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Generic name for USA style of mains transformer?

Discussion in 'Electronic Repair' started by N_Cook, Dec 19, 2009.

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  1. N_Cook

    N_Cook Guest

    Well I only see it in USA kit. A toroid but flattened into an elipse shape
    in plan view and a coil around each straight section. The curved ends of the
    ring are exposed. Laminated core construction so easy coil winding ?
  2. N_Cook

    N_Cook Guest

    Not sure if you are referring to a 'flat pack' or a 'C' core
    transformer. The Flat pack has squared 'U' shaped laminations, so if
    you look at the core the lams are stacked [like in the common 'EI'
    tranformer with the coil on the centre leg], but the two coils are on
    the legs of the'U'.
    The C core is more like what you describe with the core curved around
    at each end and is made by winding the lamination strip around a
    rectangular form, then compressing it on each long side to bond the
    lam together, then cutting it in half midway along the 'long' side and
    polishing the cut ends. Two coils are wound in the conventional manner
    then the core halves slipped in and clamped [we used to use steel band
    wrapped around the perifery of the core]. The ends could be epoxied
    together, but that introduced a tiny air gap that affects the core
    performance. This core design came, originally, from Germany IIRC. I
    believe that the ones we were using back in the '60s came from Vacuum-
    Schmeltz [sp?]

    Neil S.

    "image" searching on
    "C core " "mains transformer"
    didn't show any like the one in front of me
    is similar but this one has a core more circular in cross-section , or maybe
    circular , under an all over moulded epoxy-like coating .
    I will take a pic tomorrow
    I can't see how the core could be moulded over the joins and then couils
    placed over, no other bracing strips around the core .
  3. **Sounds like an 'R' core tranny to me. Excellent isolation, but higher loss
    than a toroidal.
  4. **Like these?
  5. N_Cook

    N_Cook Guest

  6. Phil Allison

    Phil Allison Guest

    ** An R-core is wound with one continuous strip of steel - tapering at each
    end to get a round cross section. The two plastic bobbins are made as halves
    and glue together around each straight limb of the core.

    There are also gear like teeth on the ends of the bobbins - allowing a
    machine to spin them on the core while an operator feeds them with wire.

    Then the bobbins and wire ends are secured and an overall insulation wrap

    A steel claming frame is finally attached to allow chassis mounting.

    Clever - huh ?

    ..... Phil
  7. N_Cook

    N_Cook Guest

    Ah! its now so obvious, had me scratching my head.
    I never thought of winding the bobbins while on the core, yes clever.
    I'd worked out how fully enclosed toroidal transformers with solid cores
    were wound, a few months back, even made a sort of m/c for doing it, but
    this type had me flumoxed

    On a side matter relating perhaps to their efficiency.
    The one in front of me gives off various voltages and the associated DCs are
    marked on the overlay (no schematic available).
    All the DC voltages , amplifier but just quiescent no load, all the actual
    DC levels are about 10 percent less than the overlay marked DC. If one of
    these C or R type cores is knocked/ abused / thermal stress/vibration and
    the closure face opens up muicroscopically, could that cause a 10 percent
    drop in secondary voltages?
  8. Phil Allison

    Phil Allison Guest


    ** Nope.

    Look elsewhere for the explanation.

    ..... Phil
  9. Phil Allison

    Phil Allison Guest


    ** What " iron powder " ?

    Wot an annoying bloody imbecile.

    ..... Phil
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