Hi Gary,
I'm using a 6" x 30" secondary with an 8" x 34" toroid (plans are to use this with a larger coil in the future, and these are very expensive so I chose a single purchase of the larger between the two sizes considered). 10Kva pig that is current and voltage adjustable, flat primary with .045uF caps using an asynchronous rotary spark gap.
Per Bert's input (thanks Bert), tuning with the barb has been accomplished, which brings me to a question about increasing bang size: Can bang size also be increased by decreasing the rpms of the spark gap, by allowing a larger charge to take place (using 8-point RSG on a variable DC motor)? Interesting thought on the decreased barb length. The current one is 1" long, I may go for 1/2" or perhaps 1/4" to see about increasing the breakout voltage.
Anyway, I do have a smaller toroid I'll try (5" by 30" - a large cast-aluminum corona ring with an aluminum plate welded in the middle, so yes, it is odd, but it appeared to be effective) to get some perspective on that.
Cheers,
Terry
From: Gary Lau <glau1024@xxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Sent: Sunday, October 29, 2017 1:52 PM
Subject: Re: [TCML] First coil
Hi Terry,
I'm thinking that if the toroid size is too big, it won't break out without
the barb. Perhaps a few more details of your coil will make for a clearer
picture. Power source, gap details, cap size, and most importantly, toroid
size? With toroids, bigger is usually better, at least as far as getting
the longest possible streamer from a breakout point, but if you're shooting
for sparks without a breakout point, a smaller toroid may be necessary.
Regards, Gary Lau
MA, USA
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On Sun, Oct 29, 2017 at 12:25 AM, Bert Hickman <bert@xxxxxxxxxxxxxxxxxxxxx>
wrote:
> Hi Terry,
>
> Racing sparks typically occur when energy is being injected into the
> secondary too quickly. Although this is _usually_ caused by
> excessively-high coupling, it can also occur when the bang size is too
> large for the size of your secondary, or if your system is significantly
> out of tune. To solve the problem(s), you'll need to first insure that your
> system is in tune, that P:S coupling is not excessive, and that your toroid
> is appropriately sized for your system's peak output voltage.
>
> 1. Tuning:
> I'd suggest initially running the system with a breakout point (or barb)
> during this phase. Reduce the primary spark gap length to reduce maximum
> bang size. Experiment with primary tap point until you get the maximum
> secondary spark length at a given variac setting. The system should be
> smooth running with consistent spark length under continued operation.
>
> 2. Coupling:
> If you don't see any racing sparks, slowly increase the "bang size" by
> widening the main gap slightly. Don't increase gap length beyond the point
> where the safety gaps begins firing or if you start to see racing sparks.
> If you see racing sparks, reduce coupling slightly and continue the process
> of increasing the main gap length until you can run at full power with no
> evidence of racing sparks. You may need to retune the primary a bit by
> increasing primary inductance slightly (i.e., moving the primary tap
> outwards 1/8 - 1/4 turn) to compensate for capacitive loading of longer
> secondary streamers. Any signs of racing sparks mean that you need to
> further decrease coupling.
>
> 3. Final tweaking:
> Reduce the length of the breakout point/bump to see if the coil can
> self-break from the toroid as you approach full power without introducing
> any racing sparks. Further decrease coupling if you see any evidence of
> racing sparks. Ideally, an appropriately-sized toroid will self-breakout
> before you reach full power. Failure to self-breakout can occur if the
> minor toroid diameter is too large (requiring excessively-high breakout
> voltage) or if the major toroid diameter (and capacitance) is too large,
> which reduces maximum topload voltage below the point of self-breakout. For
> this case you may need to operate your system with a breakout bump or point
> to insure breakout. Even with an optimal setup, you may still need to use a
> breakout point during humid weather when it's significantly more difficult
> to initiate breakout.
>
> Good luck,
>
> Bert
> --
> Bert Hickman
> Stoneridge Engineering LLC
> http://www.capturedlightning.com
> +1 630-964-2699
> ***********************************************************************
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> ***********************************************************************
>
>
> Terry Oxandale wrote:
>
>>
>> It's been a long time since I was more active on this list. I never was a
>> "technical" enthusiast, so being I've had the coil in storage for probably
>> 10 years, and have forgotten more than I remember about coiling. I'd like
>> to
>> tap the group for some help or advice please.
>>
>> My coil appears to operate as I remember it did, as long as I've got a
>> sharp
>> pointed barb sticking out the side of the toroid to promote a discharge.
>> When I remove the barb to get a normal toroial discharge, I get racing
>> sparks along the secondary, and nothing out of the toroid, all for the
>> same
>> power setting as the "barbed" setup (2kva). Thus I separated the secondary
>> from the primary in terms of vertical distance to lower any excessive
>> coupling (shooting in the dark here), but still racing arcs along the
>> secondary.
>>
>> Any ideas on the huge difference (or lack of performance) between "barbed"
>> and "non-barbed? No component changes have been made since a decade ago
>> when
>> it all worked great, and both configurations performing equally well.
>>
>> Terry
>>
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>>
>>
>>
>
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