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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