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Messages - Mads Barnkob

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1
The problem with the melting oscilloscope probe ground lead is that you are grounding your inverter through your oscilloscope! To measure on inverter outputs you always need a differential probe or an isolation transformer for the mains feeding the inverter and keep it floating off ground. I always recommend this great video:
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2
Capacitor banks / Re: Suitable capacitors and switches? 10kV
« on: August 22, 2019, 09:38:27 PM »
The standard is similar (apparently) to:

EN 13938-2 Part 2: Determination of resistance to electrostatic energy.
STANAG 4490: Electrostatic Discharge Sensitivity Tests
MIL-STD-1751A Safety and Performance Tests for the Qualification of Explosives - Methods 1031, 1032 & 1033.

But I am struggling to find the rise and fall times or impulse duration.

Any further ideas? Thx

I am not familiar with that standards and are not going to read them through for you.

But if you are struggling with rise/fall time and impulse duration, look into the design of heart-stoppers (defibrillators), this must be thoroughly documented which capacitance, impedance and output choke to form the desired pulse waveform and length.

3
Electronic circuits / Re: HV Pulser/Switcher
« on: August 22, 2019, 09:34:25 PM »
You would have to be much more specific with your application before anyone can answer that. An alternative could be thyratron replacement stacks, these are made be many companies to upgrade HVDC switch halls.

Many universities are properly building some of this gear themselves due to the price tag.

4
Dual Resonant Solid State Tesla coils / Re: Drsstc 3
« on: August 22, 2019, 09:32:24 PM »
Even a electrostatic discharge can weaken a silicon-based component, so you could have a internal failure where the insulating layer between the copper base plate of the rectifier and its silicon die was broken down through a micro channel. Just a single small flash through and some burned goo or plastic and its done :(

5
Dual Resonant Solid State Tesla coils / Re: Heavily improvised DRSSTC
« on: August 22, 2019, 09:25:16 PM »
We will not show the door to someone that showed enough effort to build and fail, you have gotten enough things right to end up with a working system, not the greatest, but a working one.

If you need PCB designs for bridge, interrupter or drivers: https://highvoltageforum.net/index.php?topic=353.0

Your secondary coil and MMC are in proportions to each other, but the 40N60 TO-247 bridge is not powerful enough to drive the rest of the system to its capability.

For experience with TO-247 IGBTs see here: https://highvoltageforum.net/index.php?topic=236.0 and in order to design a bridge with a proper impedance to match your secondary, see here: https://highvoltageforum.net/index.php?topic=113.0 DRSSTC inverter vs. secondary impedance inequality discussion

A variac is recommended for low voltage testing, but you can also just turn on-time to 0 us on your interrupter for a DRSSTC and get full voltage on the DC bus before turning up the on-time and get some current flowing.

Please do post pictures in your next update.

6
Welcome Grzegorz

Where are you from? Are you currently studying anything electronics related or is it a hobby?

Looking forward to see your projects :)

7
Dual Resonant Solid State Tesla coils / Re: Twin System Build
« on: August 17, 2019, 08:06:42 PM »
On paper the thermal impedance looks just fine. R_(th,JC)(single pulse)  for 200us PW is about 0.008 K/W and for continuous mode it is 0.125 K/W which is in the same region as a CM300.
The pulse rating is 1500A and the maximum switching current 430A. With a maximum dutycycle of 0.026 for high current pulses those bricks really shouldn't die at 600A.

I can not find the post I read, some 10 years ago, by Steve Ward, that came up with the same conclusion about the good old 40N40 and the new 60N60, where the 60N60 looked better on the datasheet, but could take much less abuse than the 40N40.

8
Dual Resonant Solid State Tesla coils / Re: Drsstc 3
« on: August 16, 2019, 10:34:46 PM »
I must admit that I never put much thought into the bridge rectifers I have used, since they are mostly just grossly overrated, but when I have used some at a more proper rating, they have went up in smoke a few times. Just a quick guess that they might not the be fastest diodes and have a reverse recovery time that is too slow for DRSSTC transients?

You mentioned that your IGBTs heat sink got slightly warm on the first light run, how about your primary coil?

9
That could get expensive if you are talking about 100 kW drives!  (Hmm . . . how big are the drives in Tesla automobiles?)

Mads, how did the unit in your video come to be on your autopsy table?

I was not aware that shelf-life was so short, which is ridiculously short, compared to some systems I have worked on/made service on/restored, they could be 30 year old systems, with some spare parts being just as old or at-least nearing 20 years. I guess it just comes down to things are not made as they used to be :)

I fetched this drive from a scrap yard, I assume it was thrown out due to upgrade or maybe defective, but it has no visible signs inside of being defective.

10
Dual Resonant Solid State Tesla coils / Re: My second DRSSTC
« on: August 16, 2019, 10:19:18 PM »
I still recommend that you do a Fmax2, switching loss calculation to make sure that the CM300 can withstand 900A at 100 kHz, it is a much higher frequency than CM300 is usually used at. I think the highest recorded I got on my page is 700A at 72 kHz by loneoceans.com

Good to see that you found the defective IGBT brick, how about the gate resistor/zener diode, were they damaged aswell? I often saw this problem when a IGBT died.

11
Solid state Tesla coils / Re: [Development] Project of an SSTC driver.
« on: August 16, 2019, 10:07:31 PM »
I would like to make some changes in the driver.
I have found a 440VA 53VAC transformer that I would like to use for the next teslacoil.

Therefore VDC will be +- 75V (that can reach +-90 without load), therefore I have choosed a mosfet of 250Vds ->  IRFB4229
With a very short and semplified thermal calculation, result that can handle about 55A with the interrupter set to 20Hz and duty-cycle of 5% (Setted as worst case).

I would like to have the same carachteristic of the small coil with an high peak current and a low duty-cycle to have an low mean power and an high pulse power.

Thereticaly the small teslacoil have an peak current of about 30A, with a 24V supply and a push-pull driver will results in a 30A*24V*2= 1440W (peak power) and an average power of 40W. The results is about 7-8cm of spark.

Therefore the average current will be about: 55A * 0.05 = 2.75A with an average power of 75V*2.75 = 206W. And a Peak power of about 75V*55A =4125W

Therefore we will have a 4x power therefore I will expect a sparklength in the range of 30cm. Can be correct?

Spark length estimation for SSTC was never really linear in my experiments, it felt more like that I could just keep adding topload capacitance to get longer arcs :)

12
Electronic circuits / ESAB Power TIG 200 Welder Teardown
« on: August 16, 2019, 08:03:18 PM »
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A teardown of a ESAB Power TIG LTR200 welder, a run down of the current paths in the system and I show which parts I kept.

13
Dual Resonant Solid State Tesla coils / Re: My second DRSSTC
« on: August 08, 2019, 08:35:57 AM »
These capacitors are also less sturdy than the CDE 942C series or snubber MKP pulse capacitors, so failure on such a MMC is expected if it does not have a large overhead for voltage and current specification.

Your new MMC layout is problematic, the inner capacitors will not be able to radiate the heat from their losses, so they will heat up faster than the outer ring of caps and will fail before the others due to temperature changing their characteristics.

14
Spark gap Tesla coils / Re: 30% power increase
« on: August 08, 2019, 08:33:01 AM »
I was never so bold to "stretch" out the spark for spark length measurements  :P

Most variacs are rated for 200-300% operation for very short periods, it will however hum violently, just if you wanted to push things a bit :)

15
And finally sold for $5/each + shipping ;)

Yeah, I saw he dumped it from 12, to 8 to 5. He wanted 75$ in shipping to Denmark, so I let it be :)

16
Vaclav wrote:
Quote
I made some simulations (primary oscillating circuit coupled with secondary oscillating circuit).
I got ~80µS to transmit all energy to the secondary side. Therefore I will go for ~80µ on time
That holds true for a perfectly tuned SGTC. In a DRSSTC you keep supplying energy to the primary coil. Since that is not immediately transferred to the secondary, there will always be some energy in the primary. Have a look at Mads docs on his TCs. He shows primary current scope shots and all show some primary current, i.e. energy in the primary tank as long as the burst persists. Once you stop the burst, most of the primary energy returns to the bus caps via the IGBTs reverse diodes. Actually a sad side effect of stopping the burst.

I got the best oscilloscope shots showing this from my small DRSSTC, as a very long on-times is less and less "necessary" on a large coil with higher peak currents, there you get the spark length more in a manner comparable to a SGTC, but for low peak currents, longer on-time gives better reults.

http://kaizerpowerelectronics.dk/tesla-coils/kaizer-drsstc-ii/

17
/>
Standard Features:
Intel Mobile Pentium III 700 or 750 MHz CPU
ATI Rage Mobility 128 with 16MB
15.0" TFT display with 1400x1050 resolution
128MB PC-100 memory standard (512MB max)
18 or 20GB HDD

18
Designed for 1000 BPS, with only RMS current being higher than MMC specifications, it is all fine! You are not going to push it that hard continuously anyway, not even with MIDI if its edited correct.

The simulated 80us transfer-time does not mean that you can not run longer on-times, longer on-time will still produce longer sparks as you keep pumping energy into the grown spark channel.

19
Spark gap Tesla coils / Re: What is the advantage
« on: July 30, 2019, 07:40:44 PM »
A third reason is also to raise up the top toroid, to gain more distance between the toroid from where the streamers come out and the primary coil/strike rail/ground, a smaller diameter near the top of the secondary coil will also have a stronger electrical field that helps prevent corona discharge and streamers from the top turn of the secondary coil if there is a too large distance from that and topload.

20
Spark gap Tesla coils / Re: First coil
« on: July 30, 2019, 07:35:22 PM »
Seems like you have all the right parts, so not much criticism to give there :)

You should properly have the topload higher up, but I assume you will once its the final assembly. For 15kV @ 120mA, you will get some serious streamers and it would just go from topload to strike rail on that short distance and with topload diameter being smaller than strike ring diameter.

Is the white MMC plate "fold-able" so it goes around the base? Seems a little big if not.

What is up with the optical illusion between base plate and primary plate? I can for the love of god not see what that is...

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