Water Sensor Alarm

Discussion in 'General Electronics Chat' started by Peter8519, Sep 23, 2015.

  1. Peter8519

    Thread Starter New Member

    Nov 18, 2014
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    Hi All,

    I come across this water sensor alarm circuit.

    [​IMG]

    If I were to use 4 x 1.5V battery cell, any idea how long it would last ?
    Thanks in advance.
     
  2. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
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    205
    Don't bother. The use of a DC voltage causes plating of the contacts and eventually it won't work. You really need AC excitation to be reliable.
     
  3. DickCappels

    Moderator

    Aug 21, 2008
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    634
    Probably hundreds of hours depending upon the buzzer but not as long as it could. You can reduce current drain in the "idle" mode by replacing the 1k resistors with some of higher values, the values depending upon the drive requirements of the buzzer.

    The electrodes will not corrode when dry. Even when they do corrode, the change in resistance might be an improvement (greater surface area because of piyying).
     
  4. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
    1,440
    368
    If it is just for raising an alarm and the probes are not expected to be immersed in water normally; it should be ok to use DC.

    How long the battery lasts in standby depends on its capacity, the circuit draws around 9mA in quiescent.

    It is possible to design this circuit so that it draws zero current in standby.

    [​IMG]
     
    Last edited: Sep 23, 2015
  5. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    3,841
    This circuit is very dependent on the conductivity of the water you use and the distance between the electrodes. If it is distilled or pretty darn free of dissolved ions, the circuit will not work. For example. If your voltage source (batteries) supply 6 volts, you will need the water gap to have a resistance of 100 ohms or less.

    The circuit activates the buzzer when the current to the base of the left BC547 stops flowing (because the voltage divider of a 1k resistor and the water gap bring the base voltage below 0.7 volts).

    It may work on well water or a sump pump circuit, I don't know if it will work on drinking water, it depends on the distance between the electrodes - the greater the distance, the higher the resistance of the water.
     
  6. Peter8519

    Thread Starter New Member

    Nov 18, 2014
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    0
    Hi Everyone,
    Thank you very much for your replies.

    It's for my alkaline water system's acidic water tank.
    I plan to put the electrodes as close as possible but not to touch each other.
    The sole purpose of this sensor is to prevent overflow.

    Maybe I should use the circuit by blocco since it draws zero current on standby.
     
  7. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    3,841
    Your water will be very conductive. And, @blocco a spirale 's is much better. Remember to add a switch to blacco's circuit if an overflow condition will lasT any period of time (but find a way to remind yourself to turn it back on at some point). Avoiding a switch is preferred if overflow is a short duration and the alarm is not too annoying.
     
  8. Peter8519

    Thread Starter New Member

    Nov 18, 2014
    6
    0
    Thanks.
    I will clear the water as soon as the alarm sound. :)
     
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