Re: Secondary coil
Subject: Re: Secondary coil
From: Terry Fritz <twftesla-at-uswest-dot-net>
Date: Thu, 01 Jul 1999 19:33:09 -0600
At 07:55 PM 7/1/99 -0400, you wrote:
>Well as I said before I was hoping to get some results out of my 400 turn
>secondary before I upgraded.....looks like it's not going to happen. The
>secondary coil was the first thing I built on my TC so naturally it was built
>when I knew the least about what I was doing.....this resulted in a 400 turn
>bell wire wrapped coil. What I didn't mention was that the form I built it on
>is wood....wood sagely coated with non-conductive paint but still wood none
>the less.....another thing I failed to mention; I stripped the wire before
>winding it. Basically I built a very nice looking copper pipe *groan* Well
>back to the drawing board, since I'm doing the secondary over again I'll take
>all the suggestions for building a nice one I can get. First off I was
>planning on using pvc pipe as a form this time, I've heard about high rf loss
>from pvc forms, how much effect will this have on spark length?
No much. Compared to the other losses in the system, the pipe will not be
a significant loss. PVC is fine just clean it well.
>we're on the subject of rf loss what exactly is it? Can someone tell me
>exactly what rf loss is (and I'm talking about a good description here not
>just a short message telling me what the letters stand for) and why it's bad?
Various materials absorb RF energy and turn it into heat. This property
depends greatly on the material. For the secondary, any reasonable
material will have low enough losses. On a high power system, one may
start to worry that the form may get hot enough to do damage but few people
push enough power for this to be a concern.
One place where RF loss is very critical is in the primary capacitor.
Heating inside the relatively small capacitor can often do fatal damage.
Polypropylene has extremely low RF loss and that is why everyone talks
about it for caps.
>Then too I've read that thick walls of the tubing used as a form is
>bad....how much effect does this have on a coil and what is the best
>thickness to get?
Electrically it won't make a difference. On a very large coil the sheer
weight of the thing may be a factor.
>I was also wondering how much there is to gain by building
>a larger coil, instead of sticking with my 4" diameter coil I could go with
>6" or even 8" what is there to be gained from a larger secondary and how
>large can I go before it's overkill?
Personally, I would build the largest secondary I could that I would still
be able to tune to. Apparently, the larger the secondary inductance, the
more power goes into the arc. Also, the larger the top terminal the longer
the arcs. You just need to be sure that the frequency does not go so low
that you are unable to make the primary tune to it.
>To help answer that last question here
>are the current specs of my TC
>Trans: 10Kv .023A OBIT
>Cap: in the process of looking for one with a .0061uF rating (I'll probably
>go with MMC's here)
>Spark Gap: RQ's air blast gap
>Primary: reconstructing it but I plan to make it 20 turns of 1/4"
>refrigeration tubing angled at 30 degrees
>Secondary: that's what I'm trying to figure out
>Toroid: plan on getting a 4" x 9" aluminum toroid (made out of dryer hose)
>Wow...now that I look at it all I really have is a transformer and a spark
>gap....I"ve had all the parts for my TC three or four different times now but
>ended up junking them for some reason or another....maybe now that I know
>what I'm doing I'll get a working product *lol* Luckily my junked parts won't
>go to waste, I'll get a great looking Jacob's Ladder when I wire all my
>unused caps in with a transformer...
>Left, left I hadda good brain but it left...
>(p.s. I'll be leaving tomorrow morning to go on a trip and I won't be back
>for two weeks so it may be a while before I get around to answering any posts)