Re: [TCML] Considering a new coil build...

[David%20Rieben <drieben@xxxxxxxxxxx>]

Hi Travis, 



Welcome back! ;^) I'm sure that you will get 

numerous repsonses to your posting but I will 

share a few of my observations. 



First of all, MMCs could definitely work on a 

coil of the magnitude that you propose but the 

purchase and soldering together of several 

hundred MMC caps (which is pret ty much 

what would be required for a p ig powered 

coil system) would prove to be impractical- 

ly expensive and laborous when compared 

to a single unit commercial pulse capacitor. 

MMCs are great and highly recommended 

for small to medium sized NST driven coils 

but when you step up to piggy power, their 

practicality starts to become more of an is- 

sue. 



Second, with your variacs, "I" would leave 

the 3 of them intact although I would opt to be 

able to manually turn the voltage control and 

remove the motor drive. To be able to use one 

as a current control, you must cut through its 

core to gap it and if you're not careful, you'll 

just end ruining a perfectly good variac. That 

has been my personal experience. You can 

use a 225 amp stick welder for very good 

voltage and current control. You may also 

consider constructiong your own ballast out 

of building wire and an iron core from a large 

discarded transformer. I used the two piece 

core from an old x-ray transformer and wound 

each "leg" with paralleled coils of #8 building 

wire, about 105 turns each . You would have 

to be sure that your core material has sufficient 

cross sectional area to handle the power that 

you will be controlling. 


Your wire size for you secondary is pretty 

much right in the "ballpark" of what you 

would want but you should really opt for 

a significantly larger secondary form than 

8"x30". As you mention, sonotube is one 

option for a larger diameter secondary 

form. Also, I went to a local plastics suppli- 

er and ask for 12" PVC duct pipe. They had 

it but I think they would only sell it in the 10 

ft. lengths and it was a bit pricey. However, 

a good coiling friend of mine was also looking 

for a secondary former so we both chipped 

in on the former and cut it in half. You should 

definitely go with a 12" or even larger secondary 

form to be able to utilize the greater induct- 

ance which is a good thing for longer sparks. 

Most suggest keeping the secondary aspect 

ratio in the 4:1 to 5:1 range so a 48" to 60" 

of 12" form would would be great. Of course, 

you'll need even more wire for this coil size and 

you may find it to be more practical to go for 

the larger 12" spool of magnet wire (~80 to 

100 lbs.) as opposed to the small 6" spools 

(~8 to 11 lbs.) You may check into a local 

distributor of wire or find a motor repair 

shop if you're in a larger city to see if you can 

purchase some wire from them. 



For the primary coil, the copper tubing is a 

great idae although I would opt for 1/2" tu- 

bing since you're building a piggy powered 

system. Some would also suggest flat cop- 

per strip as it would allow for a much smaller 

outer diameter of the primary coil which can 

help to reduce primary coil strikes. 



IMHO, the G-10 with tungsten electrodes 

ARSG is the way to go. However, I would 

opt for at least a 10 " diameter disc as an 8" 

disc would render standoff from the shaft/ 

hub quite a challenge at these voltage/power 

levels. "I" use an 11 1/2" dia. x 1/2" thick G-10 

disc with (8) 3/8" x 1 1/2" long tungsten flying 

electrodes and (4) 1/2" dia. x 3" long tungsten 

stationary electrodes. I also use a DC motor 

from a treadmill as the drive motor and recti- 

fy the 120 VAC to DC and use a variac for 

speed control. These types of motors are 

quite powerful for their relatively small size 

and lend theirselves very easily to infinite 

speed comtrol via a variac. 



You could use one of the 8x24 toroids as a 

shield toroid under a larger main toroid. I would 

go for a toroid cord diamter of at least 10", if 

not 12" and a major diameter of at least 40" 

for the main toroid for better field control and 

better E-field shielding. I think you'll find that 

a single (or even stacked) 8x24 toroids would 

really limit your coil's performance for the 10 

kVA pig power that you have available. 



RFI/EMI filters do help reduce the transients 

produced by the coil's primary circuit that tend 

to get back into the power supply lines. Just 

make sure that the filter is up to the task for 

the current that will be drawn by your coil. 



Good luck with your project and keep us in- 

formed of your progress. 



David Rieben 



----- Original Message ----- 
From: "Travis Tabbal" <travis@xxxxxxxxxx> 
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx> 
Sent: Tuesday, March 24, 2009 2:29:02 PM GMT -06:00 US/Canada Central 
Subject: [TCML] Considering a new coil build... 

It's been a while, but I miss Tesla coiling. :) 

I had purchased a number of useful parts before stopping years back, so 
here's what I have and what I'm thinking. I'd love some thoughts from you 
guys. 

Power source: 10KVA Pig 14.4KV 

Control: 3 giant variacs (I forget the rating). I planned to use 2 to 
control voltage and modify one for inductive current control. They are 
currently stacked with a motor drive for the brushes. I planed to remove the 
motor and one of the variacs. The other 2 will remain ganged up and I'll 
move the shaft by hand with a big plastic wheel or something. There may be 
better ways to handle this bit. I might be able to obtain an old arc welder 
for the ballast. 

Cap: MMC. To be determined. Ideas welcome. 

Secondary: 8" diameter ~30" long. What do people use as a form for these big 
coils? I was thinking of drying some Sonotube or other cardboard tube and 
coating with laminating epoxy or even just polyurathane. Or I could get 
ambitious and try to make a fiberglass tube by adding a release agent to the 
sonotube so I can slip the fiberglass off after curing. Considering AWG20 
magnet wire. Works out to about 1000 turns. Need a source for that much wire 
in one spool. The 11lb spools on EBay and such are too small. I need about 
15lb if I'm figuring right. 

Primary: Copper tube spiral. Probably .25". Need to run the calcs to get the 
number of turns. 

Gap: Async RSG. I'm thinking to try to build one with .25" G-10 and tungsten 
electrodes. About 8" diameter. Construction tips welcome. Particularly 
holding the flying electrodes in place. I'd like to have it be speed 
controled, so I can vary break rate around a bit. Even if it's not realtime 
adjustable. 

Topload: I bought 2 8"x24" spun toroids in a group buy years ago. Still in 
the box. It's a shame not to use them. They are so pretty. :) 

I also have some RFI filters for the pig I think I bought on the list. 

Note that I don't have a machine shop, though I do have a decent tool 
collection both power and hand types. So I can't do fancy stuff like 
machining electrode holders from bar stock. :) I can drill and tap it with 
some acuracy, but nothing too special. No lathe or mill. :) 
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