G8MNY  > TECH     28.06.25 09:00z 55 Lines 2655 Bytes #196 (0) @ WW
BID : 35644_GB7CIP
Read: GUEST
Subj: Variacs
Path: ED1ZAC<ED1ZAC<GB7CIP
Sent: 250628/0853Z @:GB7CIP.#32.GBR.EURO #:35644 [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
LÄo-oÄÄÄÄo__||)<ÄoÄoÄL   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
NÄÄÄÄÄÄÄÄo__||)______N   you can easily cook the winding as the core can put
        0    ³           out huge currents. So an input & output fuse is needed
EÄÄÄÄÄÄÄÄoÄÄÄÁÄÄÄÄÄÄÄE   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
          ÜÜÜ======³ ³    Bared                    _.úÂÂÂú._
         Ú---------------------¿                .ú~   /~\   ~ú.
         ³²²²²²²²²²²²²²²²²²²²²²³              .' \   ³ Û ³   / '.
         ³²²²²²²²²²²²²²²²²²²²²²³             /   .ú' ³   ³ 'ú.   \
         ³²²²²²²²²²²²²²²²²²²²²²³One layer   Þ   .    ³   ³    .   Ý
         ³²²²²²²²²²²²²²²²²²²²²²³of winding  Ý___    /     \    ___Þ
         ³²²²²²²²²²²²²²²²²²²²²²³           ÞÄÄÄ:    ³  0  ³    :ÄÄÄÝ
         ³²²²²²²²²²²²²²²²²²²²²²³            Ý~~~    \     /    ~~~Þ
         ³²²²²²²²²²²²²²²²²²²²²²³            Þ   '    ~---~    '   Ý
         ³²²²²²²²²²²²²²²²²²²²²²³             \   'ú.       .ú'   /
         ³²²²²²²²²²²²²²²²²²²²²²³              '.  / ' úúú ' \  .'
          ~~~~~~~~~³ ³~~~~~~~~~                 'ú._  ³³³  _.ú'
                   ³ ³Shaft                         ~~ÁÁÁ~~
                   ÀÄÙfor
                      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 "70-260V Mains Auto Transformer", "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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