1. Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
    Dismiss Notice

120 VAC voltage detection

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by embedded_sys, Sep 8, 2017.

  1. Pommie

    Pommie Well-Known Member Most Helpful Member

    Joined:
    Mar 18, 2005
    Messages:
    10,022
    Likes:
    317
    Location:
    Brisbane Australia
    ONLINE
    With your original circuit if you add four 45V zener diodes in series with the resistor - two forward facing, two backward facing, it should fix the problem. Maybe drop the resistor value to around 20k. Note that doing this will give you narrower pulses on the output but they will be at 120Hz.

    Mike.
     
  2. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

    Joined:
    Oct 30, 2010
    Messages:
    9,918
    Likes:
    1,098
    65 VAC to ground I can explain easy enough, but not across L1, L2. Induced, maybe.

    65 V is easily explained when a particular problem exists. Picture an outlet strip with a computer ( L1, L2 and G) plugged into one outlet. Now picture that the outlet that the strip is plugged into has a bad ground.

    Inside the computer is an RFI filter with generally 4 capacitors to ground. They are "identical" and each have the :same"leakage, approximately. You now have ground at approximately 1/2 120 VAC. Been there, done that at home and work and it's not a good sign, You can easily deliver a few mA.
     
  3. embedded_sys

    embedded_sys New Member

    Joined:
    Sep 8, 2017
    Messages:
    21
    Likes:
    1
    I'm having a hard time testing this configuration in the office. What is the best way to get a 65VAC input to the chip? I'm using a AC fan voltage control, but it cannot have a open circuit and work. If it is open, the terminals meature about 96VAC all the time. When I put an AC inductive load on it (AC Fan or AC Relay), as soon as the load turns on, the voltage changes.

    Also, I'm using a 3.3VDC MCU instead of a 5VDC MCU. Will this affect my Vth(+)?
     
  4. dave

    Dave New Member

    Joined:
    Jan 12, 1997
    Messages:
    -
    Likes:
    0


     
  5. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

    Joined:
    Oct 30, 2010
    Messages:
    9,918
    Likes:
    1,098

    I'd say variac, variable autotransformer, as my first choice.

    A 2400 ohm potentiometer or close to that. parallel a resistor to a 5K pot to get around 2400. Check currents and power. Use a combination of a fixed resistor and potentiometer. You need to be able to supply the current the OPTO nees without exceeding the power dissipation of the variable resistor.
     
    • Agree Agree x 1
  6. embedded_sys

    embedded_sys New Member

    Joined:
    Sep 8, 2017
    Messages:
    21
    Likes:
    1
    I bought a variac for testing, and it worked great. I was able to test it in the field, and the new circuit worked as desired.
     
  7. schmitt trigger

    schmitt trigger Active Member

    Joined:
    May 24, 2009
    Messages:
    887
    Likes:
    84
  8. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

    Joined:
    Oct 30, 2010
    Messages:
    9,918
    Likes:
    1,098

Share This Page