Low-high voltage protection circuit with time delay

[alaaj99]

Hello
Please help me understand this circuit. It's a circuit designed especially for protecting the fridge, AC units, etc.


The designer of this circuit (not me) used LM324, and he/she used only three comparators out of four available to reduce the cost of it (witch is nice).
Inside red rectangle there is the power supply for this circuit, inside the blue square there is the Time Delay for the circuit (3-5 min).
My questions :
1. C1 is a 680nf filming capacitor for voltage drop & current limit. Should the designer used a higher value for a 24v relay circuit?
(220v - 30v) \ 47ma = 4043 ohm ??!!
2. Z-DI is a 27v1W zener. I can't find a 1w or higher in my local market (and can't order online), what can we do? Using a resistor ? Using LM7824 ?
3. If I want to control the high & low voltage values of this circuit using a 2 potentiometers, where should I put them?
4. What's the purpose of D8 & D10? and can't we replace them with LEDs to indicate Low voltage & High Voltage?
5. What's the purpose of R7, R9, R10?
6. Why LED1 green has no resistor?
7. If I want to run this circuit on 12v relay, I must change the whole circuit?
I apologize for bad English and the many questions, you're the only community I can get help from.

 

[BradtheRad]

This schematic might work the way it's intended but you can expect to experiment and adjust values, to make it work for your purposes.

House voltage appears to be reduced via capacitive drop. It's taking a chance whether it can deliver sufficient current to energize a relay coil. The designer probably made a lot of assumptions in selecting component values.

(1) C1 may need to be increased to a large enough value to pass sufficient current, so as to drive the relay.

(2) You can use an IC regulator instead of the 27V 1W zener.

(3) Not sure which resistors set hi & low thresholds.

(4) D8 & D10 may be required to prevent exposing the led's to overmuch reverse voltage.

Not sure how to answer your other questions. In regard to operating on 12V: Perhaps the designer tried to make the circuit operate on 12V, but instead he found this circuit needed 24V in order to operate reliably, and to have sufficient power to energize a 24V relay coil.