I do have a current limiting ballast on the LV AC side
of my control panel but I could see where the DC Res
charging setup could preclude the need for this feature.
Yes. However, the charging choke must have significant inductance
(typically many henries), must be capable of handling significant
current without significant saturation (100's of mA to amperes
depending on power level), and it must be able to withstand Vsupply
across terminals plus prudent design margin. If the charging inductor
is too small, the rotary will fail to quench and you'll get "ring of
fire" problems that can saturate the inductor, destroy the dequeing
diode, or damage the gap.
Also, could you share a bit more info on the capaci-
tors that you use in the 2 uFd filter cap bank?
The DC storage cap should be sized to ~ 10-15X the size of the tank
cap. The DC storage caps be DC filter/Mylar type. Pulse capacitors can
be used as DC storage caps as long as they are operated at no more
than 70% of their faceplate VDC rating. Since pulse caps are designed
to operate under higher internal dielectric stress, they may
prematurely fail under extended DC operation at rated voltage. You
don't want to make the DC storage capacitor too big since you'll make
the system more dangerous (i.e., excessive high stored energy) with
little/no performance benefits. Bleeder resistors are essential. I'd
also recommend a shorting relay that rapidly discharges the storage
cap through a beefy discharge resistor (ceramic Kanthal Globar or
similar) when powered-down.
David Rieben
PS: That 10 kVA rated, 19.5 kV pole pig is a true
treasure find for an old time ARSG coiler ;^) My
pole pig is 10 kVA also, but the more standard 14.4
kV.
This was a rebuilt unit from Solomon Corporation that I had them
modify for 19.8 kV operation. It was 16" diameter x 34" high with
beautiful Frankenstein insulators and it weighed about 450 pounds. I'm
very glad to see Roger putting it to good use. My wife was elated to
no longer see it lurking in the garage - I thought it was gorgeous,
but she thought it was quite evil-looking... :^)
http://www.capturedlightning.com/photos/HVStuff/Transformers/19.8kv10KVA-Pig.jpg
Bert
----- Original Message ----- From: "Roger Smith"
<rwsmith@xxxxxxxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Sunday, July 11, 2010 7:03 PM
Subject: Re: [TCML] New coil modeled after Green Monster
Hi Dave, Id be happy to give you some more details of my coil. I will
start with the basic parameters.
Secondary Coil diameter 12.5"
Secondary winding length 54"
Secondary wire size 19 gage
Toroud 12" x 48"
Primary Coil 1/2 " OD copper wound as pan cake coil and taped on the
13th turn
Primary capacitance .08 uf
Max Break Rate 425 bps
Max Power input so far 18 KVA
Max Spark Length so far 11 feet
Power Supply 10 kva , 19500 volt pole transformer which I I'm
currently running at an output of 17500 volts
I was running this set up with a smaller transformer and at a lower
voltage but this summer I finally hooked up the bigger pole pig I got
from Bert Hickman.
The Output from it goes straight to a full wave rectifier and then to
a 2 uf filter capacitor bank. In lieu of a big variac I have a big
transformer with multiple taps
that I can use to vary the voltage to the piggy. There is no Current
limiting ballast on the AC side of the system at all.
From the filter capacitors the current flows though the charging choke
witch is many windings of # 24 gage wire wound on an "I" core for an
inductance of
6 Henrys and then I have a dequing rectifier between the charging
choke and the primary capacitors to prevent current from flowing back
out of the primary
circuit into the charging circuit. Some people have had success using
solid state diodes for dequing rectifiers but I didn't have much luck
with them. I ended up using a bunch of 8020 vacuum tube diodes in
parallel . Under the right conditions you may not need a dequing diode
but I think it reduces the risk of burning
up your charging choke.
One final comment, in theory it seems that the inductance of the
charging choke would be kind of critical but I have played around with
this a lot and it
doesn't seem to be critical at all. You will run into problems if the
inductance is too small but it doesn't seem possible to make it too
big. There might be a sweet
spot somewhere that will give you the most efferent operation but if
there is I haven't found it yet.
Roger
----- Original Message ----- From: "David Rieben" <drieben@xxxxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Sunday, July 11, 2010 9:59 AM
Subject: Re: [TCML] New coil modeled after Green Monster
Hi Roger,
Yes, I have seen pics and some description of your
coil. Very nice system you have there. Now that you
have chimed in here, I would like to get a bit more de-
tail on the DC resonant charging that you employ into
your system. As you are probably already aware, the
GM simply uses the stiff, unfiltered high voltage AC
from the pole pig to power the tank circuit assembly
and around 350 to 400 bps seems to be the "sweet
spot". However, because of the unfiltered AC nature
of the power supply and the ASRSG never being
able to fully sync with the mains frequency, I do
experience the surging (wah-wah) sound of the out-
put through much of the ARSG sped range and it seems
to me if I were to filter the HV supply to a steady DC
voltage level, it would address this issue throughout the
selected RPM range of the SG motor. I do try to finely
tweak the RSG motor speed control to blend the surging
into a more steady output but it seems to me that with a
steady DC throughput to the RSG and tank circuit, there
would be a larger average power throughput and conse-
quently, bigger sparks and hey, bigger sparks is what it's
all about, right? ;^) Feel free to contact me off-list if you
feel the details would go beyond the interest of the rest
of the list.
David
----- Original Message ----- From: "Roger Smith"
<rwsmith@xxxxxxxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Saturday, July 10, 2010 8:45 PM
Subject: Re: [TCML] New coil modeled after Green Monster
I have built a Tesla coil that is in some ways similar to the Green
Monster. The secondary is wound on a 12.5" diameter pvc sewer pipe,
and it is wound with 19 gage wire. It is a DC resonant charging type
Tesla coil with a break rate of 425 bps and it has worked very well.
I have never built a SRSG Tesla coil but the one thing I don't like
about them is that you are limited to 120 bps. That's less than a
third of the break rate of my coil. That means that if you are going
to run the same power level as my coil with 425 bps you need to put
in over three times as much energy per break. That would be hard to
do without having problems.
Roger
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