JimG's Smaller DRSSTC / Projects / Forums

Forums

4hv.org :: Forums :: Projects

« Previous topic | Next topic »

JimG's Smaller DRSSTC

1 2 3 4 next

Move Thread

LAN_403

JimG

Sun Feb 12 2006, 08:55AM

Registered Member #52 Joined: Thu Feb 09 2006, 04:22AM
Location: Austin TX
Posts: 57

9/20/2006

I just got these in today.

------------------------------

9/10/2006

This weekend I built a dedicated optical interrupter for the second tiny DRSSTC. It uses a sliding variable resistor for an on time of 50-500us with a constant off time of 11ms.

1157945432 52 FT600 Tinydrsstcinterrupter

------------------------------

7/11/2006

I built a ground target for the tiny DRSTTCs. I've been using it as a counterpoise so that I don't have to have a good ground to show off the coil.

The small size coil made it easy to take with me and show off during my July 4th vacation. It turned out to be very popular with children.

1152669893 52 FT1630 Tinydrsstc2groundrod

------------------------------

6/19/2006

I tried playing around with different break out points over the weekend and found that location and length drastically reduced the streamer length. With the reduced output the IGBTs would heat up very quickly, almost too hot to touch after only 3 or 4 seconds of run time.

Experiments with the interrupter timing have resulted in much thicker and brighter streamers. With the current timing I think I'm getting close to finishing up all of the tweaking I can do with this coil and will start cleaning up the wiring and build a dedicated external interrupter. If I find time I may rebuild the top load to something a little more presentable.

------------------------------

6/ 10/2006 Update:

I've replaced the metal supports with acrylic rods and have added a small toroid. The total height is currently at 7.25 inches. This finishes up almost all of the hardware portion of this coil.

1149993270 52 FT1630 Tinydrsstc2finished

Here are photos of the front and back side of the controller board. The lower half of the board has the controller and the top half is the h-bridge. The board size is 2 1/2 x 1 3/4 inches.

------------------------------

6/1/2006 Update:
I'm getting close to finishing up my mains powered tiny DRSSTC coil. I stole the primary design from Steve since I couldn't think of anything better. It currently puts out 2 inch streamers and at least one 4.5 inch arc to ground with my variac set to 80 volts. Anything higher and it arcs from my ground connecter at the bottom of the secondary to my metal supports that hold up the coil platform. I also have my optical detector connected to the 12v power supply so it takes a lot longer to turn off than I would like. Hopefully I will get all of these bugs worked out soon.

The calculated Fres was 950 khz, but the measured Fres is 750 khz. I'm happy with that since I was aiming for a frequency lower than 1Mhz. Hopefully when I get a more permanent topload it won't change the resonance too much.

------------------------------

4/24/2006 Update:

I didn't want to start a new thread since this just feels like I'm making small changes to my previous design.

I wound a new secondary to be smaller and allow for a lower resonant frequency. My previous secondary had a 3.5" winding height and used #36(0.127mm) wire. My new secondary has a winding height of 3.0" and uses #40(0.08mm) wire.

My previous circuit board was 3 1/8" x 1 3/4" with an on-board interrupter. My new one is a 2 1/8" x 1 3/4" on a double sided board, with an external interrupter. I also switched away from using a dual 4A UCC27425 mosfet driver to a 9A UCC27321/UCC27322 pair.

I've also switched my capacitor over from using a 500uf cap to a 340uf one. Instead of charging it through a switch mode supply I plan to have this powered directly from mains using some sort of currently limiting.

I've finished building the circuit and done continuity testing, I just want to hook it up to a signal generator to make sure that the singal is propagating correctly before I do any smoke testing.

Picture of the old board and secondary sitting next to the new board and secondary:

Schematic for the simplified board:

------------------------------

2/12/2006

Last October I was in a local surplus electronic parts store when I ran across a 1.375" x 3.5" 250V computer grade capacitor. Having just built two DRSSTCs I figured it might be cool to build a DRSSTC centered around this small capacitor. I then decided I would challenge myself with a few constraints.

1. The secondary shouldn't be any bigger than the capacitor.
2. The whole circuit should be kept small using SMT parts.
3. It should run off of a single power supply using a wall wart.
4. The interrupter should be on-board and easily updated.
5. It had to produce streamers, not just corona.
6. I wanted it to be a full bridge if possible.

On top of this I had never worked with SMT, I had never designed or etched a pcb, and I had never gotten either of my other two coils to work without flashing over with greater than 50 volts.

At home I found a small 1"x4" HDPE container similar to the vitamin C tube that I had seen others use and a small spool of 36 gauge wire. I figured that the unloaded coil would be about 2Mhz and loaded with run between 1.6Mhz and 1.8Mhz. At first I didn't think I would get anything to work based on the advice that I had read from a lot of people.

I chose to use a pic uc for my interrupter, direct feedback through a single schmitt trigger, a dual inverting/non-inverting mosfet driver and abstained from using any overcurrent, soft switching or dead-time circuity to keep everything very simple. I had my first circuit up and working toward the beginning of January using surface mount mosfets and a flat pancake primary with 6nf of primary capacitance. I experimented with a few GDT cores and found that a T50-2 gave me the best results.

This first test gave me very modest results with small 1/2" streamers. I figured I would need more current if I was going to go any bigger, but I had scoped the primary current at 40 amps and my mosfets were only rated for 14A. I almost gave up thinking that there was no way that I could get IGBTs to work at such a high frequency but decided to give it a shot anyway. To my amazement I could get a set of IGBTs to generate streamers just as long as the mosfets by tuning the primary circuit to a lower frequency.

At this point I figured it might be feasible to actually get this to produce some slightly larger streamers so I built a conical primary, added a toroid that I purchased from John Freau, increased the primary capacitance to 20nf, and set my on time to 75us. Once I had it together I set the interrupter to wait until the cap was up to about 175v before firing and applied power to the circuit. After about a second a bright white spark jumped one and a half inches from the break out point to a grounded target. I was very happy with the results and playing around with the tuning in that configuration I was able to get 4.5" ground strikes fairly easily and on occasion a 6" strike.

However, I still feel that I have a few things left to do.

* Right now the simple switch mode power supply that I've built can take a couple seconds to build up a sufficient charge for good sparks. I'm sure I can cut this down through some proper tuning.

* The primary current peaks out at about 200 amps. I think I can get some bigger sparks with shorter on times at these currents. Hopefully I can get shorter times between bursts if I can keep the main capacitor from fully discharging with each burst.

* I would like to experiment with different interrupter settings. I had pretty good success using a random number generator for random on and wait times on my larger DRSSTCs.

* The driver circuit will stop working after running for short periods and will start working a short time later. Everything is cool to the touch so I will need to investigate further into what is going wrong.

* Maybe I'll get a chance to revisit the circuit to add soft-switching.

My secondary:

On the left is the h-bridge and controller, on the right is my 12v and 200v power supply:

The final coil:

A 5" strike to a target 4 3/4" inches away:

craigsarea

Sun Feb 12 2006, 12:17PM

Registered Member #130 Joined: Fri Feb 10 2006, 08:12PM
Location:
Posts: 15

WOW

. A great looking coil and great results. That really is a display piece

.

The copper toroid looks really nice.

What IGBTs are you currently using?

Is your primary missing a strike ring? Does that matter?

Keep up the good work

JimG

Sun Feb 12 2006, 06:06PM

Registered Member #52 Joined: Thu Feb 09 2006, 04:22AM
Location: Austin TX
Posts: 57

The IGBTs that I'm currently using are IRG4BC40WSs. I didn't put much thought into this since I half expected it to not work. I just wanted a high current IGBT in a D2Pak package. The fact that International Rectifier listed the speed as "warp" led me to believe that it would be about the fastest thing I could get in size I wanted.

When I was building the primary I didn't think I would get sparks long enough to require a strike ring so I didn't add one.

EEYORE

Sun Feb 12 2006, 08:05PM

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

Nice work!

Matt

...

Sun Feb 12 2006, 08:23PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

Impressive, with all of these new drstc's coming out I may need to build one (right after the vttc I am working on and the pll sstc in the works...)

Can you give something for scale in the whole shot, like a coke can or something commonly recognizable? I am having trouble visualising the size of it after seeing all of the huge ones

What input power are you running? You said you were using a wall wort, does that imply like 20w

Keep up the good work!

JimG

Sun Feb 12 2006, 08:37PM

Registered Member #52 Joined: Thu Feb 09 2006, 04:22AM
Location: Austin TX
Posts: 57

Shot next to a Coke can.

The wall wart is marked at 12VA. I have yet to get a reading from my Kill-A-Watt so I don't know how much it is actually drawing.

Marko

Sun Feb 12 2006, 08:53PM

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

Im so sorry now for scrapping my small SGTC...

Wery nice jimG, really a tiny coil in proportions of large ones...

HV Enthusiast

Sun Feb 12 2006, 09:54PM

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

Wow! That really is small. I love the photo of the coil putting out the arc to the ground rod. Looks almost like one of those old movies from the 1950's that used miniatures for special effects. Very cool!

Dan

JimG

Sun Feb 19 2006, 06:49AM

Registered Member #52 Joined: Thu Feb 09 2006, 04:22AM
Location: Austin TX
Posts: 57

Update:

I changed my bleed resistor from a 27K to a 330K and set my SMPS duty cycle from 50% to 90%. This decreased the charge time on the main capacitor and increased the reliability of the overall circuit. I measured the power out of the wall at 30W with this new setup. I should be able to lower my off time between bursts since I'm charging much faster now.

12 second exposure to ground:

12 second streamer exposure:

1140319077 52 FT600 Tinydrsstcnightsparks

Energy transfer doesn't seem to be very good, though. The primary current peaks at around 4us, but doesn't drop off very fast. I built the secondary support to make it easy to change the coupling, but I currently have it about as high as I can get it.

Each vertical division represents 50A and each horizontal division represents 20us.

...

Sun Feb 19 2006, 07:21AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

WOW, that is tiny!
And 6" off 12w

That is the best efficiency I have ever seen! My 20w sgtc got about 6mm

To get 6" of my vttc takes >1kw
Have you published the schematics anywhere?

1 2 3 4 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob