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Re: Interesting but not so impressive results...


From: 	Peter Electric[SMTP:elekessy-at-macquarie.matra-dot-com.au]
Reply To: 	elekessy-at-macquarie.matra-dot-com.au
Sent: 	Friday, September 12, 1997 7:23 AM
To: 	Tesla List
Subject: 	Re: Interesting but not so impressive results...

Tesla List wrote:

> 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?
>
> 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

You're probably getting sick of hearing this by now but I agree, you are
running at 3/4 wave instead 1/4.

My secondary is 6" and tunes with a 15 turn primary and .012 mF cap.
Even with .02 you're going to need more than 15T with a 12" secondary. I
think you should give away the idea of using huge caps (.1 etc) and use
a larger primary instead. It will cost a lot! less and gives you better
coupling than those old 3 turn primaries! (not to mention the latest
posts on the benefits of "surge impedance")

Cheers,

Peter E.