Can anyone please point me to any threads that will have a circuit diagram for a timer? I have a water tank than is constantly being filled up and there is a submersible pump that pumps out water in this tank. Sometimes the water going out is a lot faster than water entering the tank. To prevent the submersible pump from overheating when there is not enough water, I would like to put a timer to stop the pumps and UV lights when the level goes below a threshold using a reed float switch. Will only need to switch off for 3 mins.

I have tried a simple timer using 555 as well as a Darlington pair that is triggered by a cap and resistor to give me about 3 mins. The problem I have is that the electricity in my area is not constant and blacks out often. When the power is restored, my circuit resonates. Not only that, often the circuit will false trigger. My previous circuits consists of a DC relay that will then power an AC relay to drive the various pumps and UV lights in the tank and when triggered, everything is switched off for 3 mins.

Any help is appreciated.

 

Why dont you use a float switch/ or level sensor at the bottom of the tank to switch off the pump when the level gets too low, then you dont need a timer.

 

+1 on using two level switches.


Or:
Use the N.C. contact of an interval timer relay.

Pump will turn on immediately on power up.
Shut down for a minimum of 3 min.
Longer if tank is empty. (retriggers)

 

Why don't you post a schematic of what you have developed so far? It is far easier for us to suggest modifications that it is to play twenty questions to gather your requirements for a totally different solution.