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Re: [TCML] Finally Fired off Green Monster With New Caps.


Yes, 'kVA' being the operative word, as opposed to 'kW' of true power, as the power factor is probably around 50%, possibly even less at certain voltage ranges. I have installed 500 uFd of power factor caps that I can switch on or off that tends to reduce the wallplug amperage draw by some 40% to as much as 60% or more, depending upon the variac knob setting and of course, the inductive loading of the transformer. Unfortunately, I only have one panel ammeter, which is 'downstream' from the PFC caps, so I can't tell in real time how much power that I'm actually drawing from the wallplug. Since the single panel ammeter is downstream from the PFC caps, it reads the same current regardless of whether the PFC is engaged or not. I was only able to get some idea of the reduction in current draw from the mains by placing a handheld amprobe on the input lines to the main EMI filter, immediately 'upstream' from the PFC caps, while observing the panel ammeter to get a sense of how much the caps were reducing the wallplug amperage draw. I did notice that the power factor correction was optimal only within a certain range of the variac and that once the variac was turned up past about 85 of the dial (which would equal the incoming 240 volts), this advantage of current draw reduction quickly began to disappear and was totally gone by the time the variac knob was turned to around 95 on the 0 -100 scale.

Anywho, at the end of the day, when my panel ammeter is showing 80 to 90 amps of current draw, the 'true' power is probably closer to the 10 to 12 kW range. That being said, since my coil is equipped with a 12" x 49" long secondary coil that is topped with a 12" x 56" tophat, and its total assembled vertical height standing at about 90", this seems to limit the absolute spark length to some extent and I find that once I get beyond say about 65 or 70 on my variac dial, the sparks only seem to grow brighter, with more frequent heavy current ground strikes as well as more frequent hits to the strike ring (which is only 49" from the bottom of the tophat), as opposed to getting noticably longer. My spark output is generally in the 10 ft. to 12 ft. point-to-point range, with an occasional 13 or 14 footer here and there.


----- Original Message ----- From: "Tedd Dillard" <tedd.dillard@xxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Sunday, April 22, 2018 3:37 PM
Subject: Re: [TCML] Finally Fired off Green Monster With New Caps.

David am I missing somthing?
You said that the coil was drawing 90 amps. That is over 20 kva.
How big are the sparks?

On Apr 21, 2018 10:40 PM, "David Rieben" <drieben@xxxxxxx> wrote:

Some of you may remeber that I posted to the list an enquiry about the
suitability of GE protective power caps (2X 0.25 uFd @ 13.8 kVAC in series)
for Tesla coil operation, probably several months ago now. Bert Hickman
thought that they would be quite suitable for Tesla coil duty, so that was
good enough for me to give 'em a try. ;^) Well, between being back to
working 40 hours a week and what seems like a life time of miserable, rainy weekends, I finally got a good day to try out those caps in my coil. Since
I was replacing a 0.1 uFd Maxwell pulse cap (measured C about 0.114 uFd)
with a measured C of 0.135 uFd, the coil obviously needed retuning for
optimal operation. Since I am forced to run it outdoors in my driveway and
the primary tap takes several minutes to loosen and reattach each time I
change it, I was really only able to get a preliminary tuning down to the
nearest whole turn, but still good enough for a test run.

I have also added 0.33 ohms worth of power resistors on one of the 'hot'
240 volt input legs, in combination with my inductive ballast on the other
'hot' input to my pole pig since the last time I fired it (probably at
least a year by now!) I was trying to further 'smooth' the operation of the coil and further suppress any nasty kickbacks that may find their way back
to my control panel or even my home's wiring.

Well, she did run fairly well, although it seemed like the added
resistance throttled it back a bit. I noticed that even with the variac
wheel turned up to around 80, the coil was still only drawing around 60 to
65 amps and it seemd that this was about the 'limit' - (it was drawing
around 85 to 90 amps before without the added resistive ballasting and with
the original 0.1 uFd Maxwell cap with the variac wheel at this same
setting). Of course, even with only 0.33 ohms of added resistance, per the
I2R law of joule heating, at 65 amps, thats still about 1400 watts of
wasted energy that does NOT make it to those beautiful streamers!

Also, there seemed to be more 'wah-wah' beating of the output with my
typical 300 to 350 bps roary gap setting - (noticed this more from
observing my panel ammeter flactuate than from the actual tone of the
sparks). Never-the-less, the output (and current draw) was definitely
smoother and more steady with my original setup. I tried varying the speed of the rotary gap drive to see if I could get out of the beat fluctuations
and find a 'sweet spot', but that didn't really seem to make much
difference. So it seems that the added resistance gave me the opposite
affect than the 'smoothing' that I was looking for.

Anywho, I will probably have an audience next time I run it and the first
thing that I will likely do is try bypassing those power resistors. I have
never really liked the idea of resistive ballasting wasting power in heat
anyway, but I have read that a small resistive component in the ballasting
does tend to smooth out and knock the tops off of some of the nasty
kickback transients. I have still occasionally observed an occasional spark inside my control panel where you DON'T want to see sparks! That's the only
reason that I was trying the resistive ballasting approach.

Those GE protective capacitors DO seem VERY robust, though and never even
broke a sweat - can you say 27,600 volts AC rating with never more than 17
kVAC input??!! (plus they have internal bleeder resistors, making them
safer than the typical pulse cap) so at least for now, I'm leaning more
toward staying with them and working out the few preliminary kinks that I
am having with their operation than changing back to my original 0.1 uFd,
75 kV Maxwell pulse cap.

Any comments or suggestions from any of the resident geniuses and/or other
experienced pole piggy coilers?

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