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when can power supplies be connected in series, and when can they not?

Discussion in 'Electronic Basics' started by Michael Noone, Mar 29, 2005.

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  1. Hi - I remember hearing that some DC power supplies cannot be connected in
    series, while others can. Can anybody tell me what
    features/specifications/etc. to look for in a power supply that can be
    connected in series with other power supplies? Thanks!

    -Micahel Noone
     
  2. John Fields

    John Fields Guest

     
  3. Chris

    Chris Guest


    Hi, Michael. In addition to Mr. Fields' note, both power supplies
    should be capable of carrying the current requirement of the load. For
    instance, if PS 1 is 5V @ 3A, and PS2 is 5V @ 1A, you'll get 10V if you
    put them in series, but you can't draw more than 1 amp from your 10V
    supply.

    If you're dealing with high voltage, you also have to look at the hipot
    between the transformer primary and secondary, and the hipot between
    the secondary and the chassis, if that's at another potential.

    If your power supplies are regulated, the combined supply will have
    different (and usually somewhat worse) specifications for load
    transient response. That's because the output capacitors of the
    supplies are in series, too. Also take a look at load regulation.
    It's best to do some experimentation if these are critical.

    Good luck
    Chris
     
  4. mike

    mike Guest

    You can hook power supplies in series if they're designed to be hooked
    in series.
    Make sure the outputs are designed to float as far as they will in series.
    Make sure they can withstand reverse current, negative voltage at rated
    current.

    Sounds like any old supply will do as long as the load is happy.
    But what happens when you short the output. One will limit first and be
    ripped negative by the other one. I've seen power supplies, even with
    reverse protection diodes, latch up when the output was pulled negative.
    You can get some interesting turn-on transients, especially if you have
    to throw two switches.
    Some VERY interesting things can happen when the supplies have foldback
    current limiting.
    If your supplies are mismatched, your problems multiply. You really
    don't want your 40A supply trying to reverse your 4A supply.

    Safest is to tell the vendor what you intend to do and get their blessing.
    mike

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  5. This would be batteries I presume. What power supplies does now have
    floating outputs?


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  6. John Fields

    John Fields Guest

     
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