Author Topic: I started making a drsstc  (Read 1640 times)

Offline Miki_407

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I started making a drsstc
« on: November 30, 2020, 11:58:29 AM »
Hello,
I am 14 years old and this is my first true drsstc. Does the secondary need to be changed? I used 0.1mm wire for it and a 75mm pvc pipe, length of windings is 14.5cm. Would it be better to make a 24cm long windings with 0.2mm wire on a 75m pvc pipe? I plan on using a full bridge with parallel 40n60n igbts. Also i wanted to ask is my topload ok, i made it myself from some copper pipe. Any later questions i have i will make in this post.

Offline Mads Barnkob

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Re: I started making a drsstc
« Reply #1 on: November 30, 2020, 12:56:05 PM »
Hi Miki and welcome to HVF :)

It is great to see young people taking on the challenge of building a DRSSTC.

I calculated your tesla coil resonant frequency and you have around 1300 turns and which your topload you are properly around 130'ish kHz resonant frequency, looking at the tesla coil impedance list, you properly have a impedance higher than 60k, so you should be designing for a high impedance inverter. This means lower peak current, longer on-time and that means you should have more turns on the primary coil and a smaller MMC in order to hit high impedance in the primary circuit. You should also check out the MMC calculator to make it easier to get it right in your Tesla coil.

What are you planning to use as driver? There is a great variety of the old school universal driver 1.3b and up to the latest fully digital and PC controlled NextGen UD3
https://kaizerpowerelectronics.dk - Tesla coils, high voltage, pulse power, audio and general electronics
https://www.youtube.com/KaizerPowerElectronicsDk60/join - Please consider supporting the forum, websites and youtube channel!

Offline Miki_407

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Re: I started making a drsstc
« Reply #2 on: November 30, 2020, 01:16:04 PM »
I am planing on using ud2.7. I have used this coil before with a smaller topload and 16 turns primary. I was afraid with this bigger topload it would arc back to primary.
This is the video of it on 300vdc. It sadly died shortly after. I think a biggest problem was phase lead as i have been using a pll circuit also long wires from bridge to primary, no snubber capacitors.

Few other questions.
1.How long sparks should i expect?
3.Should i make a primary with tap points or go with a primary simular to one shown in my video?
« Last Edit: November 30, 2020, 07:47:05 PM by Mads Barnkob »

Offline davekni

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Re: I started making a drsstc
« Reply #3 on: November 30, 2020, 08:49:30 PM »
Your primary looks fine.  With it being fixed inductance, you will need some way to add and/or remove capacitance of the MMC between H-Bridge and primary coil.  That is my preference - adjusting MMC rather than primary winding.  However, tapped primary winding is much more common.  (Ferrites can be used to adjust primary frequency, but there are many complications to consider for that option.)

Arc length depends on many factors, especially enable pulse width and repetition frequency.  I've had best success with high (1kHz+) repetition with ramped pulse width.

For H-Bridge layout, I recommend copper planes as in this post:
https://highvoltageforum.net/index.php?topic=1324.0

Good luck!  Nice progress already!
David Knierim

Offline Miki_407

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Re: I started making a drsstc
« Reply #4 on: November 30, 2020, 08:58:41 PM »
I am using a layout of loneoceans easybridge. Soon parts should arrive so i will post when i find new problem or finish it. Adjusting a mmc wont really be problem as i am using 50 capacitors(2kv 4.7nf). Thank for the help.

Offline Miki_407

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Re: I started making a drsstc
« Reply #5 on: January 09, 2021, 03:53:25 PM »
         So a little problem has risen. I used non inverting mosfet driver UCC27424 instead of UCC27423. Will making a mod board that fits on phase control and inverts the inputs be good enough until i order replacements.

Offline davekni

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Re: I started making a drsstc
« Reply #6 on: January 09, 2021, 07:42:20 PM »
Yes, inverters on those two 74HC08 outputs should work fine.  The inverters will add a bit more delay, so require slightly more phase lead to compensate.

Another option is to change the 74HC08 to a 74HC00 (AND to NAND gate).  If you do that, bypass the inverter on pin 8 of the NAND gate to keep enable logic correct (bypass 74HC14 pins 12 and 13).

For your previous concern about arcs to the primary coil, most DRSSTC designs include a strike rail near the top of the primary coil.  That's a grounded not-quite-complete turn of exposed conductor (ie. copper pipe or ...) with diameter a bit larger than outside of primary.  Any arcs that head down will hit that rail before reaching the primary.
David Knierim

Offline Miki_407

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Re: I started making a drsstc
« Reply #7 on: January 11, 2021, 09:15:11 PM »
Finally made the mod board work :D. Turns out my first ic was broken. It isn't tuned right. Primary side is 150kHz and secondary is 185kHz with no arcs. No phase lead is set jet. I had issues with it arcing back to primary but lowering the primary fixed it. Later I might change to pancake primary.
So here is a video of it working:
 
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Offline davekni

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Re: I started making a drsstc
« Reply #8 on: January 11, 2021, 09:41:53 PM »
Congratulations!
David Knierim

Offline Miki_407

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Re: I started making a drsstc
« Reply #9 on: January 16, 2021, 06:38:11 PM »
I need to ask some questions.
On what amperage should I put ocd for my 2 parallel 40n60n igbt full bridge?
What is easiest way to see if I am not too far away from zero point switching? I don't have a differential probe and I only have usb oscilloscope.

Soon i will upload another video.

Offline davekni

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Re: I started making a drsstc
« Reply #10 on: January 16, 2021, 07:06:13 PM »
What is the full part number for "40n60n"?  I'd need to see a datasheet in order to estimate current capability.  Also, what gate voltage are you running (in other words, what supply voltage is running to the UD2.7 board)?

Do you have a scope probe capable of measuring 340V waveforms even if not isolated?  If so, you can capture useful H-Bridge output waveforms even on top of the line-frequency base.  Of course, DO NOT CONNECT THE SCOPE PROBE GROUND TO THE H-BRIDGE BUS SUPPLY.  (However, response will improve if the scope ground is wired through a ~0.1uF 400+V capacitor to H-Bridge VBus- rail.)  Trigger on the H-Bridge output waveform, adjusting trigger threshold for the lowest (most negative) voltage that captures waveforms.  You will be capturing waveforms once per line cycle, enough to be useful.  When voltage phase is lagging current, the H-Bridge output will show a larger noise spike at switching (caused by IGBT diode reverse-recovery snap-off).  At zero-phase there is sometimes a triple-transition on H-Bridge outputs - rising,falling,rising in rapid succession instead of a clean rising edge.  Slightly more phase lead (ideal point) and H-Bridge outputs will transition cleanly and smoothly.
David Knierim

Offline Miki_407

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Re: I started making a drsstc
« Reply #11 on: January 16, 2021, 09:38:08 PM »
What is the full part number for "40n60n"?
Full number is 40n60npfd.

Also, what gate voltage are you running (in other words, what supply voltage is running to the UD2.7 board)?
I am running 20v.

Do you have a scope probe capable of measuring 340V waveforms even if not isolated?
I have 10x probe rated at 600v CAT II but I think my scope is made for max 6v with 1x probe so answer is I cant measure 340v. I haven't tested my coil at 300v yet max i have gone to is 120v.

Offline davekni

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Re: I started making a drsstc
« Reply #12 on: January 16, 2021, 10:09:21 PM »
I've found data for an IGBT part SGT40N60NPFDPN.  I'm guessing that is what you have.  It is rated for 120A peak, 40A at 100C case, 80A at 25C case temperature.  My rule-of-thumb is that IGBTs fry around 2x rated peak current or 4x rated average current in DRSSTC use.  That would be about 240A per IGBT, 480A for a pair IF they share current perfectly evenly.  That is destruction current, so you want OCD a ways below that, perhaps 300A.  I'd start even lower, ~200A until you have phase lead dialed in.  Others here may have more experience with similar parts.

Sometimes there is enough switching glitch showing up when probing driver output (GDT input) to use for phase lead adjustment.  It is hard to predict exactly what you will see there.  Another option is to form a couple turns (loops) of wire from scope probe tip to ground lead.  Tape over the wire ends (over the probe tip and ground clip) to avoid bumping any high-voltage nodes.  Use this as a magnetic-field probe around the IGBTs or VBus leads to the bridge.  That will often pick up enough signal to see the switching edges.  You will need to experiment with loop size and placement to get clear pulses (or at least spikes and ring-down) at switching times.
David Knierim

Offline Miki_407

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Re: I started making a drsstc
« Reply #13 on: February 01, 2021, 09:45:45 AM »
Long time no update.
I tested it at 30v and this is what  i get:

It looks bad. I added a small inductor and forgot to place a jumper so now some resistors burned and I suspect comparator is dead.  I haven't yet replaced it.

Offline davekni

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Re: I started making a drsstc
« Reply #14 on: February 01, 2021, 06:55:21 PM »
Yes, UD2.7 has the issue that a missing SV1 jumper can fry downstream parts.  Such mistakes are frustrating, but part of learning.  I've made plenty of such mistakes over the decades.

The scope plot shows 5V/division.  Is that really 50V/div using a 10x probe?  Are you scoping from one H-Bridge output to the other?  If so, grounding one side of the H-Bridge through the scope is not good practice even if the H-Bridge power supply is isolated.  There is often enough capacitance from supply to ground to cause problems.  Connect the scope ground to VBus- (negative H-Bridge power input), then scope one or the other H-Bridge output.  (Of course, do not connect the scope ground to VBus- if VBus- is not either isolated or grounded through the power supply.)

Hope repairs go well!
David Knierim

Offline Miki_407

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Re: I started making a drsstc
« Reply #15 on: February 01, 2021, 08:24:27 PM »
I scoped from Bus- to one output but got waveform looking like a sine wave. Switching to the other output I got waveform attached in my last post. I will have to get a adjustable inductor soon.
After replacing passive components it seams that comparator died.
But for now I have more important things to do.

Offline Miki_407

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Re: I started making a drsstc
« Reply #16 on: February 09, 2021, 07:03:06 PM »
Is this good? I dont have a adjustable inductor so this is the best i did:
First with no inductor:


With inductor


Max sample rate of my usb oscilloscope is 48MSa/s.

Offline davekni

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Re: I started making a drsstc
« Reply #17 on: February 09, 2021, 08:25:50 PM »
What circuit node are you probing?  If this is one of the H-Bridge outputs, it shouldn't be going below ground.  Both H-Bridge outputs should switch from ground (VBus-) to VBus+.  Is there offset in your scope?  If you probe VBus- and then VBus+, do you see the correct DC voltages with your scope?  It should display a flat line at 0V for VBus- (with scope probe grounded to VBus-).  It should display a flat line at 15V or whatever voltage you are feeding to VBus+ when probing that.
David Knierim

Offline Miki_407

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Re: I started making a drsstc
« Reply #18 on: February 09, 2021, 08:56:12 PM »
Seems like i forgot to put probe ground to Bus-. But i cant test anymore tonight so i will do it properly tomarrow. And another thing is that i get arcing to primary. Seems like i will have to make a pancake primary. Still testing at 120v and not putting it mains (220vac) rectified.

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Re: I started making a drsstc
« Reply #19 on: February 09, 2021, 09:09:04 PM »
Of course, don't connect scope probe go VBus- when mains-powered!

Were you running 15V for the scope test?  The scope is showing about 15V waveform.  The second (with-inductor) waveform looks clean towards the later (right) side.  Perhaps current is ramping up across that capture.  It is handy to capture current on the second scope channel if that is possible.  Either probe across the 51ohm feedback input resistor or add another current transformer for scoping.  If scoping the 51ohm feedback resistor, scope just the resistor even when an inductor is added in series.  That way the scope trace matches current phase, not the lead-compensated version.
David Knierim

High Voltage Forum

Re: I started making a drsstc
« Reply #19 on: February 09, 2021, 09:09:04 PM »

 


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