Circuit for controlling overfilling of a water tank

Discussion in 'The Projects Forum' started by sureshparanjape, Oct 7, 2015.

  1. sureshparanjape

    Thread Starter Member

    Feb 10, 2012
    12 V Controlling Circuit.png
    My friend and myself has a circuit on board which controls 3 phase 220V motor suitable for my need. My need was to start the motor manually. If the tank is full, the motor shouldn't start; otherwise the motor should run till the tank is full. I have attached circuit drawing. The left part in it is the circuit and right part is the circuit of a standard three phase motor.My friend had earlier connected the motor so that the need was met. Recently some fault was developed in the circuit and we have to do redo the wiring. I put in new demand on the circuit that if the circuit fails I should be able to switch on the motor. I have obtained three poles, double throw switch for this purpose on my friend's recommendation.
    I feel that if the controlling circuit controls the starter's circuit as shown in the figure,it shouldn't need the switch. If the manual switch for the circuit is not operated, then starter controlling relay would be in "NO" position, and the starter would receive the power through the circuit,enabling operating starter manually.If the manual switch is pressed, the starter controlling relay would be either NO or NC positions, controlling starter.

    Have I given all information for any one to opine who is correct?
    My friend has about 40 years of practical experience and I have none!

    12 V Controlling Circuit.png
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    I find it difficult to follow the logic of what you're trying to do, but can't you simply use a float switch in parallel with the STOP switch?
    blocco a spirale likes this.
  3. Dodgydave

    Distinguished Member

    Jun 22, 2012
    You have no hysteresis for high and low levels, the pump will keep tripping in and out.
    like Alec said, whats wrong with a couple of float switches, one for full (stop) and one for low level (start)...?
  4. MaxHeadRoom


    Jul 18, 2013
    You could use both the NC and NO contact on the relay RLY2, for manual overide if the float switch does not close.
  5. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    I always use 2 float switches for each state (2 x high, 2 x low) for a bit of redundancy..
    Then routine preventative maintenance schedule to ensure both are working and replace as needed..

    Only time I've ever had electrical type floats "fail to switch" is due to buildup on the float shaft or other substance stopping float operation.
  6. sureshparanjape

    Thread Starter Member

    Feb 10, 2012
    I did think that I wouldn't be clear about my intentions.
    This project came out as an exercise( for my self!) as a beginner to use transistor switches . I have two tanks , one ground and another overhead. The part in the circuit on the left is for the upper tank and there was one for the lower tank to control motor stopping if water level in the lower tank is below certain level by adding one more transistor switch. To my disbelief my probes in the lower tank was grounding the whole circuit! Both tanks are cement concrete; the upper tank's probe weren't grounding the circuit while the lower tank probes were! I f I were to keep them in a plastic bucket, the circuit was functioning as desired. My friend had completed circuit and what I can gather was that he has taken out three connectors, one at one side of the Start button, another between Start and and Stop and the third to the other side of the stop button. He has connected these to the Relay2 to operate the motor by the circuit.
    My thinking is that the purpose of the part of the starter's circuit between A and B is to control starting or stopping the starter's function and the circuit on the left just does that. A parallel circuit to the circuit between A and B should do the same job if it is connected between A and B.
    My friend works and thinks as he works. It is very interesting to see him working. Upon hearing my solution he was surprised - how come he couldn't think of it. He opened the starter and disconnected (what I think) the latching of the Stop button, started motor manually and did see that Stop button was not coming back to its initial position. Hence he concluded that the modification I am suggesting wouldn't work. He is carrying out the modification in the near future. I pointed to him that my suggestion bupasses both Start and Stop, which he disagrees.He would carry out the work as per his thinking. This is my academic interest. So this thread. If there is validity in my claim, I can ask him to try it out
    I would rephrase my question. Would the motor work as desired when the circuit is used to control it or when the motor is started manually using starter's Start and Stop buttons?
    My sincere thanks to all the contributors. I agree that float switch would work.This was my first project and naturally I like it !
    As regards to the comment " You have no hysteresis for high and low levels, the pump will keep tripping in and out." by Mr.Dodgyhave, I add that the configuration of two transistors on the left circuit guarantees that if both probes are in water the motor will not start and would start manually ( bu pushing the push button) if they aren't. The motor would continue running till water touches the upper probe. This has been working satisfactorily over six months.