reduce 125VAC to 120VAC, small form factor, and clean 60Hz s

[VWWall]

P E Schoen wrote:

"Fred Abse" wrote in message
newsan.2013.05.28.19.58.35.835800@invalid.invalid...

Try this: Note the syntax of the last line. The
exclamation point shows it to be a directive.
This example gives 9.118 volts peak at the tap.
Take the 1 milliohm rser out of the voltage source,
the matrix goes singular.

I used the RMS values and I get a ratio of 0.0914, rather than 0.1 as
might be expected. 100 H should be 10 times the number of turns for 1 H,
but because the inductors are coupled it does not quite work that way.
99 H corresponds to 9.95 turns while 1 H is 1 turn. Thus the turns ratio
is 1/10.95 = 0.0913.

Changing the K factor to a comment shows a ratio of 0.01, proving that
non-coupled inductors function as pure reactance and their inductances
may be used for the voltage ratio, just like resistors.

A coupling constant of 0.09 yields a ratio of 0.084.

0.5 shows a ratio of 0.054

0.1 => 0.0196
What sort of transformer might have such a low coupling factor?
Could two isolated inductors be arranged mechanically to have an
adjustable coupling factor, and thus function as an isolated variac?

0 => (what do you think?)

Paul

The old "constant current" transformers, used to power series street
lights, was an example. There are still lots of these around!

--
Virg Wall

 

[P E Schoen]

"Fred Abse" wrote in message
newsan.2013.05.28.22.29.38.762451@invalid.invalid...

On Tue, 28 May 2013 17:25:36 -0400, P E Schoen wrote:

Could two isolated inductors be arranged mechanically to have an
adjustable coupling factor, and thus function as an isolated variac?

It *is* possible to make a double-wound variable transformer ("isolated
variac"). Grundig, In Germany used to make exactly that. Wound on a toroid
about 9" dia, giving a 5 amp rating at 0-270V, from a 220V supply.
Originally sold under the Hartmann & Braun trademark, and sold as a
workshop unit, cased, with current and voltage meters, they are still
highly sought after. Lighter and less bulky than the usual 1:1
double-wound-plus-conventional-variac that most makers offer.

Those are still available, and simply consist of a fully insulated primary
winding and a secondary winding on top of that, with the insulation removed
and the surface flattened for the brush. Here are Staco's isolated models:
http://www.stacoenergy.com/engineering-drawings.htm#IsolatedSeries

But my idea was to have two separate inductors and vary the coupling between
them. It might not be very practical or efficient, but just an interesting
"thought experiment".

Paul

 

[Fred Abse]

On Tue, 28 May 2013 13:35:27 -0500, John Fields wrote:

And, yet, the dial is linear

To disambiguate:

The dial is turns ratio, ie. voltage ratio, which is linear.

We have been discussing simple modeling, which necessarily has to use
inductance ratio.

The curve I posted is inductance ratio.

You *could* model turns ratio, using the Chan model, if you knew
everything about the core hysteretic properties, or using a behavioral
model, such as the one in the LTspice "educational" examples.

--
"For a successful technology, reality must take precedence
over public relations, for nature cannot be fooled."
(Richard Feynman)

 

[Fred Abse]

On Wed, 29 May 2013 02:26:24 -0400, P E Schoen wrote:

But my idea was to have two separate inductors and vary the coupling between
them. It might not be very practical or efficient, but just an interesting
"thought experiment".

It's been done for generations, with coupled tuned circuits. Varying the
coupling varies the bandwidth.

I posted a simulation of two identical tuned circuits with varying
coupling a while back. In fact I posted it on two separate occasions.

Do I have to post it again, assuming I can still find it?

It's more efficient than you'd think.I've had tens of watts through
loosely coupled, tuned, pairs.

Some CO2 laser power supplies do a similar thing. They're kilowatts.

--
"For a successful technology, reality must take precedence
over public relations, for nature cannot be fooled."
(Richard Feynman)