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Tesla Coil Capacitors

 * Original msg to: Cwolins-at-orion.it.luc.edu
 * Carbons sent to: usa-tesla-at-usa-dot-net

Quoting Mattthew <cwolins-at-orion.it.luc.edu>:

> Rich, I just got a list of Tesla coil capacitor from Condenser 
> Products in Florida.  I am considering using a 20,000Vrms 
> 0.01uF w/my 15kV 60mA neon.  

If you are going to go out and purchase a commercially
manufactured pulse discharge capacitor I would suggest buying
something a bit larger. I would not even consider ordering a
single .01 uF capacitor. I think a .02 is about the smallest I
would go out and buy from a commercial supplier, and a .025 is
better still (I just bought one). The reason for this being that
the larger the capacitance, the more cost effective the purchase.
The larger capacitor gives you a bit more room to grow. You may
(and most likely will) go through a few neons while coiling. If
you buy the right commercial capacitor, it should last for years.

> I have seen several people talking about ordering from this 
> company and I just wanted to know you opinion about their 
> products.  

Top flight. I have purchased several capacitors from Condenser
Products, and have steered quite a few others in their direction.
I have yet to hear of a complaint. They are quite reputable,
build a very high quality product that is specifically engineered 
for Tesla coil tank circuits, and stand behind their product
after the sale with a written 1 year warranty against
manufacturing defects. Each unit is high-pot bench tested before
it leaves the factory, and this testing is serious. I have yet to
hear of one of their capacitors failing in a Tesla tank circuit.

> I recently called Plastic Capacitors in Chicago after reading 
> a paper written by William Meskan at Plasti Cap.  I called and
> asked for him and promptly recieved his desk.  He gave me all 
> the information that I requested and offered me a tour of the 
> facility. Since I only live 10 minutes from Plasti Cap.  I am 
> going to take him up on his offer.  Plastic Caps offered me a 
> 15kVrms 0.01 for $160 while Condenser Prod. offers a 20Kvrms 
> 0.01 for $160..  Pending what I hear from you and others I plan
> on ordering the 20kV from Cond. Prod. to ensure longer life for
> my cap.  The only downfall I see about ordering <from Condenser
> Products> is the 6-8 week lead time. Oh, well I am sure it will
> be worth the wait.  

They don't stock these capacitors, each unit is made to order.
Condenser Products has been going that little extra length to
gain market share (and repeat orders) from the growing Tesla
community. They are doing this by offering an equal or better
product at a highly competitive price. As far as I can tell they
are not only producing a very high quality, custom taylored,
product; they are offering it at the best possible price.

> Oh, One more question if I may.

> What type of wire did you use for the interconnects in the 
> Tesla circuit?  For example the wire supplying power from the 
> neon to the safety circuit and to the capcitor should be of 
> what type.  And also the wire from the capacitor to the primary
> coil should be of what type.  I don't believe I have seen this
> spec'd anywhere so I would appreciate your help.

The 60 cycle feed lines that connect the HV power supply to the
tank circuit need not have any special conductor. The amperage
requirements here are such that even 18 AWG is overkill on all
but the largest of coils. The high voltage current from the
supply transformer is usually measured in miliamps. The problem
is the HV hazard. Generally what I do is place my bypass
capacitance, safety gap, and RF chokes on an insulated board (I
call it the "filter board") very close to the transformer. I use
plain old solid copper bell wire (or whatever else is handy) to
connect the HV transformer terminals to the well insulated filter
board; 15kvac neon sign wire would be ideal here. These high-
voltage components are obviously situated somewheres away from
the operator (we frequently fire in poor light don't we?).

To make the run from the output terminals on the HV filter
board, to the tank circuit, I recommend using coax with a solid
polyethylene insulation around the core. I use RG-213 coax: it
has a stranded center conductor that is jacketed with solid
polyethylene. This holds up well even with tank circuit input
voltages in excess of 20kvac. There are other grades of coax as
well that are available with solid polyethylene jackets around
the core. With RG-213 coax the polyethylene insulation around the
core conductor is about 80-100 mils thick and offers an excellent
voltage safety margin above and beyond the 15kvac rated wire that
is commonly found in neon shops. I do not feel that neon type
15kvac HV wire is safe in this application; it is just too light
and is subject to cuts, punctures, and compression damage when
run across the floor. 

The sheath of the coax is grounded to the system RF ground (which
also grounds the HV transformer core), offering another barrier
of safety around the HV conductor. The coax is topped off with
yet another layer of insulation, offering HV protection,
durability, and safety that is hard to beat. This type of coax is
very tough, withstanding lots of physical abuse and still lasting
for years.

Now the Tesla tank circuit is the high current, oscillatory loop
around C1-L1-G1, where: C1 is your pulse discharge capacitor, L1
is your primary coil, and G1 is the main system spark gap. These
three components need to be placed close together and wired in
the straightest, shortest, possible path with heavy conductor
offering a large surface area. As a guide for the gauge of
conductor required to wire your tank circuit look at your primary
coil. It is best to wind your primary with copper tubing, smooth
strap, or heavy Litz wire. I like soft copper refrigerator tubing
best. This is also an ideal condutor for connecting the rest of
the tank circuit, except that it lacks flexibility. My favorite
conductor for connecting the pulse cap, gap, and primary coil is
fine stranded DC power cable. This includes battery cable,
welding cable, and DC power transmission wire. The strands in
this wire are parallel, the diameter wide, and it is flexible. I
have boxes of different lengths that I have soldered ring
terminals on the ends that I use for wiring the tank circuit.

Richard Quick


... If all else fails... Throw another megavolt across it!
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