G8MNY  > TECH     28.02.21 09:00z 54 Lines 2624 Bytes #153 (0) @ WW
BID : 25210_GB7CIP
Read: GUEST
Subj: Variacs
Path: ED1ZAC<ED1ZAC<GB7CIP
Sent: 210228/0849Z @:GB7CIP.#32.GBR.EURO #:25210 [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
Lo-oo__||)<ooL   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
No__||)______N   you can easily cook the winding as the core can put
        0               out huge currents. So an input & output fuse is needed
EoE   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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