Redundant Power Supplies

Discussion in 'General Electronics Chat' started by savage, Mar 6, 2012.

  1. savage

    Thread Starter New Member

    Sep 9, 2010
    2
    0
    Hi All,

    Just have a quick question... Would something like this work, real-world wise?

    Supply 1 220VAC -> TRANSFORMER -> BRIDGE RECTIFIER -> OUTPUT
    Supply 2 220VAC -> TRANSFORMER -> BRIDGE RECTIFIER -> OUTPUT

    If Supply 1 and Supply 2 are COMPLETELY independent (different Live, Neutral, and Earth supplied from separate Earth Leakage Units) - can I combine the output of both supplies provided that the transformers and the like are equal?

    I want to basically take 220VAC down to about 30VDC, but the 30VDC is very important, and don't want to risk power going out. Thus, two completely separate supplies...

    Is it as simple as that? Or am I missing something?

    From what I can see, the two 220VAC supplies are isolated from each other by using two different transformers, so I -think- I should be safe to do this, but I would appreciate some confirmation from the better experienced crowd out there :)

    Many thanks,
    Chris.
     
  2. crutschow

    Expert

    Mar 14, 2008
    13,021
    3,235
    I don't see any problem as long as you are not trying to draw more current then either one can supply by itself.

    At what point in the circuit are you planning on connecting them in parallel?
     
  3. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    Bridge rectifiers contain diodes so DC supplies with simple bridge rectifiers can be safely paralleled.

    However there is no guaratee they will share the current equally, in most cases the inbalance will be bad, so one supply will supply most (or all) of the load current. That is why Crutschow said to make sure you don't draw more current than one supply itself can handle. (I hope you don't mind me re-stating your point in different words Crutschow). :)
     
  4. savage

    Thread Starter New Member

    Sep 9, 2010
    2
    0
    Hi,

    Thanks for the responses and clarifications. Outputs will be combined after the bridge rectifiers, and will feed through LM7805 and LM7830 1A regulators there after. So not much power needed at all, even though I'm making sure there is enough (two transformers rated 2.5A at 36V ea.)

    Not really too concerned about the fact that the inputs more than likely won't be balanced in terms of power usage. I'm more after the high availability here than consumption...

    Again, many thanks :) Now I can move on....

    --
    Chris
     
  5. MrChips

    Moderator

    Oct 2, 2009
    12,446
    3,362
    Bridging the supplies before the regulators will be fine. If you bridge after the regulators you can almost guarantee that one of the regulators will be running flat out.
     
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