RE: Please Help Me Prepare for BIG Coil

["David Dean" <deano-at-corridor-dot-net> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Hi Spud,

Some comments:

>
> Original poster: "Ryan Ries" <spud-at-wf-dot-net>
>
> 	Okay, it seems to be the going trend nowadays that everyone
> builds the
> biggest coil they can fit in their budget.

While this  does seem to be the case, some of us still find smaller coils
more practical as a research tool or just for fun, they are more convenient
and don't take so much recourses.


> 	After searching for months on end, my partner and I found a
> place only a
> few hours drive away that would sell us a new, single phase, 120v in,
> 14.4KV out, 10KVA pole pig for $150.

I'd like to know who, and where. More details please.

 I'm not going to pass that deal up
> after all the time we've spent looking, even though I still need
> to learn a
> lot about upgrading our coil to handle the additional power.
> Now, here's a
> pretty comprehensive rundown of our current coil setup:
>
 snip

>
> 120v in, 0-145v out, 1.4KVA Powerstat variac.  (Very nice variac, don't
> wanna blow it up, and a 1.4KVA variac very obviously is not going
> to handle
> a 10KVA pig. :-)
>
snip
> housewire.  Nevertheless, with 120v, I reckon it'll take some 84amps to
> create 10KVA of power.  I have a feeling that it won't be easy to find
> equipment to handle 84 amps, although wiring a new, dedicated circuit from
> my breaker box is no problem.

One thing that comes to mind that might just be easy to find is a "pigtail"
from a mobile home.
Lots of folks have their houses hard wired and have the pigtail left over.
The pigtails have 4 wires in them, all 6AWG fine stranded, and a heavy
PVC(?) overcoat. The conductors are good for 70 amps each as individual
conductors, but the whole bundle is derated for mobile home use to 40 amps.
If you are really going to use 120 volts, you could parallel the red and
black for hot and the green and white for neutral, you won't be using ground
anyway, (past the controls I mean) as the pig case and all the HV stuff on
that end should be grounded to its own dedicated RF ground. Of course if the
pig could be used at 240V in, which is likely,  a 40 amp 2 pole circuit
would be more than adequate.

> The spark gap is a single static 120psi air-blasted gap with 1/4" solid
> brass bolts as electrodes.  It works wonderfully for our NST power, and
> replacing the old steel bolts with the brass actually added over a foot of
> arclength to our Tesla coil.  Still, I have a bad feeling that 10KVA will
> tear the poor spark gap to shreds, and it will be very inefficient for the
> while that it lasts.  But, if you do feel that this spark gap is adequate,
> it would make me very happy to stick with it, because I don't know if we
> have the knowledge, and certainly not the materials, to build a
> rotary gap.
>  We do, on the other hand, happen to have a portable, powerful air
> compressor. :)

A static gap blown by an air compressor will work OK, and brass electrodes
will work OK.
Copper is better than brass, tungsten (as well as some of it's alloys)
better than copper.
You are right about the efficiency though. I found that pushing the limit of
a air blast static gap consumed 20 to 25 amps (240 volt input) and changing
to a SRSG dropped that to 4.5 to 5 amps. The whole rig was much quieter,
most of the noise came from the streamers rather than the sparkgap and air
compressor, and adding to the increased power efficiency was the replacement
of a 5 Hp compressor motor drawing about 20 amps with the gap motor drawing
a mere 1.5 amps.
Total KVA input for 34" sparks (arcs) with static gap blown by compressor-
9600 to 10800
Total KVA input for 34" arcs to a grounded target (same as above) with srsg-
1440 to 1560
Just a little bit of difference.

snip

> closer to .03µf.   High voltage caps are just too hard to come by for us.
> They certainly don't sell any in town (I live in the middle of nowhere, in
> the wastelands of Texas), and any that might appear on eBay quickly jump
> above the $100 mark.

Where in the great wastelands of Texas, if I may ask? Maybe we should think
about organizing a Teslathon for the wastelands! I think some of the guys in
the Dallas area had one a couple of years back.

snip
>
> The secondary is wound on 8" PVC (9" outside diameter).  It is 21ga magnet
> wire, and the winding is 32" tall.  I'm worried that 21ga wire might also
> be too small to handle the 10KVA pig.  The secondary is grounded to a 6
> foot copper pipe that I drove all the way into the earth, pulled back out,
> filled the hole with salt, then drove the pipe back in.  The grounding
> cable is a piece of (galvanized alluminum?) real power-line that we got
> from a local electrical contractor.

I think your secondary sounds fine. The grounding conductor doesn't.
Aluminum isn't galvanized, but it does oxidize readily. You really need
copper. A copper pipe, or tubing, or strip, or parallel several wires, or
use a welding cable, or if you must use aluminum, use a sheet of flashing.
I'd be willing to bet that at TC operating frequencies that a single strand
of 10AWG solid house wire is better than that aluminum stuff you have.

>
> Anyway, I am pretty confident that I am going to buy this distribution
> transformer, even if we have to spend more months building a new
> Tesla coil
> around it.  I thank you very much for your time, and I would be incredibly
> happy to get any advice you can give me about upgrading my system to
> accomodate the extra power, especially in the areas of ballasting the pig,
> and finding equipment to handle the potential 84 amps that the pig will
> draw.
>
> 	Thanks,
> 	   Ryan Ries
>
>
>