Connecting a 20A variable transformer

Discussion in 'General Electronics Chat' started by Michael Cheng 1, Aug 12, 2018 at 3:51 PM.

  1. Michael Cheng 1

    Thread Starter New Member

    Mar 8, 2018
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    Hi
    I just bought a 20 amp variable transformer with 270V max and having difficulty understanding on the connection points and not much knowledge.
    I had asked many people but every single one has came with a different answer. Just want to know which lugs the LIVE and NEUTRAL in and LIVE and NEUTRAL out
    Transformer is for adjusting the voltage on a generator mainly around 200 to 270 volt.

    I have attached a photo.
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Looks to me like the output is across A to E with E being the slider and A being the 'common' end, which would be the neutral if one conductor were set up as such.
    The other supply in would be C.
    Max.
     
    Michael Cheng 1 likes this.
  3. Michael Cheng 1

    Thread Starter New Member

    Mar 8, 2018
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    Hi Max, thanks for your help, so far I have 2 others with your same connection and 5 people with other variations. Think i'll stick with yours.

    Thanks again
     
  4. BillB3857

    AAC Fanatic!

    Feb 28, 2009
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    Definitely, terminal A would normally be the common to both input and output and C would normally be the input IF (big if) the output would be ranged from 0% to 100% of the input. Many variacs are set up to provide an output range that could exceed the input voltage. Since your unit shows an INPUT of 240 volts and an output of 0-240/270 volts My thought is that your unit is one of those. If you require the 270 volt output, you would use terminal A as the neutral and terminal D as the line input. Terminal E would be the output in either case.
     
    Michael Cheng 1 likes this.
  5. Reloadron

    Distinguished Member

    Jan 15, 2015
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    I agree with Max so you can include me in that group. :)

    Ron
     
    Michael Cheng 1 likes this.
  6. Xavier Pacheco Paulino

    Member

    Oct 21, 2015
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    Agree with Max and Bill.

    [​IMG]
     
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  7. Michael Cheng 1

    Thread Starter New Member

    Mar 8, 2018
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    Thank you all guys, this forum is more like it :)
     
  8. ebp

    Well-Known Member

    Feb 8, 2018
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    If the maximum input is 240 V, use C as input if you want a maximum of 240 V output.
    It the maximum input is 240 V, you must use D as the input if you want up to 270 V output.
    If the maximum input is 270 V then you absolutely must use C as the input, otherwise you run a very real risk of saturating the core which can result in destructively high current. [EDIT - fixed the following part of this paragraph - my arithmetic was wrong] The transformer is rated for 50 Hz so at 60 Hz the voltages could be 20% higher. 270 V at D would be OK at 60 Hz, but then the max output would be almost 304 volts, which you probably don't want in any case. Generally it isn't a good idea to exceed the maximum voltage on the nameplate.

    - common and output as others have said.

    A variac should have a suitable fuse (20 A time-delay type should be OK) in the output (connection to E). The maximum current the winding (and the carbon brush) can safely be subjected to is 20 amperes (brief overcurent is OK). If you only fused the input at 20 A and set the output at half of the input voltage for example, transformer action would result in input current of 20 A when the output current was 40 A, which quickly would be destructive. I would probably put a 20 A fuse in the input circuit, too, for added protection.
     
    Last edited: Aug 12, 2018 at 6:48 PM
    Michael Cheng 1 likes this.
  9. be80be

    AAC Fanatic!

    Jul 5, 2008
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  10. Michael Cheng 1

    Thread Starter New Member

    Mar 8, 2018
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  11. Michael Cheng 1

    Thread Starter New Member

    Mar 8, 2018
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    Thanks a lot, great information
     
  12. Michael Cheng 1

    Thread Starter New Member

    Mar 8, 2018
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    Thanks a lot, great information
     
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