Hi Bert,much thanks for this info. I was already on the road for picking up the PFN's and read your mail via smartphone, just in time. So I was a little bit forewarned that there could be internal inductors. Then I saw the caps and what a relief - I was very happy to see nice EXTERNAL inductors mounted to the insulators :-) Looks pretty cool, never seen anything like this before, made a short video:
https://www.youtube.com/watch?v=mO7sVuXbDYUSo after we eliminated the 4,5µsec thing, I think when removed the inductors, these caps will give damn nice low inductance tank caps for some biggg tesla project :-) The capacitance can be varied in 30nF steps up to 210nF, when all 7 caps are in parallel. The 2 big ones, as mentioned:
40kV 7 x 0.03µF 300pps (4,5µsec) The small one: 25kV 7 x 0.01µF 360pps (4,0µsec)By the way, what would happen, if you push the 300pps caps to lets say 400pps? Thermal issues? Think this would be not critical for short run times?
Regards, Stefan----- Original Message ----- From: "Bert Hickman" <bert@xxxxxxxxxxxxxxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx> Sent: Thursday, October 23, 2014 1:12 AM Subject: 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 *********************************************************************** World's source for "Captured Lightning" Lichtenberg Figure sculptures, magnetically "shrunken" coins, and scarce/out of print technical books *********************************************************************** 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 questionHi 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 standfor? Is this the maximum ocillating frequency, the caps can withstand? f= 1/T = 1/4,5µs = 222kHz? Regards, Stefan _______________________________________________ Tesla mailing list Tesla@xxxxxxxxxx http://www.pupman.com/mailman/listinfo/tesla_______________________________________________ Tesla mailing list Tesla@xxxxxxxxxx http://www.pupman.com/mailman/listinfo/tesla _______________________________________________ Tesla mailing list Tesla@xxxxxxxxxx http://www.pupman.com/mailman/listinfo/tesla_______________________________________________ Tesla mailing list Tesla@xxxxxxxxxx http://www.pupman.com/mailman/listinfo/tesla_______________________________________________ Tesla mailing list Tesla@xxxxxxxxxx http://www.pupman.com/mailman/listinfo/tesla
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