Re: (Fwd) Re: Secondary Coil design *Correction*

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "G by way of Terry Fritz <twftesla-at-qwest-dot-net>" <bog-at-cinci.rr-dot-com>

>Original poster: "Malcolm Watts by way of Terry Fritz 
><twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>
>
>Dear all,
>            I said:
>
>On 16 Nov 2001, at 8:05, "Tesla list" <tesla-at-pupman.co wrote:
>
>>  Hi Gregory,
>>
>>  On 15 Nov 2001, at 11:54, Tesla list wrote:
>>
>>  > Original poster: "G by way of Terry Fritz <twftesla-at-qwest-dot-net>"
><bog-at-cinci.rr-dot-com>
>>  >
>>  > Hello List,
>>  >
>>  > I have noticed a failure pattern in all of my secondary coils and am
>>  > searching for a solution. Each one has had a failure within the
>>  > bottom 25 turns (shorts between turns).During the most recent
>>  > failure, I was watching the operation very carefully in a dark room
>>  > and I am sure there wasn't any arc struck between the secondary and
>>  > the primary, or even corona.
>>
>>  The highest voltage gradient per turn occurs in the bottom portion of
>>  the coil. Polythermaleze wire should fail in that fashion so it
>>  suggests to me that the wire insulation is not the best for this
>>  application.
>
>The "should" in the second sentence should of course be "should not"!
>
>My apologies all.
>
>Regards,
>Malcolm
<snip>

Hello Everyone,

Yes, I believe the insulation is not as good as it could be. It is 
polyurethane nylon, which feature seems to be a 155 degree celsius 
rating. But I bought it cheaply from Brigar (thanks Michael), so I 
will definitely try spacewinding the wire. Will spacing the first 100 
turns or so be sufficient?

Here are some specs for those interested:

power supply: MOT doubler for 12 kv, 240 v 20 a circuit, contactor actuated

primary: 23 turns 1/4" copper, 1/4" spacing, tapped at 21 (21 to 23 
seem to have exactly the same performance)

cap: Geek cap MMC, 0.041 uf 20 kv

gap: variac controlled right angle grinder ASRG, 11000 rpm,  5 
tungsten flying electrodes, 1 or 2 gap for bps selection, plywood disk

secondary: 8.5" dwv pvc pipe, 28 gauge wire, 2000 turns, 26" winding length

topload: 3" flex drain pipe/al tape corona shield, 2 4" x 25" stacked 
flex pipe toroids

extras: strike ring with inline 2" spark gap, 20 a emi filter ($1.95 
-at- meci-dot-com)

So far, I have measured sustained 55" strikes to ground. I will try 
increasing my tank wire gauge from its current 8 ga to gain some more 
efficiency. Also, a larger topload is needed. I have 7" drain pipe to 
use for that. I have pfc caps to be added.

QTC predicts a 50 khz operating frequency. I have not verified this 
with any measurement.

I found that the doubler circuit works nicely to limit line current 
draw (by way of inline capacitors). I am not sure if it is possible 
to have a resonant rise in a doubler circuit, but the doubler circuit 
capacitors would be near resonance with the transformer when the 
diode is forward biased. I am quite pleased with the jump in streamer 
intensity versus my 15/60 nst supply. I am sure with the new wiring 
and topload this baby will be pushing 6-7 feet.

As a side note, I found that my home furnace thermostat wire runs 
nearby the coil- after its control board mysteriously stopped working 
:)

Thanks to all of you for supplying your ideas and inspiration, and, 
again, to Chip and Terry for making this community possible.

Gregory