Re: [TCML] How to Fix Damaged Secondary

[Yurtle Turtle <yurtle_t@xxxxxxxxx>]

Nice coil.
I haven't had any problems with my 10" coil, but often had to fix flashover damage on my small 4" one. I simply cleaned it real good with alcohol and got in with magnifying goggles to remove any trace of carbon, then recoated it.

I always do what David recommends and wipe the secondary down good, to remove any dust or fingerprint oils before running.

I used to use ten of the 30 nF 35 kV caps with five rows of two, as David described, for a total of 75 nF 70 kV. Kinda pricey, but I bought them over the course of several years, and 
paid around $75 - $80 each, if I remember. I now have a nice 100 nF cap 
that David sold me.



________________________________
From: drieben <drieben@xxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Sent: Wednesday, October 26, 2011 10:25 AM
Subject: Re: [TCML] How to Fix Damaged Secondary 

Hi Amir,

In light of the  DRSSTC craze, it's kind of refreshing
to see someone who's STILL working with large scale
SPARK GAP driven Tesla coils these days ;^))

First of all, from what I can see on the video, congrats
on a great looking and performing system.  From the
way that you describe your secondary flashover issue,
you may be able to get by with the patch up that you
describe. I would suggest giving the secondary form
a thorough wipe down with a clean dry cloth prior to
each fire up to address this issue in the future. I have
had this happen with my Green Monster coil (which is
very similar to yours in specs, size, power and perform-
ance) but the damage that was done was too great for
a simple patch up. Fortunately, my failures occurred
much lower on the secondary coil, closer to the primary
plane, so I was able to simply remove the few turns be-
neath the burnt spot and make this point the new ground
point for the secondary. This also automatically reduced
the pri/sec coupling too, which in turn reduced the tendancy
for this to occur. You didn't mention the physical coupling
of your primary to secondary (how many inches or cm is
the bottom most turn of your secondary above or below
the plane of your primary spiral?) Since this did occur and
assuming that you started with a cleanly wiped secondary
coil, you may need to slightly reduce the pri/sec coupling
to prevent future replays of this event.

Another thing that i noticed is your primary capacitor
choice. Since you state that your .12 uFd is achieved
with (4) paralleled 35 kV rated Maxwells, I'm assuming
that you are using the cat. # 37667, .03 uFd, 35 kVDC
rated Maxwell pulse caps, like this:
http://www.ebay.com/itm/Maxwell-37667-High-Voltage-Pulse-Capacitor-/160653424737?pt=LH_DefaultDomain_0&hash=item2567b0b861#ht_500wt_1156
I hate to rain on your parade, but from what I have heard
from others on this forum, these caps do not hold up too
well to the rigors of pole pig power, especially at >12 kV.
I believe I've even heard of these failing in 15 kV NST
systems, probably due to overvoltage. Now if you were
to get enough of them for a series-parallel set up, you could
double the 35 kV rating to 70 kV. Unfortunately, you would
need 16 to get the same capacitance at double the voltage
rating, if you were to use these same caps. This cap combo
would likely be nearly bullet proof, though, especially since
these are the 37*** series Maxwells, which are rated for high
PPS rate (either 500 or 1000, I beleive). Also, MMCs would
also prove impractical for the caliber of cap that you require,
as it would require multiple hundreds of them to achieve the volt-
age and capacitance that you require. Sometimes, suitable sized,
single unit pulse caps in this range can be found on eBay. Of
course, they mostly used ones and you do take a chance of
getting one that's near the end of its design life, but I have per-
sonally always had good luck with these myself.

BTW, of what type of construction is your massive 12x60
toroid (homemade/professionally made)?

David Rieben


----- Original Message ----- From: "Amir Mojarradi" <ln2guy42@xxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Wednesday, October 26, 2011 12:57 AM
Subject: [TCML] How to Fix Damaged Secondary


Hi everyone!


I recently finished completion of a fairly large Tesla coil, (specs and video below), and have been testing it.


Maximum Arc Length (so far) 9 feet
Secondary Diameter: 12"
Secondary Coil Winding Height: 57"
Wire Gauge: 18awg
Number of Turns: 1400
Toroid Minor Diameter: 12in
Toroid Major Diameter: 60in
Power Supply: 14.4kv 10kw Pole Pig
Ballast: Lincoln Arc Welder (240 Volts @~ 26 amps)
Primary Capacitance: 0.1289 uf
Asynchronous Rotary Spark Gap



Video: http://www.youtube.com/watch?v=KfQYHF6Z62c&feature=related



When testing at about 5 Kw, I noticed some arcing one individual turn at exactly one point about 12" on the secondary. Upon examination, there is a small burn mark at the point on the turn where it was arcing. At this point on the wire, the varnish is melted and has left the point exposed. I have re-varnished the entire coil already. Is there anything I can do to "heal" the damaged point to prevent further arcing? I was originally planning to step up the power to about 12 Kw, but I might have to hold off, or possibly reduce coupling. Any suggestions or advice would be much appreciated.


Thank you for your kindness,


Amir Mojarradi
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