transformer question

Discussion in 'General Electronics Chat' started by jonisonvespa, Aug 9, 2012.

  1. jonisonvespa

    Thread Starter Member

    Mar 25, 2012
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    hi,
    could someone please help me with a transformer question, ive got a transformer
    output windings are, 2 * 5v each winding rated @ 3kv, how do i work out the max current i can draw from it, im going to be using them in series.
    thank you
     
  2. #12

    Expert

    Nov 30, 2010
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    The 3kv means nothing about the output ability. Trying to find the current of a transformer without a label is almost impossible. The best you can do is look it up with a part number or guess what it can do, based on how much it weighs.

    I just thought of another method. If you can give it exactly the labeled input voltage, you can load the output until the voltage drops to 5.00 volts RMS.

    What? No label? Still stuck!
     
    PackratKing likes this.
  3. ifixit

    Distinguished Member

    Nov 20, 2008
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    108
    Did you mean 3kw (3 killowatt) per winding?

    If so, then you could run a maximum of 600 Amps (3kw/5vrms) through each winding. Connected in series, that would be 600A X 10V = 6000 Watts. That's a BIG transformer!

    Can you post a picture of it?

    Regards,
    Ifixit
     
  4. jonisonvespa

    Thread Starter Member

    Mar 25, 2012
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  5. #12

    Expert

    Nov 30, 2010
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    3VA means "volt-amps" (which is a lot like watts).

    So...if the volts are 5, the amps are .6
     
  6. jonisonvespa

    Thread Starter Member

    Mar 25, 2012
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    0

    hay thanks

    is that .6a total when the two 5v windings are in series, ie 10v

    and each winding 0.3a on their own?

    thanks
     
  7. #12

    Expert

    Nov 30, 2010
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    Slap forehead...think....two 5v windings in series makes 10 volts...true.
    10 volts times .6 amps makes 3 Volt-Amps...false.
    10 volts times .3 amps PER WINDING makes 3 Volt-Amps...I don't think so.

    The problem is in the phrasing and meaning of "per winding".
    I've never seen a transformer labeled that way.
    I believe the proper answer always ends in "3 Volt-Amps" sum total for the whole transformer.

    But then, after confusing KV with VA, (read my signature line).
     
    Last edited: Aug 9, 2012
  8. jonisonvespa

    Thread Starter Member

    Mar 25, 2012
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    0
    slapped,

    ok if 1, 3va winding @ 5V =0.6A

    2 windings in series 10v total current = 0.6 + 0.6 is this correct?

    how was the 0.6a concluded can someone show me the equation please

    thank you
     
  9. #12

    Expert

    Nov 30, 2010
    16,284
    6,797
    I guess it's time to stop joking with you and get down to serious.

    If you put both the 5 volt windings in parallel, with the correct polarity to be in parallel, you could get .6 amps from them. 5Volts x .6Amps = 3Volt-Amps

    If you put the 5 volt windings in series so that the voltage adds together, you will have 10 volts (RMS).

    3VA/10Volts = .3 amps

    Then, you consider a rectifier to make some DC voltage and it changes. You can't get what you expect from a transformer when you rectify the output (most of the time). Here's a chart.
     
  10. jonisonvespa

    Thread Starter Member

    Mar 25, 2012
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    hay thanks number 12 i got it now i think, thanks for taking the time
     
  11. #12

    Expert

    Nov 30, 2010
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    2 way street.
    It's always a matter of discovering what you have to work with, and that takes time.
    Patience is required from both ends.

    adios
     
  12. ifixit

    Distinguished Member

    Nov 20, 2008
    638
    108
    Number Twelve,

    I don't think it is a 3VA transformer.

    According to the spec sheet in post #4 it is a 6VA transformer (3VA per output winding). So: 5V+5V=10V and 6VA / 10V = .6 Amp total through the two windings in series.

    Regards,
    Ifixit
     
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  13. #12

    Expert

    Nov 30, 2010
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    The first line on the page clears this up! It's a 6VA transformer.
    I wish I had noticed that he posted a datasheet :(
    instead of getting focused on the fact that transformers aren't labeled, "per winding".
    I just believed that he saw, "3VA" somewhere and assumed it was, "per winding".
    He just changed the way it was worded and got me focused on the wrong issue.

    At least he has the math now.
     
    Last edited: Aug 10, 2012
  14. vk6zgo

    Active Member

    Jul 21, 2012
    677
    85
    Yes,but also remember that 3VA per winding is 3VA/5V ,again giving 0.6A max through each winding.
    So it doesn't matter how you connect them,in every case,the max rated current for each winding is 0.6A
     
  15. #12

    Expert

    Nov 30, 2010
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    If only they were labeled, "per winding" I wouldn't have gotten it so wrong.
     
  16. jonisonvespa

    Thread Starter Member

    Mar 25, 2012
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    0
    the transformer in question, im thinking its 3va per winding is that correct?
     
    Last edited: Aug 10, 2012
  17. #12

    Expert

    Nov 30, 2010
    16,284
    6,797
    Ah! You're back!

    The transformer in question is a 6VA transformer. Each of the two output windings can deliver 3 volt-amps.

    So glad you have the opportunity to plug the numbers in and get answers for the transformer you really have. I hate it when I make a mistake like that!
     
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