Author Topic: DRSSTC design questions + project progress  (Read 5774 times)

Offline Vaclav

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Re: DRSSTC design questions + project progress
« Reply #40 on: March 25, 2020, 03:31:55 PM »
I already hit the current limit of 800A, idk if I should go higher.
I did all my calculations based on 800A peak, I really don't want to risk the IGBTs or MMC....
But at lower BPS a higher current should work.

I ran a test without the secondary. Just to try out where the limit of the mains input current is (my varica gose up to 10A)
I used the maximum On-Time to get 800A. (I can't remember the On-Time and the bus voltage...)
With about 1700BPS I hit the 10A input current restriction.
The heatsink got warm (was easily touchable).
But the 16mm² cable to the primary started smelling...

I know 1700BPS is huge, I don't think a higher current and lower BPS would be a problem temperature wise.

I have absolutely no clue where the limit of my IGBTs is.
I used FF400R12KE3 for my inverter.
Where is probably the limit of these IGBTs?

I planed to tune the coil a litle bit better (don't have mutch hope ^^).
When the tuning is perfect, I will shorten the rest oft the excess cable to the exact length.
I although want to do some tests with an MIDI-Interupter.

Unfortunately I can't do tests that often because one of my neighbours complained about the Teslacoil.
I really don't want to get in trouble with him.

Nevertheless, destroying the coil would be horrible because I want to bring it to school for the presentation of my project.
Maybe I'll run it there.

I will share my documentaion here, but first I have to complete it.

Offline davekni

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Re: DRSSTC design questions + project progress
« Reply #41 on: March 25, 2020, 05:51:20 PM »
FF400R12KE3 is specified at 800A pulse current (at 1ms), so that should be plenty safe.  Looking at the typical plots, there appears to be quite a bit of headroom past 800A, especially if the gate voltage is above the specified 15V.  Hopefully others here will offer advice from their more extensive experience.  My limited info from other IGBT bricks is that they tend to fry at about 2x their pulse rating or 4x their continuous current rating, which would be 1600A for this part.  I'd suggest staying well below 1600A.

Inductance of your bus voltage routing, from the IGBT parts to snubber and bulk capacitance can be limiting too, if transients exceed 1200V.  A good layout with low inductance should keep internal IGBT voltages well below 1200V even up to 1600A.
David Knierim

Offline Mads Barnkob

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Re: DRSSTC design questions + project progress
« Reply #42 on: March 30, 2020, 12:12:15 AM »
Similar "400A" rated IGBT bricks have been pushed to 1300A in reliable operation. So 800A is certainly nursing them :) I think you could push it to 1000A and still be playing it safe. Depends on your MMC design if the resulting higher voltage and current is still within the limits of it.

See the table for IGBT proven speeds/currents at bottom of article here: http://kaizerpowerelectronics.dk/tesla-coils/drsstc-design-guide/igbts/
http://www.kaizerpowerelectronics.dk - Tesla coils, high voltage, pulse power, audio and general electronics

Offline Vaclav

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Re: DRSSTC design questions + project progress
« Reply #43 on: April 03, 2020, 03:07:13 PM »
Here is the promised data.

The documentation is unfortunately larger than 5MB. Therefore I upload it here in 2 parts and as "better" version in my dropbbox.
Link to documentation with clickable links: https://www.dropbox.com/s/lohkbcrhsjiszgs/Doku_klick.pdf?dl=0

I will first do some experiments with a musical interrupter.
After that, I'll crank the current up.

Offline Vaclav

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Re: DRSSTC design questions + project progress
« Reply #44 on: May 03, 2020, 09:22:27 PM »
Hi all,

I turned the current up to about 1100A and did some tests without the secondary.

I noticed that sometimes there are suspicious cracking noises, probably from the inverter?
With a lower peak current, I can't hear any cracking sound.
Does anybody have an idea where the cracking noise is coming from? I reckon that this noise isn't good for the inverter.

Here is a video of the sound. Yellow is the inverter output voltage. Blue is the primary current (current=voltage*9).
/>
Greetings Vaclav

Offline ElectroXa

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Re: DRSSTC design questions + project progress
« Reply #45 on: May 03, 2020, 09:43:54 PM »
Hi

this cracking sound may be produced by film capacitor being  abused  by the high resonant voltage in this high current test :)

I would suggest you to measure capacitance before and after a run, to confirm or not if the cracking noise is coming from caps.
Indeed, when a capacitor is cracking, it loses capacitance a little bit, as the metal film is vaporized.

Have a great time  ;)

Offline Vaclav

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Re: DRSSTC design questions + project progress
« Reply #46 on: May 06, 2020, 07:34:23 PM »
According to my calculations the MMC shouldn't be the limiting factor in terms of voltage.

The MCC has 400nF. The primary frequency is 87,5kHz.
Xc = 1/(2*3,14*87,5kHz*400nF) = 4,55 Ohm
The Primary peak current in the video is 1125A (125V*9A/V).
Therefore, the MMC peak voltage is 4,55*1125A = 5119V.

My MMC consists of 3 of these (https://www.mouser.de/ProductDetail/Cornell-Dubilier-CDE/940C20P1K-F?qs=%2Fha2pyFaduiMLcfaRzv3woPpAk8YuhxuLigMYBA%2FFjg%3D) caps in series.
12 of these rows are connected in parallel.

So the absolute maximum voltage of the MMC should be 6000V.
I thought that should be enough...


Since I don't want to kill my expensive MMC, I just dropped the current to about 900A (one full period of the Primary current).

I would say for my second Teslacoil I ever build, the result is pretty good.
Maybe I will make some changes in the future, like a water cooled primarycoil and a MMC with a higher maximum voltage.


Unfortunately there are no presentations of the school projects due to corona...

I' ve made some small changes to my documentation. For the sake of completeness I' ve attached the new documentation.


Thank you all so much for all your help.

Greetings Vaclav




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Re: DRSSTC design questions + project progress
« Reply #46 on: May 06, 2020, 07:34:23 PM »

 


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