Re: Variac Reality

On Thu, 12 Feb 2009 07:27:43 -0800 (PST), "J.A. Legris"
<jalegris@xxxxxxxxxxxx> wrote:

On Feb 12, 10:03 am, John Larkin
<jjlar...@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
On Thu, 12 Feb 2009 00:06:26 -0800 (PST), Jacko <jackokr...@xxxxxxxxx>
wrote:



On 11 Feb, 19:06, John Larkin
<jjlar...@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
Calrad 5-amp variac:

No-load primary excitation current = 116 mA RMS at
120 volts in.

Calculated inductance = 2.75 H

This idle current is independent of wiper position!

Output voltage is settable to within 50 mV of a target, with a little
fiddling. That's a resolution of about 1 part in 3000.

With wiper at the 60 volt position, output impedance measures about 3
ohms.

If you treated the thing as a voltage divider that used two
independent inductors, each 1.37 H, Zout would be around 250 ohms.

John

A variac is a variable transformer. It contains a primary winding with
full supply accross it. A secondary winding is placed atop this and
has one end as a variable tap. It is not a single winding.

Such an un isolated single winding would be dangerous, and would not
pass safety legislation.

cheers jacko

Tell that to the many Variac makers. Every one I've seen is a single
winding.

Why do newsgroups attract so many people who make declarations that
are flat wrong, about things they know nothing about but could
research in a couple of minutes?

John

We all drop bull*** from time to time. The problem is that newsgroups
won't let us just walk away from it. With practice we learn to choose
our on-line words carefully, but some of us are slow learners.

Well, I don't make absolutist statements about things I know nothing
about, even in real life.

John

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