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Messages - sjsimmo

Pages: [1] 2
1
Spark gap Tesla coils / Re: Where to buy Tesla coil capacitors?
« on: May 08, 2019, 01:29:47 PM »
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.

2
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

3
Dual Resonant Solid State Tesla coils / Re: DRSSTC Driver Logic
« on: March 12, 2019, 06:35:17 AM »
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).

4
Dual Resonant Solid State Tesla coils / Re: DRSSTC Driver Logic
« on: March 11, 2019, 12:59:16 AM »
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

5
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  :)



6
Dual Resonant Solid State Tesla coils / 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 :)

7
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

8

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.

9
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.

10
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.

11
Dual Resonant Solid State Tesla coils / 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?)

12
Dual Resonant Solid State Tesla coils / 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)

13
Dual Resonant Solid State Tesla coils / 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.)

14
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.

15
Dual Resonant Solid State Tesla coils / 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

16
Dual Resonant Solid State Tesla coils / 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

17
Dual Resonant Solid State Tesla coils / Re: My First DRSSTC
« on: December 12, 2018, 11:57:02 PM »
Thanks for the advice.
The video makes it look closer to the wall then it actually is. The actual distance is about 1 metre, But I'll give it a little more space, to see what happens. I'll also do the function generator/scope check on the secondary resonant frequency, to see how much it's affecting it.
After that, I'll try turning up the current  :D

On a side note, I'm glad to see your still working on the DRSSTC design guide. It's a brilliant resource for beginners like me :)
Thanks for the advice.
The video makes it look closer to the wall then it actually is. The actual distance is about 1 metre, But I'll give it a little more space, to see what happens. I'll also do the function generator/scope check on the secondary resonant frequency, to see how much it's affecting it.
After that, I'll try turning up the current  :D

On a side note, I'm glad to see your still working on the DRSSTC design guide. It's a brilliant resource for beginners like me :)

EDIT 1:
I turned the current up to 200A! Spark the length is now 20-25cm after tuning, with ~100uS on-time and 180VAC input (limited by OCD firing again).  :)

The bridge is now getting noticeably warm after ~30 second runs, so I think it's time to look at fixing the IGBT gate waveform again.

EDIT 2:
I fixed the gate waveform!  :). Turns out Laci's original thought was correct, The UCCs weren't powerful enough. I'm now using 2 paralleled (stacked on top of each other), and the waveform looks much better now (about 0.5uS 0<->20V rise/fall time):

Interestingly, fixing this waveform caused the tuning point on the primary to become much closer to where I originally thought it should be tuned (which was done using a function generator to find resonant frequencies). I believe that the slow gate waveform must have been causing some phase-shift...  ???
The maximum voltage I can put into the bus (without the 200A OCD firing at 100uS on-time), is now 125VAC, indicating that the current must be ramping up faster with the better waveform, and the bridge is also slightly cooler now. Spark length is now approximately 25-30cm, although I don't have any pictures yet.

18
Dual Resonant Solid State Tesla coils / Re: My First DRSSTC
« on: December 12, 2018, 11:45:08 AM »
Thanks for the feedback :) . The lack of spikes is probably just because I'm using a 20Mhz USB oscilloscope (the 'Bitscope Micro').

I added the secondary and succeeded in first light yesterday, but didn't record it till today. Here's the video :D :

Is it normal that the coil is only outputting 8-12cm sparks at 100A? The OCD triggers at above 60VAC input (set to 100A) causing spark length to decrease significantly, so maximum spark length is at 60VAC, 200uS interrupter on-time. I've tuned the primary coil as best I can (starting from a value determined using the function generator/oscilloscope method, then adjusting as far as about 1/4 turn each way (in 2cm increments), until I found the point at which I could have the highest bus voltage without triggering the OCD.

Also, I'm using the garage walls as RF ground (in addition to mains earth). From what I've read, I believe this should work well, but I'm not certain...

Do you think it's ready for turning the OCD up to 200A? (I will eventually set it to 300-350A, once I'm sure everything is operating correctly).

19
Dual Resonant Solid State Tesla coils / Re: My First DRSSTC
« on: December 11, 2018, 12:03:54 AM »
I've decided to upload some of the scope shots, to show how it's currently operating.  :)
Firstly, the bridge output and primary current (~20VDC on the bus):

Secondly, the IGBT gate waveform and primary current:

and Finally the primary current at ~75VDC on the bus, triggering the 100A OCD:


Do these waveforms look right? My only concern is that it looks like it's switching close to peak current, rather than zero current... This could of course just be my measuring equipment/methods, or the fact that it was been tested at low voltage. :-\

20
Dual Resonant Solid State Tesla coils / Re: My First DRSSTC
« on: December 10, 2018, 11:13:38 AM »
It's fixed now as I said in the previous post, it turned out to just be a dry solder joint on an IGBT collector. The heatsinks are even cooler now, and the driver is outputting a nice square wave. The current also ramps to 50A in half the time (30us at 50 vac input). I'm now testing it with the OCD set to 100A, and everything still seems to be working fine.  :)
On a side note, is it normal for the MMC to buzz at the interrupter frequency? Mine is buzzing quite audibly, proportional to the primary current. I checked the capacitance and they're all still 0.1uF. Since the circuit is working fine, I presume that this is ok, but it would be nice to have a second opinion.  ???

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