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Banned on April 7, 2007 Registered Member #277
Joined: Fri Mar 03 2006, 10:15AM
Location: Florida
Posts: 157
I have a HV cap charged to about 3kv. Does anybody know of a device (ala SCR,etc) capable of releasing the cap energy in a series of short pulses, about 300 ns for each pulse duration? ie: the HV cap energy being released over a period of several seconds (or more) by several thousand On/Off pulses, each pulse with a voltage pulse width of about 300 ns? Tried VERY tightly spaced spark gap, but as you might expect, all the energy is released in one spark. CM
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
I doubt you will find any common switching device capable of what you are asking for, switching a 300 ns pulse from 3 kV would need a device capable of enormous dv/dt the nearest I can imagine is a hydrogen thyratron with some kind of resonant network.
Intrigued by your mystery project; there are some very smart people on this forum with more information I think you'd get more specific help unless it's toooo secret.
Registered Member #10
Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424
If you really have a rotary spark gap with the right spacing (which I doubt) then simply use a low inductance resistor in series with value calculated to give the right current for the brief on time. A quick calculation, for my asynchronous gap running at 9000 rpm (= 150rps), with 8 electrodes of 0.4 inch, 6 inch diameter. The electrodes will pass by at 1200/sec. At 0.8 inch time each two electrodes are opposed out of the circumference of 18 inches this gives an "on" time of 0.8/(150*18) = 0.0003 sec or 300us. This is 1000 times too slow for you. This is a fearsome gap already so you can't really run it faster. Use needle electrodes and you can drop the 0.8 inch to 0.1 inch but not much smaller as 3kv will jump further. So you have a 50us spacing which is still 120 times too slow.
So what else can you do. Probably a big transmitting valve dropping it through a resistor. I have one that runs up to 30MHz, stands off 12kV and is rated at 60kW.
Note that 1000 impules from a 1000J cap is only 1 joule per shot but 300ns would mean peak power is 3MW.
Registered Member #118
Joined: Fri Feb 10 2006, 05:35AM
Location: Woodridge, Illinois, USA
Posts: 72
Hmm.. it sounds like you might need two switches - one to briefly connect the main cap to an interim storage device (such as a small capacitor (~1/3000 the value of the main cap), a PFN, or a short length of transmission line), and another to switch the charged cap, PFN, or X-line, to the load. This could be a specially designed multi-pole rotary spark gap (although 3kV is on the low side), or a hard tube modulator (to charge the interim store) and a thyratron to actually discharge it through the load. What type of load are you trying to drive?
Registered Member #135
Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
I have a Quantel PU430 YAG drive thats capable of switching almost 3kv in several hundred micro seconds. Maybe if you could find a schematic of that somewhere it could help you get close.
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HV Cap discharge by series of fast pulses?
