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Messages - Laci

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1
Great to hear about some cheap fiber optic solutions. :)
I had a hard time recently choosing a suitable kit. From the versatile link series two HFBR-1531Z transmitters and two HFBR-2531Z receivers turned out to be the cheapest with a 10m long duplex cable with latching connectors, for around 50 USD including shipping.
I saw some gigabit interface converters for around 5 USD, like this:



They should work with cheap patch fiber cables, but I have no idea what additional parts are required to convert serial data to their communication method. Perhaps somebody used something like this before and knows if this works?

Are these similar to the toslink you disassembled? They are cheap tho... :)  If they are good for the purpose, do you know what type of connector/fiber cable they work with?

https://www.tme.eu/en/details/fcr6842032r/optical-connectors/cliff/orj-3-fcr6842032r/
+++
https://www.tme.eu/en/details/fc6842032t/optical-connectors/cliff/otj-3-fc6842032t/


https://www.tme.eu/en/details/fc684208t/optical-connectors/cliff/otj-8-fcr684208t/
+++
https://www.tme.eu/en/details/fc684208r/optical-connectors/cliff/orj-8-fcr684208r/


https://www.tme.eu/en/details/fc6842135tr/optical-connectors/cliff/

2
Solid state Tesla coils / Re: SSTC interruptor not working
« on: July 05, 2019, 09:47:02 AM »
Neat setup.  :D
I'm worried about your ferrite core. It should be a high permeability core. If you have an oscilloscope you can check the gate signals at low voltage while operating(be careful with the ground leads of the scope) or connect a function generator with your running frequency to the antenna input without voltage on the bridge.

If you have noise problems, maybe grounding the heatsink could help too.

3
Solid state Tesla coils / Re: SSTC interruptor not working
« on: July 05, 2019, 01:07:34 AM »
The problem is that interruptor seems to do nothing. Even if i tie the ENBL pin of both gate drivers (UCC372x) it still produces arcs. Has anyone else encountered this problem?

If both enable pins are tied to ground, there should be no gate driving, so no arcs. The interrupter should always work accurately, unless if you have noise problems.
Have you grounded the unused inputs of the 74HC14, as Mads suggested?

Please upload some pictures about the driver, inverter, coil, etc.

4
Dual Resonant Solid State Tesla coils / Re: My first DRSSTC on bricks
« 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?

5
Dual Resonant Solid State Tesla coils / Re: My first DRSSTC on bricks
« 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:


Secondary resonant frequency with a 100cm wire simulating a long spark is 132kHz:



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:


One IGBT gate:



6
Dual Resonant Solid State Tesla coils / Re: My first DRSSTC on bricks
« 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.





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?  ::)

7
Dual Resonant Solid State Tesla coils / Re: My first DRSSTC on bricks
« 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)?

8
Dual Resonant Solid State Tesla coils / Re: My first DRSSTC on bricks
« 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...











While testing a big Tesla coil fan appeared. :)




9
Which part of the driver was striked? If it hit the logic circuit on the green PCB, it's gonna be harder to repair without an oscilloscope.

You have a red LED (between the ICs), which probably indicates the 5V and a green LED on the board behind the fiber optic receiver which I think indicates the interrupter signal. If you power the board and connect the interrupter it should blink visibly at low frequency. There's another red LED in front of the relay, which does the precharging, I guess. If that doesn't light up after a few seconds after powering up, you probably have no voltage on the inverter.

Checking the feedback signal's logic circuit isn't that easy for you without a function generator. Otherwise it requires feedback signal which you get only if everything is working.



10
Hello!

I had a similar failure a week ago. In my case a secondary to primary coil flashover blew two transistors(IGBTs) because I grounded the bottom of the secondary to the wall outlet. Do you have a good grounding?

The overall design of your DRSSTC looks nice to me and if it uses a gate drive transformer(which probably is) there's a high chance that the driver circuit is OK. In this case you should check the IGBTs, TVS diodes, gate diodes and resistors; basically the power electronics. They usually go short circuit when they fail, so a resistance, diode or continuity test is good for this.

For further troubleshooting let us see the internals! :)

11
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:













12
Dual Resonant Solid State Tesla coils / Re: QCW music with Midi
« on: May 08, 2019, 05:30:54 PM »
I THINK Steve Ward did something similar with his QCW:
https://www.youtube.com/watch?v=QpKNbvonSic

I didn't make anything similar to this,but I'm interested,so keep up the good work!

13
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.



I calculated a maximum of 100 bps at 800us for the 80A IRMS. What do you think about this choice?

14
Electronic circuits / Re: Attempt to repair a welder
« on: May 04, 2019, 05:31:10 PM »
Thank you for the answer and searching, petespaco!
The manufacture is Awelco,made in Italy.I only found some informations and troubleshoot on a russian website.The welder is nice and compact for the first look,but it has many disadvantages for the person who wants to repair it.Not only the SMD parts make the repair hard,but the shunt based current sensing kills many components in case of a failure.

While probing on the working module I accidentally shorted the UC3845's pin 7 to pin 6.This made the chip to act the same as on the not working module: low duty cycle driving signal.I think these ICs can partly die.
I'll order some replacements and try again...

15
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

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...

16
Please upload some gate waveforms to see how the UCCs perform.

17
Dual Resonant Solid State Tesla coils / Re: My first DRSSTC on bricks
« 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)

18
Dual Resonant Solid State Tesla coils / Re: My first DRSSTC on bricks
« 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?

19
Dual Resonant Solid State Tesla coils / Re: Phoenix's Large DRSSTC II
« on: April 29, 2019, 08:42:52 PM »
...and I thought my SKM400s are huge...
I wonder how big your heatsink will be too. :D

Good luck for the building and looking forward to steal some techniques.  ;)

20
Electronic circuits / Re: Attempt to repair a welder
« on: April 29, 2019, 07:22:32 PM »
After a painful explosion and fail on this project,I thought of trying the repair of this welder again,because it only takes up space in my lab otherwise.

Since many components blew up last time,I replaced those,the UC3845 current mode IC,the L6386 bootstrap driver,the BJT output transistors and some infinite ohm resistors on the current sensing part.

Right now it turns on and nothing blews up,but compared to the other module(the welder is made out of two same inverters in parallel)I get a lower,1.6V at the compensation pin 1 of the UC3845,while the other has 2.7V.It's weird because this pin is the output of the error amlifier,which has an internally referenced input and another is the voltage feedback pin 2,which is 2.5V on both modules!If you take a look at the schematic you can see that pin 1 only connects to higher or equal potentials(VFB=2.5V, VREF=5V) and a connector.Probably this wrong voltage results in a low pulsewidth driving signal,so the inverter's energy transfer is limited.

Does anybody have an idea what causes this?Maybe replace the UC3845?




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