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Water level sensor

Discussion in 'Sensors and Actuators' started by Karthik rajagopal, Jan 1, 2018.

  1. Karthik rajagopal

    Karthik rajagopal

    174
    4
    May 9, 2016
    Hi all,
    I recently did the water level circuit . I used a Darlington transistor in my water level circuit as I needed more current to control my 12 v relay. The thing that I noticed is that when I dropped one probe into a bucket of water and held one in my hand and touched water with my other hand , I felt a mild shock. But when I measured it using my multimeter it read only 12 v which was the power supplied from my 12 v adaptor( regulated voltage) .
    What could be the reason?
    I didn't fell the shock when I was holding one wire in one hand and the second wire on the other hand.( I mean without water as a means of conduction).

    Thanks in advance.
     
  2. kellys_eye

    kellys_eye

    4,286
    1,145
    Jun 25, 2010
    What type of 12V adapter?

    If it is a cheap 'Chinese' version it may just be a capacitive dropper circuit - potentially deadly. Use a linear power pack for this application or, better still, batteries.
     
  3. AnalogKid

    AnalogKid

    2,271
    638
    Jun 10, 2015
    Which water level circuit? Schematic? Photo of power supply?
     
  4. Karthik rajagopal

    Karthik rajagopal

    174
    4
    May 9, 2016
    Nope. It is a normal step down adapter ( with transformers, rectifiers,....) that gives 12 v DC regulated supply.
     
  5. kellys_eye

    kellys_eye

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    Jun 25, 2010
    In which case did you REALLY feel a shock? or was this just a nervous reaction?

    It takes a few mA of current to make a shock 'feel-able' (around 1mA for AC and 5mA for DC and at the appropriate voltages). Perhaps it was just static?

    Has it been repeatable?

    Might be worth checking that the DC negative side of the power pack isn't capacitively coupled to the mains earth/neutral.
     
    Karthik rajagopal likes this.
  6. Karthik rajagopal

    Karthik rajagopal

    174
    4
    May 9, 2016
    I really felt the shock every time I dipped my hand in water.
     
    Last edited: Jan 1, 2018
  7. Karthik rajagopal

    Karthik rajagopal

    174
    4
    May 9, 2016
    I have enclosed my circuit diagram. The circuit what I was talking about above was actually a project for automatic plant watering system. It was to be made with simple components and mainly without the use of arduino. So I developed this circuit. This actually has two Darlington transistors ,one switches the relay ON when the water is available in the bucket, and the other Darlington has probes which are buried in the soil which will switch ON the second relay when there is availability of water in the soil ( which means it will switch off the motor as the motor is connected to normally closed pin of the relay). The second part which is responsible for detecting the water in the soil and controlling the motor gets its power supply from the first relay ( which means the second part will be ON only when there is water in the bucket else it will be in off state irrespective of the dryness in the soil) in order to avoid the motor going into dry run.

    Looking into the circuit diagram along with the above description hope will make you understand my actual idea.
    The problem stated above was a part of this circuit.
    But the circuit works well.
     

    Attached Files:

  8. 73's de Edd

    73's de Edd

    2,558
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    Aug 21, 2015
    Sir Karthik rajagopal . . . . . . .

    GADZOOOOOOOKS ( and that's being heavy on the ooooooooooks ), now what a wicked web, you DO spin . . . . .

    Looks like you have just met inductive back EMF . . .say hellooooooooo.

    Try those two diodes shown . . . . .

    upload_2018-1-1_12-7-44.png


    73's de Edd . . . . .
    .
     
    Last edited: Jan 1, 2018
  9. Karthik rajagopal

    Karthik rajagopal

    174
    4
    May 9, 2016
    Ya sure. Will try adding those diode. I have basic doubt, aren't these EMF short lived? Bcoz i dont just get shock for a second it persists till I take my hand. Please correct me if I am wrong bcoz I am just a beginner in electronics.
     
  10. 73's de Edd

    73's de Edd

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    Aug 21, 2015
    Sir Karthik rajagopal . . . . . . .

    True, the EMF will only pop up at a relay opening time . . . . . . .which you will have damped with those diodes installations.

    NOW . . . to move on to the crux of the situation . . . .
    I read only 12 v which was the power supplied from my 12 v adaptor( regulated voltage)

    This time you need to take your metering and put it in AC voltage monitoring mode and at its lowest range, if not being auto ranging.

    Black meter probe goes to your earth ground and the other meter probe to the negative and then the positive output of your AC line powered, converting to DC power adapter, to see if leakage is causing your undesired voltage . . . .as being an AC leakage instead of DC as you initially tested for.

    73's de Edd . . . . .

     
    Karthik rajagopal likes this.
  11. Karthik rajagopal

    Karthik rajagopal

    174
    4
    May 9, 2016
    Thanks for the reply Edd. So do you mean that if my meter reads an higher AC voltage leak , it might be the cause for the shock that I experienced?
     
  12. 73's de Edd

    73's de Edd

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    Aug 21, 2015
    I could only see two things causing a shock . The first thing would be the opening of a set of relay contacts which would only be at that instant of opening.
    That would be taken care of by the diodes shutting the relay coils.
    The second situation would be any significant AC leakage through the wall wart .
    That situation will be presenting a continual shock hazard at any time the fingers could be touching the water.
     
    Karthik rajagopal likes this.
  13. Karthik rajagopal

    Karthik rajagopal

    174
    4
    May 9, 2016
    Thanks for the reply Edd.
     
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