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Registered Member #941
Joined: Sun Aug 05 2007, 10:09AM
Location: in a swedish junk pile
Posts: 497
They do make variacs like that but they are very expensive so you don't see them often, and they look virtually the same as any other variac so you cant tell unless you take it apart.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
I use an industrial isolation transformer in front of my main variable transformer - in front of everything in fact, as all 12 sockets on my bench are fed by it.
Registered Member #205
Joined: Sat Feb 18 2006, 11:59AM
Location: Skørping, Denmark
Posts: 741
Inducktion wrote ...
How come they don't make variacs like that? This gives the addition of isolation, and allows amperage to be changed with the amount of turns.
Mr. "Inducktion", sir!
Allow me to quote from page 4 in The Art Of Electronics - 2nd Edition Paul Horowitz Winfield Hill: -------------------------------------------------
-- Incidentally, don't call current "amperage"; that's strictly bush-league. The same caution will apply to the term "ohmage" when we get to resistance in the next section. ------------------------------------
---------------
Registered Member #3610
Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506
It's MUCH easier to wind a single layer of turns. If you look at how a variac is made, it's a layer of turns on a toroidal form which is varnish impregnated to hold it all in place. Then the bottom edge of the windings is ground flat to make a surface the wiper can ride on. If you had to have a separate primary, it would have to be very neatly wound under the secondary, it can and has been done, but it's much harder so it's more expensive.
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
This is the winding diagram of a "variac" used in the Eico power pack of about 1960s era. It is hanging on the wall of my shop, It has three pairs of windings and two contact sliders.
Rough drawing from note file; This seems to be made for maximum copper efficiency with a split core and 3 layers.
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True Variable transformer?
