This circuit monitors the power-line (ac) voltage. When a power failure occurs, on restoration of power, the circuit a
dds a five-minute delay before energizing Kl, which protects the compressor against limited low voltage. Ul is a 16-stage counter with an integral oscillator that is set to divide by 8192. R7, R8, and C4 set the oscillator frequency to about 25 Hz, which produces a total count interval of 300 seconds (5 minutes). After this time, pin 8 Ul goes high, which forward biases Ql, triggers SCR1, and activates Kl. Up to 30 A can be switched.