RE: Primary loss measurements

["Lau, Gary" <Gary.Lau-at-xxxxxxxxxx> (by way of Terry Fritz <twftesla-at-xxxxxxxxxx>)]

Hi Richie:

I have no doubt that the losses that I have measured are very small when
compared to gap losses.  Several months ago I reported on a series of
experiments involving measuring the linear ringdown of my pressurized vortex
gap vs. my single vacuum gap.  While the true model of a gap is dynamic and
complex, Bert Hickman showed how an equivalent gap resistance could be found
from these measurements, and that my two gaps showed equivalent resistance's
of 0.43 (vortex) and 0.52 Ohms (vacuum).  Note that these figures include
all AC and DC resistance and losses in the tank circuit.  And these figures
are probably lower than most static multi-gaps or rotaries.  So the
incremental losses that I have measured of 0.015 to 0.081 Ohms are
comparatively not too significant.  If anything, they serve to underscore
what has long been known - Focus our efforts on reducing gap losses!

I think the most interesting outcome my experiment was that the concrete
floor 17" below the primary had no effect.  And I also wanted to prove that
there's no reason to avoid metal hardware as some have suggested.

Good question about the MOSFET body diode.  I don't think it comes into play
but I'm really not certain.  Anyone else?

Gary Lau
Waltham, MA USA

=======================================================
		Gary, and all,

Excellent work Gary.
There has always been speculation about the effects of metalwork and
nearby ground,  but I have never heard of anyone actually doing a test to
quantify this.

The increase in resistance certainly seems significant compared to
the total resistance in the circuit.  Ie.  going from R=0.229 to R=0.310
represents a 35% increase in power dissipation if the current remains the
same.  _However_ the Rds on figure for MOSFET is particularly low.  

I wonder whether the change in resistance would be so significant compared
to a lossy spark gap ???  If the gap has a "resistance" of several
ohms then the increase due to metalwork near the primary may not be
significant ???

Did you consider the effect of the MOSFET body diode in your experiment?
If the body diode carries the current of negative cycles,  then its
forward voltage-drop may be significant enough to effect your results ???

Very interesting work,  please keep us informed of your conclusions.

							Cheers,

							-Richie,


On Fri, 10 Nov 2000, Tesla list wrote:

> Original poster: "Lau, Gary" <Gary.Lau-at-compaq-dot-com> 
> 
> Hi All:
> 
> I'd like to report on a series of experiments I've made recently.  I've
been
> trying to quantify various losses related to the primary and nearby
objects.
> To do this I measured the ringdown time of a low voltage-excited primary
> tank circuit, with no secondary.  In place of the spark gap I used a small
> N-channel MOSFET with a very low Rds-on parameter of 0.01 Ohm, and
activated
> the FET with a square wave from a signal generator.  A 9V battery and 10K
> resistor across the FET charged the cap up to 9V for each cycle.  The cap
> was a pair of .015uF metalized polypropylene caps, totaling .03uF.  The
> primary is a flat spiral of 1/4" copper tubing, 69.5uH.  Tank frequency
was
> 110KHz.
> 
> If the circuit is a three element series R-C-L loop, then the envelope of
> the ringdown follows V = Vo e^(-tR/2L), with R being all of the AC and DC
> resistance and losses in the circuit.  If I measure the time t1 it takes
for
> the envelope to decay to 1/e or 0.368 times initial amplitude Vo, then R =
> 2L/t1.
> 
> With just the primary 17" above a concrete basement floor (and nothing
else
> near it), R = 0.229 Ohms.  Doubling the height off the floor made no
> difference, so I conclude that 17" proximity to the floor had no losses
> associated with the floor.  I consider this the base level measurement
with
> no proximity-based loss components.
> 
> If I add two 15/30 NST's on the floor below the primary, R rises to 0.236
> Ohms.  Incremental loss R is 0.007 Ohms.  If I put my coil back together
> with its usual 15/60 NST, static vortex gap, PFC caps, and Maxwell cap all
> below the primary, R goes up to 0.244 Ohms.  Incremental loss R is 0.015
> Ohms.
> 
> If I then add a 6"x23" toroid 24" above the primary (again with no
> secondary), R rises still to 0.253 Ohms.  Incremental loss R is 0.024
Ohms.
> Lowering the toroid to 14" above the primary increases R to 0.310 Ohms.
> Incremental loss R is 0.081 Ohms.
> 
> Lowering the toroid further really kills the ringdown, as does a shorted
> strike rail.  A small handful of metal screws directly within the primary
> made no difference to losses.
> 
> It remains for me to convert these resistance figures to Watts of losses.
> Should it turns out that these incremental losses consume only 1W of power
> out of a kilowatt, then its all just academic, but interesting none the
> less.  They are certainly small compared to gap losses.  I also plan to
make
> a similar primary out of heavy stranded wire to see if that is actually
> significant towards losses.
> 
> Regards, Gary Lau
> Waltham, MA USA
> 
> 
> 
>