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Idea for an Ultra cheap Power Supply - will this work?

Discussion in 'Power Electronics' started by royalmp2001, Apr 4, 2017.

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  1. royalmp2001


    May 20, 2014
    Hello everyone,
    I was in my local Dollar General store recently and had an idea for an ultra cheap lab power supply.

    I can buy eight 5V 1A power adapter cubes for USB devices at $1 each.

    I would mount them in a case and power them all from one mains cable going to the wall.
    All the cube's mains inputs would be wired in parallel. The outputs would all be wired in series.
    Would have to find an easy way to take positive and negative lines from each USB socket somehow.

    Then I have an 8 way rotary switch on the front panel that will tap off a feed after each power cube.

    I would mark the rotary with 5v, 10v, 15v, 20v, 25v, 30v, 35v, 40v

    Voila - a 1A power supply with switch variable output voltage from 5v to 40v - really cheap

    Would this work?.
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    In theory: yes.
    In practice: maybe.

    These cheap 'power supplies' are typically of very low quality:
    • not very precisely regulated output voltage
    • rather noisy output voltage
    • no well defined overcurrent protection
    Even a comparatively cheap 'lab supply' like this one is probably better.

    You get what you pay for. A good lab supply is not just expensive to make the producer rich (that's part of the prize ;)). A good lab supply has a well regulated ourput (stable, low noise), has adjustable voltage and current limits, short circuit protection, displays for the actually measured voltage and current etc. In the long run you'll be better off with one of those than with your makeshift setup.
    hevans1944 and davenn like this.
  3. Herschel Peeler

    Herschel Peeler

    Feb 21, 2016
    Results might vary but I tried it with some 12 V supplies I had and it works.
  4. DiffAmp


    Jan 5, 2016
    One concern is overcurrent shutdown. In an overcurrent situation one of the supplies will shut down first. That supply will then be presented with the sum of the remainder of the supplies as a reverse voltage across its output. To prevent this situation, you'll want to put a 1N4002 or similar diode back biased across the output of each supply.
    Harald Kapp likes this.
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