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Long pulse DRSSTC pictures

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EEYORE

Mon May 22 2006, 06:06PM

Registered Member #99 Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637

I used to run my first drsstc this way...I would set the modulator for 10ms and have about 1bps. My power supply was a voltage doubler using two 10,000uF 400volt electrolytics. The sparks looked just like those and were very intimidating, just not nearly so long...Despite much anxiety, I never did lose any parts this way...

Matt

Steve Conner

Mon May 22 2006, 07:25PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Whee, good stuff Steve! O_O 245J is very impressive. I bet it's about the same bang energy as Bill Wysock's Super Model 13 or something. As for maintaining the DC bus voltage throughout the burst, who cares, it's not rocket science

Steve Ward

Tue May 23 2006, 12:37AM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

Well, im up to 4 foot solid sparks now, and the base of the spark looks to be about 1" thick

. I found a neat trick to produce these sparks. First, send out 3-5 good "bangs" quickly to form a long, thin streamer channel. Then, on the final bang, let it ring out for 3-5mS so as to build up all that plasma that surrounds the spark. It just so happens that this is the exact sequence of events that happens with my over-current limiter scheme.

But, soon (probably tomorrow) im going to test out a "PWM" scheme instead, where when the current reaches its limit, only 1 or 2 RF cycles are cut out, and then the inverter resumes adding energy. Im still not sure what the transient and steady state response will be on the primary, im hoping it will decay like one long burst does, but keep the primary current to a more sane level (ive been running 1000A regularly now). More on that when i actually test it.

Steve Conner

Tue May 23 2006, 01:14PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Wow, that's crazy! I've got to try this. I already have the PWM current limiting on my coil, so it should just be a case of changing one little cap in the interrupter, for one 10 times bigger.

Having said that, I found that when I do the longest burst I can on my coil (300us at the moment) the streamer seems to split and fork a lot. It looks for all the world like a tree that shed its leaves in winter. But maybe making it longer still, one of the branches will dominate and the others die out?

Desmogod

Wed May 24 2006, 12:56AM

Registered Member #139 Joined: Sat Feb 11 2006, 11:01AM
Location: Perth, Western Australia
Posts: 358

Maybe the heating of the air by previous discharges gives the streamer a "warm" path to arc through and prevents the branching?

Steve Conner

Sun Jul 02 2006, 09:20PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

OK, I modified my interrupter with a switch that makes the pulse 10 times longer, so it can go up to 3ms now. The results are pretty cool!

A 3ms burst drains the filter cap drastically, and makes a dull POP! noise like a flashgun going off but much louder. When I fire one with the cap charged to 300V, it grows a streamer that looks like a 3ft white tree. It looks much the same as what I get when the coil is doing 250us bursts repetitively at 100-200Hz, but thicker and blue-white. The breakout point flashes bright white as if it was actually glowing white hot for the duration of the pulse.

The current limit indicator doesn't light, so I guess the primary current is staying below the 400A setpoint of its own accord.

I'm doing a demonstration at the uni High Voltage Technologies Group on Thursday, and I'll try and get some pics of these crazy looking sparks while I'm there, and do some ground strikes too. I don't much like doing ground strikes in my house.

Marko

Sun Jul 02 2006, 10:19PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

I ran my DRSSTC at about 500us continuously, producing about a 40cm long, very neat looking CW-ish spark until it died. I seem to have some energy loss problems because of coupling to ferrous metal plate under the primary, thin primary wire, MKT caps, and only halfbridge drive also add up :/

Look of spark is a bit washed out because of long-ish exposure..

Steve Conner

Thu Jul 06 2006, 02:33PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

OK here we are...... These pictures are of 3ms single shot bursts which have an energy of about 50J. They look pretty neat!

While firing these off, I had a number of primary-to-secondary flashovers. I think one of these developed into an arc between primary turns, because there was a pretty loud bang and I saw pieces of molten copper fly. Afterwards I could see a tiny crater blown out of the copper pipe. However the electronics all still work fine

This was done in one of the Faraday cages at Strathclyde University's High Voltage Technologies Group, as part of their open day tour.

Steve Ward

Thu Jul 06 2006, 04:25PM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

Awesome pics Steve

. Was your current limiter kicking in much?

Im almost tempted to try this on my big coil... Could you imagine 8+ footers looking like that?

HV Enthusiast

Thu Jul 06 2006, 06:09PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Lookin' good Steve. Now its time to beef up the pulse. With my new modulator, and a huge honkin' capacitor bank behind it, i'm running about 20ms pulses which are pretty spectacular. Of course, you need a lot of capacitance behind it to minimize the droop to maintain energy transfer.

I've also experimented with hooking up a rectified high voltage source, gated with the pulse (normal continous operation) and fed into the base of the secondary. This provides some nasty serious ground arcs - extremely loud. And QUITE dangerous!

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