Re: Cap Dissipation Factor, Plasic Capacitors for TC tank

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Bert Hickman by way of Terry Fritz <twftesla-at-qwest-dot-net>" <bert.hickman-at-aquila-dot-net>

Hi Sean,

The dissipation factor (sometimes called the loss tangent) is a measure
of how lossy a capacitor is when passing an AC current. Most of these
losses come from the dielectric material and resistive losses in the
capacitor plates. Capacitor vendors typically provide dissipation
factors at one or more operating frequencies. Obviously, any capacitor
intended for Tesla Coil tank service should have a low dissipation
factor at RF frequencies. 

Certain dielectrics (polyethylene, polypropylene, polystyrene, teflon,
ruby mica) have much lower dielectric losses at RF frequencies than
others (Mylar/polyester, PVC, glass). However, actually measuring the
dissipation factor is not simple - it's usually simpler to select a
capacitor/dielectric that is known to have low losses under RF or fast
pulse application. If you have a model number for your cap, you can
check the Plastic Capacitors web site or email them to get the details
about your cap. In general, caps listed as being for DC Filter or
limited discharge will be Mylar and are not recommended for TC service.

The Plastic Capacitors types best suited for Tesla Coils are type BNZ
(best), HC, and HG (Note: this style, with a sky blue body color, is one
of the few "Glassmike" packaged caps that CAN be used in moderate duty
for Tesla Coils). Plastic Capacitors' various capacitor families and
associated characteristics can be found at:
http://www.plasticcapacitors-dot-com/product_index.html

Best regards,

-- Bert --
-- 
Bert Hickman
Stoneridge Engineering
"Electromagically" Shrunken Coins!
http://www.teslamania-dot-com

Tesla list wrote:
> 
> Original poster: "Sean Taylor by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<taylorss-at-rose-hulman.edu>
> 
> What exactly is the cap dissipation factor - i.e. is it just a
> representative figure used to tell how much a cap will dissipate? How does
> frwquency figure into it, and how do you measure the dissipation of a cap?
> I ask because a) I am curious, and b) I have a Plastic Capacitors 0.05 uF,
> 20 KVDC cap and want to know it's suitability for TC tank use.  I doubt that
> it is any good for a TC tank because the thing is so tiny, well, about 2" x
> 3" x 4" without insulators.  Maybe a mylar dielectric?  Any thoughts greatly
> appreciated!
> Sean Taylor