Re: Size and weight of portable coils

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

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi John,

I move my coils around a lot so here are my words of wisdom ;-)

I like the corrugated dryer ducts for a toroid.  They are not smooth and
beautiful, but you can throw them in the car without any worry of damage.
$9 and 1/2 hour, and they are new again.  I have some really nice big
toroids that are almost "too nice" to use.  The dryer duct toroids are also
light and easy to carry especially since you can bump them into things ;-)

Hopefully, the rotary gaps will be replaced soon buy the much lighter
triggered gaps.  Carrying the motors and the heavy mountings for the rotor
and electrodes presents a major "chunk" to carry.

I agree totally that the secondary should be made long enough to remove the
worry or racing arcs.  A few more inches in secondary length can save a ton
of problems.  This also helps when the coil is used after rain and such
outdoors :-))

The variac is always like an iron brick to carry.  Maybe the lamp (fan)
dimmer control will someday replace it or the newer electronics that are
being worked on.

The NST may be around for awhile...  Having carried around and shipped a
few of the 15/120's has given me a new respect for the force of gravity.
Maybe a few smaller NSTs and opposed to one big one...

Those oil filled caps waiting to explode all over the car are long gone.
MMC are carried without a second thought.  However, they do need to be made
sort of solid to withstand a throw in the trunk...

It is best to try and put the parts together in easily carried "chunks".
Too many light parts need lots of trips to the car while a few big heavy
chunks will break your back.  All the wires and such should be basically
preassembled so only the connections need to be made.  Those light little
travel carts used at the airports can be really handy!

Cheers,
	
	Terry



At 08:14 PM 8/11/2001 -0400, you wrote:
>Hello all,
>
>Often it is desired to build a portable coil which can be taken
>to various places and events.  Often too, a coil of reasonable
>power and spark length can be heavy and bulky.  I think it 
>would be useful to consider how a coil can be made compact
>and light, yet powerful.
>
>Many components are heavy such as rotary gaps, blower
>motors, large spun toroids, large NSTs, etc.  To keep the
>weight and size down, here are some possible approaches.
>
>Let's say for instance we want a 65" spark.  This demands
>that the secondary be about 26" tall to prevent coil breakdown
>at 120 bps.  It is likely that the sparks will have a tendency to
>arc down and strike the primary however.  One therefore 
>wonders if it may be better to make the secondary taller to
>eliminate the need for a small toroid under the main toroid
>to keep the sparks away from the primary.  Certainly this
>approach is simpler.  I estimate the secondary should be
>about 28" tall.  The form should be a lightweight, thinwall
>plastic.  It will also help for both size and weight to make
>the secondary narrow at maybe 5" or so, perhaps 4".
>Next consider the toroid.  A corregated one
>is light, but doesn't give such nice moving sparks, so a spun
>one may be better.  The spun one can be removed for
>transportation so weight is not so much of an issue here.
>I estimate that a 6" x 21" toroid is large enough.
>The weight of the secondary wire on the form can be quite 
>heavy if thick wire is used.  Thinner wire will give better or
>at least as good results and is a lot lighter and cheaper.
>For the base of the coil, a lightweight wood such as pine
>can be used.  For the gap, a very small rotary can be used,
>or perhaps a triggered gap, although the blower used to cool
>the gap may add to the weight, and give no weight advantage
>overall.  The primary can be made from 1/4" copper tubing which
>is not that heavy, or possibly aluminum tubing.  The primary
>can be supported by a ribbed structure for light weight.  If an
>NST is used for power, it can be unpotted to reduce the weight,
>and to increase reliability.  Also some shunts can be removed
>to give the NST a little more zip.  Safety gaps only can be used to
>protect the NST since they can be built lightly and compactly.
>In a properly built sync gap or triggered gap coil, the safety
>gaps will never fire.  The capacitor can be an MMC for light
>weight.  I like to make the secondary so it simply plugs into
>the base.  There is a brass contact at the bottom of the secondary
>and in the base.  Contact is via gravity.  I use this method for
>my TT-42 coil with excellent results.  Casters can be mounted
>to the coil's base, to allow it to be wheeled through
>large buildings instead of carried.  Special carrying cases can
>be made to protect the toroid and secondary during transport.
>
>John Freau
>