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Re: [TCML] How to Fix Damaged Secondary
Hi David,
Thank you for your helpful insight. In fact, your Green Monster Tesla coil served as inspiration for the construction of this coil. I'm 18 now, and I have been wanting to make a "monster" coil just like yours for a couple years now, and I definitely remember your high voltage monster arcs and your colossal coil standing out as a quintessential Large SGTC. Your comments mean a lot to me and it's wonderful to finally communicate with it's designer!
On the next run, I will thoroughly wipe the coil with a dry cloth as you suggest. There are now 4 coats of Polyurethane on the coil. It's interesting that, on your coil, the initial secondary coil turns were burnt out. The same exact problem happened earlier with my coil, too, and I was easily able to fix that the same way that you did by removing four turns and making a new ground. This permanently fixed it until the point damage higher up on the coil emerged. Currently, the secondary coil winding and the primary coil sit on the same plane with about 2 inches of clearance between the first primary turn and the secondary. If the issue is not solved through my re-coating attempts, I will raise the secondary.
Yes, the Maxwell 0.03uf 35k, are the capacitors I am using to acheive the 0.12 uf. Thank you for bringing this issue to my attention. They are the most powerful capacitors I have at the moment. They seem to be holding up okay through my short runs. I will definitely search ebay for either more of them, or for a larger single unit capacitor.
My toroid is made of 12 inch diameter aluminum ducting wrapped around a 36" diameter round wooden disk, and strapped securely with aluminum tape. I am considering adding aluminum roof flashing similar to your toroid design. Regardless, it seems to work very well.
My concern is the secondary ability to handle more power. Although I was originally planning on utilizing the full power availability of my breaker ~ 12 Kw to approach 12-15 feet arcs, it easily produces ground strikes that are 8-9 feet long with the current limiter set to about 5 kw. So I am unsure how much more power to safely add to the coil.
David, thanks again for your help and for being a high voltage badass!
Amir Mojarradi
-----Original Message-----
From: drieben <drieben@xxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Sent: Wed, Oct 26, 2011 5:23 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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