Author Topic: My first DRSSTC on bricks  (Read 2403 times)

Offline Mads Barnkob

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Re: My first DRSSTC on bricks
« Reply #60 on: May 03, 2019, 07:49:06 PM »
I found this ebay listing with 0.1uF 2.5kV paper in oil capacitors:
https://www.ebay.com/itm/K41-1a-Paper-PIO-pulse-capacitor-0-1uF-10-2-5kV-Lot-of-2/251259264733?_trkparms=aid%3D888007%26algo%3DDISC.MBE%26ao%3D1%26asc%3D20131227121020%26meid%3Dc3967893df3249af835219ad5cd172cc%26pid%3D100009%26rk%3D1%26rkt%3D1%26mehot%3Dag%26sd%3D162844731444%26itm%3D251259264733&_trksid=p2047675.c100009.m1982

Does anybody have experience with this kind of capacitors?Are they any good for a MMC?

Another thing: in series connection the overall pulse resistance(dVdT) of the MMC gets multiplied by the amount of series capacitors? In this case the voltage gets shared by the series capacitors and they see a smaller voltage rise across them,so 1.8kV/us capacitors would already be good with 4 in series at 6kV across the MMC?
I just saw Futurist's DRSSTC1 and he used C4BS capacitors,which have around 1kV/us rating if I remember right and they worked fine for him...

I doubt old PIO capacitors will last long in a DRSSTC, unless it is some special Russian secret cold war indestructible super caps :) As mentioned, their losses at high frequency is most likely very bad, but check their datasheet if you can find one.

I think you are mistaken about the AC voltage rating needed for a resonant capacitor vs. dV/dt, dV/dt is simply a value derived from capacitance and the peak current it is rated to pass through it, and the pulse capacitors we use are almost always high peak current specced or low capacitance, so there is rarely a case of dV/dt being broken.

I wrote the math down used in my calculator, just beneath it: http://kaizerpowerelectronics.dk/calculators/mmc-calculator/

If you want to design your MMC correct, I give 3 alternatives to do so here: http://kaizerpowerelectronics.dk/tesla-coils/drsstc-design-guide/mmc-tank-capacitor/
« Last Edit: May 03, 2019, 08:47:43 PM by Mads Barnkob »
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Offline Laci

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Re: My first DRSSTC on bricks
« Reply #61 on: May 04, 2019, 09:48:14 PM »
I did some more calculations and choose the KEMET R76TR31004030J. 4 in series, 8 in parallel gives 0.2uF at 6400V,so around 850A peak. They are cheap and common so I can update the MMC in the future if needed.Their RMS current rating is just under 10A around 100kHz.This gives around IRMS=80A for 8 in parallel.



I calculated a maximum of 100 bps at 800us for the 80A IRMS. What do you think about this choice?

Offline Laci

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Re: My first DRSSTC on bricks
« Reply #62 on: May 12, 2019, 09:49:02 PM »
After waiting a week for the components and another few days of work, I could finally make some better tests.It looks like with longer pulses at lower peak currents I get good results,just like with short pulses at higher currents.I tested midi notes up to 300A peak and transient up to 500 and the midi notes can already destroy 4A fuses.I'm a bit worried about huge sparks,because I blew up my SSTC2 bridge yesterday. I was running it from mains ground and cranked up the power to maximum.A secondary - primary flashover killed it...Stupid!...RIP 2pcs HGTG30N60A4D...

The MMC is the same that I planned, 0.2uF 6400V KEMET R76 series, around 80A IRMS. They are working,but didn't make any measurements yet.
I painted the metal enclosure blue,just like the MMC and added plenty of screw terminals.

For higher power running I want to make sure that it won't kill the bridge. I don't have strike rail and bus negative to earth capacitor.Adding these should hopefully save the bridge from flashovers. Another thing that might result in a fail is the IGBT losses.I have to calculate this...

The sparks already scary to me, I have to get used to them. :)
One bigger spark from the video, spark length is as much as secondary + topload length:












« Last Edit: May 12, 2019, 09:50:47 PM by Laci »

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Re: My first DRSSTC on bricks
« Reply #62 on: May 12, 2019, 09:49:02 PM »

 


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