Can I connect 2 transformers to the same mains outlet

Discussion in 'General Electronics Chat' started by iinself, Feb 13, 2015.

  1. iinself

    Thread Starter Member

    Jan 18, 2013
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    Hi,
    can I connect the primaries of 2 transformers to the same main outlet as shown in figure?

    Thanks
     
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    yes, don't forget to fuse the input line.
     
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  3. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Yes, Ideally separately fused and not exceed 1800Va total.
    Max.
     
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    It depends what the ratings are for your outlet and transformers. The transformers must not draw more current than the maximum the outlet can safely provide.
     
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  5. cmartinez

    AAC Fanatic!

    Jan 17, 2007
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    Yes you can... just make sure to verify with a voltmeter that the polarity of each transformer is as shown in your figure.
     
  6. iinself

    Thread Starter Member

    Jan 18, 2013
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    Forgot to add, the transformers are rated for 3A each.
     
  7. cmartinez

    AAC Fanatic!

    Jan 17, 2007
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    Also, you can add transformers in parallel in case you need more current
     
  8. crutschow

    Expert

    Mar 14, 2008
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    Only if they are identical transformers.
     
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  9. cmartinez

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    Jan 17, 2007
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    :eek: A very important detail that I forgot to mention... thanks for clarifying...
     
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
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    And phased right!
    Max.
     
  11. iinself

    Thread Starter Member

    Jan 18, 2013
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    I am bit confused - isn't the way I have added them in parallel? Do you mean the secondaries can be connected in parallel? In the figure above the secondaries on are series, right?
     
  12. iinself

    Thread Starter Member

    Jan 18, 2013
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    Ok, thanks.

    One more question, can I add 2 primaries in series with ratings of 110/40V and 110/12.5 to reduce the voltage coming out of the 110/40V transformer? I will be using only the output from the 40V secondary.
     
  13. cmartinez

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    Jan 17, 2007
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    Yes, in your figure the secondaries are in series. AND if you need more current, you can add parallel transformers to that array. Under the condition that they're identical and phased right, as has been already stated.
     
  14. cmartinez

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    Jan 17, 2007
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    What's the output voltage that you'd like to obtain ?
     
  15. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Your diagram shows the DC in series, if you connect the secondaries (AC) in parallel or series , you will have to phase them correctly.
    Not necessary when connecting series or parallel on the DC side.
    Max.
     
  16. iinself

    Thread Starter Member

    Jan 18, 2013
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    I would like to reduce to about 28V on the secondary.
     
  17. iinself

    Thread Starter Member

    Jan 18, 2013
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    Would this eliminate the need for 2 rectifiers, since the secondaries are center tapped, I could create a virtual ground on the dc side.
     
  18. MaxHeadRoom

    Expert

    Jul 18, 2013
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    You will need to series up one half of one secondary and wire it in series with the other 12.5 to get close to the 28vdc.
    Wire them up in SERIES and measure the voltage, if less that 12.5v, swap one pair, then connect to a Bridge rectifier and the caps.
    It should result in around 26-28v.
    Presuming you want a single supply?
    Max.
     
  19. iinself

    Thread Starter Member

    Jan 18, 2013
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    The primaries are in parallel and the secondaries are in series but we use only half of one secondary.

    So we get 12.5V + 6.25V = 18.75V ac.

    DC = 18.75 * 1.41 = 26.5V

    In this case does it matter if the transformers are not identical?

    Thanks
     
  20. MaxHeadRoom

    Expert

    Jul 18, 2013
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    No, just that the Va rating applies to the lower rated one.
    Max.
     
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