Two Wall Warts For A Dual Rail Power Suppy?

Discussion in 'General Electronics Chat' started by forumer, Oct 25, 2014.

  1. forumer

    Thread Starter New Member

    Oct 24, 2014
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    hi everyone,

    i saw some postings mentioning the use of two wall warts for a real, standard, not fake, not virtual, dual rail power supply, but without details on how to construct them, pros and cons, what to watch out, etc.. i'm very interested in building such a power supply. could knowledgeable members please post some schematics on this?

    are such postings talking about AC wall warts only? i have DC wall warts only.

    but i imagine once i understand how such power supplies can be constructed, i might be able to take the DC wall warts apart and do whatever mods necessary to them, then still come up with real dual rail power supplies.

    all comments and helps welcome, thank you!
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    With two DC wall-warts you can connect the negative of W1 to the positive of W2 to make your new '0V'. The positive of W1 then is your 'V+' rail and the negative of W2 is your 'V-' rail. I don't think you need a schematic :).
     
  3. forumer

    Thread Starter New Member

    Oct 24, 2014
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    thank you very much Alec for the very much needed help!

    so i plug both DC wall-warts into the 120v line voltage source, and do the above to their outputs, correct?

    i thought the negative output is an actual ground, a return to the actual ground of the 120v line voltage source?
    so when i connect the negative of W1 to the positive of W2, why it won't be a power ground short?

    now i realize i'm not clear on how DC wall-warts work. they have only two prongs, so there's no distinction be power and ground? what about after rectification, what becomes the negative output?

    i'm just trying to understand what i'd be doing, before i do. further explanations would certainly be appreciated!
     
  4. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    The only caveat is that they may need to be turned on and turned off at the same time. You could plug both of them into a switched plug strip...
     
    Last edited: Oct 25, 2014
  5. crutschow

    Expert

    Mar 14, 2008
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    Yes, there is no distinction between power and ground in a wall-wort. The output is completely isolated from the AC mains input and normally is not connected to the safety/earth ground.

    After rectification of the AC you have two outputs, one output positive with respect to the other (negative) output. Think of it as two-terminal battery. Since there is no distinction between the two outputs you can use either one as "ground" or common.
     
  6. forumer

    Thread Starter New Member

    Oct 24, 2014
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    thank you very much crutschow!

    that makes a lot of sense, if i choose the positive of W1 as ground, W1 would be providing for the negative rail then, instead of the positive rail, as Alec described.

    i got it now, really appreciate your help/explanation, great stuff!
     
  7. forumer

    Thread Starter New Member

    Oct 24, 2014
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    thank you for helping Mike!
    why such a caveat?
    what happens when they are not turned on/off at the same time? dangerous?

    in order to have them turned on/off at the same time, could i connect the two wall-warts in parallel and have only one plug to plug into the mains?
     
  8. MikeML

    AAC Fanatic!

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    Depends on the tolerance of the circuit being powered...
     
  9. forumer

    Thread Starter New Member

    Oct 24, 2014
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    cool Mike, i know that fact now, but don't understand why, could you expand on that?
    would plugging both wall-warts into a switched power strip have the same issue?
     
    Last edited: Oct 25, 2014
  10. forumer

    Thread Starter New Member

    Oct 24, 2014
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    oh, sorry guys, one more question...

    if i make such a power supply with say two 500mA wall-warts,
    for a classB pushpull audio output arrangement, i might get 1A at the output,
    but for anything else, say a resistor connecting across the +/-, the current capacity is still 500mA, correct?
     
  11. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    I have run into circuits that run on split supplies that get stinking hot (possible failure) if one of the two supplies is missing...
     
  12. crutschow

    Expert

    Mar 14, 2008
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    You should be able to get 1A peak push-pull output from the 500mA supply if you added a large filter capacitor. Otherwise the peak would be closer to 500mA.
     
  13. MrChips

    Moderator

    Oct 2, 2009
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    Who wants to carry around two wall warts when one will do. I prefer to source a single appropriately rated wall wart. It is not difficult to create a pseudo ground for an audio amplifier.
     
  14. forumer

    Thread Starter New Member

    Oct 24, 2014
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    thank you very much crutschow for all the great help!
     
  15. forumer

    Thread Starter New Member

    Oct 24, 2014
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    thank you Mike for the tip!
     
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