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Re: Series-linked Microwave caps? any good?
From: Bert Hickman[SMTP:bert.hickman-at-aquila-dot-com]
Reply To: bert.hickman-at-aquila-dot-com
Sent: Tuesday, December 02, 1997 9:02 AM
To: Tesla List
Subject: Re: Series-linked Microwave caps? any good?
Tesla List wrote:
>
> From: Alfred A. Skrocki[SMTP:alfred.skrocki-at-cybernetworking-dot-com]
> Sent: Sunday, November 30, 1997 8:53 AM
> To: Tesla List
> Subject: Re: Series-linked Microwave caps? any good?
>
> On Sunday, November 30, 1997 1:56 PM Matthew Mills
> [SMTP:megavolt-at-usa-dot-net] wrote;
>
> > Hi, thanks to all the people on this list who have helped me so far, as
> > you can see I am still asking questions....:^)
> >
> > I have a number of Capacitors from microwave transformers laying around
> > and I was wondering whether or not I can series link these for Tesla
> > use....
> >
> > My theory is that if each one is rated at 2100vAC eff and have a value
> > of around 0.95uF then I should be able to run 10 of them in series for a
> > capacitor rated at 21000vAC -at- 0.095uF which sounds quite reasonable....
> > any comments?
> >
> > PS I hear that these caps have a resistor built in (to drain off the
> > charge maybe?) would this make them unsuitable? can i remove the
> > resitor?
>
> If they have a resistor built in forget it it is going to disapate too much
> energy but if they don't have any bleader resistor then it should work
> fine.
>
>
Alfred and all,
I also used to be concerned that bleeder resistors would be a problem
due to additional losses until I looked at some of the numbers. It turns
out that bleeder resistors add a negligible amount of loss when compared
to the typical losses stemming from the spark gap and (in the case of
Mylar) dielectric heating. For example, a typical uwave cap may have a
10 MegOhm bleeder resistor. Even if the cap was stressed at its maximum
DC voltage rating (say 2100 volts), the power dissipated by the bleeder
is less than 0.5 watt, and should be even less in pulse-discharge
applications.
Mylar dielectric heating, on the other hand, accounts for much more.
With an applied voltage V, and a current I, the power dissipated by the
cap will be V*I*tan(X) where tan(X) is the dielectric loss. For Mylar,
tan(X) is around 0.02, and increases with temperature. This says that
I'll dissipate about 2% of my tank circuit reactive power (VI in the
cap. Using the example above, with 10 caps in series, operating at 6000
V. gap firing voltage, I'd see about 1.71 Joules/bang. If the gap fires
at a rate of 360 Bangs/Second, then the reactive power being processed
by the cap/tank circuit is about 360*1.71 watts or 615 watts. On the
average, the cap dielectric will be dissipating 2% of this, or about 12
watts.
Safe coilin' to you!
-- Bert --