. Make a simple check before use. Adjust VRI to reduce the voltage VM below 5V or to increase . the voltage VM above 8V. In both cases, the relay should de- energize. If it does, bring back VM to 7V again and leave it there. Now the cutout is ready for use. Precise voltage settings can be made by varying the input supply using a variac. With a 220V supply, set VRI to give a monitor voltage of 7V; with l80V input, set VR2 to just de-energise the relay; and then with 250V input, set VR3 to just de-energise the relay. Now connect C2, as shown in Fig. 2, to get back the delay feature.

This device ensures safety and protection to your gadgets, but will not regulate the power supply. If the voltage excursions are too much and too often, or if uninterrupted operation is required along with safety, use this cutout in addition to a voltage regulator. V The load current is limited by the relay contact ratings. Therefore care should be taken to avoid using it with high current load. Otherwise, suitably modify the relay for higher currents. The stability of voltage limits depends mainly on the . potentiometers. Use good-quality potentiometers, either cermet or wirewound types. Do not try to use the usual trimpots instead. 

PARTS LIST

IC1 —747C integrated circuit, I0-pin metal case ·
T1  —SL I00 (SEM) transistor
T2 —BC 108c (BEL) transistor
T3 -—BC177 (BEL) transistor
D1-D4 —Selenium rectifier bridge or BY 126 (4 Nos.)
D5 ——Zener diode, BZX6l—Cl2 (BEL)IW
D6-DI0 —BYl26 diodes
R1 —-500-0hm, I/2 W resistor
R2 -5.1kilohm, % W resistor
R3, R7 —10-kilohm, IA W resistor
R4 -500kilohm trimpot (variable resistor)
R5, R6 —1kilohm, I4 W resistor
R8 —1megohm, % W resistor -
VRI-VR3 -5-kilohm wirewound potentiometers (see text)
C1-500 uF/25V electrolytic
C2 — 500 pF/l2V electrolytic
C3 —— 0.68uF400Vbipolar or electrolytic .
C4 — 2000uF,I2V electrolytic
NI — Neon bulb
R -9V, 20mA relay (see text)
Xl -220V to I5V step-down transformer