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Registered Member #2028
Joined: Mon Mar 16 2009, 08:13PM
Location: Norway
Posts: 319
Since you don't need precise triggering AND you want reliable switching at 5 kV, a simple mechanical gap is simply the way to go. You can use a solenoid, an air cylinder, or even a pull string(!) to reliably fire it.
If you want some inspiration on pneumatically fired spark gaps you could look up The Geek Group's Project Thumper:
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
My 10 kJ capacitor works fine with a mechanically triggered spark gap, as advocated by familiar experts here. An initially wide gap is closed by yanking a lanyard. A spring returns the moving electrode to wide open position when cord is released.
Some pros, cons, and don't cares for my current application (no pun intended):
* Event time is not predictable to the microsecond.
* At high energies the gap makes loud bangs. A high priority improvement will be to enclose it.
* By adjusting a limit screw, the minimum gap can be set to zero so we have a mechanical switch. That's handy for observing the linear system behavior at low voltages, without otherwise changing the circuit. Contact bounce has been a minor annoyance, but this is wandering into a topic for a different thread.
Registered Member #1500
Joined: Sat May 24 2008, 04:38PM
Location: Ojai, Ca.
Posts: 44
Hi Bert et al, Suppose I was to keep my suspended electrode setup and raise it some. Remeber these are 2"machined face brass dowels very parallel, one suspemded from a very robust superstructure by figuring out a way to drop it an inch or two or spring load it. The 1/2" allthred (fine thread) is 12" long (uncut) and could be guided accuratly by a perdicular 1/2" copper pipe. I have a electromachinacal device the allows for charging through (4) big ceramic HV resistors (NC), and can toggle to dump the energy intp a big water resistor (CU) if something goes wrong.
What would be the effect of dropping the the dowel or spring loading it down? Will most of the energy be gone by the time they meet or will they weld? Jim
Registered Member #118
Joined: Fri Feb 10 2006, 05:35AM
Location: Woodridge, Illinois, USA
Posts: 72
Wavetuner wrote ...
Hi Bert et al, Suppose I was to keep my suspended electrode setup and raise it some. Remeber these are 2"machined face brass dowels very parallel, one suspemded from a very robust superstructure by figuring out a way to drop it an inch or two or spring load it. The 1/2" allthred (fine thread) is 12" long (uncut) and could be guided accuratly by a perdicular 1/2" copper pipe. I have a electromachinacal device the allows for charging through (4) big ceramic HV resistors (NC), and can toggle to dump the energy intp a big water resistor (CU) if something goes wrong.
What would be the effect of dropping the the dowel or spring loading it down? Will most of the energy be gone by the time they meet or will they weld? Jim
Hi Jim,
There is obviously no welding problem if they are prevented from making contact. Welding can occur when switching lower voltages when the very first small bridging area to make contact melts and resolidifies. At higher voltages, the gap flashs over before the electrodes make contact. Whether the discharge is over before the electrodes physically close is a function of your load and the closing velocity of the electrodes. I have personally never encountered welding when the open circuit voltage was over 2-3 kilovolts, even at 10's of kA. However, I use a hairpin loop configuration with the gap and electrodes being one leg and busbar, flexible braid being the other two legs. When it fires, the arc is swept across the electrode faces via Lorentz forces, preventing any spot from getting excessively eroded. This (combined with the thermal mass and high thermal conductivity of the large brass electrodes) seems to prevent welding even if they do make contact.
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Triggered Spark Gaps...
