Re: More Coupling...

["Tesla list" <tesla@pupman.com>]

Original poster: "by way of Terry Fritz <twftesla@uswest.net>" <paul@abelian.demon.co.uk>

Barton B. Anderson <tesla123@pacbell.net> wrote:

> ... a second look at your graph and the coupling direction was
> clear.

OK, I just made a similar mistake too - I asked for your winding
inductances when in fact you already mentioned them in an earlier
post. Doh!

Comparing acmi output numbers with your measurements, we have

|              acmi            Bart
|            predicts        measures
| 
| Primary    108.6 uH        107.13 uH   
| Secondary   80.3 mH         87.6  mH
| 
| Mutual     439.8 uH        627.0  uH 

I'm pleased with the primary agreement because that's the one acmi
will struggle with, if anything.

Your reported secondary inductance is way too high. I took the
dimensions of your secondary from your web page

 http://www.classictesla.com/photos/gizmos/bart.html

as 12.75" diam, 45.0" length, and 1000 turns. The Nagaoka inductance
for this winding comes out at 80.532 mH, which agrees very well with
acmi. (As usual, acmi does a good job with the secondary because a lot
of small turns are well approximated by current filaments).

Could it be that you have a few more than 1000t as indeed your web
page hints? If I adjust the turns to match your quoted secondary
inductance I find 1043 turns are required. With this change, I get

|              acmi            Bart
|            predicts        measures
| 
| Primary    108.6 uH        107.13 uH
| Secondary   87.4 mH         87.6  mH
| 
| Mutual     458.6 uH        627.0  uH

which puts the self inductance right, but the mutual is still out
by some 30%. That counts as a large discrepancy and more than I would
have expected.

A couple of questions: You measured 2.59V across the secondary when
the primary was carrying 10.95A at 60Hz. Did you measure the
secondary V when the primary current was turned off, as the secondary
will pick up a certain amount of induced voltage just from the back-
ground field of surrounding mains wiring? Was the hair dryer anywhere
near the secondary - near enough for its AC magnetic field to couple
directly to the secondary? I take it your 2.59V was RMS and not peak?

Ed Phillips <evp@pacbell.net> wrote:

> Will have to try a similar measurement here
> using a small flat primary I happen to have.

Any coupling measurements you can make would be very welcome - for
any shape of primary.

Regards,
--
Paul Nicholson,
Manchester, UK.
--