Re:

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

Original poster: Bart Anderson <classi6-at-classictesla-dot-com> 

Hi Chris,

Yes, all the items you listed would improve the coils performance. With 
more energy across the gap, it's a good idea to start thinking about a good 
gap design. Many on the list have built excellent gaps and there are many 
variations of good designs. I built a tungsten/G10 rotary disc which was an 
excellent choice over my previous "goofy" gaps (I'm not sure what else to 
call them). It was spendy, no doubt, but worth it. I am not one of those 
who can just spend at a moments notice, so it took a while until I managed 
to scrape up enough funds for the gap. But, if your going to spend cash on 
a nice rotary gap, take your time designing it and looking around at what 
others have done. My gap has the capability of 12 electrodes, however, I 
typically run 8 or 4 on synchronous 1/4HP motor.

MMC caps are probably the preferred, unless you just want to build a poly 
cap for the experience of it (there's nothing wrong with that). I built my 
MMC a few times until I set on a mechanical design that I liked (which 
ended up as rows of Geek Group caps around an 8.5" diameter pvc pipe. I 
painted the pipe a bright red to give it that "dangerous" look). Works 
great! Use it on smaller coils. I still run my prof. pulse caps on the 
medium size coil I'm running these days.

The variac I would recommend would be something along the lines of a 30A 
Powerstat. I came across a couple of these searching through surplus 
electronic houses. I picked them up for $40ea. They were inside some type 
of simple control unit housing. This was a good deal considering new variac 
pricing. I looked for a long time until one day I just happen to hit the 
right place at the right time. Just keep your eyes open and keep looking 
around. Don't look for just variacs, units which might house variacs.

Take care,
Bart

Tesla list wrote:

>Original poster: "Chris the great" <downnessisgoingup-at-hotmail-dot-com>
>I will try to get a variac sometime soon, although lack of funds is a big 
>problem right now :(
>I will try adding 3nF caps to the design (big bottle capacitors) until I 
>get a good arc length, starting at 20nF.  I will try to limit spark length 
>to reasonable limits (50-60 inches)
>I will hopefully be able to scrounge up enough money for my new sparkgap, 
>because my current one has an annoying tendency to burn the rubber hose 
>and light it on fire.  (looks cool though)
>
>
>
>
>>From: "Tesla list" <tesla-at-pupman-dot-com>
>>To: tesla-at-pupman-dot-com
>>Subject: Re: Date: Mon, 17 Nov 2003 07:21:10 -0700
>>
>>Original poster: Bart Anderson <classi6-at-classictesla-dot-com>
>>
>>Hi Chris,
>>
>>I know your running a lower voltage, and can allow the use of a larger 
>>cap size, but the coil length to spark length needs to be considered. 
>>200nF will certainly burn up the coil. The coil is only 22 inch in 
>>length. If I were you, I would shoot for a target of a random sparklength 
>>at about twice the coil length. Lets say you want roughly twice that 
>>length (approx 50"). I would then recommend something hovering around 
>>20nF, which isn't far off of your original cap size. In fact, you may 
>>want to try this with your original cap before going onto a larger cap. I 
>>also recommend the use of a variac to control the input voltage to the 
>>MOT stack so that "you" have physical control of the MOT's output voltage 
>>and can ramp up as needed. You'll probably find the length you desire at 
>>about half the input voltage.
>>
>>Take care,
>>Bart
>>
>>Tesla list wrote:
>>
>>>Original poster: "Chris the great" <downnessisgoingup-at-hotmail-dot-com>
>>>The main reason for the cap size is the output current on the transformer.
>>>The number of primary turns will be around 4, meaning I may have 
>>>problems with primary arcing.
>>>However, I am not sure if 200nF is a good idea, ss I could experience 
>>>alot of secondary arcing at that power level.
>>>I am new at this, and 200nF DOES seem to be on the large (huge) size for 
>>>my coil, however, would it work?  Or would my coil destroy itself?
>>>Should I keep cap size to perhaps 50-100nF at the very maximum?
>>>
>>>Chris
>>>
>>>
>>>
>>>>From: "Tesla list" <tesla-at-pupman-dot-com>
>>>>To: tesla-at-pupman-dot-com
>>>>Subject: Re: Date: Sun, 16 Nov 2003 11:36:31 -0700
>>>>
>>>>Original poster: Bart Anderson <classi6-at-classictesla-dot-com>
>>>>
>>>>Hi Chris,
>>>>
>>>>Are you sure you want to run a 200nF cap size? That's on the huge side 
>>>>for a 4.5" coil. Have you looked at the number of turns required on the 
>>>>primary when using a cap of this size? Also, the cap energy is going to 
>>>>be way up there for a coil this size. I run between 20nF and 80nF on my 
>>>>10KVA pig. David Rieben runs 85nF on his. These are just a couple 
>>>>higher powered coils for reference. BTW, these are roughly 13" diameter 
>>>>coils. What made you consider a 200nF cap? Was it the transformer 
>>>>output current?
>>>>
>>>>Take care,
>>>>Bart
>>>>
>>>>> > Original poster: "Chris the great" <downnessisgoingup-at-hotmail-dot-com>
>>>>> >
>>>>> > I have done some work on my coil since I have last posted, and I have
>>>>>found
>>>>> > my problem.  I think my tank cap is WAY to small for my MOT power 
>>>>> source,
>>>>> > which will soon be a 4 MOT stack.  I have calculated (from
>>>>> > http://home.earthlink-dot-net/~electronxlc/tccalc.html) that my tank 
>>>>> capacitor
>>>>> > should be 200nF at 8kV, 650mA, not 13nF.
>>>>> > I would like to make sure that this is indeed a good tank cap size, 
>>>>> so I
>>>>> > don't go and make a huge poly capacitor for nothing (actually 3 in
>>>>> > parallel).  Or would another type of capacitor be easier to
>>>>>transport/make,
>>>>> > or cheaper, or better?
>>>>> >
>>>>> > Needless to say I will need a very large topload, I was thinking 
>>>>> about a
>>>>>40
>>>>> > inch toroid on top of a 24 inch toroid, for a total secondary 
>>>>> capacitance
>>>>> > of 77.6pF, with an inductance of 19.6mH.
>>>>> > My primary inductance will be very small, however I have found that a
>>>>>lower
>>>>> > primary inductance produces brighter sparks that are slighly longer.
>>>>>I
>>>>> > will have 2 series static sucker gaps, until I can get a rotary gap.
>>>>>More
>>>>> > on my coil here
>>>>> > http://hot-streamer-dot-com/chris/4inchcoil.html
>>>>> >
>>>>> > Are these good values for my 4.5 inch coil?  I expect a major 
>>>>> increase in
>>>>> > performace over my 12 inches of spark so far, but will they be around
>>>>> > optimum values?
>>>>> >
>>>>> > Thanks!
>>>>> > Chris
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