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Re: Interesting but not so impressive results...


From: 	Malcolm Watts[SMTP:MALCOLM-at-directorate.wnp.ac.nz]
Sent: 	Sunday, September 07, 1997 5:11 PM
To: 	tesla-at-pupman-dot-com
Subject: 	Re: Interesting but not so impressive results...

HI Rod,
            Well that was a bit of a disappointment.....
 
> From:   Rodney Davies[SMTP:rgd872-at-anu.edu.au]
> Sent:   Sunday, September 07, 1997 8:24 PM
> To:     tesla-at-pupman-dot-com
> Subject:    Interesting but not so impressive results...
> 
> Hi All,
> 
> Well, tonight I finally got around to arcing up my old 12" coil...
> I'm using a 500W bar-heater as a current limiter, and a pole-pig 10KVA
> 11KV SWER transformer.
> The capacitor is approx 0.02uF. (home made rolled job).
> 
> Here's some brief specs -
> Secondary - 
> 900+ turns, self-resonates (unloaded) at 77Khz.
> 1mm enamel coated wire, space-wound at 21 turns/inch.
> PVC former diameter - 12.5"
> Aspect ratio - 1:3.75
> 
> Primary -
> 5 turns of 3/8" copper pipe spaces at 3/4" between turns (archimedes).
> 
> spark gap at this stage is a single static.
> 
> >From tonights effort, I figured I was getting around 5-7KV out of the
> transformer, probably about 200-300Watts...
> 
> The coil is currently unloaded, so the wire was merely sticking up in the
> air from the top of the secondary... (yup, I know...should be loaded).
> 
> Well, I did actually, with various round metal objects, but that decreased
> the output significantly, so I left it unloaded since that was where the
> longest arc was occuring...
> 
> Now here's the dissappointment, I was only getting about 4-5" of arc...
> 
> Yup, you're right, she's way out of whack! out of tune, out of
> everything...even the capacitor is too low, should be around 0.1uF...
> Anyway, plenty of time for the fix-ups...
> 
> The major point of tonights exercise was to observe the wave of the
> secondary coil... Here's what I did, and I know what you'll say - don't
> arc from the windings!!!
> 
> Ok, I held an earthed wire in my hand, holding it approx 6" away from the
> side of the secondary and observed the corona.
> There was a definate faint corona occuring, but the interesting part is,
> what sort of corona I obtained whilst moving the earth wire up and down
> the length of the secondary.
> 
> Ok, about 5" from the bottom, the corona was bright and dense and the arcs
> that did occur were fairly violent... I then moved the wire further up the
> secondary and observed that approx 1/3 the way up, I had the strongest
> corona and most violent arcs. 
> Then, I moved the wire further up and noticed that the corona almost
> dissappeared at about 2/3rds the way up, but then became brighter within
> 4" from the top.
> 
> Perhaps a diagram may help explain...
> 
> 
>     Secondary.
> 
>     _________
>     |   |   <---- started to become brighter.
>     |   |
>     |   |
>     |   |
>     |   |   <----- virtually no corona
>     |   |
>     |   |
>     |   |   <----- brightest.
>     |   |
>     |   |   <----- earth wire ---+
>     |   |   medium brightness    |
>     ---------           ---
>     Base.                \\\
> 
> 
> I guess this is an indication of what the wave is doing...
> 
> Also, there could be alot of contributing factors -
> 1/ zero quenching on the single-static gap
> 2/ completely out of tune
> 3/ No toploading
> 4/ primary circuit no where near in resonance
> 5/ secondary re-coupling energy back to primary
> 
> etc..etc...
> 
> But, I'm sure I'll fix it up soon, just need more money... 
> Some, if not most of you will agree, big coils are an expensive hobby! :-)
> 
> Anyway, I was just wondering if anyone would like to elaborate on the
> corona effects I observed with the secondary?

Be happy to. My reading of that is that you tuned to the second 
harmonic and the response will be appalling from a coil that size. Hi 
Q resonators are pretty narrow band in response. Your gap will be 
taking a beating I'd think. Rather than increasing the primary cap, 
how about increasing primary L. You won't get the best from you 
supply with a static gap but I think you'd be pleasnatly surprised at 
the results.

Malcolm 



> Yes, I know, never arc to the windings...but it's a really bodgy coil, so
> I guess it really doesn't matter...
> 
> 
> Thanks Guys!
> 
> Have fun!
> 
> Catchya!
> Rod
> 
> 
> 
> 
>