Re: 577D1 itching issue - Haven't touched since, currently in storage
Dennis,toggle quoted messageShow quoted text
It is a very bad idea to short out a turn on a transformer.
But it is a very good idea to load a turn or two on a transformer...
after all, that is the transformer's job.
Here is what your variac's brush really is:
Turn2 <--Resistor---+-----Brush terminal
The voltage between turns is around a volt on most variacs.
The resistance of the brush material is chosen so that its
the power dissipation will be 1 or 2 watts, for a typical
If it is essential that a variac go all the way to zero, there
will be a metallic landing pad for the brush to land on after
it falls off of the last turn.
Absent the landing pad, the lowest voltage will be on the
order of 1/2 turn's voltage.
The variac was originally designed to be a lamp dimmer for
theater use... it replaced the very wasteful carbon pile
rheostats originally used.
This curve tracer application is forcing an oval peg into
a round hole. It sort of fits... if you force it.
Dennis Tillman W7PF wrote:
Chuck, Bruce, and Arden,