magnetic wire guage ratio between primary and seconday windings

Discussion in 'General Electronics Chat' started by adeel, Jun 28, 2008.

  1. adeel

    Thread Starter Member

    Jun 28, 2008
    hi ,
    Friends i need ur help i want to build a transformer to step down voltage i have 1.5*2 (inch) core and i want to make 25 amp 12 volts transformer but i am surprised i have no guage ratios i have turn ratio formula but not the guage ratio. Description is here
    220 volts for primary 50/60 hz
    12 volts for seconday
    if u know guage ratio for primary and secondary (like 22 or 12) please give me the formula thanks .
  2. bertus


    Apr 5, 2008
  3. The Electrician

    AAC Fanatic!

    Oct 9, 2007
    A good working rule of thumb is to make the current density in each winding the same.

    In other words, the current divided by the cross sectional area of the winding should be the same for both the primary and the secondary. You will have to select primary and secondary wire gauges such that the winding window is as full as possible while maintaining equal current density in the two windings.
  4. beenthere

    Retired Moderator

    Apr 20, 2004
    Transformer voltage ratios go by turns in primary/turns in secondary. The wire gauges are important, but the core structure is the determining factor in the amount of power the transformer can handle. Winding the primary and secondary with heavier gauge wire will not increase power handling.
  5. SgtWookie


    Jul 17, 2007
    Sorry to dissapoint you, but with that size of transformer core at 50/60Hz, you will be lucky to get over 2 Amperes of current at 12v. You need a much larger core, more like 5" * 6" or thereabouts (this is a "ballpark" guess.)

    The wire size is determined by the amount of current expected in the circuit.
    Here is a website that has a table of wire gauge vs current:
    You can use "chassis current" for your transformer. The smallest size you could use for a 25A secondary carrying 25 Amperes would then be AWG 15.
    Your primary side will likely have around 1.5-1.6A of current. The smallest size you could use would then be AWG 27.