Re: Barts Flat Coil Dimensions Was: Dimensions of my flat spiral coil

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Paul Nicholson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <paul-at-abelian.demon.co.uk>

Bart wrote:
> how about checking the resonant frequency of the coil
> (by itself) and back calculating inductance?

Not a good idea, until we can calculate the effective
capacitance.  We'd just end up swimming in a sea of numbers.

Incidentally, I'm looking forward to calculating the current profile
for a flat spiral, as the radial coupling due to internal capacitance
might well be as dominant in the flat spiral as it is in a small H/D
solenoid.   If so, then at resonance, the effective inductance might
well be considerably higher (my guess: 30% higher?) than the DC
inductance - with consequent potential advantage for reduced gap
loss.

I wrote:
> Can you measure the resistance of the windings, see if they are
> each around 1.8 ohms?
Dave Thomson wrote:
> Two of the leads measure 5.1 Ohms and one lead measures 5.2 Ohms.

OK, that suggests that something is wrong with the wire length or
number of turns.  You've about 3 times the expected resistance
(1.8 * 3) and about 9 times the expected inductance, which agree.
Somehow you've got a little under 3 times more length of wire in each
strand than you think you have.  Forget inductances for now, lets just
get Ohms law to apply first.  Have you actually counted the turns? 
Is it definately 21 awg wire?

> [The 3 strands] They're all shorted at the terminal.

Ah, ok. That limits the diagnostics we can do.

> [Measurements at 60Hz] Help me here.  Where do I find the formula
> for converting voltage and current measurements into inductance? 

For now, just report your raw measurements.  The conversion is a bit
tricky, because you have to carefully allow for the coil's resistance,
which is likely to dominate at 60Hz.

Does anyone else have a flat spiral coil with L and R measurements
so that I can check acmi?  I've already found one mistake in the code.

When it comes to flat spirals, has anyone considered printing them
(PC, acetate, photo-etch, etc) directly onto a copper clad?  Now
that's something you can't do very easily with a solenoid!
--
Paul Nicholson
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