Re: variable transformer for dc power supply

--- In CAD_CAM_EDM_DRO@y..., mmiami johnson <mmiami2002@y...> wrote:

>
> I am not sure of what isolation of a transformer exactly means.

An isolation transformer has two seperate (insulated from each other)
windings.

ILLISTRATION ONLY, DO NOT DO THIS!!!

Think of it this way, take a piece of insulated wire and wrap it
around a large bolt. Take a second piece of insulated wire and wrap
it over the first winding (wrapped wire). You just made a crude
isolation transformer.

ILLISTRATION ONLY, DO NOT DO THIS!!!

If you put a AC voltage on one winding and were to grab either side
of the other winding and ground, you'd feel nothing, your isolated
from the first (primary) winding and from the AC line.

ILLISTRATION ONLY, DO NOT DO THIS!!!

A variac is like taking one end of each of the above wires and
hooking them togeather and putting AC on that junction, with the
other AC connection on either of the free ends of a winding. Now if
you grab the last free end and ground you'll get shocked, hopefully
you won't end up in a hospital.

ILLISTRATION ONLY, DO NOT DO THIS!!!

Would you willingly cut an extention cord in two, strip the
insulation off the two wires, plug it in, then grab one of the wires?
Thats basically what you do when you use a variac to power a DC
supply and ground the negative side.

ILLISTRATION ONLY, DO NOT DO THIS!!!

I hope this clears things up.

mike