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The name 'Battery Load Priority Selector Circuit' simply describes what the circuit does. In any electrical system where battery is being used as back-up power in the event of primary power source failure or outage, there is always a need to select priority for our loads as some loads are more important than others. What this circuit does is to cut off those less important loads from the supply if the battery has discharged to certain preset value so as to reduce energy being taken from it to allow more important loads work for longer period before battery completely discharged or primary power restored.
In this circuit, three level of load priorities are selected: the least important load will be cut off from the supply when the battery is 20% discharged, second set of loads which I called less important load will be cut off when it is 40% discharged. Finally, the important loads (load given highest priority) cut off when the battery is considered 'zero'(i.e, complete discharge) to prevent it from deep discharge. It is your duty to choose which load is important, less or least important according to your need and connect to the load points as shown in my circuit. Feel free to check my Battery Level Monitor and Lead Acid Battery Charger for description of how battery level is sensed by IC4, how IC4 send processed signals to IC1, IC2 and IC3 accordingly and finally produce outputs that energise or de-energise the relays.
IC1 to IC3= NE555
Transistor: T1 to T3= BC337
Resistors: R1= 1K2
R5 to R14= 100K
R15 to R17= 33K
R18 to R20= 1K
Variable resistors: VR1= 20K
LED1 to LED3= red light emitting diode
D1 toD4 = 1N4001
Capacitors: C1= 10µF 35V
C2= 0.1 µF ceramic
Relay1 to Relay3= 12V DC (select contact's current rating according to your load demand)