Yea, I guess I did indeed commit a big 'no-no' by introduing more than one
modification between runs of my coil. Shame on me! ;^)) Sometimes I just get
bored and too impatient to wait until I can run her again to hold off on
trying out new ideas. LOL.
I too was wondering about the different size caps being at least one factor
for the beating. I will definitely try bypassing the resistive ballast next
time I fire her off. I really highly doubt that my transformer/inductive
ballast combo (that has already proven to be able to effortlessly process
240 volts at 100 amps!) has reached or surpassed its limit as far as to how
large of a primary cap that it's able to fully charge in between the RSG
electrode presentations. As I have already stated, fine tuning is really
difficult for me to obtain in my current situation, having to run her
outdoors while keeping the neighbors in mind and the fact that it takes
several minutes for me to detach and reattach my primary tap. Even if I tune
her in perfectly at low power, it may require somewhat more inductance to
remain perfectly tuned in max power mode due to the extra loading of the
streamers themselves.
Thanks for your insightful input and good to chat with you once again.
David
----- Original Message -----
From: "phil" <pip@xxxxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Sunday, April 22, 2018 4:52 AM
Subject: Re: [TCML] Finally Fired off Green Monster With New Caps.
David,
Nice to know you blew the moths out of the coil after a lay-up. I like you
always tend to consider the wastage of putting resistance in the circuit
rather than any benefits it may provide. 1.4kW is a lot of power to use,
albeit not as dramatic as loosing the same 1.4kW on a NST coil, but none
the less it highlights the importance of getting all losses to a minimum
on big coils. I know some coilers consider it a good idea, but whether
there is any benefit gained on adding resistance may depend on individual
coils though.
I hate to say it, and with all due respect to you, but I think you have
committed the cardinal sin (along with 99% of us here who have done it at
one time or another) and introduced two new factors that could affect
things, (or even three if you consider the tuning may be out a bit),
rather than just the one new factor (the caps). I just wonder if the
"beating"is now down to the different C value you're now using; beating
with the 60Hz mains (assuming it's not tuning related). We've had beating
issues with my friends (Phil S) 10" piggy ARSG coil.
As you say bypass the resistance for now and try the caps again, with a
retune obviously, and then later maybe investigate whether the resistance
is the cause of the 80% power issue.
If it's sparked in the cabinet before, you could argue it can spark again
with out harm, as long as your own safety is not affected and it's only
occasional stress on the components.
Phil T
On 22/04/18 03:31, David Rieben 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?