On Wed, 3 Jul 2002 12:09:30 -0500 (CDT), jwelser@ccwf.cc.utexas.edu wrote:
>
> I think what you're describing would still isolate the secondary
>from earth ground, which is exactly what an isolation transformer (or any
>transformer for that matter) does -- the secondary(s) are floating with
>respect to earth ground -- there is just "X" volts across the secondary
>coil.
>
> I've never heard of an auto-transformer before. Basically,
>it's a physical fact that any transformer that works by induction
>(basically any transformer, or so I thought) has it's secondary floating
>with respect to the primary -- put another way, because a transformer is
>an AC device, there can be any DC offset present between the primary and
>secondary and things still work. I'm not sure why any transformer would
>have its primary and secondary windings connected together, but, like I
>said, I've never heard of an auto-transformer before, so it's quite
>possible that's what's happening there.
Most of those adjustable transformers you see with the big knob on top are
auto-transformers which share a lead with the AC and are wired like this:
)
-------------(
||)
||(
Primary ||)<-------------
||) Adjustable Secondary
|
-------------+--------------
It saves a bunch of wire, and makes for a smaller transformers. Notice that the
wiper can go beyond the tap of the primary winding. Auto-transformers can raise
or lower the secondary voltage over/under the primary voltage.
These transformers are NOT isolation transformers and should not be used to
drive a monitor that requires isolation.
-Zonn
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Received on Wed Jul 3 11:18:34 2002
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