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G8MNY > TECH 30.08.10 09:51l 54 Lines 2621 Bytes #999 (0) @ WW
BID : 60947_GB7CIP
Read: GUEST
Subj: Variacs
Path: IZ3LSV<IW8PGT<HB9ON<IW2OHX<UA6ADV<GB7CIP
Sent: 100829/2252Z @:GB7CIP.#32.GBR.EU #:60947 [Caterham] $:60947_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
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
0o__||) lower. However using a few % from the top or bottom
NÄÄÄÄÄÄÄÄo__||)______N you can easily cook the winding as the core can put
-10 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 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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