Dec 28, 2016

Submersible Timer Circuit with Pause Feature during Mains Failures

The post explains a submersible pump timer circuit programmed to cycle at 60 minute interval for watering the fields consistently. It also includes a time "memory" feature which ensures that the timer "remembers" the counting during mains failures, and restarts exactly from where it was interrupted when mains power is restored. The idea was requested by Mr. Siva.


The Request


I want to utilize the submersible bore well pump ground water
based on online AC power supply.

stage 1:

1) Timer A start from zero end with 60 minutes(1 hour).
2) output power supply provided to stage 3 contractor coil.
3) Timer A should resume where it stop (e.g:stopped after 10 minutes successful running it should resume from 10 min until step 1 complete)
4) After 60 minutes completion it will stop & stage 2 will start running.

stage 2:

1)Timer B start from zero end with 60 minutes(1 hour).
2)Timer B will have inbuilt power supply(eg: AAA size rechargeable battery)
3)After 60 minutes completion it will stop & stage 1 will start running.

stage 3:

1)3 pole contactor used to allow the AC power supply.
2) Contactor coil power supply received from timer A circuit.
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I)There is an frequent power failure in our area.
II)Cant run the submersible bore well pump at an desired interval time period.
III)For agriculture use only.
IV)Pausing a timer during a power failure could be difficult using discrete components.
V)suggest me any other components available in online.
VI)I am ready to purchase it.

The Design

The stage#2 timer circuit is perhaps not required since the stage#2 alone can be used for implementing the 60 minute ON/OFF cycle for the submersible pump motor.

The main challenge in the design is the pausing of the timer IC such that the timer circuit is able to freeze itself during a power failure and initiate the timing from the same point as soon as the power is restored.

This seems a little complex since the IC might require some kind of memory feature to remember and retain the time period for which it was stopped due to a power failure.

However, with a simple trick it may not be so complex to implement the mentioned time pause effect, and could be done simply by cutting off one of the timing capacitor leads during mains interruptions, and then joining it back once the power came back.

The following diagram shows the set up, which will hopefully be able to perform the intended pause effect in the timer circuit.





The design is nothing but a simple IC 4060 timer circuit. The Cx, and Rx form its timing components, meaning altering the values of these proportionately alters the output frequency timing at pin#3 of the IC.

A low current relay can be seen attached with the timing capacitor of the IC whose contacts keep the capacitor connected with the circuit configuration during normal operations or when mains power is available. However in the absence of mains, this relay quickly cuts off the capacitor from the circuit.

Since the charge content inside the capacitor fundamentally determines the time delay periods across the outputs of the IC, disconnecting the capacitor enables freezing of the charge content inside the capacitor intact until the power arrives back.

As soon as power gets restored the IC reads and responds to the available charge inside the capacitor and initiates the counting from the same period onward where it had stopped. This system ensures that the IC resumes from the point where it was stopped due to the mains interruption.

The output pin#3 of the timer is connected with a 30 amp relay stage which may be configured with the submersible pump contactor unit, for the necessary triggering of the pump and for watering the farm at the specified time intervals.

The timer circuit is designed to cycle ON/OFF with time delays as set by the values of the Cx and Rx, which may be calculated using the formula presented in this simple 4060 timer circuit article:


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