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Sensing AC voltages

Discussion in 'General Electronics Discussion' started by Karthik rajagopal, Oct 7, 2019.

  1. Karthik rajagopal

    Karthik rajagopal

    191
    5
    May 9, 2016
    Hi all,
    I was recently thinking of the ways to measure an AC voltages wirelessly. I came across many solutions which use a current transformer to measure the current while the load is connected to the AC source. But my problem is that I want to just detect AC voltages even if no load is connected to it.
    Is there any way I can do it? As far as my understanding, current won't flow unless we have a load .
    Under that condition, I thought of detecting the varying magnetic field using a hall effect sensor to detect the presence of the voltage. Is my understanding and method correct?
    It would be helpful if you can suggest some methods to achieve this.

    Thanks in advance.
     
  2. Bluejets

    Bluejets

    3,489
    706
    Oct 5, 2014
    I believe the sensor inside contactless volt sticks is hall effect.
     

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  3. Karthik rajagopal

    Karthik rajagopal

    191
    5
    May 9, 2016
    Thanks for the reply.
    So, does that mean my logic is correct?
    After seeing a lot of YouTube videos, I thought they might have also used the same decade counter to sense voltages.
     
  4. Bluejets

    Bluejets

    3,489
    706
    Oct 5, 2014
    Another method....

     
    Karthik rajagopal likes this.
  5. Karthik rajagopal

    Karthik rajagopal

    191
    5
    May 9, 2016
    That was exactly what I was looking for .
    Thanks for sending me that video !!
     
  6. Harald Kapp

    Harald Kapp Moderator Moderator

    9,306
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    Nov 17, 2011
    Hall sensors sense current, not voltage. The stick works very liekly in a capacitive way.

    AC voltage can be sensed in many ways, e.g. using voltage transformers or capacitors, to name the most typical ones.
     
    Karthik rajagopal likes this.
  7. Bluejets

    Bluejets

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    Oct 5, 2014
    Everyone learns something new everyday I imagine.

    https://www.jameco.com/shop/keyword=Hall-Effect-Voltage-Sensor
     
  8. Harald Kapp

    Harald Kapp Moderator Moderator

    9,306
    1,889
    Nov 17, 2011
    I'm open to learn new stuff, but in this case: read the datasheet. While the website offers "Hall effect voltage sensor"(s), a look in the datasheet shows that these are actually magnetic field sensors with open collector outputs:
    upload_2019-10-11_8-32-3.png
    Since a voltage alone cannot create a magnetic field - only a current does - the advertising is misleading. These are not voltage sensors.
     
  9. WHONOES

    WHONOES

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    May 20, 2017
    Look at the following link for a DMM that measures voltage without physical contact. Not very expensive either.
     
  10. Karthik rajagopal

    Karthik rajagopal

    191
    5
    May 9, 2016
    I built a non contact voltage detector using a decade counter like others did on YouTube. When I pointed it towards an open ended live wire(i.e without any load ), the output went high.
    How did that work?
    The circuit works by sensing the magnetic field ,then how did that sense a magnetic field when no current was passing through it ?
     
  11. KMoffett

    KMoffett

    687
    66
    Jan 21, 2009
    There is a difference between "detecting" an AC voltage and "measuring" an AC Voltage. Which do you want to do?
     
  12. Karthik rajagopal

    Karthik rajagopal

    191
    5
    May 9, 2016
    I want to detect the AC voltage.
    Even for detecting an AC voltage, we will need it's magnetic field which won't be present if no current is going to flow.
    So, how did my AC detector work (that I have mentioned in my previous message )?
     
  13. Harald Kapp

    Harald Kapp Moderator Moderator

    9,306
    1,889
    Nov 17, 2011
    Hard to say without knowing your circuit.
    It very likely detected the electric field from the AC, not the magnetic field. An electric field can be present even without current flowing.
     
    Karthik rajagopal likes this.
  14. Karthik rajagopal

    Karthik rajagopal

    191
    5
    May 9, 2016
    That must be the reason as my circuit uses a piece of wire as an antenna ,it must be the electric field. Thanks for the clarification .
     
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