Cap specs (help)
I have been besieged by many of you to give a spec. or for info on the
company I buy from in light of the recent CP business.
First of all I can't really spec for you. You must realize that each
system is different and if you first spec a certain break rate, voltage,
whatever, and then later move up to a higher break rate, voltage,
whatever then your caps are in danger of failing not because of the
manufacturer but because of you! It only takes an inadvertent moment at
the rotary motor speed variac to over pulse a capacitor.
I use NWL (National Winding Labs) and not for any deep or meaningful
reason either. To my knowledge they offer all finished capacitors as is
with not warranty or promise or guarantee whatsoever, other than a normal
and reasonable "infant mortality clause" due to original manufacturing
defect discovered at time of installation and first use.
This is how it is in the real world guys! You supply the spec. They
build to your spec. You place it in service (it is assumed immediately
upon reciept.) It works..., it is yours! If you put it in a closet
while you build your system and it blows up four months later on first
trial... well... you might have no leg to stand on as a one time buyer.
If you were Dupont Co. and had ordered (20) $1,500 high energy caps and
two failed in the first year, I am sure the company would bend over
backwards to assist in repair at no charge. Because they were ordered
engineer to engineer! Specs gotta be good. Right?
When a yahoo calls who is making a tesla coil and stutters and stammers
as the capacitor manufacturere,s engineer rattles off questions on specs
for the proposed single unit sale, it doesn't give them a warm and fuzzy
feeling about the user or his ability to know what he is ordering. Most
manufacturers are somewhat sympathetic, but they are just going to make
1-4 of this units at most and for a highly variable and uncontrolled
operation to boot!
Don't expect more than you spec'd out or any sort of special treatment
beyond a sympathetic ear. It is generally a given in the industry, as a
whole, that warranty on special impulse caps is a rather loose thing
between the two engineers of the buyer and seller. Each able to give and
take as needed to keep things running smoothly. Usually, the engineer
that bungles the deal is the buyers engineer! The cap manufacturer's guy
is locked into doing one thing mindlessly every day....Knowing his
product and all about capacitors only!!
I wouldn't hold any manufacturer to an ironclad warranty in court, unless
you can have an engineer in charge of your system testify that at no time
were the specs exceeded.
Now as to general specs. I have a routine that works for me.
I spec the capacitance to +/- 5-10%, I state that the capacitor will be
brutilized in AC operation and will be disruptively shorted or pulsed to
supply its maximum energy from the reversing 60 hz AC source 1000 times
per second. The online operational duty cycle will be under .05%. I
demand a maximum impulse current rating of 70,000 amps with a normal
operational design range of 30% duty cycle with 600 amp RMS RF current
capability in 2 minute bursts separated by 10 minute rest times for 3
sessions per day.
I choose my AC voltage rating as 3-4 times the AC RMS voltage of my
transformer. (20KVAC transformer- 60-80 KVAC on cap) I have them place
VAC after the voltage rating on the capacitor. No DC rating accepted. I
Also, spec that they put 1000 bps or 1khz on the capacitor following the
voltage. This is the only proof you have as to their satisfying your
spec on the cap itself.
I choose a rectangular molded polypropylene case. I demand female
5/16" or 3/8" threaded brass recepticles on each end of the monolithic
You are all alone on this matter gentlemen. It is a cold and very cruel
world out there in specialty capacitor land. They are not out to take
advantage of you or rip you off. They are also not out there to spoon
feed or wet nurse you. Your total sales to them in a year won't pay for
the hotdogs and beer consumed at their company picnic.
Frankly, I wouldn't build for individuals if I were them! It is
probably more hassle than it is worth. But I'm glad they do.
The CP matter is unfortunate. Especially now that some parts of it are
gettin' nasty. Bad vibes and paranoia will also play a part here too.
I say unfortunate because, to my knowledge, CP has been the only
manufacturuer who ever courted and embraced the Tesla coil building
community! No other manufacturer has ever even issue a catalog sheet
like CP with Tesla specific caps offered for ready sale. Some even go
out of their way to scare off this kind of business! (no names)
Genuine harm, insult and injury may have taken place, but regardless, we
may yet be the losers. If you build 'em, you know what you have. If you
buy 'em you are in a trusting relationship with the builder and your
money is gone. These capacitors are not "off the shelf" items! They are
a literally an energy bomb! They can be used to store and release
energy in a controlled and orderly manner (as designed and specified) or
can explode with the violence of a grenade (if mis-manufactured or taken
outside of spec.) This includes the homemade ones!
Richard Hull, TCBOR