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Messages - sjsimmo

Pages: [1] 2
1
Dual Resonant Solid State Tesla coils (DRSSTC) / Re: My First DRSSTC
« on: March 21, 2020, 02:26:22 AM »
Zipdox:
Sounds cool. Let us know how it goes, if you get something working :)

Mads:
The MMC is 2 series 2 parallel 0.1uF/2kv 942c capacitors (942C20P1K-F), so 0.1uF effective capacitance. I have considered reducing it by perhaps adding another set in series, for 3 series 2 parallel giving 0.067uF effective, and also making a new secondary with 1000 turns and a larger toroid, but I'm happy enough with performance at the moment anyway, so I haven't got around to doing it.
The resonant frequency ended up been somewhere close to 160Khz. The primary current figure of 350A peak is going purely off the OCD setting, as I haven't actually been able to measure it directly at full power due to interference crashing my USB oscilloscope. The OCD was showing correct behaviour at 100A, so I presume it to also be correct at the full 350A (a somewhat dodgy assumption, I know).

2
Dual Resonant Solid State Tesla coils (DRSSTC) / Re: My First DRSSTC
« on: March 20, 2020, 08:35:31 AM »
Of Course  :)

I have attached the Arduino code to this post. It should be noted however, that whilst the code works, it is quite badly written, and I would recommend to anyone considering using it that there are better alternatives out there (The OneTesla interrupter code, for example).

Some notes About the functionality:
  The code runs on an ATmega328, with a 16Mhz external crystal, more or less simulating an Arduino Uno.
  The Interrupter is only monophonic, and takes the melody line from Midi Channel 1 when in midi mode.
  Changing between Manual frequency/Midi mode requires the microcontroller to be turned off and on again.
  The interrupter only responds to Midi "Note on" and "Note off" messages. Pitch bend, All notes off messages etc. are ignored!

Atmega328 Wiring (Using Arduino Pinout names):
  RX: Midi input
  TX: Output to fibre optic transmitter
  A0: Mode Set: Manual Frequency (LOW signal)/ Midi Mode (HIGH signal)
  A1: Pulse width set (0-100uS)
  A2: Frequency Set (Up to 500Hz when in Manual Mode/lowers pitch by  0-2 octaves when in midi mode)
   2: Mode indicator (Outputs HIGH when in midi mode)

EDIT: I have also added the toner transfer compatible PCB layout for the interrupter (as a word document), in case anybody wants to try and create the PCB for themselves. There is however no silk screen or schematic, so you'll have to trace the PCB and guess where components go.

Let me know if you have any questions  :)




3
Dual Resonant Solid State Tesla coils (DRSSTC) / Re: My First DRSSTC
« on: March 19, 2020, 05:29:43 AM »
Sorry that I haven't given any updates on my DRSSTC for a long time (more than a year, as I see now...),
but here is one final post, just to show the completed coil and modifications made since my last post.

After the IGBT failure, I decided to complete the coil with a fiber-optic midi interrupter, as I suspect that the failure was caused due to the Arduino used as a make-shift interrupter crashing. I also replaced 30v TVS that was used to limit voltage on the output of the feedback CT with the Zener diode/Schottky diode configuration used in the UD1.3B, in order to reduce the possibility of phase shift due to transformer saturation.

This is the layout of the driver circuitry, in its final housing (including LV PSU and fiber-optic/Indicator PCBs, which were not previously made):



This is The Midi Interrupter with its housing open:



And Finally, The Coil with the primary secondary installed:



In addition to this, I found out why Steve Wards UD1.3 includes a RC timeout circuit for the feedback signal. If it is omitted (as it was in my original design), the circuit will sometimes start up in a state in which the interrupter cannot start an oscillation. The same thing could occur if the coil lost feedback due to no voltage on the bus etc. As a result, I made the following modification to my driver circuit:



As a result of all these modifications, the coil now operates reliably with 350A peak primary current, and produces sparks up to ~60cm. I am not entirely sure why longer sparks cannot be achieved anymore, but I suspect it is due to the faster current ring-up time and lower on-times that have resulted from slightly less phase shift in the feedback CT. The OCD triggers constantly if I increase on-time past ~40uS at 240VAC input, despite careful tuning. This behaviour may be due to the low impedance of the primary coil, and high impedance of secondary coil (~2000 turns, rather than the generally recommended 1000).

Here is a video, showing the coil operating in midi mode:
/>
Thanks again to everybody on the forum who gave advice throughout the project  :)

4
Electronic Circuits / Re: Cost reduction in consumer electrics
« on: December 05, 2019, 11:09:20 AM »
Interesting teardown, klugesmith.


I pulled apart a fairly normal pop-up toaster a few weeks back. It was constructed in a very similar manner. had welded wires to connect the heating element, and an electromagnet which held the toast down, whilst also acting as a relay for the 240V. Rather than a capacitor based dropper for the power-supply though, it simply took a tap off the main heating element, and used it as a voltage divider to provide ~12VAC to the control board.

5
Condensor Corps website shows how to check what type of dielectric the capacitor is using:http://www.condenser.com/projects/condenser/

It is a Kraft/Polyester not polypropylene, so it's probably not suitable.

6
I'm not Steve Ward, but I think I can answer your question.  ;)

First you have to note that not all 60N60s or 40N60s are the same, the extra letters at the start and end matter a lot.

The 40N60 IGBTs Steve used, were mini-brick IGBTs (specifically the HGT1N40N60A4D). They have a much higher failure current compared to the TO-247 package 40N60 varieties, due to their larger die size, and hence larger thermal mass.

The FGH60N60SMD is a TO-247 IGBT, and it can only handle about 300Apk before failing (as you have observed). mini-brick package 60N60 IGBTs tend to be able to take much higher peak currents. The IXGN60N60C2D1 for example, has been found to be reliable at up to 500Apk.

Mads has a table of IGBT proven working and failure currents at the bottom of this page: http://kaizerpowerelectronics.dk/tesla-coils/drsstc-design-guide/igbts/

Hope this helps.  :)
-sjsimmo

7
You could also use the standard D Flip Flop without enable (instead of the D flip flop w/ enable): https://www.cypress.com/documentation/component-datasheets/d-flip-flop
It can be configured to have both PRE and reset (CLR) inputs (see datasheet linked).

Just note that you'll have to add inverters to the PRE and CLR inputs, to make it logically identical to the 74hc74 (which has the PRE and CLR inputs inverted).

8
Hi Laci,  :)

Not sure if this is what's causing your problem, but your FliPC looks like it would update its output whenever the CLK pin is high. Whereas the 74HC74 is edge triggered, meaning that it will only update as the CLK pin changes from a low signal to a high signal. As for CLR signals, a logical LOW on the CLR' pin should cause the flip-flop to output 0 instantaneously (since the PRE/CLR inputs are inverted for both your schematic and the 74HC74).

Generally the OCD should actually disable the driver output on the next ZCS point (the same effect as the interrupter turning off), otherwise the IGBT would have to switch with the full peak current. I think that's what your circuit would do too, if the flip-flops were edge triggered.

Hope this helps,  :)
-sjsimmo

9
Hi VNTC,

I'm not sure as to the exact reason that you're having failures (I'm fairly new to DRSSTCs myself), however I do notice a couple of things. It looks like you're using TO247 package FGH60N60SMD, and FGA60N65SMD igbts (am I correct?). These have a failure current of ~350A, opposed to the minibrick 60N60s which can typically take over 500A (what you seem to be trying to do).

I also agree with you that your gate waveform doesn't look great. Are you running half-bridge or full bridge? If you're running full bridge, it may be worth trying doubling the UCCs (stack two ICs on top of each other), to increase drive current.

Hope this helps (and sorry I can't help more),
-sjsimmo  :)



10
Dual Resonant Solid State Tesla coils (DRSSTC) / Re: My First DRSSTC
« on: January 19, 2019, 08:08:58 AM »
So I had my first IGBT failure recently  :(

One of my IGBTs has always noticeably run warmer than the others (for unknown reasons), and I suspect this to be the cause of the failure. The coil had not been run in over a week, and so had been packed up since the last full power run. I ramped the coil up to 240VAC input. Everything seemed normal for about 5 seconds. However, before i could turn the interrupter from 10uS on-time up to 50uS on-time, one half of the bridge failed short circuit (Gate, Collector and Emitter now read ~0 ohms on both IGBTs), blowing up the 3A slow-blow fuse in my variac. Neither of the IGBTs have any sign of physical damage on the package. Is it normal for IGBTs to fail without any visible damage, and when not operating at full-power?

Thanks again for your help, everyone :)

11
Hi FilipŠebík,

I came across this website a while ago: http://schmidt-walter-schaltnetzteile.de/smps_e/smps_e.html when I was trying to design an smps lab power supply (I never got round to actually finalizing the design or building it though...).
It contains calculators which may be helpful with working out the suitability of your core, and required wire thickness.  :)
I'm sorry I can't help with doing the calculations though, I don't understand much about the mathematics myself...

Hope this helps,
- sjsimmo

12

Hi Ect1453, :)

Some people just use shielded RCA cable, or similar. Of course this doesn't give the same amount of isolation as Fibre Optic though.

On my first SSTC I used an optocoupler at the SSTC end, and shielded RCA cable to the interrupter. This works, but probably shouldn't be used at the high power levels of a DRSSTC, unless using a simple 555 interrupter (or similar micro-controller/midi/laptop free design).
When testing my SSTC, I did notice some noise making it into the interrupter circuit. This may be prevented by another optocoupler at the interrupter end of the RCA cable, but I'm not entirely sure.

13
Hi nabzim,


TVS diodes are recommended, because of voltage transients on the bus which are hard to avoid without incredibly good bus layout design. They are different to the internal diodes, and are generally required as a safety feature. Gao probably got away without using them due to a good bus layout.


The snubber capacitors only need to have as high a rating as your bus voltage. The most important thing for snubbers is their peak current rating. If you are using less than 400v on the bus, than 600v snubbers should be suitable.


I'm not sure about the frequency drop, but I'd assume it to be similar. If you use copper pipe for you primary, then it's easy to tune the primary with a tapping point. just make sure that you've got an extra turn or two worth of primary so that you have some tolerance for tuning.

14
Electronic Circuits / Re: Isolated Series Li-ion Charger
« on: December 24, 2018, 01:26:17 AM »
I've also used the TP4056 and they work fine, although they're limited to 1A charging current. The have internal current sense resistors, so they don't need one externally (just a current set resistor is required).  :)


Ideally the 'temp' pin should be wired to the battery with a NTC in series, but this is only really needed if it's going to be on charge, with an old/faulty battery, and you're not around to keep an eye on it.

15
Dual Resonant Solid State Tesla coils (DRSSTC) / Re: My First DRSSTC
« on: December 24, 2018, 01:15:00 AM »

Yeah, I've seen that page. It's a really good resource  :)


I've previously tried reducing the gate resistance from 6.8R to 3.3R with no effect (it's still using the 3.3R). This resistance change was before I doubled up the UCCs which had dramatic improvements, resulting in the waveform in my previous post. Previously it was more of a sawtooth wave. I'd think that needing less than 3.3R would be very unusual, considering I'm using a TO-247 IGBT full-bridge.
One thought that occured to me is that maybe I need to run 3 UCCs in parallel, but this also seems a bit ridiculous, given the IGBTs that I'm using.

On a side note, the biggest spark so far is now 68cm to a grounded object with 300A peak current, 240VAC input and ~50uS on-time. (increasing on-time causes the OCD to fire constantly, may need tuning?)

16
Dual Resonant Solid State Tesla coils (DRSSTC) / Re: My First DRSSTC
« on: December 19, 2018, 12:19:32 AM »
Thanks for doing the calculation :) 

It's interesting to see how much effect changing those values had on the maximum frequency, especially since they're all from reading the same graphs. I guess it's a pretty big guessing game once we go outside the values shown on the data sheets...

So should I proceed to turn up the current until I either get 350A, or an explosion? (going by our two wildly different results...)
Out of curiosity, how much can an IGBT overcurrent failure affect other components? Is it likely for example, to kill the UCCs?

I'm also a little concerned about the fact that my gate waveform still has about 500 nS rise/fall times. Whilst this is a lot better than before, I'm not sure what effects it will have on reliability at higher peak currents. Should I be concerned about this?

EDIT: I've attached a scope shot of my gate waveform (1uS/div)

17
Dual Resonant Solid State Tesla coils (DRSSTC) / Re: My First DRSSTC
« on: December 18, 2018, 10:45:01 AM »
I'm confused now, that is the datasheet I was using...


The calculated current at switch on is 11.6A, and switch off current is 22.7A. These values are both below the minimum current shown on the graph of figure 15. extending the graph gives a switching loss of about 0.25mJ and 0.4mJ at 80 degrees celsius respectively, or am I reading the graph wrong?  :-\


These values can then be multiplied by 0.2, giving the final values that I wrote down.


The reason for using 1000BPS for the calculations, is because I want to midi modulate it eventually, and I figure that 1kHz should be a sensible limmit... (or is this actually too high?) ??? . As for on-time, I might make that a bit longer, at 200A anything above 80uS has little effect on spark length, but I suppose at 350A this time will grow (although by how much, I'm not sure, since I can almost double bus voltage still.)

18
loneoceans used FGH60N65SMD (electrically equivalent to the FGA60N60SMD) in his QCW2 coil which had a resonant frequency of 308kHz. Note that the 'UFD' variety of FGH60N60 only has about half the power dissipation of the 'SMD' variety, so if you want to use a FGH60N60, I'd go for the SMD model, rather than the one you've listed.
Steve Ward also used the FGH60N60SMDs in his '"Fat Coil" QCW Tesla Coil', which had 8 H-bridges paralleled.  :)

I don't know of anyone (other than yourself) who has used IRG4PC60U in a DRSSTC or QCW coil. Looking at the datasheet, it seems that it's about twice as slow as the other two, so probably not as good a choice (looking at rise, fall, turn-on delay and turn-off delay times)... But I could be wrong ;). That said, it does have a higher peak current rating, which could be useful at lower frequencies.

I'm currently using the FGY75N60SMD in my DRSSTC, but I haven't pushed them very hard yet, so I don't know their limits. They're slightly slower than FGH60N60SMD, but still faster than IRG4PC60U, and are rated for 225A peak.

19
Dual Resonant Solid State Tesla coils (DRSSTC) / Re: My First DRSSTC
« on: December 18, 2018, 02:08:57 AM »
Thanks for the guidance :)

I just finished doing the calculations, and got the following values for my coil at 350A peak, 100uS on-time, 1000BPS:
- Fmax1=1290kHz
- Fmax2=984kHz
These values seem about 5 times bigger than what I was expecting. Am I doing something wrong, or are these IGBTs invincible?


Thanks again,
-sjsimmo

20
Dual Resonant Solid State Tesla coils (DRSSTC) / Re: My First DRSSTC
« on: December 17, 2018, 06:49:52 AM »
A quick question about the FGY75N60SMD IGBT... What's the maximum current I can run these at?
I've had a look around, but can't find anybody actually using them... (I saw Hydron's review of them, but he didn't specify how much they could handle in DRSSTC use). Since the FGH60N60SMDs are 180A pules rated, and are good for 300A, I figure the 225A pulse rated FGY75N60SMDs should be good for 350A... Does this sound accurate, or will things explode?

Also, I tried using a strike target today, and managed to get 45cm arcs at 170VDC bus, 80uS on time, and 200A peak  :D

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