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Re: First light, and a poor performance
Stephen Rodway [Legion-at-Bigfoot-dot-com ] wrote:
>Subj: Re: First light, and a poor performance
>
> Thanks for all the suggestions, here's a summery, and my response to
>them.
<snip, responding to my suggestions..>
>>3) You didn't mention anything about airflow over your gaps. Quenching
>> will be nonexistent without forced airflow, and at the power levels
>> you're operating at, difficult even with massive airflow.
>>4) Don't waste your time even thinking about operating without a top load.
>> A 4" sphere isn't much better. Even your proposed (finite element
>>array?)
>> 3x14" toroid is too small to extract good performance from a pig.
>>Gary lau
> Airflow over them is blown by a high capacity 80mm fan, as for top load,
>I chose 3x14" because it was the correct size to enable the system to meet
>the LpCp=LsCs and the quarter wave resonant conditions simultaneously. What
>size would you suggest?
An 80mm (~3") fan is probably too small, depending upon how well you've
channeled it's flow. It's necessary to not only waft air over the metal
to cool it, but to keep the air moving _through_ the spark channel to
remove conductive hot metal ions. As others have suggested, using only
static gaps with a pig is going to be an uphill battle, nothing but massive
airflow will work.
As to top load size, it's a difficult balancing act, several criteria
must simultaneously be met. You've met the resonance criteria, but not
the radius of curvature and top capacitance requirement. You cannot get
huge sparks if your toroid breaks out too soon. Also, understanding of
this is only slowly emerging, but it seems that high top capacitance is
essential in getting big sparks, probably because it acts as an energy
reseviour. You'll want something on the order of 6" x 30" (total guess
here as I have NO experience with pigs), and you'll have to either
increase your primary cap or add to your primary to maintain resonance.
>>With small and medium size systems never start with a fixed primary of
>>10-11 turns. You probably don't have enough inductance to bring the system
>>into tune. Always use some scrap wire affixed to edgewise cardboard and
>>use 25-30 turns with a scraped tap at each turn.
>>With this setup your main cap
>>value should be around .02 MFD (2.0 nF) for effective tuning. It sounds
>>like you have way too much cap for this system with a 14 x 3 toroid. The
>>lowest turn on the sec. coil should be at least 1 inch above the horizontal
>>plane of the primary coil for proper coupling -- you are way over coupled if
>>you have them even, and the pri-sec spacing should be at least 1 to 1 1/2
>>inches.
>>D.C. Cox
.02 uF is 20 nF, not 2.0, this may have caused some confusion.
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Regards, Gary Lau
Waltham, MA USA