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Re: Another Capacitor Order?

Hi Kevin,

Scott Myers here, addressing your questions.

> I am interested in ordering a cap with you guys.
> I am in the process of getting a 5kw xfmr, what would be a good value cap for
> this xfmr. same question for using a 10kw xfmr (eventually).

Well, first thing is I would need to know what the voltage of the transformer is.
For the sake of this conversation, I will assume it is 14,400 VAC RMS.  A 5 KVA
transformer can produce approx, 350 mA continuously.  A 10 KVA, twice that.  Now
if we look at the maximum capacitance value from a transformer matching pooint of
view, this 5 KVA transformer could handle .1 uF and the 10 KVA could handle .2 uF.
Those are whopping big capacitors.  If you wanted to run a balanced circuit, you
would need twice those values.  So, as far as matching capacitors to your
transformer(s), you can handle very large caps indeed.

The down side to these large caps is cost and the number of turns in your primary.
In classic Tesla system (2 coils), coupling is very important.  With such large
capacitors, the number of turns on the primary coil will be few.  That will hurt
your coupling.  You will not get as efficient of an energy transfer to the secondary
as you might want.

You might want to look at choosing a capacitor size(s) based upon the range of coil
size(s) you are going to build.  Look at the maximum length of the secondary winding(s).
It is a good practice to have the primary winding's diameter near the same as the
length of the secondary winding.  This promotes efficient energy transfer between
the two coils.  It also helps in getting critical coupling set-up easily.  Once you
have selected the diameter of the primary you can select the number of turns on the
primary and capacitor size for the appropriate tuning range needed.  All of these
calculations involve many trade-offs.  You will probably calculate several dozen times
to see where it is all going.  There is no hard and fast rule on selecting these
components.  Many different ranges will work very well.  The only real rule I can think
of here is use common sense.  Don't choose a primary with 80 turns and a capacitor of
.005 uF in size, or vice-versa.  The most popular capacitance ranges for Tesla tank
circuits with primarys of 15 turns or so ranges from .01 uF to .05 uF. By going to these
smaller capacitors you will save yourself  much cash and still end up with a very efficient
Tesla systems, and that means big sparks.

> Also,what does condensor products do differently in manufacturing their caps
> form the ones that you roll at home? Is that type of cap as good as a
> homemade plate cap? doesn't a rolled cap have more impedence and less pulse
> capability than a stacked plate cap?

Nearly all commercial capacitor manufacturers, including Condenser Products, uses
many small capacitors wired in series/parallel to get to the required capacitance
value and voltage rating.  These individual capacitors inside of our pulse capacitors
use what is called an end-foil design.  It is a small rolled capacitor that gathers
the thin foil plates on opposite ends of the roll. It resembles a Tootsie Roll left in
its covering.  By using this method, the "coil" of the rolled capacitor construction
has no inductive effect.  This same construction technique can be used at home, if a
thin foil is used for the plates.  This keeps the pulse capability very high while squeezing
every bit of capacitance out of the material used.  They are also very careful in the
series/parallel arrangement and connecting busses to keep the internal inductance  very
low.  Theoretically, a plate style will have better pulse characteristics and lower impedance
than a rolled style, but it would be nearly impossible for an individual to acheive homemade
capacitor quality that equals my commercially built units.

Are these types of capacitors as good as a homemade plate style?  They are much better.
These caps are made by machine and are very uniform.  Vacuum and heat are also used in
their manufacture.  They are high-pot tested to ridiculously high values.  Generally if they are 
going to fail, it will happen then.  They don't drift in value and are relatively small in size. 
 They have a 1 year warranty.

I have built several homebrew capacitors.  Considering the price of the materials required,
time involved, quality achieved and the chance of capacitor failure in a homebrew unit,
it is my opinion that is is cheaper to buy a pulse capacitor made commercially.

Scott Myers