Re: Cage type secondary former

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

Original poster: "Malcolm Watts by way of Terry Fritz <teslalist-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Stephen,

On 12 May 2003, at 17:41, Tesla list wrote:

 > Original poster: "Stephen Conner by way of Terry Fritz 
<teslalist-at-qwest-dot-net>" <steve-at-scopeboy-dot-com>
 >
 > Dear list,
 >
 > I've been wracking my brains to try and find a suitable former for my OLTC
 > secondary. I was looking for a thin walled plastic pipe 10" dia x 30" long.
 > Then I thought, why do I need to use a large pipe at all? I could make a
 > round cage-like structure from a number of 30" long PVC drain pipes and a
 > top/bottom/stiffening plates made out of PVC or wood.
 >
 > I'm not sure if this would work, though. On the plus side it might have
 > lower losses since the winding is mostly in air. On the minus side though,
 > the field control might be poor because it's not perfectly circular and
 > there's no way to fit baffles. Mind you, I noticed Bill Wysock's Super
 > Model 13M used a secondary/extra coil wound on a wooden cage and it seemed
 > to perform reasonably well &) However, just because it works for a 30 foot
 > tall 700 turn extra coil doesn't mean it'll work on mine... Has anyone ever
 > tried an open frame secondary like this on a more realistically sized coil?
 > How did it go? Was it a pig to wind?

It was to some extent. I built a 17" dia ribbed structure with an
acrylic disk at each end and one in the middle to support the ribs
which were made of strips of acrylic about 2" wide fitted into slots
in the disks. The design called for a closewind of 0.9mm Cu dia wire
but on starting to wind this, the ribs started to bow, even though
the winding was edge-on to them. I gave up and wrapped the entire
structure with an 1/8" sheet of LDPE which was continuously welded to
form a cylinder. It still bowed somewhat making a closewind difficult
but worked in the end. I wound it suspended between a lathe chuck and
rotor on a stand.
      Being mostly affected by the winding design (which ended up with
a middle-of-the-road Q), the performance didn't justify the effort
and it wasn't worth trying considering the time it took and the cost
of the wire. I've wound better coils with far less effort on former
material such as old ABS (I think) drainpipe. The worst thing was
that the windings started slipping when the coil was stood upright
despite heavy varnishing. I've had that problem with HPDE gaspipe
formers too.

Malcolm