Multiple Project Updates Coming Soon

I've been working to update a number of projects that have been sitting on my to do shelf for way to long.  In the next few weeks I'll be doing write ups on the following:

• Rebuild of my 12kV (~900Watt) Spark Gap Tesla Coil (Old Sparky). Mainly a build of a new DIY low inductance High Voltage capacitor that should allow for better resonance and energy transfer (and bigger arc's).
  
  
  
• My DRSSTC build using OneTesla parts - I couldn't afford the complete OneTeslaTS kit so many of the parts I've fabricated on my own.
  
  
  
  
  
  
• Further work on my Voight Kampff machine - its been a long break but I'm back at it
  
  
  
  
  
  
  

Project SSTC2 - Part 2 (Just a quick update - more to come)

Current issues that I'm addressing (to finish this coil).  I want to do it right so I'm trying not to rush it (even though I want to - just so I can have it done).

• rewinding secondary coil (DONE)
• My initial coil I ruined when I tried removing some inclusions trapped in the resin coat I applied - ended up pulling and breaking one winding.
• Decided to completely rewind new coil (wanted it to look good)
• made a winding rig and cut winding time in half
• Question regarding capacitor on MOSFET gate drive chip in Guangyan's schematic
  
• The datasheet for the UCC27425 and schematic differ.  Page 10 of the datasheet recommends 
• "two VDD bypass capacitors are recommended to prevent noise problems. The use of surface mount components is highly recommended. A 0.1-μF ceramic capacitor should be located closest to the VDD to ground connection. In addition, a larger capacitor (such as 1-μF) with relatively low ESR should be connected in parallel, to help deliver the high current peaks to the load."
• Primary Side of coil
• voltage double (DONE)
• difficulty finding capacitors that I could pull from older scrap
• ended up breaking down and ordering them
• Concerned about minimizing stray inductance in half bridge (DONE)
• etching/making multi layer pcb (unable to)
• make connections with copper sheet/plate
• unable to solder to wider or thicker copper
• heat conductivity of copper so high that entire area would need to be heated enough to melt and bond solder which would require higher temps for a longer period of time (would end up killing sensitive components).

• compromised by using narrower copper sheet/plate

• Want to get an actual measure of the resonant frequency of my secondary coil
• Need to finish making a working Frequency/signal generator (DONE)
• AD9850 working - set up to scan from 100kHz to 200kHz (as a start, each second frequency increases by 1kHz) - Yes I'll be posting an update to my AD9850 Signal Generator Project.

• Finish making a nicer looking Topload for Secondary Coil
• Not an immediate concern - I do have Topload's I can use for testing
•  Make shielded enclosure for electronics
• Add optical connection for external interrupter
• Also not an immediate concern - more something to add after all is working reliably.

SSTC2 part 1

Project SSTC2 - Small tabletop coil

I've been at work on this coil for a while now (taking it slow and careful in an effort to limit my release of magic blue smoke as much as possible).  This coil design I credit to Gao Guangyan and his SSTC2 (Small Tabletop Coil) project - which is presented as a complete tutorial on SSTC design, very detailed and well written.  For anyone wanting to build an Solid State Tesla Coil - I encourage you to check out his site (besides the great information he has great photos and video of his coils in action).

I began this project just after the Barnes and Noble Mini Maker Faire, after my first SSTC failed to perform at a second Maker Faire (I had issues not long before at the Chicago Southland Mini Maker Faire). These failures motivated me to make a more robust and easier to transport coil for demonstrations and education.

Current project goals include:

• solid modular design 
• modules cleanly attach together (well marked and secure connections)
• modular components well secured within case (secure but still accessible for repair/trouble shooting) 
• Indicators and/or test points for each module accessible for inspection/troubleshooting
• sturdy and clean looking case 
• Grounded metal case (to shield from EMF generated by coil)
• Better grounding of  HV side with bypass caps on AC supply to prevent/reduce interference
• TVS Diodes across MOSFET's/IGBT's to clamp voltage at gates and prevent overloading gates

My first step, as it usually is with my Tesla Coils, is winding the secondary coil.  Not having and 34AWG magnet wire on hand I had to order it and wait for it to arrive (thankfully the company I order from is in Illinois, like me, and their order processing plus shipping time means I only need to wait 2-3 work days before it arrives).

Secondary PVC form cut down and winding just begun

Secondary after stopping to rest (slow going so far)

 This 34AWG wire is by far the thinnest wire I've used so far to wind a secondary (with the exception of a super mini 1.5inch secondary that I made but haven't used yet).  Winding at this point was very slow due to the wire spool rolling away as well as trying to keep winding's lined up (if they overlap I have to unwind and rewind them).

Finally keeping the wire spool stationary

 I finally did the smart thing and secured the wire spool, to speed up my coil winding.

Finished

 For such a small coil, it took a long time to wind (just about 3 hours - not including rest times).

Power and Control Electronics

Half Bridge

Half Bridge

Gate Drive Transformer

Power Supply for Low Voltage Side (5v and 12v)

Power Supply for Low Voltage Side (5v and 12v)

Bottom of etched pcb for Low Voltage Side PSU

 The pcb for the low voltage PSU - etching removed a portion of the trace on the left (bottom) side - repaired with solder bridge.

Controller Board (point to point soldering on perf board)

Feedback Transformer coil

I'm trying out Gao Guangyan's feedback (essentially using a step down transformer) instead of an external antenna.

My coil is not up and running yet (I'm taking my time and making certain that I test each portion before I connect sections together - I've fried enough silicon by rushing things so far).  I've gotten a bit further - so I'll be posting more updates to this project very soon.

Project SSTC1 update

Continuing work on improving my Musical SSTC.  Here is a newer video of the coil with an actual top load:

I've also added a fiber optic connection for the interrupter to reduce EMF interference - which solves a number of issues in testing.  Prior to adding the fiber optic connection - feeding interrupter signals to the coil using an Arduino controlled adjustable interrupter with a 16x2 LCD display (to enable me to see the frequency and duty cycle) did not work - as soon as the coil was powered interference would scramble the display.  I did try shielding the Arduino etc. but the direct wired connection to the MOSFET controllers carried too much interference back to the Arduino.

I 'have also done some experiments involving input to the MOSFET drivers - the UCC37321/2
chip enable pins are pulled HIGH (internally, according to the datasheet) so I was/am confused as to how to use them.  Other people have used the enable pin to turn on the enable pins (providing a HIGH - 5v logic signal).  Since the datasheet indicates that they are normally pulled HIGH I thought that possibly using a totem pole configuration (NPN and PNP transistors tied together) could keep the enable pin pulled LOW (off) when there was no HIGH (on) signal.  I tested this and it did not seem to change performance except that the coupling between the primary and secondary coils increased and the current levels through the primary coil increased to the level that the wires heated up and melted the polypropylene insulation I had between the primary and secondary coils.

As you can see, the polypropylene was effectively cut in half by the wire on the primary coil.

I have also built the audio modulation board from The Geek Group, with a few changes (which I will post soon).  I decided to put this together myself after I found that The Geek Group no longer had kits in stocks. In addition, the schematics they put up are missing the actual interface between the interrupter board and the driver board for the primary coil (not that hard to figure out, but is missing - I will also post this when I'm able).

A little side note - I'm trying to collect materials to build a DRSSTC, which requires high voltage/high current capacitors for the primary coil.  When I can find these I'll be able to build a coil of the same size that has a much greater output (more impressive display for the same size coil).

Project Signal Generator - ICL8038

The first chip I've had success in testing is the ICL8038 Precision Waveform Generator  (I have also tested the AD9850 DDS Synthesizer - but I'll post that separately).  This chip is fairly inexpensive off of eBay (just a couple of dollars a chip).  The ICL8030 only needs a few external components (resistors, potentiometer's and capacitors) to generate a sine, triangle or square wave.

Vary stable chip (I haven't accidentally fried even 1 of them).  I have not been able to test the frequency sweep function due to some issues with my bench PSU.  Using the test circuits presented in the datasheet I was able to produce sine, triangle and square waves.

Sine wave

Triangle Wave

Square wave

Datasheet Test Circuit

Formula for determining resistor and capacitor  values

Frequency range is ultimately determined by the capacitor value, so it would be necessary to be able to change  values for different ranges.  You are able to sweep through frequencies by varying input voltages across pins 7 and 8.

Current ranges at pins 4 and 5 are set by the resistor values Ra and Rb and need to fall within the range of 0.01mA to 1mA (so resistor values depend on supply voltage - I'm using 12v so my range is 2.6k to 260k).

Project SSTC1 - I've got Sound!!!

After reviewing datasheets, yet again, for the MOSFET drivers I'm using (TI's UCC37321/2) and re-reading some sources on interrupters for SSTCs and methods of audio modulation with SSTC's I finally had that Ah-Ha moment.

I've made Plasma Speakers / Singing Arc's just after building my first Spark Gap Tesla Coils.  These, generally took an audio signal (normally fed to a speaker or earphones) and put it through the driver for a Television Flyback Transformer.  The only method I used involved amplitude modulation (AM-like radio) and SSTC audio drivers seem more focused on frequency and pulse width modulation.  Correction, after re-reading datasheets for the LM555 timer chip I learned that pin 5 actually modulates the frequency (some descriptions I had read stated, incorrectly, that pin 5 adjusted the output amplitude.  I finally understood how you combine frequency and pulse width modulation (it's actually pretty simple and involves pretty simple calculations).

I'll get more into the difference later, for now here's the video: