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G8MNY > TECH 22.11.25 11:45l 56 Lines 2666 Bytes #2 (0) @ WW
BID : 45632_GB7CIP
Read: GAST
Subj: Variacs
Path: DB0FFL<OE2XZR<OE6XPE<UA6ADV<LU4ECL<VK2RZ<VE3CGR<PY2BIL<GB7CIP
Sent: 251122/1031Z @:GB7CIP.#32.GBR.EURO #:45632 [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 and 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 and 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 and windings. Do check the brush and 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 and 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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