• Variacs

    From G8MNY@21:5/101 to TECH on Fri Aug 2 11:00:01 2019
    R:190802/0948Z 34397@N3HYM.MD.USA.NOAM BPQ6.0.18
    R:190802/0954Z @:GB7CIP.#32.GBR.EURO #:14492 [Caterham Surrey GBR]

    From: G8MNY@GB7CIP.#32.GBR.EURO
    To : TECH@WW

    By G8MNY (New Dec 07)
    (8 Bit ASCII graphics use code page 437 or 850, Terminal Font)

    Varaic is a traded name of The General Radio Co. for a variable tapped toroid mains auto transformer (non isolating) usually with up to 17% overvoltage.

    260o__ Ratings are normally in amps. But this can be
    240o__||) fuse confusing as the laminate core will have a power L─o-o────o__||)<─o─o─L rating as a 50% step down auto transformer which is
    fuse 220 ||) when the core has the maximum work to do of half the
    ||) output rating, as half the output current flows
    INPUT ||) OUTPUT through the top section & half comes up from the
    -10o__||) lower. However using a few % from the top or bottom N────────o__||)______N you can easily cook the winding as the core can put
    0 │ out huge currents. So an input & output fuse is needed E────────o───┴───────E to protect it! e.g. 250VA one needs a 1.5A slow blow
    mains fuse & a 3A fast blow on the output should do.

    Wiper _ Turns
    ▄▄▄======│ │ Bared _.·┬┬┬·._
    ┌---------------------┐ .·~ /~\ ~·.
    │▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓│ .' \ │ █ │ / '.
    │▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓│ / .·' │ │ '·. \
    │▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓│One layer ▐ . │ │ . ▌
    │▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓│of winding ▌___ / \ ___▐
    │▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓│ ▐───: │ 0 │ :───▌
    │▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓│ ▌~~~ \ / ~~~▐
    │▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓│ ▐ ' ~---~ ' ▌
    │▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓│ \ '·. .·' /
    │▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓│ '. / ' ··· ' \ .'
    ~~~~~~~~~│ │~~~~~~~~~ '·._ │││ _.·'
    │ │Shaft ~~┴┴┴~~
    └─┘for
    knob

    Bad arcing can damage the brush & windings. Do check the brush & spring out if you have arcing. Insulation damage can cause fires as a shorted turn has almost infinite current available.

    With toroidals the winding are exposed on the outside & variacs even more so if the bare windings are not fully encased,


    See my buls on "Constant Voltage Transformers", "Maplin Mains Meter 2000MU-UK", "Portable Appliance Testing" & also "Mains Power Protection".


    Why Don't U send an interesting bul?

    73 de John G8MNY @ GB7CIP


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    * Origin: HAMRADIO telnet lu9dce.dynu.com (21:5/101)