Interesting but not so impressive results...
From: Rodney Davies[SMTP:rgd872-at-anu.edu.au]
Sent: Sunday, September 07, 1997 8:24 PM
Subject: Interesting but not so impressive results...
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 -
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
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...
| | <---- started to become brighter.
| | <----- virtually no corona
| | <----- brightest.
| | <----- earth wire ---+
| | medium brightness |
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
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...