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Building a transformer

SethG

Hi all
I read Kkazem blog regarding: "Basics of Transformer Design" but still got some unanswered questions ...

given:

  Primary: 10V, 10mA, 50Hz

  Secondary: 5V, 20mA, 50Hz

(Iron Core)

So it's pretty obvious that I need a 2:1 step-down transformer. I'll use copper wire, but what diameter and how many windings shall I choose?
Given the low current I'd expect an diameter of around 0.2 mm² to be sufficient - no ? Also 50hz is kinda low-frequency.
And the receiving signal doesn't need to be "good" as it gets rectified afterwards.
But how do choose the amount of windings ? 200:100 gives me the same ratio as 2000:1000 or 762:381 ...

  • 0


    Is this a real use-case, or a homework type question?

    If real scenario, could you describe it? Because what youre asking for might not be the best option. I'm asking because I'm struggling to think of a scenario where 5V 20mA 50Hz could be required using such a method. Your comment about 'receiving signal' just makes me question it more, so you may as well tell the actual purpose, to make it easier to help you.

    If homework, you might be expected to be using a textbook and show some working out. The blog you mention already contains a formula with regards to your question about how many windings, but I don't think just using that replaces whatever the aim of the question was (if it was a homework type question).

  • 0 in reply to shabaz

    Hi shabaz

    No, I can assure you this is not a "homework" question (I left school 20years ago ;) )

    When I said "the receiving signal doesn't need to look good" I was referring to the sine wave.
    Basically I'm powering an simple LED on the secondary side which also acts like a half-wave rectifier. At 50hz it will "give you the illusion" it's permanently on.

    The whole thing is more a demo to show how a transformer work. Usually your school-textbooks will simply state: 2 coils combined with an iron core ...
    But gives you (very) little clues on "how to design" such a device. What coil diameter to use and how many windings to use and why/when ...

    I'm not trying to reinvent the wheel here, but to understand how certain statements/conclusions were/are made. And whether they're right or wrong. 

    I was asking a physics-teacher the other day and he simply replied: If you don't have a "special application" and the signal shape doesn't matter you may choose anything you like ... (regarding windings, materials, diameter ...) 
    But that's not a satisfying answer to me. I can't picture some engineers just sitting in their labs suggesting designs for a new prototype over their coffee grounds! (... or do they ??)