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
--- Mystic BBS v1.12 A43 (Linux/32)
* Origin: HAMRADIO telnet lu9dce.dynu.com (21:5/101)