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