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RE: Ryan's Coil = Salvaged :-)



Original poster: "David Dean by way of Terry Fritz <twftesla-at-uswest-dot-net>" <deano-at-corridor-dot-net>

Hi Ryan,

> Original poster: "Ryan Ries by way of Terry Fritz
> <twftesla-at-uswest-dot-net>" <spud-at-wf-dot-net>
>
> 	Okay, it looks like I live on to coil another day.  I'm not
> sure what all
> was said about the thicker PVC and absorbing more RF, but I was able to
> completely sand away the carbon track and reveal fresh PVC underneath.  I
> then applied a new coat of polyurethane to the inside of the form. It's
> drying as we speak...
>
Cool. PVC is considered fairly loosy at RF (high dielectric constant) and
will heat up to some degree. The thicker it is the more it heats. I'm not
sure about this, but I seem to remember some one saying something about the
loss increasing by the square of the thickness, that is four times the
amount of energy absorbed for a one inch thickness than for a half inch
thickness. I would not worry about that so much at this point. Just keep the
run times to a few seconds and you will not generate enough heat to do any
harm.

After the poly dries, be sure to install a couple of disks of some kind of
insulating material (acrylic or lexan would be fine) inside the tube to
break the space up into sections. Glue the disks in place with a good
insulating material like epoxy or silicone. Make sure it is well sealed
around the outside edges where the disk contacts the inside surface of the
tube. Install a top disk in the same fashion and make sure there is no metal
inside the tube. If you put a bolt (metal) through the top disk, cover the
head with epoxy or silicone and put a baffle disk about an inch below it.
Make sure the top disk (and the top baffle disk in the case of the bolt)
have no holes in them and are well sealed (air tight). The inside baffle
disks may have a small hole about an inch from the edge (make sure the holes
do not line up in a straight line if you put holes, some say you need them
to let air escape in case of temperature change). The bottom disk should
also be sealed and have no exposed metal going inside the tube. (If you use
vent holes, the bottom disk should have one.) Doing all this will help keep
sparks from going down through the inside of the secondary.

> 	So now I salvaged the coil, but I desire to find out what
> is truly wrong
> with the system and make this coil work.  Starting with the ballast.  I
> have no powerstat/variac.  I had one for the 120v power for the neon sign
> transformers, but I have no idea how I'm going to get a 240v 10kva
> powerstat for the pig. ($$$) I have been using microwave oven transformers
> as ballasting, some fuses, and a master switch.  The extension
> cord used to
> transport the power is that oilfield stuff made with 3 6-gauge conductors
> coated with HEAVY insulation.  We lucked out by having a relative that
> works in the oilfield.
>
At this point I would suggest swapping the MOTs for the resistive ballast.
Yes it wastes power, yes it lowers the voltage, but it does have one
distinct advantage which is that it is linear. If you don't still have the
dryer element use the MOTs but hook the neutral conductor to the center lug
on the low voltage side of the pig and don't use the other side of line.
That will give you the same output voltage as 220 operation but the
inductance of the MOTs will have four times the current limiting ability.
That will keep output to a more manageable level. Put a good breakout point
on the topload. Set the primary tap to the calculated position. Double check
your math, and better yet have someone else check it too.

Now it is time to hold your breath and hit the switch. Hopefully you will
get something off of the breakout point. Kill it. Move the tap point 1/4
turn one way or the other. Hit it again. It will be better or worse. Maybe
not enough to notice. Kill it again. Keep repeating the procedure until you
find the optimum tap point. Now you know it is in tune.

While you are tuning keep eyes, ears, nose, etc. open. The best test
equipment in the world are the senses God gave you. If you notice anything
that does not seem right stop and investigate till you find out what it is.
Have someone else watching from another vantage point. If you get a racing
spark on the opposite side you may not see it and damage can be done before
you know it.

Once you know that the coil is in tune you can increase the power level. At
this point let me tell you that when I ran my coil with no variac and a
blown static gap I had to have some resistance in the primary circuit to get
it to work right. Now with a sync. rotary gap I can run with no resistance
and it is really pretty smooth. Also let me point out again that MOTs and
Welders are non linear. They will have some odd characteristics at some
operating point. If you are lucky you will not encounter this phenomena. It
is more likely that at some point you will.

Hope this helps, best of luck, and keep us posted.

later
deano


> Just don't tell me to tap my primary in any further. :-)
>
> -- Ryan Ries
>
>
>