main (120VAC/240VAC) detection

Discussion in 'General Electronics Chat' started by bug13, Aug 23, 2016.

  1. bug13

    Thread Starter Senior Member

    Feb 13, 2012
    Hi guys

    What is the safest way to detect main? I need to be able to detect if main is available, what is the safest way to do this? Thanks guys!
  2. tcmtech

    Distinguished Member

    Nov 4, 2013
    Mini neon bulb inside one end of a tube with a photodetector at the other end.
  3. #12


    Nov 30, 2010
    Buy an electrician's voltage detector pen for $10 at Home Depot.
    Get a neon panel-mount indicator lamp built for 240 volts and learn to tell if its at full brightness or half brightness.'re not in 'Murica.
    I don't even know if you have 120/240V in NZ.
    Anyway, both methods will work for 240VAC.

    Whole lot of guessing going on with no application specified.
    Last edited: Aug 23, 2016
  4. markdem

    Active Member

    Jul 31, 2013
    I am guessing this has to do with the power supply? Did the current power supply not have a power good output?
    Safest - Just get the smallest transformer you can find that outputs 5 volts. You can connect that directly to your logic. No need to scale anything after.
  5. MaxHeadRoom


    Jul 18, 2013
    I thought NZ had the same as Australia which is a 240v single phase and neutral I believe?
    Either use @#12 method or use a DMM (meter).
  6. bug13

    Thread Starter Senior Member

    Feb 13, 2012
    I like this non-intrusive detection, now I need to find out how a voltage detector pen works. Thanks for the info.

    We only have 240V, but I added 120V to make it a more general question.

    The info need to be readable by a MCU, I am detecting main fail to sound alarm.

    Yes, this is part of my power supply. No the current supply does not have a power good output. It only have two outputs, one for charging a battery, one for a load. When main is available, it charges the battery and power the load. When main is gone, it powers the load through the battery, and it also do low voltage cutoff.

    You are absolutely correct.
  7. MaxHeadRoom


    Jul 18, 2013