Transformer Question

Discussion in 'General Electronics Chat' started by vladtess, Dec 8, 2011.

  1. vladtess

    Thread Starter Member

    Jan 5, 2011
    43
    1
    Hi there! I decided to work with my 1A, 14 volt transformer's output to make sure I don't get hurt w/ transformers.

    I know that that formula where there is a relationship between the voltage in/turns and voltage out/turns around core. But the question is.. is there a minimum number of turns that must be maintained? I mean. For example if I want to make an isolation transformer, would 1 turn on pri and 1 turn on sec. be enough? I think it might just short due to low resistance.

    Any thoughts? I want to use as little magnet wire as possible.

    Thanks!!!
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    You were right; 1 turn on the primary and 1 turn on the secondary would result in nearly a dead short if you were trying to operate it from 50Hz or 60Hz.

    Transformers are a pretty complex subject. I've been in electronics for many years, and I still don't claim to know all the ins and outs (pun intended) of transformers. There are engineers who spend their lives doing nothing but figuring out the best way to make transformers. It's a pretty specialized field.

    It frequently winds up being an iterative process. You go through a whole series of calculations on desired VA, Vin, Vout, Frequency, materials to be used, core size, core losses, permeability, eddy currents, turns ratio, desired impedance at the operating frequency, wire sizes for primary, secondary, tertiary etc, windings ... lots of things to keep in mind.

    And even if you're a specialist in such things, it usually doesn't work out exactly right the first time, and you have to make adjustments.

    Here's a page for some basic "ideal" transformer calculations:
    http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/transf.html
    Keep in mind that the calculations are much simplified from what you'd need to use with real world components.

    There is an experiment in our E-book; "Build a Transformer", on this page:
    http://www.allaboutcircuits.com/vol_6/chpt_4/3.html

    It's based on information contained in Volume II, chapter 9, here:
    http://www.allaboutcircuits.com/vol_2/chpt_9/index.html

    Have a read through the chapter, and if you're up for it, get yourself some flat plates and some magnet wire, and give it a try.
     
  3. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
    507
    You have to have enough primary turns to create a proper amount of flux density in the core. It's sometimes called magnetizing inductance.
     
  4. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,170
    395
    Generally the smaller the core the greater no of turns per V. Take a one pound core, 60Hz, might use 4 turns per V,
     
  5. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    Weller Soldering guns use the "many turns to few" method to get low voltage, very high current to go through the soldering gun tip, it heats up from the massive amount of current, the "soldering tip" is just a piece of copper. I'm unsure how many amps those put through the tip, but I wouldn't doubt high double digits.
     
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