High Voltage Forum

Tesla coils => Dual Resonant Solid State Tesla coils => Topic started by: Laci on February 18, 2019, 05:17:53 PM

Title: My first DRSSTC on bricks
Post by: Laci on February 18, 2019, 05:17:53 PM
I started the building of my first DRSSTC using two used SKM400GB126DH2 modules.Had some problems because not getting what I ordered,but eventually I got generously what I ordered.

The busbar is made out of two 135x22x2mm aluminium rails,with the large DC bus capacitor in the middle for good current sharing.Two 1uF 1250V snubber capacitors are coming,an aluminium heatsink soon and the gate drive components on perfboard/PCB left to do.I'm also trying to modify an ATX PSU for higher voltage and current for proper gate drive supply.

The MMC is rated 0.094uF,4000VDC using 2 in series,4 in parallel WIMA FKP-1 capacitors mounted on a painted piece of tough cardboard(hopefully good enough insulation).Soldering to aluminium was impossible,so soldered the capacitors together using a large solder joint,with a copper wire in the middle.This is probably the weakspot,we'll see how it turns out to be while operating.

Some pictures about the inverter and MMC:
 [ Invalid Attachment ]

 [ Invalid Attachment ]

I have a question regarding the inverter and another about the UD3. I see everybody hooking up the CTs between the inverter and the MMC.My MMC fits perfectly on the inverter and that would be satisfying and also really low inductance.Is it possible to connect the CTs to the other side,between the inverter and the primary?
About the UD3:does it uses internal comparators in the Cypress chip instead of external ones,like the TL3116?In this case the expensive comparators are omitted,but is the chip fast enough?(in my case about 150kHz)
Title: Re: My first DRSSTC on bricks
Post by: Hydron on February 18, 2019, 06:38:29 PM
CT between inverter and primary is fine - the place to avoid is between primary and MMC due to high voltages present there.

As for the MMC it is indeed likely the weak part - 4kV sounds like a low rating for a coil that needs brick igbts, and will limit your max current.
Title: Re: My first DRSSTC on bricks
Post by: Teravolt on February 18, 2019, 09:11:48 PM
lead solder will not flow on aluminuim
Title: Re: My first DRSSTC on bricks
Post by: Mads Barnkob on February 19, 2019, 08:48:51 AM
Good to see you are taking on building a large DRSSTC, atleast that is the feeling I got when you are using SKM400 bricks.

There is a few plot holes in your plan. Driving SKM400 at 150 kHz is that something you calculated first? ( http://kaizerpowerelectronics.dk/tesla-coils/drsstc-design-guide/igbts/ ) Sounds like its going to take some gate driving power and will dissipate quite some switching losses.

Your MMC is grossly underrated, you simply need to build something better and bigger. At 150 kHz that little poor thing will only handle 24Arms and even at 400Apeak you will be hitting 4500Vpeak and then you are not far from destruction of it. I used the Wima FKP as a substitute in MMC calculator ( http://kaizerpowerelectronics.dk/calculators/mmc-calculator/ ), but that also shows a 33 degree Celcius temperature rise at 200 uS/BPS, you are going to scorched that little cardboard and caps :)

I am not sure, but I think the UD3 was built to be used for QCW aswell, so I would expect it to work into some 500 kHz region.
Title: Re: My first DRSSTC on bricks
Post by: Laci on February 20, 2019, 08:42:24 AM
Thanks for the suggestions!We talked about switching speeds and losses here: https://highvoltageforum.net/index.php?topic=549.msg3415#msg3415

The MMC is poor because they had no more in the local store.The plan was to build a 4 in series,8 in parallel MMC

I plan to use freewheeling for long pulses if the losses won't be much.Philip probably used 2kV CDE caps,2 in series for 4kV and 4 in parallel just like my MMC.

What about the primary?I can buy copper tube from a local store from 0.6 cm diameter.The thicker tube stays cooler than the thinner?
Title: Re: My first DRSSTC on bricks
Post by: Netzpfuscher on February 20, 2019, 10:02:24 AM
That's right, 500kHz is the maximum for the UD3.

Perfboard is not ideal for a high current gatedriver. I would prefer SMD mit big ceramic decoupling to keep the switching noise out of the driver.

I drive my SKM400 with a 13 to 10 GDT with 24V on the GDT driver so you get 18V at the gate.

Title: Re: My first DRSSTC on bricks
Post by: Teravolt on February 20, 2019, 06:45:41 PM
the universal driver can do 500khz but the SKM400 probly can not what frequency is your coil? your snubber will not work if you are soldering to aluminuim. at least bridge the cap connection to the screws with copper at the end of your assembly
Title: Re: My first DRSSTC on bricks
Post by: Laci on March 02, 2019, 10:14:41 AM
That's right, 500kHz is the maximum for the UD3.

Perfboard is not ideal for a high current gatedriver. I would prefer SMD mit big ceramic decoupling to keep the switching noise out of the driver.

I drive my SKM400 with a 13 to 10 GDT with 24V on the GDT driver so you get 18V at the gate.
Thanks for the suggestions!I'll try to etch a PCB and use 10uF THT X7R capacitors,two in parallel for each N-P MOSFET pair(IRFZ44NPbF and IRF4905PbF).If I succeed to modify an ATX PSU,then I can change the gate drive voltage.
I also received a CY8CKIT-059 board and checked your UD3 firmware,but some files are missing.Do you have a simpler firmware something like the UD2.7 or I should make one on my own?

the universal driver can do 500khz but the SKM400 probly can not what frequency is your coil? your snubber will not work if you are soldering to aluminuim. at least bridge the cap connection to the screws with copper at the end of your assembly
The SKM400 bricks definitely can't do 500kHz,but hopefully they can 150kHz.I plan to enhance the MMC connections or even make a completely new one if this fails.The snubbers are good,1uF and mounted directly to the bricks with the screws.
Title: Re: My first DRSSTC on bricks
Post by: Netzpfuscher on March 03, 2019, 02:28:50 PM
There are no files missing, I think psoc creator didn't find the bootloader files. This is a common issue, go to the schematic of the UD3 QFN project, double click the bootloader component and set the path to the correct booloader binary "\common\binary\UARTldr". Then it should compile.

I have no smaller firmware, because I'm not interested in a step back ^^

If it still not compile send me the log file.
Title: Re: My first DRSSTC on bricks
Post by: profdc9 on March 04, 2019, 12:58:48 AM
I made a board for the CYC8KIT-059 based UD3

https://github.com/profdc9/DRSSTC-PCB-Pack/tree/master/Psoc5-power

so you don't have to etch a board.

Dan

That's right, 500kHz is the maximum for the UD3.

Perfboard is not ideal for a high current gatedriver. I would prefer SMD mit big ceramic decoupling to keep the switching noise out of the driver.

I drive my SKM400 with a 13 to 10 GDT with 24V on the GDT driver so you get 18V at the gate.
Thanks for the suggestions!I'll try to etch a PCB and use 10uF THT X7R capacitors,two in parallel for each N-P MOSFET pair(IRFZ44NPbF and IRF4905PbF).If I succeed to modify an ATX PSU,then I can change the gate drive voltage.
I also received a CY8CKIT-059 board and checked your UD3 firmware,but some files are missing.Do you have a simpler firmware something like the UD2.7 or I should make one on my own?

the universal driver can do 500khz but the SKM400 probly can not what frequency is your coil? your snubber will not work if you are soldering to aluminuim. at least bridge the cap connection to the screws with copper at the end of your assembly
The SKM400 bricks definitely can't do 500kHz,but hopefully they can 150kHz.I plan to enhance the MMC connections or even make a completely new one if this fails.The snubbers are good,1uF and mounted directly to the bricks with the screws.
Title: Re: My first DRSSTC on bricks
Post by: Netzpfuscher on March 04, 2019, 08:26:45 AM
You must double check the pinout of the dev-board project in psoc creator and the pcb files. I shuffled the pins around to fit the Ethernet-Interface.

I work on a second ethernet option, which uses a ESP32. With this you get WIFI and wired ethernet and a small problem with noise is solved. The W5500 ethernet chip uses a unprotected SPI protocol (no checksums) which can lead in false data under some conditions. The ESP32 interface connect through the UART of the UD3 and uses a packet based protocol with a transport layer. every packet is protected with a CRC32 and a sequence number. If a packet gets corrupted the transport layer resends the packet until it was received correctly. It's like a simple version of TCP/IP.

This is the new interface board for now: https://www.olimex.com/Products/IoT/ESP32/ESP32-POE/open-source-hardware
I think I integrate it in the new PCB if I find a little bit time.
Title: Re: My first DRSSTC on bricks
Post by: Laci on March 08, 2019, 08:35:31 PM
I made a board for the CYC8KIT-059 based UD3

https://github.com/profdc9/DRSSTC-PCB-Pack/tree/master/Psoc5-power

so you don't have to etch a board.

Dan

Looks great,although I'll make most of the driver on a perfboard.

There are no files missing, I think psoc creator didn't find the bootloader files. This is a common issue, go to the schematic of the UD3 QFN project, double click the bootloader component and set the path to the correct booloader binary "\common\binary\UARTldr". Then it should compile.

I have no smaller firmware, because I'm not interested in a step back ^^

If it still not compile send me the log file.

Thanks,it works!Not sure if the bootloader location was the problem or something else,but it's OK now.
I want to use a bluetooth 4.0 BLE module and android app for interrupter instead of fiber optic,which I bought for cheap and it's of course clone and can't pair my phone with it.Firmware update can solve this hopefully.
Another idea was the using of an ethernet module,which I received factory defective:none of the two ethernet LEDs turns on.
Sadly I don't know how to get started with the UD3,so it'll take for a long time to make a working board.



Title: Re: My first DRSSTC on bricks
Post by: Laci on April 04, 2019, 09:14:28 PM
Some progress updates around here.The inverter is almost done,just the GDTs should be mounted somewhere(B64290L0082X830) and add the precharge circuit.Driving these large bricks seems to be possible!I will upload some scopeshots soon and hopefully estimate switching losses.
Title: Re: My first DRSSTC on bricks
Post by: Laci on April 06, 2019, 05:46:30 PM
I'm getting close to the destination of this project. :)
The inverter only requires the precharge circuit now.It looks nice,doesn't it? :D
 [ Invalid Attachment ]

I still can't send gate waveforms because I don't exactly know how to run a test on the UD3 without feedback signal.In this picture you can see the four LEDs.LED2 blinks not constantly,while LED1 and LED4 is ON and LED3 is OFF.Is this how it's supposed to work?
 [ Invalid Attachment ]
Title: Re: My first DRSSTC on bricks
Post by: Netzpfuscher on April 06, 2019, 11:31:50 PM
The UD3 should produce output without feedback, without feedback you see the start oscillator.
I think the watchdog has triggered. You can reset the watchdog with "kill reset"

But for operation the UD3 needs a watchdog reset signal at least every 20ms. Your controller should send this "0xF0 0x0F 0x0F" (In Binary!) or you need to disable the watchdog.
Just set the "watchdog" configuration to 0. But if the connection dies the UD3 won't stop to fire the coil  ;)

LED1 = Interrupter
LED2 = System fault
LED3 = Over current
LED4 = Receive data
Title: Re: My first DRSSTC on bricks
Post by: Laci on April 06, 2019, 11:45:05 PM
LED1 is always on no matter what I do."tr start" should start the interrupter,so turn LED1 ON and "tr stop" should stop the interrupter,so turn LED1 OFF?
LED2 still lights up randomly and with the "eeprom save" command
LED3 is always off yet,without OCD
LED4 turns off when I connect to the bluetooth module so that should work :)

I extended the app with a terminal to use every command,but noticed problems with the serial communication colours,so that needs some improvements.

EDIT: LED3 and LED4 turns ON when I start the bootloader.What's the purpose of it?I tested the UD3 with many settings changed,still no output signal...

UPDATE: some waveforms with a simple pwm(130kHz,800us ontime).Yellow is the gate of one IGBT,blue is the inverter output with a resistive load.I tried to increase the gate resistance which removed the overshoot on the rising edge,but not on the falling edge.The current gate resistors are just 1 ohm.Rise and fall times are pretty much the same,around 450ns from 0% to 100%.Overall I'm quite pleased with the waveforms,didn't expect such a good result.We'll see how they perform with a proper load after getting the UD3 to work! :)






2nd UPDATE: I forgot about the UVLO,now the UD3 passed transient mode,hopefully other functions works too.I think I saw a maximum value of 100kHz for the autotune functions(which by the way seems to work too-outputs <10A without CT).Is the autotune really limited to 100kHz?
Title: Re: My first DRSSTC on bricks
Post by: Mads Barnkob on April 08, 2019, 08:21:27 AM
Good progress on the coil and inverter, this really shows that if you pay enough attention to the brigde design and making it as compact as possible and with good snubbering, the resulting waveform show it was not in vein, good job.

Netzpfuscher: There is a lot of good trouble shooting and background information about UD3 in this thread, maybe make a FAQ in your own original post with a copy of these answers? Or just a link to different threads where it is dicussed?
Title: Re: My first DRSSTC on bricks
Post by: Netzpfuscher on April 08, 2019, 09:03:39 AM
I think I write a FAQ in the github wiki, that everyone can benefit from this.

No, the autotuning function isn't limited to 100kHz, this is a bug. I correct this as soon as possible.  Edit: It's fixed: https://github.com/Netzpfuscher/UD3/commits/master

If you find more bugs please feel free to write an issue:
https://github.com/Netzpfuscher/UD3/issues


If transient mode works all system faults should be gone. Due to this thread I think it should be a big thing to add a alarm monitor where you can see which signals are not good.

Title: Re: My first DRSSTC on bricks
Post by: Laci on April 11, 2019, 07:31:53 PM
I did a small test on 50V with experimental tuning on an old primary and already see some nice sparks.
The driver seems to work in transient mode.At the start frequency the interrupter is also working,might need some more smoothness and fix the unexpected behaviour of the app with fast clicks.
Primary current feedback is not working yet.I have a 1000:1 CT with 5.1 ohm burden resistor.What settings should be changed to get it working?When do I know if the UD3 senses the primary current?

An alarm monitor would be nice in the app too even as simple as four indicators like the LEDs. :)

Related to the inverter: I see not much overshoot on the output.In this case how should I adjust phase lead?
One thing I noticed while putting the driver into a plastic box is that the wire lenght and type from GDT drive to GDT primary is critical.Rise and fall times increases drastically if two thick twisted wires are used instead of multiple thin twisted wires from driver board to the frame of the box.
Title: Re: My first DRSSTC on bricks
Post by: Netzpfuscher on April 11, 2019, 10:39:44 PM
Have you connected the CTout, ZCDA and ZCDB?
Have you set the "ct1_ratio 1000" and "ct1_burden 5.1"?

If you connect over putty and connect to the UD3 type: "status start" then you should see the current.

You test with transient mode and it runs? What do you mean with interrupter, the transient mode is the normal interrupter.

You know that the UD3 sees zero crossings if it switches more cycles than the set start_cycles. I should add a indicator ^^
Title: Re: My first DRSSTC on bricks
Post by: Laci on April 12, 2019, 06:32:13 PM
I spent hours today on getting the autotune fixed version working,but after uploading the onboard blue LED lights up and can't communicate with it over serial(bluetooth module).I did the same changes with the UART_2 as before,changed clock to internal,bits per second to 9600,buffers size to 256.Is this a possible problem or I did something wrong?

I was not sure about the meaning of transient,now it's clear!

The "how to set phase lead if I don't see any overshoots across the inverter output" question is still active. :)
Title: Re: My first DRSSTC on bricks
Post by: Netzpfuscher on April 12, 2019, 06:50:42 PM
Why did you change the buffer size? But I don't think that is the problem. It slows down the communication.

You use SKM400 like me, so the default parameters should be not to bad. Activate transient mode and give the driver another lead_time and look if the spikes get better or worse.

Edit:
Checkout the new commit. The ESP32 interface was enabled by default and this uses the serial port. I disabled it by default. But over USB you should get a connection and then you can disable the ESP32 interface with: "set eth_hw 0" and save everything to eeprom with "eeprom save"

9600 baud is very slow ^^ if you want to enable telemetry later it eats up 50% of your bandwidth. For the SID Synthesizer you need at least 19200 baud
Title: Re: My first DRSSTC on bricks
Post by: Laci on April 12, 2019, 09:25:42 PM
The cheap bluetooth module only runs on those low settings.Sadly I still can't communicate with the UD3 over the serial pins.The onboard blue LED is constantly ON,unlike the autotune bug version,where it was OFF.
Here are the settings:


Pinout is the default.I only have VCC,GND,TX and RX on the right way connected from the bluetooth module to the standalone development board,so no hardware connection issues.
Another error(?):


And here's another error which I think is more like a bug in PSoC Creator as it shows that UART_2 requires connection when it's visible,but I run it on internal clock:



Title: Re: My first DRSSTC on bricks
Post by: Netzpfuscher on April 12, 2019, 11:03:56 PM
First of all, 20 start cycles is waaaaay to high. A normal DRSSTC runs fine with 3. I think your feedback is still not working, if you get no output with 3 cycles.
Is the 130kHz resonant frequency correct? Have you measured it? When it is off by a big amount your coil will not swing up and you get no feedback.

Have you pulled the new files from github or did you only change some files manually? I have made several changes to the min library and other files when I implemented the ESP32.

Have you restarted the UD3 after you saved the disabled ethernet interface? The interfaces change only after a restart.

I get a error free build with the latest revision:


Please check if this works before you make any modifications. Some timing violations can be ignored.

Yes psoc creator has some bugs in the schematic with deleted connections. This should be gone if you restart creator.

You can set the task info in the "FreeRTOSConfig.h" Line 120 to 1 and give me the output of the "tasks" command, then I can check if the UART task is running.
Title: Re: My first DRSSTC on bricks
Post by: Laci on April 13, 2019, 09:54:41 AM
Yesterday I set the startup cycles to 3.The 130kHz is about 10% lower than the secondary Fres.To start the coil I start transient,which locks the drive frequency to the startup frequency and feedback never takes over while the coil already produces 10 cm sparks.

I downloaded completely the new UD3.

Restarted everything many times,including PSoC creator and the dev.kit.

Here are the tasks.Many things are different after the UART_2 changes.The serial communication speed over USB looks a lot faster with the new version,have you speeded up all serial communications which might not be accepted by my bluetooth module?

Tasks without modifications:


With the UART_2 modifications:


Old(autotune bug)version which works:


Small update: the bluetooth module now runs at 115200 bps,the dev.kit still can't communicate with it.
The onboard blue LED is connected to pin 2[1] just like LED4,so if it constantly lights something is really busy on serial...
Title: Re: My first DRSSTC on bricks
Post by: Netzpfuscher on April 13, 2019, 06:00:05 PM
Check the latest commit.

It was a bug caused by me. I forget to enable the UART in pure serial mode. I also re enabled the blinken light ^^ 
Title: Re: My first DRSSTC on bricks
Post by: Laci on April 13, 2019, 09:40:09 PM
Woww,this fix was quite fast! ;D
I tested many functions and so far almost erverything works.While taking scopeshots I saw a strange high frequency after around the 3rd cycle.You know what that is. :D
-Yes that's the feedback which works but quite inaccurately.It stays at the same frequency,then in a 1 cm primary tap zone the frequency jumps from 130kHz to 240kHz.The new primary will be completed soon,with 11 turns of 8mm copper tubing and 4x wood holders in "+" shape.

I had to decrease the bluetooth module speed back to 9600 as the app couldn't receive long strings like a "help" command.Most of the settings in the app are pointless anyways so I might remove the unnecessary functions and leave it as a simple interrupter or make a better app in java.

Is this what they call "freewheeling current limiter"?  8)
 [ Invalid Attachment ]
Title: Re: My first DRSSTC on bricks
Post by: Netzpfuscher on April 13, 2019, 11:16:20 PM
Please use putty and make a "tune_p" from 80khz to 180khz and post a screenshot of the frequency response. 60V on the bridge should be enough for the sweep.

Have you installed a common mode choke in the feedback lines?

Why is your min_tr_current at 0? The default is at 100A. This is how low the midi velocity can modulate the current down.
Set the "offtime" back to 2µs this is a midi only parameter. It describes the minimal offtime between two pulses.


Title: Re: My first DRSSTC on bricks
Post by: Laci on April 14, 2019, 09:20:52 PM
I finished the new primary.Like always,it's probably a complete overkill for a 50cm tall 12.5cm diameter secondary coil.Feedback is kind of working.It changes nicely when moving the tap point over around 5 turns,but at the desired frequency of about 140kHz it jumps up to 240kHz as before.Running an autotune gives correct values(140kHz),but it keeps driving at 240kHz.

The common mode choke isn't installed.The settings you mentioned are back to defaults.

5 turns(too high frequency):


6 turns(frequency is OK):

Title: Re: My first DRSSTC on bricks
Post by: Laci on April 15, 2019, 09:28:09 PM
Today's progress update:
I continued the mechanical assembly and it's almost done,the primary connections should be made.Did some tuning too,but I wouldn't speak about them until the design is completed(right now the peak primary current is found at 134kHz,but the drive is at 128kHz...)

The next electrical thing to add is the precharge circuit.I have some questions regarding that.If I'm right,the "bus" command turns ON or OFF Relay1 which should bypass the precharge power resistor(s).Can use "bus" command just after powering up,destroying fuses by the inrush or some additinal things are used to always avoid the inrush,like time delay or bus voltage sensing?
For current sensing can I use a module which gives 100mV/A?


 [ Invalid Attachment ]

 [ Invalid Attachment ]

Title: Re: My first DRSSTC on bricks
Post by: Netzpfuscher on April 15, 2019, 10:02:19 PM
Have you used a wide range for the autotune? The thing is, the UD3 divides the range in 127 frequency's and sweeps these. If you resonant frequency is not in this table it won't show up it is the nearest. I must test this function a little bit further. But 134 to 128 is not so much off ^^ I don't know how high the current was, but with more voltage on the bridge the result is more accurate. You can play a little bit. Also there are options for longer ontimes, more delay between the cycles and more averaging.

The precharge in default works like so:
"bus on" relay1 is activated and connects the precharge resistor to the mains. The UD3 measures the voltage on the bus and if it rises no more it activates relay2 which shorts the resistor.

You need a current transformer with current output (1000:1 works great). There is a shunt on the board and the UD3 senses this voltage and calculates the current with the ct2_ratio and ct2_burden. But if you set the burden and ratio right, you can use voltage output current transformer. You need to play with the calculation.
Title: Re: My first DRSSTC on bricks
Post by: Laci on April 16, 2019, 08:46:05 PM
I pretty much finished the assembly today.Sadly the results aren't quite good.I suspect primary EMI causing many problems,like UD3 turning OFF(or at least fault mode) after a few seconds of running,noisy gate waferom and even the bluetooth module disconnects.I was afraid of this,as shielding wouldn't be easy.Many pictures are attached below,feel free to watch them and -hopefully- correct me if I'm wrong or leave your suggestions.

Title: Re: My first DRSSTC on bricks
Post by: Laci on April 17, 2019, 08:14:52 PM
Here's a video of the driver's strange behaviour at 50V.Basically it randomly changes ontime and the gate waveform is really noisy,even the bricks got warm.I noticed one capacitor arcing in the MMC,so I'm gonna rebuild it.Which one would you recommend,etching a small PCB with some large traces or just solder the series caps together by their leads and make the parallel connections with thick wires?

https://mega.nz/#!QXpAQCpD!VHqH3mPHddox_w0hZAlNTeqkEotdEfFRFYnVgWgklCk (https://mega.nz/#!QXpAQCpD!VHqH3mPHddox_w0hZAlNTeqkEotdEfFRFYnVgWgklCk)
Title: Re: My first DRSSTC on bricks
Post by: Fumeaux on April 17, 2019, 08:22:30 PM
strange behaviour at 50V

I'm no expert by all means, but could it be that:
ontime changes is a result of current limiting
and
the current limiting is a result of the arcs?
Title: Re: My first DRSSTC on bricks
Post by: Laci on April 17, 2019, 08:34:44 PM
I don't think it's current limiting.For one,the current limit is set quite high and also the ontime changes randomly.I'd say EMI,but not sure.The arcing is happening due to high voltage.One thing that might happen is that the voltage rises at the frequency without that cap,then it arcs and the frequency changes.This should be gone after I remake the MMC.The gate noise is yet another mistery-it could be caused by wrong feedback,primary EMI to the GDT and primary EMI into the driver...
Title: Re: My first DRSSTC on bricks
Post by: Fumeaux on April 17, 2019, 08:51:47 PM
The thing is that the arc cause the cap to short out which causes a current spikes. Fast changes of voltage/current and inductors don't go together too well. So it is possible that the current limit threshhold can met by a spike. Then the driver ramps the ontime down and back up.

How often does it ark anyways? And what do you mean by gate noise?
Title: Re: My first DRSSTC on bricks
Post by: Laci on April 17, 2019, 09:01:40 PM
I already took the MMC apart,so no more informations about it.  ::)

By gate noise I mean unwanted switching and spikes in the waveform.At the end of the video you might be able to see the sharp,almost vertical pulses,which increases the losses significantly.
Title: Re: My first DRSSTC on bricks
Post by: Netzpfuscher on April 17, 2019, 10:44:02 PM
Have you connected the CT2 input to gnd? I think you have a floating input which picks up noise. The UD3 thinks there is to much current from mains flowing and ramps down the dutycycle / ontime.
This is one of the new features, a i2t Controller.
Title: Re: My first DRSSTC on bricks
Post by: Mads Barnkob on April 18, 2019, 09:51:49 PM
Great progress and big thumbs up to Netzpfuscher for the support!

You driver is just sitting in a plastic enclosure, I always use a metal box which gets grounded, switching noise is pretty massive so close to the primary coil. My large DRSSTC can knock out my camera at 50 cm distance when running with a static load.

Looking forward to see your first sparks on the UD3 and also a big thank you for sharing your fault tracings on the UD3, this will all help future builders!
Title: Re: My first DRSSTC on bricks
Post by: Laci on April 19, 2019, 09:05:15 PM
You driver is just sitting in a plastic enclosure, I always use a metal box which gets grounded, switching noise is pretty massive so close to the primary coil. My large DRSSTC can knock out my camera at 50 cm distance when running with a static load.
A metal enclosure could probably save me from the few days already spent on troubleshooting.I have more space now,since moved the inverter and MMC to one side and I'll look for some metal boxes.
Right now the only thing I'm sure about is that EMI causes many problems.Even moving the driver box around changes the output.The driver still limits pw when the box isn't under the primary and stops driving as well as refuses to change pw from 0 when it's under the primary.

With 50V on the bus the driver gets crazy over 50us,but that depends on the distance between primary and driver box.
Gate at 50us:


Gate at 60us:

Title: Re: My first DRSSTC on bricks
Post by: Netzpfuscher on April 19, 2019, 09:51:51 PM
There is no software function which alters the pulse width. If you can't set parameters while the coil is running it is much likely due to corrupted bytes on the serial line. That's why I added the MIN-Protocol to the firmware, it's a protocol like TCP with checksums and re-transmission of packets. But with a BLE adapter you can't use this, it's included in the new ethernet and wifi interface.

I cannot say very much about the stability of a UD3 on perfboard, we only have two UD3 coils with a proper PCB. On the big coil with 1200A primary current the driver is around 40cm away under the primary coil in a metal box. It works without problems, only the UART connection sometimes catches false chars (50cm CAT5 cable to the fiber modules) we solved this problems with the MIN protocol. But in essence it works also without.

The new layout I'm working on is a 4 layer PCB and should be even more stable, because of the inner power planes.

I like to put the inverter in a separate box (without the MMC). It gives more flexibility, less EMI in the driver, less weight to carry and I can change the resonators to the needs. I use thick welding cables (twisted) and welding connectors for the connection to the resonator.
Title: Re: My first DRSSTC on bricks
Post by: Teravolt on April 22, 2019, 07:24:49 PM
Hi Laci, are your mmc caps soldered to the aluninuim because leaded solder will not flow on aluminuim and you may have a bad connection. get some copper wire or tubing or brass and solder to that.
Title: Re: My first DRSSTC on bricks
Post by: Laci on April 22, 2019, 07:48:58 PM
Thanks Teravolt,I paid attention to your previous suggestion on this and rebuilt the MMC since then.This time I soldered the parallel caps to a copper wire,enhanced the connections with a lot of solder and soldered the thick wires from inverter and to primary too.You might be able to see this on this picture:
 [ Invalid Attachment ]
Title: Re: My first DRSSTC on bricks
Post by: Laci on April 26, 2019, 09:39:32 AM
I put the driver into a metal enclosure.After trying it out,signal noise appeared again.It looks like there's too much noise if the enclosure is floating and even worse if I ground it to mains earth,because the PSU for the driver is on the same ground.Any ideas about this?

 [ Invalid Attachment ]

 [ Invalid Attachment ]
Title: Re: My first DRSSTC on bricks
Post by: Netzpfuscher on April 26, 2019, 10:03:03 AM
The red and black wires on the right side are from the power supply? Is the red wire connected at the top of pcb? Is the supply for the UD3 connected at the bottom of the right pcb?
With such a configuration you couple all of the switching noise of the GDT drivers into the UD3. Connect the red wire at the bottom.

Have you scoped the AC part of the 5V rail? I bet you see the switching there. This could explain the problems with the analog signals. The ADCs are referenced to the 5V rail.
Title: Re: My first DRSSTC on bricks
Post by: Laci on April 26, 2019, 10:19:06 AM
The + of the PSU goes to the buttom + bus of the output stage(4xNMOS,4xPMOS + capacitors)and the black goes to the upper - bus.The multiple wires from the 4xdriver ICs goes to the gates.The wires which have the ferrite bead are feedback and the other white wires are the PSU wires too.

There's plenty of noise on the +5V!
Title: Re: My first DRSSTC on bricks
Post by: Netzpfuscher on April 26, 2019, 11:07:59 AM
 [ Invalid Attachment ]

please change the layout to a star configuration. Like this:

 [ Invalid Attachment ]
Title: Re: My first DRSSTC on bricks
Post by: Laci on April 26, 2019, 04:05:09 PM
I think the 5V noise got lowered to an acceptable level after soldering the 5V regulator close to the input,adding some ceramic capacitors and some thicker wires.

Quickly put everything together and now I get noise from the secondary.Its base is connected to mains ground for testing.If I connect the enclosure to mains ground the waveforms gets worse,but if I only connect the heatsink to mains ground I see some improvements like longer arcs and more current flowing.Should the ground rod connected to the enclosure and heatsink solve this issue?I'll get the rest of the components next week,then hopefully make this ready for a mains test,unless you say that the ground rod would solve the noise,then I test it before. :D
Title: Re: My first DRSSTC on bricks
Post by: Netzpfuscher on April 26, 2019, 04:26:00 PM
The secondary needs a separate ground. No connection to the driver/bridge an what so ever.
Use the water pipes or the pipes from the heater or a rod in the garden.
Title: Re: My first DRSSTC on bricks
Post by: Laci on April 27, 2019, 08:21:51 PM
First light...on video!
I'd say about maximum 40-50cm sparks under 100us ontime at 250A limit!This 1:1 spark to secondary size is already promising I think. :)
Still many things to do,like thermal protection,RMS current measurement and a WIFI or ethernet interface for better control.For now the app works great,but the BLE distance decreased significantly after the metal enclosure to around 5m,which is still enough in a room.

The largest improvement that can be done is a better MMC.My dream was to find some screw terminal high pulse duty capacitors at affordable price.These are quite rare,for cheap even rarer.If the current WIMA FKP-1 caps can keep up the stress,then I'll probably buy plenty of these in the future to get some 8kV and current up to like 800A.Is this too much for a 12.5cm dia. and 50cm tall coil?! ::)

The grounding is still questionable.Now the secondary base and the heatsink is connected to the ground rod,but the driver enclosure is floating.The general DRSSTC grounding diagram suggests to connect the driver enclosure to the same ground,but I get a lot of noise in the gate drive with that...Also I don't have strike rail and the bus negative to ground capacitor placed.
(https://i.imgur.com/wVByasw.jpg)

A pretty spark from the video:


Video: https://mega.nz/#!AKgCGSaD!bLG60IWPkzon7V5Krxq0VxgPT3-mpxzL3VsgE7QD4Fc (https://mega.nz/#!AKgCGSaD!bLG60IWPkzon7V5Krxq0VxgPT3-mpxzL3VsgE7QD4Fc)


(Sorry for the bad quality,the photographer job is the next.  :P)

Title: Re: My first DRSSTC on bricks
Post by: Mads Barnkob on April 27, 2019, 09:23:56 PM
Congratulations on first light!

800 Apeak will properly work just fine, you just have to monitor your secondary coil temperature when pushing it around its limits, you might need a larger/wider topload to get the longer sparks away from the primary coil and to shape a larger magnetic field to keep the sparks from flying inwards.

Grounding everything together only works if you have a low impedance ground rod that it all connects to, else it will find a way for the noise to couple in through the other parts, I have also used floating driver enclosures before but I have not seen a difference when throwing out large sparks from grounded or floating shielded. I did however not have any measurements on the drivers imposed noise from when doing so either, so its just a qualified guess based on it not exploding and taking a beating :)

Maybe your app could use one of the external buttons on a phone as trigger? So you dont have to control it with a turning up/down of the pulse width.

Title: Re: My first DRSSTC on bricks
Post by: Laci on April 27, 2019, 09:41:30 PM
Thanks,Mads!

A larger topload with less sharp edges is in the plans.

The ground wire is relatively thick;thicker than the primary and around 6-7m long.The ground rod is made out of aluminium,about 1m long with many holes in it.All in all I think this grounding is pretty low impedance and something else causes the problem,but if it's good floating then I don't care. :)

The external buttons are great idea,I never thought of this!Since processing MIDI files in app inventor looks not really possible,I plan to switch to something more professional like android studio,that might take some time.
Title: Re: My first DRSSTC on bricks
Post by: Laci on April 29, 2019, 09:42:07 PM
After spending hours on choosing the greatest and cheapest capacitors to upgrade the MMC,I realised they all have small dVdT rating.With heavy spark loading the frequency should drop to around 110kHz which is 9us period.In this period are two cycles so the rise and fall times of the primary current are 2.25us.At a high voltage,like 8kV,they should be rated over 4kV/us if we are lazy and assume the primary current rises linearly.

The WIMA FKP1 series have the best dVdT rating I could find.I planned to buy 20pcs 0.047uF 2kVDC of these,the same as the current ones,just with 5% tolerance(the current ones have 2.5%).If I combine all of them,I get a 4 in series,7 in parallel MMC,rated 0.0822uF and 8kVDC.

The interesting thing starts here.With the heavy spark loading I mentioned at 110kHz, the MMC's reactance is 17.6 ohm.The highest MMC voltage I would allow is 8125V with the 325V bus.From these,according to ohms law the maximum current is 8125/17.6 = 461A. This was a bit disappointing after making the calculations and the only way I can think of to increase the maximum current is increasing the MMC capacitance.
Am I right in the calculations and should I really increase the MMC's capacitance for higher peak currents?Perhaps knows somebody about affordable capacitors for MMC I can buy?
Title: Re: My first DRSSTC on bricks
Post by: Phoenix on April 29, 2019, 10:04:02 PM
Hello Laci

Your calculations about the MMC's reactance at 110kHz are correct, but there is a very important thing that happens in an LC circuit: The reactance of the capacitor and the reactance of the inductor cancel each other out. If the LC circuit gets exited with the exact resonance frequency, the impedance will be 0 Ohms, but you will still have the ESR of the Primary and the MMC limit your current. The impedance will be 0 because with each cycle the voltage increases and so does the current. Theoretically, the LC circuit would ring up infinitely.

If you use more capacitance, you will have a faster current rise and you could get more peak current with the same ontime and number of primary cycles. The more time you give your DRSSTC to ring up, the more peak current you will get. If you use less capacitance it will just take more cycles to reach the same current than with more capacitance. Of course you need to make sure that the voltage rating of your MMC gets not exceeded during the ringup. The calculation about the maximum peak current you can allow with the MMC is correct.

I think the Wima FKP1 are a really good choice for your coil. I have also used these capacitors for my DRSSTC I. But I do not know how much RMS current your chosen capacitors can handle, Wima doesn't provide datasheets with a lot of information. Have you already tried the MMC calculator from Mads? It is really good for doing the calculations.

EDIT:

I just calculated your primary inductance and I think lowering your primary inductance using less turns and increasing your MMC capacitance to get to the 110 kHz would be a good idea. If you use 4 Wima FKP1 1600V 100nF caps in series and 8 of these strings in parallel, you get 200nF at 6400V. You could go up to 880A with this MMC.

Here you can buy Wima FKP1 capacitors new and for a very good price: https://www.reichelt.at/pulse-capacitor-fkp1-1600-100n-p7733.html?GROUPID=7175&START=0&OFFSET=16&SID=94XE7uy6wQAT4AAEAgW0ke260e2724a5569dec4ba647f3dc371a5&LANGUAGE=EN&&r=1


Greetings
Phoenix
Title: Re: My first DRSSTC on bricks
Post by: Laci on April 30, 2019, 12:09:19 AM
Thanks for the useful informations,Phoenix!

I did my calculations until the limitations of the MMC,but you are right about resonance.

The current rise time is not critical for me as I want to run with long pulses,up to 800us with freewheeling.

I used Mads MMC calculator hundread times for now. :)

Many thanks for your calculations and for the webshop.The capacitors are really cheap indeed,although the 10 euro shipping is a bit painful compared to the them.I have to do my calculations about these.
At first I thought 0.2uF is too much and will require only a couple of turns.After running a JavaTC simulation it showed that one less turn,so 5 will be at 113kHz which is good!

What about the number of series and parallel capacitors?The datasheet doesn't mention the current rating,but in theory the more capacitors in parallel,the less the ESR is or in these applications it makes not much sense?For example at 110kHz,800A which one should I choose, 0.2uF 6kV(more in parallel) or 0.15 8kV(more in series)? (in theory more in parallel)
Title: Re: My first DRSSTC on bricks
Post by: dexter on April 30, 2019, 12:32:24 AM
What about the number of series and parallel capacitors?The datasheet doesn't mention the current rating,but in theory the more capacitors in parallel,the less the ESR is or in these applications it makes not much sense?For example at 110kHz,800A which one should I choose, 0.2uF 6kV(more in parallel) or 0.15 8kV(more in series)? (in theory more in parallel)

You can calculate Ipk=C*dV/dT

If 6kV is enough for your coil i'd go for 0.2uF (more capacitance and more caps in parallel)
Title: Re: My first DRSSTC on bricks
Post by: Phoenix on April 30, 2019, 08:01:39 AM
Hello Laci  :)

I would also use more caps in parallel to get the 0.2uF 6400V MMC. Because you are planning to use freewheeling, you really need a high RMS current MMC, if you want to run moderate BPS values. As you said correctly, more caps in parallel decrease your ESR value. Low ESR is very important in such an application, because with more ESR there are more losses generated in the capacitors (P=ESR*IRMS^2).

Because you are building the same MMC like I did, just with less capacitors, I can really recommend you a very good design for equal current sharing between the capacitors. I am also using Wima FKP1 1600V 100nF capacitors (4 in series 15 strings parallel for 375nF at 6400V). Here you can see the MMC of my DRSSTC I:



As you can see, the connections from the copper rails to the inverter/primary are not on the same side. This ensures good current sharing.

Greetings
Phoenix

Title: Re: My first DRSSTC on bricks
Post by: Netzpfuscher on April 30, 2019, 08:36:53 AM
If you find some old high voltage oil capacitors for really cheap they are worth a try.

I use a old capacitor in my coil and a bunch of them are used in a big SGTC and work reliable with low heating.
 [ Invalid Attachment ]
Title: Re: My first DRSSTC on bricks
Post by: Laci on May 02, 2019, 10:25:11 PM
I found this ebay listing with 0.1uF 2.5kV paper in oil capacitors:
https://www.ebay.com/itm/K41-1a-Paper-PIO-pulse-capacitor-0-1uF-10-2-5kV-Lot-of-2/251259264733?_trkparms=aid%3D888007%26algo%3DDISC.MBE%26ao%3D1%26asc%3D20131227121020%26meid%3Dc3967893df3249af835219ad5cd172cc%26pid%3D100009%26rk%3D1%26rkt%3D1%26mehot%3Dag%26sd%3D162844731444%26itm%3D251259264733&_trksid=p2047675.c100009.m1982 (https://www.ebay.com/itm/K41-1a-Paper-PIO-pulse-capacitor-0-1uF-10-2-5kV-Lot-of-2/251259264733?_trkparms=aid%3D888007%26algo%3DDISC.MBE%26ao%3D1%26asc%3D20131227121020%26meid%3Dc3967893df3249af835219ad5cd172cc%26pid%3D100009%26rk%3D1%26rkt%3D1%26mehot%3Dag%26sd%3D162844731444%26itm%3D251259264733&_trksid=p2047675.c100009.m1982)

Does anybody have experience with this kind of capacitors?Are they any good for a MMC?

Another thing: in series connection the overall pulse resistance(dVdT) of the MMC gets multiplied by the amount of series capacitors? In this case the voltage gets shared by the series capacitors and they see a smaller voltage rise across them,so 1.8kV/us capacitors would already be good with 4 in series at 6kV across the MMC?
I just saw Futurist's DRSSTC1 and he used C4BS capacitors,which have around 1kV/us rating if I remember right and they worked fine for him...
Title: Re: My first DRSSTC on bricks
Post by: Max on May 03, 2019, 06:16:10 PM
I always thought that paper oil capacitors had terrible losses at high frequencies...? Or in other words that PP film caps are the only type of caps that are suited for this frequency/power range. Apparently that's not true?

Kind regards,
Max
Title: Re: My first DRSSTC on bricks
Post by: Mads Barnkob on May 03, 2019, 07:49:06 PM
I found this ebay listing with 0.1uF 2.5kV paper in oil capacitors:
https://www.ebay.com/itm/K41-1a-Paper-PIO-pulse-capacitor-0-1uF-10-2-5kV-Lot-of-2/251259264733?_trkparms=aid%3D888007%26algo%3DDISC.MBE%26ao%3D1%26asc%3D20131227121020%26meid%3Dc3967893df3249af835219ad5cd172cc%26pid%3D100009%26rk%3D1%26rkt%3D1%26mehot%3Dag%26sd%3D162844731444%26itm%3D251259264733&_trksid=p2047675.c100009.m1982 (https://www.ebay.com/itm/K41-1a-Paper-PIO-pulse-capacitor-0-1uF-10-2-5kV-Lot-of-2/251259264733?_trkparms=aid%3D888007%26algo%3DDISC.MBE%26ao%3D1%26asc%3D20131227121020%26meid%3Dc3967893df3249af835219ad5cd172cc%26pid%3D100009%26rk%3D1%26rkt%3D1%26mehot%3Dag%26sd%3D162844731444%26itm%3D251259264733&_trksid=p2047675.c100009.m1982)

Does anybody have experience with this kind of capacitors?Are they any good for a MMC?

Another thing: in series connection the overall pulse resistance(dVdT) of the MMC gets multiplied by the amount of series capacitors? In this case the voltage gets shared by the series capacitors and they see a smaller voltage rise across them,so 1.8kV/us capacitors would already be good with 4 in series at 6kV across the MMC?
I just saw Futurist's DRSSTC1 and he used C4BS capacitors,which have around 1kV/us rating if I remember right and they worked fine for him...

I doubt old PIO capacitors will last long in a DRSSTC, unless it is some special Russian secret cold war indestructible super caps :) As mentioned, their losses at high frequency is most likely very bad, but check their datasheet if you can find one.

I think you are mistaken about the AC voltage rating needed for a resonant capacitor vs. dV/dt, dV/dt is simply a value derived from capacitance and the peak current it is rated to pass through it, and the pulse capacitors we use are almost always high peak current specced or low capacitance, so there is rarely a case of dV/dt being broken.

I wrote the math down used in my calculator, just beneath it: http://kaizerpowerelectronics.dk/calculators/mmc-calculator/

If you want to design your MMC correct, I give 3 alternatives to do so here: http://kaizerpowerelectronics.dk/tesla-coils/drsstc-design-guide/mmc-tank-capacitor/
Title: Re: My first DRSSTC on bricks
Post by: Laci on May 04, 2019, 09:48:14 PM
I did some more calculations and choose the KEMET R76TR31004030J. 4 in series, 8 in parallel gives 0.2uF at 6400V,so around 850A peak. They are cheap and common so I can update the MMC in the future if needed.Their RMS current rating is just under 10A around 100kHz.This gives around IRMS=80A for 8 in parallel.

(https://i.imgur.com/rW6U0Wu.png)

I calculated a maximum of 100 bps at 800us for the 80A IRMS. What do you think about this choice?
Title: Re: My first DRSSTC on bricks
Post by: Laci on May 12, 2019, 09:49:02 PM
After waiting a week for the components and another few days of work, I could finally make some better tests.It looks like with longer pulses at lower peak currents I get good results,just like with short pulses at higher currents.I tested midi notes up to 300A peak and transient up to 500 and the midi notes can already destroy 4A fuses.I'm a bit worried about huge sparks,because I blew up my SSTC2 bridge yesterday. I was running it from mains ground and cranked up the power to maximum.A secondary - primary flashover killed it...Stupid!...RIP 2pcs HGTG30N60A4D...

The MMC is the same that I planned, 0.2uF 6400V KEMET R76 series, around 80A IRMS. They are working,but didn't make any measurements yet.
I painted the metal enclosure blue,just like the MMC and added plenty of screw terminals.

For higher power running I want to make sure that it won't kill the bridge. I don't have strike rail and bus negative to earth capacitor.Adding these should hopefully save the bridge from flashovers. Another thing that might result in a fail is the IGBT losses.I have to calculate this...

The sparks already scary to me, I have to get used to them. :)
One bigger spark from the video, spark length is as much as secondary + topload length:












Title: Re: My first DRSSTC on bricks
Post by: Laci on June 15, 2019, 09:27:30 PM
I posted here quite a while ago. Not because I didn't want, but I made small changes and I needed time. Some of the changes I made:
-cut the primary at 5.75 turns and added a strike rail
-added a 0.22uF 1000V MKT capacitor from the heatsink to the bus negative
-paralleled two 50A 1000V full bridge rectifiers after the single one blew up
-added a 10A circuit breaker and a 7.5kW contactor
-finished the UD3 by using the bus voltage sensing circuit and installing the LEDs on the metal enclosure

The parts used up all of the space under the coil, so wires are everywhere.
I wanted to upgrade the 30A current sensor to a 50A, but either it was factory defective or I overheated it while soldering and it doesn't work.

The cheapest communication was bluetooth for me, the android app can already control the UD3 without being able to play MIDI files. For that I got myself a USB-BLE dongle and tried to use it as a master device to connect to the slave HM-10 module on the UD3's side. Sadly the dongle doesn't want to automatically connect to the HM-10 after trying many settings...

 [ Invalid Attachment ]

 [ Invalid Attachment ]

 [ Invalid Attachment ]

 [ Invalid Attachment ]



While testing a big Tesla coil fan appeared. :)
 [ Invalid Attachment ]

 [ Invalid Attachment ]
Title: Re: My first DRSSTC on bricks
Post by: Laci on June 16, 2019, 09:00:31 PM
I made a test a few minutes ago. Plenty of things confirmed to work, like temperature sensing, fan control and internal fuse.
After around 10 minutes of not continous run I smelled something melting or burning and turned the coil off, but I couldn't see any problems so that might be just coming from the neighbourhood.

The goal was to achieve sparks that can hit the floor. The breakout point is 110cm over it and at 800A, 800us I was hoping this to be possible. For some reason no overcurrent occours over 600A which should be displayed by the LED. Can something prevent the primary current from ringing up, or the UD3 goes too early in freewheeling/limits ths current? Maybe because my primary frequency is tuned too low(Fpri=120kHz Fsec=135kHz)?
Title: Re: My first DRSSTC on bricks
Post by: Laci on June 24, 2019, 09:26:47 PM
After doing many measurements, the only thing I can think of that limits the spark length is inadequate tuning. The secondary Fres is 136kHz with the "bottom FG, scope antenna" measurement.
The primary is a bit more complicated. Right now the driving frequency is 120kHz which is the lower pole. I suppose this is a bit too much undertuned and some heavy spark loading would be required to lower the secondary's frequency to this level.
The upper pole is already over the secondary's frequency, so basically the secondary is between the primary poles.
Steve Ward mentioned in his DRSSTC log book:
Quote
I found something interesting with the tuning of this coil now. Originally the primary was tuned somewhere in the middle of the 2 modes. This worked well with very high coupling as normal, but I did see some limit to my spark length (about 24" max). I really liked the idea of tuning to the lower pole, because when the coil starts making streamers nearly 3X its length, its going to detune considerably! So I started tuning the primary lower. Instantly I noticed the primary current had a much nicer linear ring up, instead of the choppy looking current ring up when tuned in the middle. I had to reduce my coupling to about .15-.2 because arcs began racing up the side of the secondary, and jumping to the primary nearby. When tuned lower, it took more input voltage to get it to produce real streamers, but once streamers start forming, the result is like an explosion of streamers! Looking at the primary current, its forming a notch at the end of the burst (current rises and then returns back to 0). If I turned the
power even higher, a second "burst" began to form after the notch. The notch occurs at about 18 cycles or so... and I'm not sure what causes it, but I think its a sign that the coils need to be tuned better. So I slapped on a turn of 12 awg at the base of my primary to get more tuning room. Now it takes even higher input voltage (about 60-70% input) but the resulting sparks are even longer! Interestingly, primary current increases with voltage input, until long streamers are formed, then the primary current doesn't increase any more at all! Right now I'm running about 420A. But even still, as I'm getting about 30" sparks, the notch is occurring again at the end of the burst... need more primary L! Its easy to see the improvement that adding more primary inductance has. I'm tuned at least 1.5 turns lower than before (the coil only had 5 turns to start with!),
obviously these streamers really do detune things a lot.

One other benefit I see to running at the lower pole is that you are reducing switching losses. You now have fewer RF cycles per burst length, and also, any delays in the gate driver become less significant as each half-cycle is now longer. I think my primary circuit is running at about 170khz, the secondary Fr is something like 220khz. Hey, but it works great so far!


It looks like the UD3 locks to the pole where the current is the highest. As I decrease the primary turns, so the frequency goes up, the upper pole starts to overtake which is already higher than the secondary's frequency.

 [ Invalid Attachment ]



The problem is that I see no overcurrent over 400A, which I think is caused by the weak energy transfer caused by too much undertuning. What am I doing wrong here?  ::)
Title: Re: My first DRSSTC on bricks
Post by: Netzpfuscher on June 25, 2019, 07:46:25 AM
I think you have run the tune command with the secondary in place? Then you see the secondary resonance around 131 kHz in the graph. The secondary is sucking energy out of the primary.
Title: Re: My first DRSSTC on bricks
Post by: Laci on June 25, 2019, 09:02:09 PM
Some more tests without the secondary in place. Function generator was connected to the bottom of the secondary and probe used as an antenna to find the largest amplitude signal.

Secondary resonant frequency without breakout point is 137kHz:
 [ Invalid Attachment ]

Secondary resonant frequency with a 100cm wire simulating a long spark is 132kHz:
 [ Invalid Attachment ]


I decreased the primary turns by a half and got weird results. While the peak current was found at 146kHz, the UD3 drives at 135kHz! Is this how it's supposed to work?

Graph:
 [ Invalid Attachment ]

One IGBT gate:
 [ Invalid Attachment ]

Title: Re: My first DRSSTC on bricks
Post by: Netzpfuscher on June 25, 2019, 10:07:24 PM
Have you set a new start_freq? The autotune writes nothing to the configuration.
By the way I see a high current in the tune graph. During the tune the IGBTs are switching hard. You should consider this. Do not run this with high bus voltage. I think I add a interlock in a future revision.
Title: Re: My first DRSSTC on bricks
Post by: Laci on June 25, 2019, 10:15:08 PM
The start_freq is 136kHz and 3 cycles. I measured between the 3rd and 4th cycles, but the following cycles seems to be at the same frequency. Shouldn't primary feedback take over and switch at the tune_p result?
Title: Re: My first DRSSTC on bricks
Post by: Laci on September 29, 2019, 04:20:30 PM
After 3 months, I'm back here again. The goal is to rebuild many things to improve on the previous results. A few of these things:
-each brick on a different heatsink with 2 fans
-increase bus capacitance to 2*4600uF
-PC interface with TOSLINK

This is how the new bridge looks like. What do you think about it? :)

 [ Invalid Attachment ]

 [ Invalid Attachment ]
Title: Re: My first DRSSTC on bricks
Post by: Hydron on September 29, 2019, 08:45:16 PM
This isn't the lowest inductance way to design a bridge, but with 1200V bricks running at <385V bus (assumption based on the caps I can see) you have a lot of headroom for any spikes etc caused by stray inductance.

As for TOSLINK, be aware that the receivers may be AC coupled, i.e. a standard interrupter signal will likely not work with them. This is unfortunate given the price and availability vs expensive industrial fibre optics, but could potentially be worked around with a fancier driver and controller if required.
Title: Re: My first DRSSTC on bricks
Post by: Laci on October 11, 2019, 09:03:38 PM
I started putting everything together. One thing that every day comes into my mind is the inverter to primary connector. Until now I used 3 5x20mm fuse socket pieces. I wonder what else can be used for better connection?

(https://i.imgur.com/it2s2EX.jpg)

As for TOSLINK, be aware that the receivers may be AC coupled, i.e. a standard interrupter signal will likely not work with them. This is unfortunate given the price and availability vs expensive industrial fibre optics, but could potentially be worked around with a fancier driver and controller if required.

I want to use TOSLINK as serial communication with the UD3 at high speed. I built a small box to convert USB to serial with a FT232 module, then to TOSLINK. On the UD3 side I added a small board with the TOSLINK transmitter and receiver.

Previously I rarely got a few incorrect characters using an arduino for testing instead of the UD3. Now with the UD3, the serial is pretty bad. Only at 1Mbps are some good characters. Does anybody have an idea how could I improve on this?

@Netzpfuscher
Can the min protocol fix this? Also when I run the UD3-node windows executable the command line briefly shows up and says "mDNS discovery is not available". Am I missing something?


(https://i.imgur.com/AGdypaW.jpg)

(https://i.imgur.com/9ye7M2J.jpg)


1Mbps:



500Kbps:






EDIT:
While testing with an arduino again, I found out that the serial signal pulses often go into a high frequency noise on the receiver side. What is causing this?

A correct 'a' character:


A distorted 'a' character:


HF noise closeup:


Title: Re: My first DRSSTC on bricks
Post by: Netzpfuscher on October 11, 2019, 11:17:17 PM
As Hydron says the Toslink receivers are AC coupled. Some may be more sensitive than others, my Sharp receivers do a great job also at very low baudrates.

I think the MIN protocol should solve the problem. If a connection over MIN is established there is a constant stream of data from the UD3 to the PC and back. That should be lot better for the AC coupling in the receiver. If some packages are corrupted they get simply re transmitted by the protocol. You can observe the link quality with the "minstat" command.

The mDNS warning is "normal" there is a problem in the MIDI RTP lib. But this only affects the auto discovery feature. MIDI RTP works fine if you specify the IP and port manually on the PC side.

If you run the UD3-Node correct it shouldn't exit automatically. Have you run it over the command line? It throws a warning whats missing.

Like this:
 [ Invalid Attachment ]

If you run it correctly it looks like this:
 [ Invalid Attachment ]
 
Title: Re: My first DRSSTC on bricks
Post by: Laci on October 12, 2019, 02:12:59 PM
Thanks. I tried to run it from cmd, but without the -c argument. Now it seems to work.

This is what I receive from the minstat command at 1Mbps. While typing in the commands many characters are still incorrect. But using the sliders the values changes nicely if I see it right. Playing midi should be this good, right.
Also, should I enable watchdog and min at the same time?

(https://i.imgur.com/1avVnnN.png)



EDIT:
After reconnecting a few times the measurements appeared on the monitor, but the dropped frames increased. I bet they are too much now...

(https://i.imgur.com/UMZ8urP.png)


Title: Re: My first DRSSTC on bricks
Post by: Netzpfuscher on October 12, 2019, 03:53:12 PM
The dropped frames are not a problem of the noise. Some dropped Frames are "normal"

For explanation:
-Dropped frames-
This are frames which can't added to the transmit queue. If the PC disconnects without to inform the UD3 the UD3 try to transmit telemetry frames but the PC did not ACK these, so the queue runs full. If the connection is more than 1s idle the UD3 closes the connection.
-Resets received-
If the other side is not responding, a reset is send to clear all queues and reset the sequence number.
-Spurious acks-
If the other side ACKs a frame which is not in the right order or is not in the transmit window
-Sequence mismatch drop-
The UD3 receives a frame which is not expected. Let's say the UD3 expected a frame with the sequence numer 150 and gets a frame with 152 the UD3 knows that two frames are missing
-Max frames in buffer-
The high watermark of the transmit queue
-CRC errors-
This are the frames which are corrupted during transmission <-- This is the counter which gives you a hint of the link quality

Yes you can activate the watchdog. UD3-node sends a watchdog reset every 100ms. But I have seen that you using a old version on the UD3, I think for this version 100ms is to slow. You can update if you want.

Have you tried lower baudrates? I use 500kBaud.

Can you check for the high frequency noise? If it is still there you can try to low pass filter the 5V to the receiver with a RC or LC filter. If this all doesn't help, I can send you a pair of my Toslink receivers. I bought a 50 pcs bag (0,15€ a piece)  ;D
 
Title: Re: My first DRSSTC on bricks
Post by: Laci on October 12, 2019, 11:21:39 PM
I tried 500Kbps too with the same results. Right now the the problem is the following: correct data is sent over TOSLINK from the UD3 to the receiver, the bits are all OK, but about 20us after the stop bit the receiver goes low for some reason with a small noise burst. In theory when the transmitter's signal is high, there is light and the receiver's output should be low. Shouldn't the AC coupling prevent this?

I wonder what the shipping costs to Romania from you. I would definitely like to buy plenty of those, maybe for future coils too. :)

Scopeshots with the min signal at 1Mbps (blue-transmitter's input, yellow-receiver's output):

(https://i.imgur.com/SL2ovmo.gif)


End of the bits:
(https://i.imgur.com/hHOXBgu.gif)


Start of the bits:
(https://i.imgur.com/0lhO4Tk.gif)


EDIT:
By connecting the UD3's TX pin to the FT232's RX pin with a wire and leaving the other connection over TOSLINK, I get perfect (I would say) communication. Probably the TOSLINK receiver is bad on the FT232 side.

(https://i.imgur.com/JdTPDWU.png)
Title: Re: My first DRSSTC on bricks
Post by: Hydron on October 13, 2019, 12:17:39 AM
Another option to avoid the expensive DC coupled fibre transcievers and the hard-to-use AC coupled TOSLINK would be to grab an ESP32 module and use the WiFi mode than is built into the UD3 firmware. I managed to get it working on my board, though it did take a bit of fiddling and work to get the environment running, code building etc (and also note that the ESP32 is _not_ 5V tolerant).
Title: Re: My first DRSSTC on bricks
Post by: davekni on October 13, 2019, 07:04:20 AM
If you can find some, there's a part called IF-D92.  It's just a phototransistor in a housing for 1mm plastic fiber.  That's what my DRSSTC uses.  I've also used TOSLINK couplers with one end partially drilled out and a 3mm photodiode glued in the hole.