Thanks Eric,
In fact this is an element used in Voltage stabilizers, in India, but, the low and high detection is better done using LM324 with preset reference inputs and sense voltages using a pot as used by Kris1.
I wonder whether we can use the trigger and threshold pins of the timer independently. (i mean use it as a single comparator).
BTW, on the way Kris1 designed, he could perhaps use more gating logic and finally drive a single transistor driving a relay.
AG's comments are just Nice.
perhaps the 4011 can be operated at 5V Vcc and the potentiometers so adjusted to meet the needs. The 555 output can be level shifted to match 4011 input. The output of gate(with Pins 1,2&3) can be inverted by the 4th spare gate and used as input at pin5. and finally have only Q2 driving the relay. ... I have to think of refining the present circuit even. All floating concepts.I shall come out shortly with a reasonable logic.