Power Amplifier Safety Modifications

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  • diydidi
    Member
    • Sep 2012
    • 17
    • South Africa
    #1

    Power Amplifier Safety Modifications

    I have a Large power amplifier that needs repairing for a client of mine.
    It's a no-name brand stereo power amplifier and uses TO-3 lateral mosfets.
    It has a large 500VA toroidal power transformer as well as a smaller 60VA toroidal transformer for the relay speaker protect circuits.
    The builder didn't add any fusing except for a large 20A trip-switch wich doubles as the power-on switch too. I'm afraid the switch is too big in my opinion and will not trip during a fault situation. Removing it is not an option. Too much metal work.
    Amp at least has a soft start circuit built in for the large transformer.
    I would like to make it safer by adding a fuse on the mains side where the power enters.
    My question is, do each of the transformers need its own primary fuse, or will one suffice.
    Also how does one go about sizing the fuse/s? I assume they will all be slow blow.
    Mains where I am is 230V.
    Tags: None
    • redwire
      Badcaps Legend
      • Dec 2010
      • 3912
      • Canada
      #2
      Re: Power Amplifier Safety Modifications

      You already posted this on EEVBLOG, how many answers do you need?

        Comment

        • madan1
          Badcaps Veteran
          • Nov 2016
          • 691
          • Bulgaria
          #3
          Re: Power Amplifier Safety Modifications

          Brief google search got me this - max Amps = KVa / Volts x 1000

          you have 0.5/230x1000=2.17A
          If you use a fuse for each transformer, probably a 2A one will be a good choice here.

          I do not guarantee that this formula is the correct one.. just found it on the internet .

            Comment

            • budm
              Badcaps Legend
              • Feb 2010
              • 40746
              • USA
              #4
              Re: Power Amplifier Safety Modifications

              TOROIDAL transformer by itself has very large inrush current so by the time its outputs are connected to rectifiers and filter cap, the inrush curent will have to be figure out to be able to use proper type and size of the fuse.
              Just do the search on TOROIDAL transformer and inrush current associate with it.
              It should have softstart circuit.
              Never stop learning
              Basic LCD TV and Monitor troubleshooting guides.
              http://www.badcaps.net/forum/showthr...956#post305956

              Voltage Regulator (LDO) testing:
              http://www.badcaps.net/forum/showthr...999#post300999

              Inverter testing using old CFL:
              http://www.badcaps.net/forum/showthr...er+testing+cfl

              Tear down pictures : Hit the ">" Show Albums and stories" on the left side
              http://s807.photobucket.com/user/budm/library/

              TV Factory reset codes listing:
              http://www.badcaps.net/forum/showthread.php?t=24809

                Comment

                • diydidi
                  Member
                  • Sep 2012
                  • 17
                  • South Africa
                  #5
                  Re: Power Amplifier Safety Modifications

                  Originally posted by redwire
                  You already posted this on EEVBLOG, how many answers do you need?
                  As many as I can get until I find the right answer.
                  I don't want the guy's house burning down.
                  End of my bussiness and hefty fine etc...
                  Thanks for your reply.

                    Comment

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