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Re: [TCML] Pulse Cap question

Hi Stefan,
You have a Pulse Forming Network (PFN)... or at least the capacitors that are part of such a network. In many common PFN's, capacitors and inductors are interconnected to form a synthetic transmission line. When charged, all the capacitors are fully charged to the same voltage. When switched to ground (through a spark gap or thyratron and usually the primary of a pulse transformer), the PFN is designed to generate a relatively square output pulse that has a specific pulse width - 4.5 usec in your case and impedance - often 50 ohms.
One end of all the capacitors is likely connected to a common case/ground. Ideally the other ends of each capacitor are isolated from one another (if the PFN used external inductors). If the PFN has internal inductors, each capacitor will be connected to its neighbor through an internal inductor. Either type is often usable as the tank cap within a Tesla Coil by simply connecting all the caps in parallel. 

Bert
--
Bert Hickman
Stoneridge Engineering, LLC
http://www.capturedlightning.com
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Teslalabor wrote:

Hi Matt,

so you would say, this cap isn't the best for tesla use? Not as good, as
good old Maxwell caps are for example?
In particular, this is a special capacitor from US manufacturer
"Hipotronics", it has 7 single caps in one big metal housing, which can
be connected in parallel. The cap is rated as follows:

40kV
7 x 0.03µF
300pps
4.5µsec

I think it comes from a pulse forming network, powering a big magnetron
or such things. The cool thing with this cap would be, you can easily
increase/decrease the capacitance in 30nF steps by simply tapping 0-7
capacitors.

Regards,
Stefan


----- Original Message ----- From: "mddeming--- via Tesla"
<tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Wednesday, October 22, 2014 11:30 PM
Subject: Re: [TCML] Pulse Cap question



Hi Stefan,


Usually, this is the discharge time into essentially a dead short, not
the time of one oscillation. One cycle consists of
charge-discharge-reverse charge-discharge. Therefore, the the minimum
time for one cycle would be not less than four times this, limiting
the oscillating frequency to something less than ~55.5 kHz. Trying to
operate above this frequency will result in high heat dissipation and
very fast damping of voltage. The internal resistance may even be high
enough to prevent oscillation altogrther.

Matt D




-----Original Message-----
From: miles waldron <mileswaldron@xxxxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Sent: Wed, Oct 22, 2014 4:28 pm
Subject: Re: [TCML] Pulse Cap question


Probably discharge time. It can take 300 discharges per second, and each
discharge elapses in 4.5 microseconds.

On 10/22/2014 11:31 AM, Teslalabor wrote:

Hello,

the nameplate of a pulse cap says the following:

40kV
4,5µs
300pps

So it's rated at 40kV, 300 pulses per second, but what does 4,5µs stand
for? Is this the maximum ocillating frequency, the caps can withstand? f
= 1/T = 1/4,5µs = 222kHz?

Regards,
Stefan
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