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How to determine voltage on transformer

Discussion in 'General Electronics Discussion' started by seanspotatobusiness, Feb 5, 2017.

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  1. seanspotatobusiness


    Sep 11, 2012
    I have what I think is a transformer and I've got mains voltage going in at the top of the image and I'm trying to measure the voltage that I get from the bottom of the image with a DMM set to 500 V AC. The top resistor is 33K and the bottom resistor is 20R. When I apply mains voltage to this circuit I get a reading of 0 V on the DMM but I'm expecting some value much higher than 0 V. Have I set it up wrong? Is this thing not a transformer?


    [Mod Note -- image resized]
    Last edited by a moderator: Feb 6, 2017
  2. davenn

    davenn Moderator

    Sep 5, 2009
    1) what is wrong is that this isn't a mains power transformer ... it isn't even a transformer
    it's a dual filter inductor that usually will have a couple of high voltage capacitors associated with it

    if it wasn't for your resistors ... you would have had a big bang, a cloud of smoke and a shower of sparks

    Better smps-schematic.JPG

    2) .... on another note .... can you please resize images before uploading or linking to them
    this one was huge ... I have resized it to a max of 1000 pixels on the longest side
    CDRIVE and seanspotatobusiness like this.
  3. seanspotatobusiness


    Sep 11, 2012
    Sorry; I thought the forum software automatically limited the size of the image.

    Thanks for the information!
    davenn likes this.
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