Connect with us

Homebrew Transformer

Discussion in 'Electronic Basics' started by Jamie, Jun 13, 2006.

Scroll to continue with content
  1. Jamie

    Jamie Guest

    Hello! I'd like to try building a step-down power transformer from
    scratch. Can anyone recommend any how-to sites? Googling didn't turn up
    anything useful, maybe I was using a bad search string.

    If you don't know of any sites, is it easy to build a step down
    transformer? I'm uncertain about what would be a decent easy-to-find
    material for the core. I'd like to try building one that steps down 120
    volts to 15 volts.

    From what I've read, the primary winding should have 6-8 turns per
    volt, so I would want 960 turns on my primary, and 64 turns on my
    secondary winding.


    - Jamie

    The Moon is Waning Gibbous (98% of Full)
  2. Far more common when someone needs a custom transformer, is to
    find one that's the same sort of specs, take it apart, and rewind it.
    That gives you the core material and the rest. There have been plenty
    of articles on such things in hobby magazines over the years.

    At the very least, if you want to build a transformer, you ought
    to take a commercial one apart to see what's involved.

  3. Don Taylor

    Don Taylor Guest

    How about buying a spool of iron wire? Preferably insulated in some way.
    Then you form the wire into a coil, looking something like an overgrown
    toroid core. Bare the two ends of the iron wire and bond them together,
    solder would probably do. Then wrap your windings around that. Putting
    your winding wire onto a spool that you can easily move around and around
    the core as you unspool it onto the core will probably be necessary.

    The insulation on the iron wire is to reduce "eddy current" losses.
    I vaguely remember guidelines like that.
  4. Phil Allison

    Phil Allison Guest

    "Don Taylor"

    * WARNING !!

    This is a completely insane idea.

    FORGET IT !!

    ........ Phil
  5. Pooh Bear

    Pooh Bear Guest

    Winding transformers is a bit of a 'black art' or indeed 'black science' perhaps
    and it's certainly not as simple as you seem to think. . On account of the
    safety implications I have to discourage you from doing this until you
    understand the safety principles used in winding them.

    It used to be possible to get 'transformer kits' that had prewound primaries

  6. Pooh Bear

    Pooh Bear Guest

    You're an idiot who's seriously dangerous.

  7. Guest

    Ive seen "cores" made using insulation hangers.....small "sticks" of
    iron used to push up against insulation between floor joists to hold
    the insulation can lightly spray them with laquer to insulate
    the rods from each other before making a bundle....

    Ive also heard you can make your own "E" and "I" laminations from
    ordinary sheet metal....take the sheetmetal and burn it in a
    fire.....cut the laminations from that....the burning supposedly does
    something to the metal ...makes it perform better.....not as good as
    silicon steel but better than just ordinary unburned steel.

    There should be some resources on the net concerning homebrew power least there used to be in the late 90s early

    used to be a whole "book" online about it.
  8. Bob Eld

    Bob Eld Guest

    The easiest thing to use for the core are E-I laminations which are readily
    available. You can even take apart an old transformer and re-use the core.
    The size of the core depends on the power required and there are many rules
    and guidlines on this depending on core loss, heating, leakage flux, noise
    and other issues. If you start with a scrap transformer of known wattage,
    use it as a guide.

    There is NO SUCH RULE that a primary should have 6-8 turns per volt. The
    primary windings should based on Faraday's law and is dependant on the
    operating voltage, the desired flux density (Bm) and the core area (Ae). The
    equation is: Np = Vrms * sqr2 * 10^8 / (2*Pi*f*Ae*Bm) where Np = number of
    turns, Vrms = primary AC voltage (rms), f = minimum frequency (Hz), Ae =
    effective core area (cm^2), and Bm = maximum flux density (gauss).

    Typical small transformers should operate at between 10Kgauss and 15Kgauss
    using standard silicon steel transformer laminations.
  9. Phil Allison

    Phil Allison Guest

    "Bob Eld"

    ** Errr - there is, actually.

    The rule is for common magnetic steel laminations ( not GOSS), for 50 Hz
    operation and for a 1 square inch cross section. It is understood that the
    number of turns varies in *inverse proportion* to the core's cross

    For a GOSS toroidal core, the number can be reduced to 4.5 to 5 turns per
    volt per square inch.

    The rule is based on standard commercial practice and typical *off load* I
    mag figures.

    Even lower numbers apply when the transformer will always be operated under
    full load.

    ........ Phil
  10. Don Taylor

    Don Taylor Guest

    Why? It sounds like the kid wants to try building a transformer.

    He clearly didn't say "I want to buy a transformer"
    He clearly didn't say "I want to use the parts from a transformer"

    Sounds like he wants to build a transformer.
    People have done stranger things.

    Way back in high school we cut up a pile of coat hangers to get the
    iron. We taped them into a thick bundle, put a few thousand turns
    of wire around them and made ourselves an induction coil.

    You would put a heavy copper ring over the end of it, plug the coil
    into the wall for a second, and shoot the ring to make dents in the
    ceiling tile.

    The only insane thing was I decided to hold the ring in place and
    told them to plug it in. A little surprisingly, I was able to hold
    the ring in place. More surprisingly, it suddenly became REALLY
    hot and I was left with two burns on the ends of my thumb and finger,
    before I yelled and let go of it to fly towards the ceiling. I didn't
    try that again. But I did learn about induction heating that way.
  11. Bob Eld

    Bob Eld Guest

    I guess if you want to be sloppy about it and not calculate anything then
    you can use one of these rules. Five turns per volt on a 1sq inch core at
    90% stacking would give a flux density of 15.5kGauss at 50 Hz. That's ok for
    many applications but a bit high for low noise applications such as audio
    preamps. If you want to know what your transformer or any circuit for that
    matter is predicted to do you calculate the values, you don't pull them out
    of your ass (arse).
  12. Phil Allison

    Phil Allison Guest

    "Don Taylor"

    ** Because it is VERY STUPID and VERY DANGEROUS !!!

    The OP wants a transformer to use on the AC Supply.

    THAT means DANGEROUSLY high energy and FATAL electrocution risks are

    YOU have no comprehension of these matters, at all.

    F U C K O F F - B L O O D Y I D I O T !!!

    ........ Phil
  13. Phil Allison

    Phil Allison Guest

    "Bob Eld"

    ** The rules are based on careful calculations & actual commercial

    The "sloppy" one is you - Mr arrogant asshole.

    ** Massive red herring - Mr arrogant asshole.

    It is BLINDINGLY obvious that by using MORE than 5 turns per volt per sq
    inch one can reduce I mag to any desired level below that of a typical mains

    ** Crapology.

    Most folk buy ready make transformers and use them as is or adapt them to
    their needs.

    ** **** off - YOU ARROGANT FOOL.

    ......... Phil
  14. Don Taylor

    Don Taylor Guest

    Well then I guess I have to apologize. You see I was born,
    raised and trained in a different century, I guess back
    before all this stuff became so VERY DANGEROUS!!!

    I do wonder now and then how some of those around me stayed
    alive long enough to procreate with all the terrors in the

    I would say to you what I once said to a manager,
    but I'll let it go.

    But I would caution you, do you realize how deadly
    soldering irons and automobiles are? I'd recommend you
    staying at least 1000 meters away from any of those.
  15. Phil Allison

    Phil Allison Guest

    "Don Taylor"



    MAYBE YOU ................

    ........ Phil
  16. Maybe they should just pack Phalluson in bubble-wrap and stick
    him back inside his Mom's womb.


  17. Why? So he can be aborted a second time?

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
  18. Phil Allison

    Phil Allison Guest

    "Don Taylor"



    MAYBE YOU ................

    ........ Phil
  19. Guest

    Kits are readily available.

    Type these 2 words into Google:-

    Transformer kit

    RS components in the UK sell transformer kits

    They show a 100 VA E + I kit for £31.95 UK

    Maplin (UK) sell an E + I kit for £16.66 UK price, delivery extra, no
    mention of frequency.

    A US firm called Toroid Corporation of Maryland sell kits 80VA = $30,
    1400VA $106. "Made for 60 Hz" it says.

  20. Guest

    The easiest thing to use for the core are E-I laminations which are readily
    I tried this formula with some approximations:

    Np = Vrms * sqr2 * 10^8 / (2*Pi*f*Ae*Bm)

    Vrms = 230
    sqr2 = 1.41 ..?
    f = 50
    Ae = 1 cm^2
    Bm = 10000 Gauss (Get a feeling this value is wrong)

    Np = 230 * 1.41 * 10^8 / (2* 3.14* 50* 1* 10000) = 10328 turns


    44 turns/volts seems a lot..

    For mains transformers I prefer to buy. But for signal or small dc/dc it might
    be useful.
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day