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Discussion in 'Home Brew' started by dejaskysdad, Jun 13, 2013.

  1. dejaskysdad

    dejaskysdad Member

    May 21, 2013
    Likes Received:
    I have a transformer that shower 19v ac and when I ran it through a rectifier and a capacitor I now have 26vdc WTF I don't understand I thought when it goes through rectifier I loose a volt or two is the capacitor bringing the voltage up its a 25 v capacitor im confused....... how can I lower the power and keep the amperage?


  2. Captain Kilowatt

    Captain Kilowatt Professional Amateur
    Staff Member

    Apr 6, 2005
    Likes Received:
    19 volts is the RMS value. AC also has a peak value which is equal to 1.41 times the RMS value (Actually the square root of 2 times the value but I rounded off). The capacitor filters out the raw AC ripple and charges upo to the peak value of the AC voltage. 19 volts X 1.41 = 26.8 volts. This voltage is unregulated meaning it will change depending on how much current you draw. This is the reason power supplies are regulated. You need a voltage regulator circuit and associated circuitry to handle the required current.

    2 people like this.
  3. Sarcasm

    Sarcasm New Member

    Aug 28, 2013
    Likes Received:
    Is there a good design with high reliability regulator anywhere. All that I have searched have been pretty generic, non specific and or had many complaints for RF application reliability.
  4. hammer0630

    hammer0630 Active Member

    Sep 10, 2011
    Likes Received:
    I can't get into the technical aspects of a power supply but I am really disturbed by interference caused by one, depends on how many amps you are interested in but I have had and still have two of the very inexpensive Mega-Watt 30 and 36 amp supplies and they have been faultless with absolutely no noise or hash and are adjustable 9 to 15 watts with a wobbley screw. My old Ashtron big and heavy with small amperage output for it's size is also great with no hum or buzz. I have just purchase a QJE-50 amp switching supply with a adjustable interference knob I have yet to use. I use my ashtron just for my 148GTL only and use a separate power supply for my amp so using two supplies and get 0 noise is pretty good. The QJE 50 I will be replacing the Mega-Watt because my amp needs more amperage than my Mega-Watt can produce.
    #4 hammer0630, Sep 3, 2013
    Last edited: Sep 3, 2013
  5. linearone

    linearone King of NY

    Apr 2, 2005
    Likes Received:
    typically I use the forumla: sec volts ac x .98 x 1.414


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