Hello Bert,
Thank you for your observations and advice.
Just finished the rewind which seems satisfactory and probably better than previous efforts. I have long considered an epoxy coating which is probably the best coating of all but do not think I have the prowess do do a decent job, there is also the fear that if damaged, a repair would be near nigh impossible to repair. I have always used Dolphs AC43, often more than twenty coats and I think it definitely minimises damage. In spite of the fearsome video, the damage was minimal, no shorted or severed turns but a limited amount of carbonising causing the subsequent shorts. On this occasion, there were a few other small hits which may or may not cause trouble but since the solenoid had been repaired on a previous occasion, further repair was deemed to risky. The trouble with Dolphs and similar varnishes is that its almost impossible to achieve a sufficiently thick layer to deter such a strike, that said, I have all summer to apply a coat a day and see what I end up with!I must say that thick epoxy coats done by the experts looks fantastic.
An extended strike rail of some sort sounds a very good idea and I'll certainly work on that. The 50"x11" fabricated toroid with hindsight is inadequate for the 12" although the e-field if the streamer pattern in general is anything to go by seems reasonable. We use the same topload on Phil T's 8" coil which shares the same power arrangements and he has no such issues. We are working (very slowly) on a 60x12" ring toroid to hopefully resolve these issues for good.
I have a pair of 24x8" and 34"x8" spun toroids, one of which could be used to raise the fabricated toroid in the meantime but in truth, it is a 'life and limb' business just putting up and removing the one toroid perched on a ladder at our tender arthritic ages!
Interestingly enough, it was the 100 bps which were the hot fat"sticky" strikes which clung onto the strike balls. When experimentally run with Phil T's 200 bps SRSG, the parks had a marked preference for going outwards and upwards whereas the fatter, slower but more deliberate 100 bps arcs had no inclination for going upwards whatsoever, a personal preference actually apart for a proclivity for the strike rail..I think the stress on the coil is partly a function of the high 'bang' energy at the very low bps, the streamers have a definite "want to hang on" character whereas the 200 bps are far more frantic, brighter, probably longer but stick around less to use an expression with less time to do a nasty, this is just a subjective opinion.
Just to end, our interest in low bps and big caps was stimulated many years ago by Kevin Eldridge's BIGGG coil, those powerful, lazy streamers had enormous appeal and Phil T and myself still regard it as unique and very special. John Freau's work on low bps albeit with NST's was extremely illuminating and we share a phase controller of his design (of course..).
Our next run is not due to October so we have time to put recommendations into practice.
Kind Regards,Phillip.
_____________________________________________________________________________
14 Broad Street, Stamford, Lincs PE9 1PG
Tel: 01780 753008
On Thursday, 5 July 2018 18:31:03 BST, Bert Hickman <bert@xxxxxxxxxxxxxxxxxxxxx> wrote:
Phil, Steve, and all,
Sorry for the damage to your secondary, Phil. The videos were excellent
and will hopefully lead to good discussion here and effective
preventative measures for higher power systems.
A thick coating of 2-part epoxy or polyester may accomplish a similar
function as PMMA tubing at significantly lower cost. When uniformly
coated, errant strikes to the secondary will "splash" outward across a
relatively wide area of the outer surface of the coated secondary. The
coating dissipates spark energy by spreading it out and capacitively
conducting it to the secondary without creating damaging hot spots. In
practice, I've seen hot primary-secondary flashovers that left NO
permanent or visible effect on thickly-coated secondaries. These would
have undoubtedly caused melting and turn-turn shorts on an unprotected
secondary.
Your system also has a comparatively large topload OD compared to
primary OD. You may want to consider adding one or two additional,
larger-diameter, strike rails to spread out the E-field "footprint" of
the base. These will alter the E-field between the topload and base,
making it more vertical (in the space between the two) helping to reduce
strikes to the secondary. The larger strike rails could be an add-on
that can be removed before transporting the coil, and they would would
require any changes to your existing primary winding.
You may also want to consider adding a smaller toroid under the top
toroid. By elevating the top toroid, you'll increase the outward "throw"
of sparks while further reducing hits to the strike rail. In the latest
video there were a number of hits to the strike rail that came quite
close to flashing over to the lower half of the secondary even at 100
BPS. The hotter 200 BPS strikes combined with thermal rise seems to have
tipped the balance, unfortunately.
Good luck and best wishes,
Bert
Steve White wrote:
> I have also had this idea for some time. I would love for somebody to try this but even if it works I don't know if any of us could stand the expense.
>
> Steve
>
> ----- Original Message -----
> From: "Phillip Strauss via Tesla" <tesla@xxxxxxxxxx>
> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
> Sent: Wednesday, July 4, 2018 4:02:13 PM
> Subject: Re: [TCML] Fixing secondary strikes Re: Bad strike to a 12 inch traditional coil (somewhat terminal)
>
>
>
> Hello Jim,
> Although very costly in the UK, I was considering a 350mm diam cast acrylic 1 metre long tube (that's how it comes) with 5mm wall thickness to go over my 300mm (12") diam secondary, it would cover about the first two thirds of the tube, a good few inches higher than the previous strikes. Your comment on a dissipative tube caught my eye for that particular reason but I don't understand the concept of loading or that my idea would work, any explanation and/or prediction would be much appreciated.I'm contemplating your other suggestions (which are totally novel to me) with interest.
> Regards,Phillip.
>
>
>
> _____________________________________________________________________________
>
> 14 Broad Street, Stamford, Lincs PE9 1PG
>
> Tel: 01780 753008
>
> On Wednesday, 4 July 2018 21:26:39 BST, jimlux <jimlux@xxxxxxxxxxxxx> wrote:
>
> On 7/4/18 11:40 AM, David Rieben wrote:
>> Hi Phil,
>>
>> My deepest condolences for your loss. I know it's JUST a secondary coil,
>> but as a fellow coiler, I most assuredly feel your pain. On the bright
>> side, at least you did manage to capture some truly spectacular footage
>> of this secondary coil mishap. I have had this happen on rare occasion
>> with the operation of my big coil, though fortunately, none of my
>> mishaps turned out quite that severe! Only once did I actually have to
>> repair some damage to the side of my coil and was able to get it back
>> into full functioning mode via the repair. Since I must operate mine
>> outside, I did have one occasion where the wind actully "blew" one of
>> the streamers back into the side of my secondary coil, too. Lesson
>> learned - although refraining from outdoor operation during rainfall is
>> an obvious good rule, non-starters in windy conditions are also well
>> advised.
>>
>> I suppose this is a risk, that although may be small with a well-tuned
>> and efficiently operating coil, is never completely absent. :^/
>>
>
>
>
> I wonder if we could figure out a way to segment a large coil
> vertically, so if a segment gets damaged, you can just rewind that
> segment. Just off the top of my head, I'm thinking about something like
> segments with a hundred turns or so. Could we come up with a way of
> making the connections in a "good" way. I'm almost thinking about how
> you using field grading rings on a Van de Graaff. You don't want a
> complete shorted turn, but you could terminate the winding in some sort
> of flat terminal on the "mating face" of a segment. You'd stack the
> segments, and then put some compression on it (threaded fiberglass rod?)
>
> The other idea that comes to mind is if there is some way to "spread"
> the energy of the secondary strike.. Say your secondary were coated with
> a resistive (but still conductive) coating. Would that spread the
> current density enough to prevent burning through the insulation? Or a
> dissipative tube covering the secondary - not enough to "load" the
> secondary, but enough to "take the hit".
>
> OR, what about a second helix, space wound, that extends the length of
> the secondary, with some suitable resistive conductor, so the voltage
> profile matches that of the secondary (so no protective helix to
> secondary arcs), but so it doesn't enter into the resonant circuit. The
> protective helix would be mostly capacitively coupled to the secondary,
> establishing the voltage.
>
> What about something like a helix wound with wire, but with small gaps
> along the length.. the gaps don't break down normally, but if a streamer
> strikes, the gaps break down and provide a conductive (but lossy) path
> to the base.
>
>
>
>
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