One Pulse High Voltage Switch

On a sunny day (Mon, 16 Sep 2013 10:57:10 -0700 (PDT)) it happened Jack Bio wrote in :

Triggered spark bridge?

I was looking for something similar recently. Except this was for 1 KV and a larger capacitance. 200 amps for just a moment. Maybe 0.1 seconds or so. SCRs and triacs are a possibility except that they are too leaky.

I bet there are switches out there that would take the current a few times at least and withstand the voltage but the manufacturers will most likely not warrant them for that usage. That's a guess of course. It might be interesting to see what you eventually come up with, if anything.

boB

What's your definition of discarge?

If you're not in a hurry, it doesn't take a big device. Peak discharge current might be the critical parameter.

Relay? If you only need ONE pulse, any device that fails shorted would work.

If you expect to do something with the discharge energy other than dissipate it, you're woefully short on specifications.

Thanks for reply. I've read some info about it, but the price (400$) is too high for my budget.. There are other options? :)

Only one pulse in its life?

Discharge into what load?

Wow! So little information, so much time.

Il giorno lunedì 16 settembre 2013 18:28:29 UTC, mike ha scritto:

Thanks, you are right.. In this case , discharging the capacitor through a resistance close to 0.

On a sunny day (Mon, 16 Sep 2013 11:32:14 -0700 (PDT)) it happened snipped-for-privacy@gmail.com wrote in :

Yes, I once made a stroboscope. Look up stroboscope bulb, or get a cheap stropboscope board, those whould have a trigger circuit that you could modify so you can drive it (usually the trgger circuit for the flhas bulb is a thyristor).

homemade missile?

large relay with bent apart NC contacts (I've done this), A solenoid and some contacts?

I've done spark gap switches (at 30kV, 30uF, 4" wide aluminum parallel-plate transmission lines). No experience with 4kV and such a small cap.

I vaguely remember ignitrons and thyratrons from 50+ years ago. ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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I love to cook with wine.     Sometimes I even put it in the food.

A well grounded nosey cat should fit those sparse specs. Art

If a dropped wrench will not do, it seems to be thyratron / ignitron territory.

What are you going to blow up?

--

Tauno Voipio

--
Krytron.

Once ever, or once now and then?

What discharge time/peak current do you want?

A flashtube would work, but it would have to be long, straight or spiral, so that it won't spontaneously trigger at 4KV. You have under a joule of stored energy, so it would last a long time.

A few dinky, cheap/free flashtubes in series, with equalizing resistors, might work.

Or use a tube!

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John Larkin         Highland Technology, Inc 

jlarkin at highlandtechnology dot com 
http://www.highlandtechnology.com 

Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
Custom laser drivers and controllers 
Photonics and fiberoptic TTL data links 
VME thermocouple, LVDT, synchro   acquisition and simulation

--

John Larkin         Highland Technology, Inc 

jlarkin at highlandtechnology dot com 
http://www.highlandtechnology.com 

Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
Custom laser drivers and controllers 
Photonics and fiberoptic TTL data links 
VME thermocouple, LVDT, synchro   acquisition and simulation

I've used HV relays for this, but with controlled discharge current profiles, to simulate transient surges into (shunting) protection circuitry.

Long-stroke transmitter and vacuum relays will suite the bill for low rep rates, but the number of cycles will be finite, and they will require regular replacement. Long stroke part contacts can be visually inspected for condition.

I would not be so confident that the surge generated will be defined by anything that is 'zero'. At high current and high speed, nothing is zero, regardless of the initial impulse voltage.

RL

You're switching less than a joule of energy, but peak current may be

10's of kA. Although a number of gas tube devices (krytrons, thyratrons, or similar) could do the job, they're expensive and require triggering circuitry. They're overkill unless you need to precisely switch (time-wise). Triggerable spark gap switches and ignitrons are simple but expensive, and they also require HV triggering circuitry. IGBT's are available with 4 kV ratings, but these also tend to be expensive.

If your timing needs are not critical, an inexpensive HV relay switch should do the job. For example, to generate ultrastrong pulsed magnetic fields, I use a simple solenoid-driven high voltage switch with 2" diameter brass contacts. It has reliably switched up to 8500 joules at

9.5 kV, with peak currents up to 100 kA for thousands of maintenance-free operations.

The above switch replaced a triggered spark gap switch that required disassembly and maintenance after every 50 - 100 shots. A much smaller home-brew HV relay should do the job for your application, using repurposed 1/4" - 3/8" diameter power relay contacts. At 4 kV, you only need to bring the contacts close enough to arc over, thus avoiding potential problems with contact welding.

Bert

--
Bert Hickman 
Stoneridge Engineering 
http://www.capturedlightning.com*********************************************************************** 
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How about a small HV rectifier tube? Apply filament voltage to turn it on and discharge your capacitor.

Some of these have 1.5 volt filaments that don't require much current..

It is possible home made a trigatron? Someone have some resource for me? Thanks a lot.

Yes - but you'll need to have access to, or contract with, someone with machine tools. The spark gap is usually triggered between two electrodes. Brass electrodes are relatively inexpensive, easy to machine, and provide long life even at very high currents. Under heavy use, brass electrode do generate zinc-oxide dust that eventually coats the inside of the trigatron. Various machineable tungsten-copper alloys can also be used for heavy-duty applications.

One of the main electrodes is typically mounted directly to the trigatron housing, and is drilled and tapped to hold a spark plug. When seated, the spark plug's center electrode should just barely extend past the active surface plane of the main electrode. The opposite electrode is mounted to an insulating plate (typically made of polycarbonate (Lexan) or acrylic (Plexiglas/Perspex). Polycarbonate will withstand explosive shock (when the switch fires) better than acrylic.

The gap between the two main electrodes should be adjustable, The main gap is adjusted so that it will withstand a voltage that is at least

15-30% higher than the expected operating voltage without suffering self-breakdown. One trick is to pressurize the gas inside the trigatron to increase its breakdown voltage. This may allow you to trigger it by reducing gas pressure. Dry nitrogen gas is preferred, but dry air will also work. Because of potentially toxic byproducts, avoid using SF6.

For electrical triggering, a high voltage triggering pulse (typically

10's of kV) is applied between the spark plug trigger electrode and its associated main electrode using an ignition coil or HV pulse transformer. Here's a helpful article, with pictures:

More images and triggering information can also be found here:

Bert

--
Bert Hickman 
Stoneridge Engineering 
http://www.capturedlightning.com*********************************************************************** 
World's source for "Captured Lightning" Lichtenberg Figure sculptures, 
magnetically "shrunken" coins, and scarce/out of print technical books 
***********************************************************************