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1
Hi everyone

welcome to my latest project thread!

Universal bus precharge & fan speed controller is a board designed to be used with UD2.x or UD+ DRSSTC drivers

When building my first DRSSTC I needed 12V power source for fans and 24V for universal driver. Also I needed some way to precharge and discharge bus capacitors. Solution was to use two separate power supplies for 12V and 24V, and use 555 in monostable mode for precharge relay delay. After testing everything I noticed that fans were too loud so I decided to swap out 555 board for arduino nano and use it as fan speed controller and precharge timer. It all turned out messy and difficult to debug so for my small DRSSTC build I decided to design a board inspired by loneoceans UD2 precharge board (http://loneoceans.com/labs/sales/ud2precharge/) which would eliminate messy wiring and additional 12V PSU

Features are
- same footprint as UD2.x and UD+ which allows it to be mounted on top of or bellow the universal driver using M3 stand-offs
- 24V DC input shared with UD with built in 24V to 12V DC-DC converter
- two PWM fan speed controllers adjustable with pot with selectable 24V/12V voltage and fan type (4-wire fan or normal fan)
- precharge relay with adjustable delay and selectable 24V/12V voltage
- discharge relay with selectable 24V/12V voltage
- optional external 10k thermistor input with optocoupler which can disable UD when it detects overtemperature (selectable with pot)

Board is based on 32-bit STM32F030F4P6 MCU and is designed to be easy to assemble, program and use. Firmware is based on STM32 HAL libraries and only thing that isn't implemented are fan tachometer inputs which probably needs to be done without using HAL libraries. HAL takes a lot of memory and firmware already uses 15 out of 16 KiB of flash

Formula for precharge relay delay
 Needed delay/s = 3*chargeResistor(resistance)*busCapacitance(F)
 
 example: 150 ohm resistor charges 500 uF bus capacitor in ~0.25 seconds
 
Formula for calculating precharge relay delay (1 to 10 seconds)
 Delay/s = CHRG_T(voltage)*2.73 + 1
 
Formula for calculating overtemperature cut-off (30 to 100°C, 0V to disable)
 Temperature/°C = OTEMP_SET(voltage)*22.73 + 25
 
Setup diagram


Schematics


Almost complete board


Kicad project with gerbers
* ubpfsc.zip

Firmware (needs HAL libraries)
* ubpfsc_prog.zip

That's it for now, I'll update this thread in the following weeks when I assemble my small DRSSTC and fully test the board

Happy coiling

2
Just to quickly share my latest project

I have Weller PU81 soldering station and after watching video on Marco Reps's channel I decided to buy DSX80 desoldering handle. It's completely compatible with my station, heating control works out of the box, and the only thing needed to get it running is to add a vacuum pump. I decided to try small 12V vacuum pump https://www.ebay.com/itm/DC-Electric-12V-Micro-Vacuum-Air-Pump-Booster-For-Medical-Treatment-Instrument/282489988597 which is just 3$ delivered, and could even fit in the station.

For pump speed control and 24V to 12V regulation I decided to make a small 50x50 mm PCB with 555 PWM and LM2596 DC-DC converter





BOM, gerbers, KiCad project of the module are free to use
* buck_pwm_module.zip

Next problem is how to use internal switch to power the pump


There is no way to use the switch directly. Hydron proposed neat solution using AC relay connected to one of the terminals of the transformer and pin 7 on DIN connector (pin 6 on official Weller pinout)

24 VAC relay


Wires for the relay


Biggest part of the job was to fit everything inside existing station enclosure because free space is very limited. Friend helped with drawing models for mounts for the AC relay, PCB and vacuum pump



PCB


Vacuum pump mount


Before soldering


.stl files for 3D printed mounts
* mount.zip


Hope someone finds it useful

3
Hi everyone

I'm using opensource oneTesla interrupter for my DRSSTC and I noticed few issues in MIDI mode which were also confirmed by Mads and Hydron
Basically the interrupter in MIDI mode makes random "pop" sounds, sometimes misses a note and at note start doesn't always get the first pulse right

Here are the scope shots, yellow signal is MIDI data

First pulse problem


One pulse at note start, then pauses, then continues playing the note


Doesn't play a note + one pulse at note start


The problem affects both their old and new LCD interrupters, since many people use them I'm curious how no one got around fixing this. Loneoceans sells MIDI interrupter based on (old?) oneTesla code and today I verified it has the same issue.

oneTesla new code, LCD option removed

I tried playing same MIDI on Phil Slawinski's mini MIDI controller and it sounds ok. Also I verified that note start and note stop commands are ok
On some MIDIs those glitches almost can't be heard (if you don't know what to listen for), on some like final countdown and pink panther they sound really bad

Pink panther and final countdown MIDIs played on my coil

oneTesla coil mortal kombat

oneTesla final countdown

Problem doesn't seem to be affected by max pulse-width, sometimes sounds very bad and sometimes it sounds ok. I don't know why
I tried debugging it this weekend with a friend but we failed so I hope someone could help a bit. Thanks!

oneTesla old interrupter
http://onetesla.com/oneTesla_interrupter_firmware.zip

oneTesla new LCD interrupter
http://onetesla.com/media/SDinterrupter.zip

4
Dual Resonant Solid State Tesla coils (DRSSTC) / DRSSTC music MIDI files
« on: August 29, 2017, 07:39:25 PM »
Since several people asked for (DR)SSTC MIDI files I thought it would be a good idea to have all of them at one place in case some get deleted

There is over 100 different songs and not all are playable, I tried ones posted by Benjamin at 4hv.org and bytecode77 of which almost all sound great
I'll maintain the list in this post if people add more files or links

oneTesla has a forum section dedicated for MIDI files and song requests
https://onetesla.com/forum/viewforum.php?f=17

All rights belong to original authors
http://4hv.org/e107_plugins/forum/forum_viewtopic.php?179471
https://bytecode77.com/garage/hardware/tesla-coil-music?fref=gc
https://onetesla.com/forum/viewtopic.php?f=17&t=1964
https://onetesla.com/forum/viewtopic.php?f=17&t=974
https://onetesla.com/forum/viewtopic.php?f=17&t=2679

Feedback/comments are welcome


5
General Chat / Happy birthday to Nikola Tesla
« on: July 10, 2017, 11:29:50 PM »
Today marks my fellow citizen's birthday!

Happy birthday to Nikola Tesla!


6
Dual Resonant Solid State Tesla coils (DRSSTC) / Futurist's DRSSTC1
« on: May 31, 2017, 12:35:41 AM »
 Hi everyone,

I've been fascinated with Tesla coils since I saw one at the tehnical museum as a kid. Building one myself was the ultimate goal, but since electronics became just a hobby I never had enough courage to try to build one, until about half a year ago. Now after I solved most of the problems and got the coil running I advise anyone interested in the area to try to build one themselves. The project turned out to be great fun and valuable learning resource! I also have to mention that I wouldn't be able to build it without great community and writeups by Steve Ward, Mads Barnkob, Gao Guangyan and tips from others (Thanks to Hydron, Kizmo, zzz_julian_zzz and Uspring), so I hope this writeup will also be valuable resource for anyone wishing to build similar medium-sized DRSSTC

The coil itself is a design-hybrid of Steve Ward's DRSSTC1, Kaizer's DRSSTC I and loneoceans DRSSTC 2. The core of the inverter is CM200DY-24NF halfbridge IGBT brick driven by UD2.7C driver at around 65 kHz, with 700 A primary current. There were some design changes and problems I encountered, but to avoid confusion I'll write just the current specs. I recently changed IGBT brick to SKM400GB123DH6 and upped the OCD to 800A, but because I still didn't got around to test the coil properly I'll post those results later





Overview of the coil specs
- CM200DY-24NF 1200V 200A halfbridge IGBT inverter, set to a 700 A over-current protection
- 1200V 1uF EACO snubber capacitor
- 45 mm^2 copper bus bar (15x3mm) and 16 mm^2 welding cable for bridge-primary connections
- 2x EPCOS 4700 uF 400 V caps with KBPC5010 1000 V 50 A bridge rectifier in voltage doubler configuration, for 240 V AC in
- 340nF 16kV MMC 100 Arms
- Universal Driver rev. 2.7C
- Flat spiral primary 215 mm inner diameter, 8 mm copper tubing with 10 mm spacing, 9 turns tapped at ~6.8 turn
- Secondary 160 mm diameter on PVC drain pipe, ~2200 turns (~605 mm long), 0.25 mm double enamelled copper wire - 2x polyester resin coated
- Toroid 130 x 620 mm from flexible aluminum tube with 2x 400 mm diameter stainless steel serving plates
- Controlled over 10 m ST-ST 125/62.5 um optic cable
- Maximum 1.5 m sparks!

For the IGBT I decided to try the CM200DY-24NF which was the cheapest IGBT brick I could find, even cheaper than used ones (bought new for 62$ with shipping from aliexpress). At first I thought it may be fake, but it turned out to work greatly, even at 700Apk!

I decided to install the toroid a bit higher, to avoid constant ground strikes, it proved unnecessary because the streamers rarely hit ground with current settings. I hoped to get the same performance like fullbridge coil at 240VAC without voltage doubler, like Hydron's DRSSTC, but sparks are not that spectacular. Longer ones are certainly possible with this design - I think the coil lacks a little more coupling but I'm unable to change it until I rewind secondary

JavaTC output









Primary supports are constructed from laser cut 3x3 mm plywood glued together with PVA






For the middle part I left holes for screws, but they heated a lot so I removed them completely  and secured the supports using epoxy. Winding secondary was pretty straightforward, end plugs for drain pipe were created by pouring polyester resin. Secondary was then coated 2x with polyester resin. Didn't turned out great, but it's ok for first try




Winding primary was a little harder, it took some practice to learn how to bend copper tubing



Completed primary with strike rail, later I cut bent section of the strike rail




Whole coil








1:1024 current transformers are wound on medium-permeability 3E25 ferrite toroids (http://uk.farnell.com/ferroxcube/tn25-15-10-3e25/ferrite-core-toroid-3e25/dp/3056995)
Toroids are glued together with epoxy




Halfbridge before assembling

Also:
Gate resistors are 4.7 ohm 1W with 1N5819 Schottkys in parallel
Gates and emitters are shorted with 1.5KE33CA TVS
10kohm 20W resistor is connected across the output of the inverter




GDT is checked on oscilloscope using 100 kHz squarewave, toroid core is N87 material




Laser cut 3mm plywood capacitor supports




MMC capacitors with vishay HV 10Mohm balancing resistors
Capacitors are 0.68uF rated for 2000VDC, Irms = 25 A, per datasheet 8 caps in series and 4 strings in parallel gives 0.34 uF at 16 kV DC (5.6 kV AC) with Irms = 100 A
Originally I wanted to use 12x 942C20P15K-F capacitors for 0.45 uF at 4000 V DC. Such low impedance primary circuit isn't suitable for my design, Steve Ward used that MMC with his high-coupling helical primary coil, in my primary circuit cap ratings would be heavily exceed and they would fail soon




Cad drawings for MMC enclosure




Cutting MMC enclosure, thanks to a friend who kindly provided me with laser cutter




MMC enclosure completed






Whole bridge assembled + MMC
0.1uF 2000VDC film capacitor is connected from negative rail to ground, and Graetz bridge is connected in voltage doubler configuration




Closeup of the electronics
UD and Bus capacitor precharger/discharger and fan speed controller




Bus capacitor precharger/discharger and fan speed controller is made using ATMEGA328P and two 30A relays. Precharge resistor is 150ohm 10W, and discharge resistor is 1kohm 10W. Originally I had two LM35DZ temperature sensors for MMC and halfbridge to control fan speed, which were later removed because I had problems with EMI jamming MCU, and had to add protection for reset pin, multiple ceramic capacitors and common mode choke to deal with it. For now it seems to work fine, but in future I plan to make more reliable and universal fan speed controller and bus precharger using STM32, with protected inputs/outputs.




Scope shot of first power-on with adjusted phase lead


Playing James Bond

Playing The final countdown


The interrupter was assembled by my friend - Arduino Nano 328A with modified oneTesla interrupter code for playing MIDI directly from USB + 10 m ST-ST 125/62.5 um optic cable.
The midi sound is good and only problem are occasional "pop" sounds, they are caused by the way second note is handled; if second note plays when first is playing, the second note is ORed together but limited to some max. pulse width
Also expect stuck notes at >160us on-time with some midi files, I don't know the reason

It took me a whole afternoon to get the MIDI interrupter working, so anyone using old code from oneTesla;
to run directly from USB I did the following (gnu/linux)

in oneTesla source change MIDI boud rate to 38400
install http://www.varal.org/ttymidi/

ttymidi -s /dev/ttyUSBxxx -b 38400 &

Using aconnect connect Midi Through port to ttymidi port (to get output list: aconnect -o)
aconnect xx:xx xx:xx

To play (Midi Through port)
aplaymidi midi_file.mid -p xx:xx

Or using something like Midieditor

On windows use this as Midi-serial converter
http://projectgus.github.io/hairless-midiserial/

and this for the loopback interface
http://www.tobias-erichsen.de/software/loopmidi.html

Any feedback or questions are welcome!
Happy coiling!

Edit: Wrote description for each photo

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