RE: Primary loss measurements

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

To put my loss-resistance measurements in perspective, I found the number of
Watts that the incremental resistance would dissipate in a running coil.  I
user Terry Fritz's LTR10-31 Microsim schematic to represent the coil and
found the RMS current in the tank circuit - 9.77 Amps.

The additional resistance that I measured on my coil due to the proximity of
my NST, gap, caps, and toroid was 0.024 Ohms.  This would dissipate 2.29
Watts - not a big deal.

Terry - how did you arrive at the 3 Ohm Rgap value in your model?  When I
made my primary ringdown measurements, Bert Hickman showed that an
equivalent gap resistance could be found by noting the duration of the
linear ringdown, and finding R = 2L/t.  For my vortex gap, R came out to
0.43 Ohms, and would also include the AC and DC resistance of everything in
the tank circuit, equivalent to your Rgap.  Is your RSG really that much
more lossy?

Gary Lau
Waltham, MA USA

> -----Original Message-----
> From:	Lau, Gary 
> Sent:	Friday, November 10, 2000 2:51 PM
> To:	'Tesla list'
> Subject:	Primary loss measurements
> 
> 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