[TCML] Re: Dummy load for optimum cap size Experimentation
glau1024 at gmail.com
Sat Oct 9 08:18:46 MDT 2010
Even with the RF tank oscillations eliminated, the laptop was not totally
unaffected. When the spark gap was firing, the laptop touch pad was totally
unusable. I'm guessing that there's still a lot of RF in the air, and with
my body being a good antenna, the touch pad is capacitively coupled to me
and gets totally fouled up.
If you refer to the setup photo on page 5, you can see the blk/wht twisted
pair cable from the photodiode hanging from the corner of the box, going
through a ferrite toroid, to the LabJack box, to a USB cable, down to the
basement floor, then up to another ferrite toroid, and to the laptop. I
found that the LabJack would lock up when the USB cable was draped on the
floor, but OK if I lifted it up off the floor just a bit.
I'm not sure which anomaly at 120V you're referring to. There were curious
peaks and dips seen at both Variac voltages.
Yes this same technique could also be used to determine the best cap for a
sync gap. That was actually my motivation for building the dummy load in
the first place. Several years ago when I first built my SRSG, to determine
what cap size to use, I built the dummy load. Instead of monitoring the
lamp brightness, I scoped the cap voltage at the bang point. Then
calculated the bang size - 1/2 C*V^2. Surprisingly, using my same 15/60,
the best cap was 0.04uF. In hindsight, monitoring the lamp voltage would
have been a lot easier. Since the gap firing is now a regular 120BPS, the
problem of long term averaging goes away, and metering the light would be
trivial - a laptop would not be needed.
Regards, Gary Lau
On Sat, Oct 9, 2010 at 5:34 AM, Phil Tuck <phil at hvtesla.com> wrote:
> Very interesting results. In my ignorance I have always assumed that
> would never work anywhere near a tesla, but it is interesting to see how
> overcame this, by removal of the main 'transmitter' of any interference and
> replacing it by lamps.
> Is the anomaly that you are consistently getting at 120v related to the
> NST's inductance, with the higher voltage causing saturation and changing
> things, so the behaviour is different maybe?
> I also wondered whether this could be used on a RSG, especially a
> synchronous one, to get the best cap value for resonance of the charging
> If the lamps were put into a metal box, could you use an infrared
> thermometer to read the outside temperature I wonder? This should have
> sufficient time lag to smooth things out and also still reflect changes I
> would have thought.
> -----Original Message-----
> From: tesla-bounces at pupman.com [mailto:tesla-bounces at pupman.com] On Behalf
> Of Gary Lau
> Sent: 09 October 2010 02:25
> To: Tesla Coil Mailing List
> Subject: Re: [TCML] Re: Dummy load for optimum cap size Experimentation
> I'm pleased to have completed my experiment,to determine the optimum
> capacitor value for a Tesla coil using a static gap, by monitoring the
> output of a halogen lamp dummy load in place of the primary coil. I had
> originally planned to do this for both 15/60 and 15/30 NST, but due to time
> constraints, I just did it for three different 15/60's. Maybe later...
> When I started the experiment, I was certain that I would find that the
> table used to choose cap values based on NST specs wasn't right, since it
> was generated (I think?) using just simulation results. But it turns out
> that it's pretty close, at least for a 15/60.
> Other finding were that using a Variac to boost the NST primary voltage
> above 120VAC results in a huge boost to power throughput.
> Also, the power throughput when using a static gap, is far more chaotic
> I had ever imagined. It's not enough to try to average things over a few
> seconds, 20 seconds, or even a minute. Even after averaging for two
> minutes, there are still variations. I think this may explain why coils
> sometimes deliver the occasional exceptionally long spark, but it's not
> I have generated a comprehensive report, about a megabyte download. Please
> look in http://drop.io/garylau for Dummy Load Experiment.pdf It's a good
> To those who loaded me equipment, I thank you again.
> Regards, Gary Lau
> MA, USA
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> Tesla at pupman.com
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