RE: Perfecting my final design...

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Lau, Gary" <gary.lau@xxxxxx>


Hi Adam:

Yes, a 2-layer primary will give you a high inductance in a compact
space.  I use one and I recommend it.  My 2-layer primary may be seen at
http://www.laushaus.com/tesla/primary.htm.

Pete Komen sent me an Excel spreadsheet that does a very good job of
calculating the inductance of a 2-layer primary, and since it's such a
useful bit of code, I'll ask Terry if he could post it to Hot-Streamer.

http://hot-streamer.com/temp/2LayerPrimary.xls


The final inductance is very dependant on how close the two spirals are
to one another.  If you take the other extreme where they are infinitely
separated, the inductance is just the sum of two stand-alone spirals.
Two ten-turn spirals does seem like a lot, but I haven't done the
numbers - I'll leave that to you!

Be sure that you have an insulating sheet with no holes towards the
perimeter separating the two spirals, and try to minimize the number of
unused turns, as they generate very high voltages that want to arc to
the opposite layer.  Use at least 2 inches of clearance from the
outermost turn to the edge of the insulating sheet.

For the propeller gap, as long as the rods come in 7" lengths, you might
as well use it that way.  Are Oriental Brand motors still available?

For a 15/60 NST and a sync gap, you may want to use a slightly larger
cap than .02uF.  .03uF is more typical, and I found that a .04uF cap
delivered the largest bang for me.  You may also want to make the ID of
the coil accommodate a 6" secondary, for future expansion, although that
may be tight if you're constrained to 17"x17"..

I wish you luck with your acrylic sheet.  I originally used acrylic to
separate the two spirals, and it cracked when I cut the 6" hole in the
center.  Lexan is MUCH nicer to work with and doesn't crack, although it
is more expensive.

Regards, Gary Lau
MA, USA

> Original poster: "Adam R." <arabraxas@xxxxxxxxxxx>
>
> Hello, this is my first time to this "forum"...well, I'm working on a
> "second version" of my coil (ie, I want to make it as professional as
> possible) and would like to make sure I am doing everything correctly.
>
> Here are some specs: The secondary is 4"x18" (24.2mH), a .02uF cap
bank,
> 15-60 NST, and a Terry Filter for protection.
>
> I have a question on the primary--I'm trying to make it high
> quality/durable and compact. What I'm trying is something that I've
seen
> before and have been wanting to give it a go: a simple dual layer
primary.
> It will be 1/4" OD Cu tubing ten turns, each wound in opposite
directions
> (so 20 turns total, top and bottom layers). So each layer will be
ABOUT
> 0.0306 mH. Does this all sound right? I'm worried I might build it and
find
> I need more inductance! Or am I making it overkill with two layers of
TEN
> turns? Because the total width of the base is 17"x17", I need to get
the
> size right (I have acrylic pieces and they are expensive... cannot
mess
> up!) My coupling to the secondary is about 1".
>
> Second question is with the rotary spark gap. I'm making a simple
propeller
> gap using a cheap (ie low power) Oriental Brand motor. I'm pretty much
> sticking to what is commonly done, but what length should the rod be?
6" or
> 7"? It's my intuition to go with the latter...
>
> Any other recommedations? I'd like to get this coil working very well
and
> not miss anything or screw something up.
>
> Thanks for the help!
>