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Ac-dc adapters in series (or parallel)

  1. Nov 19, 2016 #1
    multiple 220V to 5v, 2A ac to dc adapters connected to the same 2-phase input terminals
    input voltage is 220v domestic supply.
    is it safe to i join output in series to obtain 10v /15v/25v etc. ?
     
  2. jcsd
  3. Nov 19, 2016 #2

    berkeman

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    Staff: Mentor

    Do you mean just stack the output DC voltages? Sure.

    What is the application? Can you Upload a sketch of what you want to do?
     
  4. Nov 19, 2016 #3
    get 10 v power supply
     
  5. Nov 19, 2016 #4

    berkeman

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    Why can't you find the right power adapter to get you the right output voltage and power?
     
  6. Nov 19, 2016 #5

    davenn

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    Science Advisor
    Gold Member



    I really cant understand why people want to do things the hard way ??
    get a 12V 2A plugpack and use either boost or buck converters to get the required voltages
    The converters are dirt cheap on eBay a few $$ each

    here's one ideal for your needs, for US$1.52, cheaper than a bunch of plugpacks in series

    http://www.ebay.com/itm/DC-DC-Boost...864741?hash=item258c7e1b65:g:K-IAAOSwkl5XdjBM


    Dave
     
  7. Nov 20, 2016 #6

    NascentOxygen

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    Most DC adapters incorporate filtering and deliver relatively smooth DC, but some do not have filtering—their output being rectified AC. It seems that you recognize there may be cases where you need to ensure the supply to all primaries is of identical phase, e.g., in the case of unfiltered output I mention.

    It can be safe, but only up to a point. If you keep to under 25V total then it should be okay. There's real danger of exceeding the pack's insulation rating if you try to stack these to get e.g., hundreds of volts out.
     
  8. Dec 21, 2016 #7
    cause ive a bunch of 5v , 2amp adapters lying around
    could they be stacked in parallel to get 5v, 4amps out of identical (same product) (5v , 2amp max ) adapters?
    and will it be safe if different product , same ratings (5v , 2amp max )plupacks are used in parallel?
     
  9. Dec 21, 2016 #8

    NascentOxygen

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    It is certainly not recommended. And I would not power any device of value, not until the arrangement has been well-tested.

    I think you should first plot Vo vs. Io over the full load range for the individual adapters. Then only parallel those having almost identical characteristics. You have plenty of the same model, so you should be able to find a couple that are very similar.

    Power the parallel pair briefly to start with, then for increasingly longer periods, monitoring the case temperature. If there is any more heat than expected, discontinue the experiment. Test over the full range of loads, before trusting it to power any device that you value.

    I'm assuming these are adapters incorporating transformer isolation and that include smoothing so that they output essentially smooth DC.

    https://www.physicsforums.com/attachments/110502.gif
     
  10. Dec 21, 2016 #9
    are there any 5v adapters of higher amp rating(higher than 2amp)?
     
  11. Dec 21, 2016 #10
    How about a google search for "5v 3a adapter"? You could find the answer yourself in mere seconds.

    Your question seems to be wandering all over the place. Are you falling into an xy problem? (Google it.) What is it you want to do?
     
  12. Dec 21, 2016 #11
    got this 5v 4 amp ebay
     
  13. Dec 21, 2016 #12

    jim mcnamara

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    What the others are saying is: instead of proposing solutions, tell us what you need. For example, you could say 'I need to power an XX at 5v 3amps, I have 3 converters'

    That is a so-called XY issue - confusing proposed solutions with the real problem.
     
  14. Dec 21, 2016 #13

    berkeman

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    Paralleling voltage sources is generally problematical. If they are simple transformer+rectifier+linear regulator type of power supplies, you may have a better chance of combining them in parallel.

    But if they are the smaller, lighter switching power supply type of regulators, then putting their outputs in parallel can cause regulator stability issues. The individual control loops for each switching regulator can cause interference problems with the other regulator, and you can get oscillations and even output over-voltages. That can let the smoke out of the device you are trying to power.

    As others are suggesting, just get a power supply of the correct size for your project -- that will work much better, and hopefully let you keep the smoke inside of your device. :smile:
     
  15. Dec 27, 2016 #14
    in series should I have a reverse diode across each supply output to prevent back-driving on overload ?
    if the load fails (short circuit or over-current), one of the supplies gives up before the other, then
    one supply back-drives the other as with cells in a battery, or cells in a PV-panel.
     
  16. Dec 28, 2016 #15

    NascentOxygen

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    If you are likely to be connecting the arrangement into an even higher voltage source load, then one diode in series with the output should suffice.

    In a parallelling configuration a series diode at the output of each would protect against possible damage were a source to not be powered on when the others are, but a diode here is going to lose you some of the +5V and this may be an issue.
     
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