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Step up & Step Down of Auto Transformer

Discussion in 'Power Electronics' started by Abdul Salam, Mar 6, 2018.

  1. Abdul Salam

    Thread Starter New Member

    Jul 15, 2017
    10
    0
    Hi,
    I have an auto transformer with three winding:
    1- 0 ~ 15 for circuit power supply
    2- 0 ~ 20 for step up or step down to main winding (0-40-140-220)
    3- 0 ~ 40 ~ 140 ~ 220 main winding

    this can take input from 90 volts to 265 and produce 220 volt output.

    Problem: I do not understand how it can step up and down in mentioned range?
    I do not have electronics background, just programming!
     
    Last edited: Mar 6, 2018
  2. MrChips

    Moderator

    Oct 2, 2009
    19,132
    6,148
    And the question is?
     
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
    18,847
    5,890
    Secondary windings can be connected additive or subtractive, depending on polarity connected.
    Max.
     
  4. LesJones

    Well-Known Member

    Jan 8, 2017
    2,304
    693
    An auto transformer only has one winding but it can have a number of taps on the winding.

    Les.
     
  5. crutschow

    Expert

    Mar 14, 2008
    23,124
    6,858
    An auto transformer can step up or down depending upon the secondary tap as compared to the primary.
    As shown below, the top tap steps up the voltage and the bottom four taps step the voltage down.

    upload_2018-3-6_10-54-17.png
     
  6. dendad

    Distinguished Member

    Feb 20, 2016
    2,927
    815
    If it is actually an Auto Transformer, that is, one single multi tapped winding, be very careful how you use it as there is no mains isolation.
    You need to have an isolation transformer for safety reasons.
    Do you understand how a transformer works?
    This may help. It is just one of the first search results.
    https://www.quora.com/How-do-transformers-work
     
  7. Abdul Salam

    Thread Starter New Member

    Jul 15, 2017
    10
    0
    Thanks all of you for reply .

    There are two winding on toroidal transformer 1) is 0 - 20 Volts and 2) is 0 - 40 - 140 - 220 volts.
    these both work together to give stable output of 220 volts if input volts are in between 90 and 265 volt.

    Question is how it step down from 265 to 220 and step up for 90 input to 220 output?

    I think it is simple but not for me :)
     
  8. Ramussons

    Well-Known Member

    May 3, 2013
    794
    144
    Such transformers were / are in use to Reduce the voltage Fluctuation on TV's, Refrigerators to reduce the possibility of damage. The output Voltage was maintained around 220 +/- 10 for an input variation of 90 to 265.

    Depending on the Input Voltage, the Transformer Tappings are selected by Relays to Boost or Buck to reduce the output fluctuations.
     
  9. Abdul Salam

    Thread Starter New Member

    Jul 15, 2017
    10
    0
    That's what I do not know " how to select tappings?"
     
  10. LesJones

    Well-Known Member

    Jan 8, 2017
    2,304
    693
    With the description of the two windings on the transformer in post #7 your statement "these both work together to give stable output of 220 volts if input volts are in between 90 and 265 volt." CANNOT be correct.
    You can't supply the transformer with or get 265 volts out as the most you can achieve is 240 volts. (220 + 20 = 240 volts.)
    You could not step up 90 volts 220 volts but you could get close. If you connected the 90 volts between the 40 volt tap and the 140 volt tap for the input. Then connect one end of the 20 volt winding to the 220 volt tap (Phased so the voltages add.) and take the output from the 0 volt tap and the end of the 20 volt winding that is not connected to the 220 volt tap you would get close to 220 volts output.
    (240 x 90)/100 = 216 volts. NOTE THAT neither the neutral or the live on the output would be at the same potential the neutral or live on the input.

    Les.
     
    Abdul Salam likes this.
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