Hacked Power Supply.

Discussion in 'The Projects Forum' started by hashmaster, Dec 23, 2012.

  1. hashmaster

    Thread Starter Member

    May 30, 2012
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    So I've Hacked apart my old surround system, and decided to keep all the internals. One of the internal parts I was rather eager to keep was the power supply. On this power supply there is a multitude of power options, The area labeled 1 on the picture is my main area of interest. It has -27v,Gnd,+27v. The area labeled 2 has appers to have ON/OFF,5v,gnd. And the area labeled 3 has +5v,gnd,+12v,gnd,-27v,gnd,ac1,ac2. What i would like to do is change the -27, gnd, +27 into a variable output from 0-50+v, and keep the +5v,gnd,+12v,gnd, and try to turn the other -27v into a negative variable power source. I dont know what the ac1, and ac2 lines are for, or what they put out. Now into the questions. Is my current theory sound? Will i be able to convert the -27v, and the +27v for a 54v output? And if so what voltage regulator would be the best? or how can i figure out what one to use? What are the ac1, and ac2 lines for? And would i be able to use them in the final power supply? Please ask me any questions for any info i may have forgotten to include, or to help answer any of the questions that i may have asked.
     
  2. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    The "AC" lines are probably the input power from the standard wall voltage. It has to run on something.
     
  3. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    Not likely. It looks like an offline flyback or half bridge converter so you would have to change the switching transformer ratio to get 54V instead of +/-27V. You would also need to change the resistors that set the voltage, output caps and compensation networks.
     
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  4. hashmaster

    Thread Starter Member

    May 30, 2012
    42
    0
    The ac input is on the left side of the picture. Its a 2 prong spaded cord that clips into a 2 pin connector.
     
  5. hashmaster

    Thread Starter Member

    May 30, 2012
    42
    0
    Don't know what an offline flyback converter is,will have to look that up later. I guess my next question is since I don't think I'll be using to many voltages above 25 v should I just use two adjustable regulators on the +/-27v lines and have an adjustable -27, and +27 outputs?
     
  6. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    Without knowing the schematic, it's hard to recommend a design. The easiest way is to adjust the switcher voltage itself, not hang another regulator downstream.
     
  7. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,969
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    What is the chip number, (thats the 16pin device)?

    Also what is on the silver heatsink on the right, may be diodes, to reverse the supplies output it a matter of reversing the diodes and capacitors on the output side ,

    BUT this may interrupt the feedback path for the ic, so its essential that you reverse engineer the output circuit, I have had several years of experience of designing SMPS,
     
    Last edited: Dec 24, 2012
  8. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    I would argue that Bountyhunter. The OP said the PSu was from a surround sound system so I would expect the +27 and -27v to be two high power rails that will work together referenced to a ground.

    It should work straight away as a 54v DC supply, provided the old "ground" is not connected or used, likewise the other rails can't be used as they are referenced to the original "ground".

    It's unlikely to be usable as an adjustable supply through a large range like that as the components and magnetics etc are all chosen for a fixed voltage output. It would be easier to use it as a 54v DC supply and add a separate buck converter to give the 0-50v adjustability.
     
  9. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    Without a schematic, I have no idea what it is. If it's from a surround amp, it's likely those +/-27V rails are pretty weak as far as continuous power since audio amps are usually not designed for high sustained power, but high peak currents.

    Like I said, without a schematic I have no idea what, if anything, it would be good for.
     
  10. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    It looks like a decent sized (wattage) PSU. Maybe >200W based on the size of parts?

    Based on surround amps with normal linear PSUs the +/-27v rails would be good for >3/4 of the total PSU output.

    I would take a guesstimate that the +/-27v rails on that are going to be good for >3A and maybe 5 amps or more.
     
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