Re: a few questions about secondary construction

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <FutureT-at-aol-dot-com>

In a message dated 11/2/01 2:29:39 PM Eastern Standard Time, tesla-at-pupman-dot-com 
writes:

> I just got my 9" by 30" spun aluminum toroid, and am considering
>  rebuilding my coil to do it justice.  Would it be better to have an 8" 
diameter secondary, as
>  opposed to my current 6.5"?  Perhaps even 10"???  (the primary will, of
>  course, be adjusted accordingly)

Bill,

It seems reasonable to first consider the spark length.
This toroid should nicely produce a 10 to 12 foot spark.  This
means the secondary should be 5 feet tall, if you run at 120 bps.
if the secondary is 5 feet tall, then it should be about 9 to 11"
dia.  I think 8" pvc is actually about 9", and 10" pvc is really
11".  I'd maybe go with the thick walled PVC since the thick wall
won't hurt the spark at all.  I'd use at least 1000 turns of
wire and possibly 1400 turns or so.  If you use a higher 
breakrate the secondary can be shorter from a voltage
breakdown standpoint.  But it's good for the coil to be
tall anyway, so the sparks are less likely to hit the primary,
or hit the floor.  I kind of like narrow dia. coils such as
the 8" pvc because they are more lightweight, and can use
thinner wire.  But still the 10" dia may actually be perfect,
if you don't care too much about the weight.  I do like the
secondary to be about 1/3 the dia of the toroid, and about
equal to the minor toroid diameter.  These are rough
guidelines of course.  You'll probably need 6kVA + to get
12 foot sparks.

John