RE: [TCML] Energy coupling

["Lau, Gary" <Gary.Lau@xxxxxx>]

A good question, one that I also pondered several years ago.  To answer it I performed an experiment that I posted to the TCML on Nov 13, 2000.  The short answer is that if the stuff under the primary is at a "reasonable" distance from the primary, losses are acceptable (about 2.3 Watts in my case).

Note also that I measured the degree that a toroid acts as a shorted turn.  Not much at a reasonable distance above the primary, but definitely a problem if "too" close to the primary.

Regards, Gary Lau
MA, USA

===============================================================
Original post from Nov 13, 2000:

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

End of original post
================================================================

> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> Behalf Of Chris Swinson
> Sent: Thursday, September 11, 2008 11:36 AM
> To: Tesla Coil Mailing List
> Subject: [TCML] Energy coupling
>
> Hi all,
>
> As most of the electronics is placed under the primary coil, then how much
> energy actually couples to the metalwork of all the electronics rather than
> going into the secondary coil ?
>
> Chris

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