Well, I wouldn't go as far as to say completely "abandon" my Maxwells
(catalog # 31885). Heck, I have four of them that I picked years ago on one
of those real eBay deals. Of course the Maxwell units are of the white PVC
containment system, with the both terminals on the same end, and with the
insulator barrier between the terminals. The GE caps, at about 33 lbs. each,
are of the welded metal can containment, with a single standoff bushing for
one terminal and the external case itself as the other terminal. I see that
Bert Hickman has already sent you a link to some of the spaecs of these GE
caps, although I do not see any of the more detailed spec ratings that you
were likely thinking of (peak and RMS current rating, dV/dT derivative, and
such), as this may be proprietary info. Since these caps are indeed desinged
to be placed continuously across 13.8 kVAC and can be operated at up to 15.2
kVAC, they must obviously be designed for 100% V-reversals, at least at 60
hz. I do know that these caps do encorporate the PP "hazy film" dielectric
system as well as extended endfoil connections, and are also designed
mechanically very robust. They are so well packed internally that I cannot
detect ANY oil 'slosh' sound while moving them about.
Your adjusatable air gap spacing of your inductive ballast for current
control is a really neat idea. I simply adjusted my original air gap for a
spacing that allowed me to draw about 100 amps from the 240 volt mains when
seriesed with a dead short, then fixed the gap permanently at this setting.
I simply use the main power control variac to vary the voltage at a fixed
inductive ballast.
You've really done well to keep all electronic interferance out of your home
while running you coil, although operating 75 ft. away in a seperate shop
building is probably helpful in this aspect, too. Since I have to store my
big coil inside of my attached two-car garage and, due to vertical clearance
issues, "decapitate" its topload donut to roll it out from underneath the
overhead door and then reassemble once outside, and run it outside (and
reverse the process to put it back inside), I am not as blessed with
operational space as you (and I am at the mercy of whatever Mother Nature
has in mind as to whether or nor I can operate it). I have driven three
interconnected grounding rods inconspicuously next to my driveway and the
central grounding rod only allows about 35 ft. distance from ground zero to
my home structure. Unfortunately, the wife still complains about the TV
screen going completely black while I am firing my coil (we have a satellite
dish as opposed to cable) and one of the florescent lights in my shop shuts
down while the sparks are spewing. Fortunately, the ill-effects immediately
disappear and everything seems to return to normal once the coil is shut
down. Since I reside in a suburban environment on a mere 1/3 acre lot and
surrounded by neighbors, a seperate shop pole barn is still a future dream
for me, once we can relocate to and build on our 40 acres of open property.
Yes, I have also employed just about every conceivable filtering device that
can be assembled for coil operation. MOVs on both the LV input and the HV
output (distribution arresters), and multiple EMI line filters. Seems like
sufficient distance (and possibly Faraday shielding by operation inside a
metal pole barn building) is still the operative word for keeping the
generated interferance to sensitive electronics to a minimum.
Although I'm sure that some others may disagree with me, I personally feel
that 'Terry filters' are really not really necessary for protection of
non-current limited power transformers, especially those that are designed
for the extreme rigors of line transients caused by switching surges and
lightning strikes in a 24/7 exposure to the iutdoor elements (pole pigs or
PTs designed for outdoor operation). The Terry filter was originally
designed to address the issue of run-away resonance when inexperienced
coilers ran their coils with a primary C that was near resonance with the
mains frequency, while opening their stationary gaps ever wider and wider to
get longer sparks when powered by the very fragile, current limited NSTs or
OBITs. Since pole pigs are electrically (and mechanically) MUCH MORE robust
in relation to their voltage/current ratings, and since most coils of this
magnitude are driven by a high break rate rotary gap when ASYNC, and the
primary cap is usually considerably smaller than resonant (STR) with the
mains frequency, I feel that this level of 'protection' is really
unnecessary in this situation. To me, at least, it's kind of like building a
picket fence to protect a stone wall. ;^) Of course, it certainly can't hurt
and if it gives you more 'peace of mind', then by all means, go for it. I do
utilize properly rated distribution arreser MOVs that the power company used
on their primary diostribution lines for some level of protection on the HV
side of my coil as well, though, although I did not always do it and still
never had a pole pig die in Tesla coil duty.
David
----- Original Message -----
From: "Steve White" <steve.white1@xxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Saturday, April 21, 2018 10:24 PM
Subject: Re: [TCML] Finally Fired off Green Monster With New Caps.
Just curious. Are you abandoning the Maxwell for the GEs or was this just
an experiment to see how the GE caps work? Do you have a data sheet for
the GE caps? If so I would like to take a look.
My pole pig powered coil uses a bank of 6 Maxwells in a series-parallel
configuration to get 45 nF of capacitance at a 70 KV rating. It also has
an adjustable air gap ballast that I built. I am not using any resistive
ballast, although like you, I have wondered if I should be using some.
Also, like you, I can't stand the thought of wasting precious power as
heat. That is why I built the adjustable air gap ballast in the first
place! I currently have it set for 20 amps although I designed it to
handle up to 50 amps. My control cabinet is closed so I can't see if there
are any unwanted sparks anywhere. Maybe I should look in the back while it
is operating. I do have numerous protective features such as line filters
and big MOVs in the cabinet. I haven't noticed any ill effects on anything
in my house. I have seen my wife watching TV while the coil was in
operation. The computers in the house are also on during operation. I do
turn all electronics off in my workshop before opera
tion. My workshop, where I operate the coil, is about 75 feet away from
the house and I imagine that I may be getting some kind of additional
filtering effect from the 75 feet of buried power line between the house
and workshop.
I am currently in the process of adding a low pass filter ("Terry" filter)
to the HV output of my pole pig for some additional protection for it. I
deleted the MOVs.
Steve
----- Original Message -----
From: "David Rieben" <drieben@xxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Saturday, April 21, 2018 9:31:22 PM
Subject: [TCML] Finally Fired off Green Monster With New Caps.
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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