Adam,
It looks like everyone gave you some sound answers but I wanted to share my
experience from last week with you because it might help a bit. I decided
to fire up the old SGTC for the first time in probably 5 years. I also
wanted to run it outdoors (for the first time) and have it close to the
ground (for the first time) because I figured the perspective would be
better for my young son who was watching. Anyway, nothing went flawless of
course and I found myself experimenting with different sized toroids,
different spacing and orientation/placement of each. As already mentioned,
you want to protect against corona on the top windings of your secondary to
avoid damage. I found on mine that if the lowest section of my largest
toroid was overlapping the secondary windings by maybe 1/4-1/2" then I was
fine. Otherwise, I would clearly see 2" streamers from the top of the
secondary windings. If the largest toroid was placed lower than that I
would get arcing from the toroid down to the strike rail. However, if I
first used a very small toroid which hugged the secondary just above the
top windings-- then placed the largest toroid on top, I was able to raise
the larger toroid several inches and resolve my issues with arcing to the
strike rail. In other words, the smaller toroid protected the secondary
windings and allowed me to have my working topload higher up from the
secondary. Also to note, If I spaced the two toroids too far apart from one
another, I would get streamers from both. However, having the two nearly
touching produced streamers from "only" the larger (top) toroid. I did this
all in complete darkness allowing me to see even small amounts of corona
and used a variac to start runs at a lower voltage. As also mentioned in an
earlier response you will have to readjust your primary tap point once you
find a configuration that works but it is certainly worth the effort of
experimenting!
Good luck you and I hope to see some vids of that coil running when you get
the bugs worked out.
Matt
On Wed, Jan 27, 2021, 4:40 PM Steve White <steve.white1@xxxxxxxxx> wrote:
> Yes, but you can compensate for any tuning changes caused by toroid
> capacitance changes by adjusting the tap point on the primary coil.
>
> Steve White
> Cedar Rapids, Iowa
>
> ----- Original Message -----
> From: "Adam James" <adamjamesarmy60@xxxxxxxxx>
> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
> Sent: Wednesday, January 27, 2021 9:45:20 AM
> Subject: Re: [TCML] Topload position
>
> Should I understand then, It is a"trial & error" thing? Move the toroid up
> for best performance until I get corona from the top turns, then down
> until corona stops?
> AJ
>
> On Wed, Jan 27, 2021 at 10:33 AM Steve White <steve.white1@xxxxxxxxx>
> wrote:
>
> > The top load serves 3 purposes:
> >
> > 1. Provide capacitance for the secondary circuit
> > 2. Provide a smooth surface to build up charge
> > 3. Provide EM shielding for the top turns of the secondary coil to
> prevent
> > corona
> >
> > The toroid should be placed just high enough above the secondary coil to
> > prevent corona and discharges from emitting from the top turns of the
> > secondary coil. In addition to causing power loss, corona can damage the
> > insulation of the top turns. Since toroid height also affects
> capacitance,
> > you may have to re-tune your coil after movement.
> >
> > Steve White
> > Cedar Rapids, Iowa
> >
> > ----- Original Message -----
> > From: "Adam James" <adamjamesarmy60@xxxxxxxxx>
> > To: "tesla@xxxxxxxxxxxxxxxxxx" <tesla@xxxxxxxxxx>
> > Sent: Wednesday, January 27, 2021 7:37:16 AM
> > Subject: [TCML] Topload position
> >
> > I have viewed hundreds of TC pictures and it has become apparent to me
> that
> > the placement of the toroid in respect to the top of the secondary is all
> > over the map!
> > so, WHAT determines where the topload should be placed?
> > AJ
> > _______________________________________________
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