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1
Dual Resonant Solid State Tesla coils / Re: My First DRSSTC
« Last post by sjsimmo on Today at 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)
2
I built the interrupter myself :D It uses a microSD SPI module,but the LCD screen glitches when I accidently touch it's metal screws while the coil is working.I hope the microSD module hasn't died, although the screen displays "No card found" everytime.The interrupter is already a big mess,so it'll be hard to desolder it I guess...
3
Thanks for the advices!
Sadly the store went on vacation and I can't order the parts until 20 January :( .I will try to run dual resonant with my current HGTG30N60A4D full bridge,but just carefully not to destroy them(under 250Ap)after I repair my oneTesla interrupter's SD card function,which isn't working.Another interesting experiment would be a IRFP460 bridge ramped,maybe buck modulated with high primary impedance to keep peak currents low.I will try that out with my small coils!

Just get the calculator out as sjsimmo did in his thread and you know all about those IGBTs :)

On a side-note, I had a onetesla midi interrupter returned to them because of malfunctioning sd card reader, it needed resoldering/reflow, whatever, it had bad connection and sd card would not stay in. I did not get a new unit but a repaired board back, which was not done very nicely :(
4
Thanks for the advices!
Sadly the store went on vacation and I can't order the parts until 20 January :( .I will try to run dual resonant with my current HGTG30N60A4D full bridge,but just carefully not to destroy them(under 250Ap)after I repair my oneTesla interrupter's SD card function,which isn't working.Another interesting experiment would be a IRFP460 bridge ramped,maybe buck modulated with high primary impedance to keep peak currents low.I will try that out with my small coils!
5
Dual Resonant Solid State Tesla coils / Re: My First DRSSTC
« Last post by Mads Barnkob on December 18, 2018, 12:50:45 PM »
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.)

You are right, I jumped the first step there.

I will try your numbers in a excel spreadsheet I got on my PC at home, I will take a look at it tonight.

Edit: I used a bit more conservative extrapolations on the graphs, noticeably 6V CEsat and Ton 30mJ, Toff 20mJ, (derated by 0,05% on-time and 0,2 for pulses) and I am getting 144 kHz

6
Dual Resonant Solid State Tesla coils / Re: My First DRSSTC
« Last post by sjsimmo 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.)
7
Dual Resonant Solid State Tesla coils / Re: My First DRSSTC
« Last post by Mads Barnkob on December 18, 2018, 09:47:51 AM »
1000 BPS is really extreme to calculate with, if you want long sparks I think its better to use longer on-time to transfer more power and maybe maximum 500 BPS, a 1 kHz tone is not that pleasant to listen to anyway :)

I looked at this datasheet: https://www.mouser.com/pdfdocs/FGY75N60SMD1.pdf

Did you extrapolate "Figure 15. Switching Loss vs. Collector Current" to get the real mJ losses for the higher current? Or where did you get those low values? Just by eye it looks more like it should be 10-30 mJ (before derating)
8
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.
9
Dual Resonant Solid State Tesla coils / Re: My First DRSSTC
« Last post by sjsimmo 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
10
I can tell you as much as max amps isn't everything. Especially as you want a rather high frequency, rise and fall times matter a lot. The longer the switching needs, the more power gets turned into heat. I recommend you stick to what others have used, with similar coils/frequency. Look for something ward used or possibly if these aren't produced anymore, check loneoceans qcw-coils out. Choosing your own parts isn't as easy as one might think. There are many factors to consider and there is no shame in copying someone's design.

And if noone else used it, there is probably a reason behind it.
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