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Feeding a SMPS from 2 different power sources

Discussion in 'General Electronics Discussion' started by Vindhyachal Takniki, May 18, 2015.

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  1. Vindhyachal Takniki

    Vindhyachal Takniki

    Apr 29, 2015
    This post is in continuation of post below: (starting a separate thread as suggested)

    1. I have two ac sources, 220V ac 50 Hz(from mains & generator) & have to run a circuit from it for which I need dc supply.
    There is SMPS in the circuit which I didn't shown. It makes 12Vdc.

    2. I had connected a bridge rectifier to each source. After that each output is shorted.

    3. There may be three cases: Only main available, only generator available, or both are available.

    4. I think problem may arrive when both ac sources are available.
    Also it could be one may be at different angle then other. Like if first ac source have crest, other couls have trough or at some phase from each other.

    5. I have tested the circuit by connecting two 220V ac source from plug. basically its a short i.e phase1 of ckt is connected to phase 2 & similarly neutral.
    However in this circuit both phase & amplitude is same.
    But in real circuit, there will be different phase generator & main voltage. I don't know how this circuit will behave then.
  2. ramussons


    Jun 10, 2014
    A SMPS unit has a EMI Suppression Filter followed by a Rectifiers to get a DC. It is this DC voltage that is switched ........ etc. A typical input schematic is attached.

    ATX.jpg If the issue is choosing between the Mains and the E/A, a simple 2 Pole 2 Way switch (or relay) does the job.

    But if you intend to feed the SMPS from more than 1 Independent AC source, then the issues of Frequency, Phase and Ground/Return/Earth comes into picture.

    In this case, it will be necessary to Combine the Sources at the DC across C5 and C6. A similar setup will need to be constructed for getting the DC.

    If the E/A and the Mains DO NOT SHARE share a common Neutral, I would use Isolation Transformers too.
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