Author Topic: First DRSSTC questions  (Read 1275 times)

Offline Hi-Deff

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First DRSSTC questions
« on: May 30, 2024, 11:23:35 PM »
Hi everybody!

I decided that I wanted to build DRSSTC on the smaller side due to space constraints.  This is a complex subject and I knew I would never understand it until I started actually working on it.  Also, I started building and purchasing parts before I discovered this forum and now I think I should ask you guys for a sanity check before I go any further. 

I was inspired by Loneocean's DRSSTC 2.  I bought and assembled his 80mm Full Bridge Plus (https://loneoceans.com/labs/sales/80mmfullbridgeplus/) because I though it would minimize layout issues, make my life easier and, I figured, I could upgrade to IGBT bricks or build another coil if I decided that I want bigger sparks once I had a better understanding.  I bought a Chinese UD2.7 to drive the bridge.

I've posted javatc outputs below.  I think the toroid that I impulsively bought on ebay may be too small and plan to add more primary turns in case I'd like to use a larger toroid. I didn't count how many turns I have on the secondary when I was winding.  I entered the physical dimensions that I could measure into javatc and adjusted the number of turns until the frequency and DC resistance where close to what I measured.

I'm about to build the primary coil.  I have 9 CDE 940C20P1K-F capacitors that I intend to assemble in a 3x3 MMC array, giving a total capacitance of 0.1 uF and voltage handling of 6 kV.  The primary inductance is calculated to be 4.652 uH if I use the small top load that I purchased. I'm in the U.S. and limited to 120 VAC at 15 A, giving me a maximum of 340 VDC with a voltage doubler.  Using the equations provided on Mads's SSTC page:

XL = 2 x pi x f x L = 2 x pi x 234 Hz x 4.652 = 6.84 Ohms

Primary Peak Current = Voltage / Resistance XL = 340 VDC / 6.84 Ohms =  49.7 Apk

I'm using FGH60N60SND IGBT's.  The datasheet indicates a maximum collector current of 60A and pulsed collector current of 180A.  I think I'm safe if I calculated things correctly.  Did I calculate things correctly?  If I did, then I can make the primary coil.

My next question is, how do I determine the gauge of wire to use to connect the bridge to the MMC and the MMC to the primary? Looking at a chart leads me to believe that I'll need to use 6 gauge wire to handle 50 amps.  Gao (Loneocean) included lugs to use 14 gauge wire on his bridge and that makes me think that I'm not understanding something here.

I'm working on the layout.  I've included a photo of my parts with lines drawn to show the wiring connections.  The light blue wire goes from the bridge output to the MMC and the light blue wire goes from the primary through the current transformers back to the bridge.  Will I have issues with these wires interfering with the signal wires going to the GDT's and feedback from the current transformers?

Is there a guide or tutorial for initial testing of the UD2.7?  I'm assuming that I'll need to trick the feedback transformers into thinking the coil is operating with a function generator and then I can check phase on the gates and stuff.  How do I set the OCD?
 
I don't claim to know what I'm doing, so please let me know if I'm doing anything stupid.

Thanks!


J A V A T C version 13.6 - CONSOLIDATED OUTPUT
5/30/2024, 11:53:59 AM

Units = Centimeters
Ambient Temp = 68ºF

----------------------------------------------------
Surrounding Inputs:
----------------------------------------------------
100 = Ground Plane Radius
0 = Wall Radius
0 = Ceiling Height

----------------------------------------------------
Secondary Coil Inputs:
----------------------------------------------------
Current Profile = G.PROFILE_LOADED
4.445 = Radius 1
4.445 = Radius 2
70 = Height 1
100.8 = Height 2
1480 = Turns
32 = Wire Awg

----------------------------------------------------
Primary Coil Inputs:
----------------------------------------------------
Round Primary Conductor
6.98 = Radius 1
13.652 = Radius 2
70 = Height 1
70 = Height 2
4.203 = Turns
0.635 = Wire Diameter
0 = Ribbon Width
0 = Ribbon Thickness
0.1 = Primary Cap (uF)
0 = Total Lead Length
0 = Lead Diameter

----------------------------------------------------
Secondary Coil Outputs:
----------------------------------------------------
234.12 [kHz] = Secondary Resonant Frequency
90 [deg °] = Angle of Secondary
30.8 [cm] = Length of Winding
48.05 [cm] = Turns Per Unit
0.00617 [mm] = Space Between Turns (edge to edge)
413.35 [m] = Length of Wire
3.46 [:1] = H/D Aspect Ratio
220.6966 [Ohms] = DC Resistance
67736 [Ohms] = Reactance at Resonance
0.118 [ kg] = Weight of Wire
46.047 [mH] = Les-Effective Series Inductance
49.987 [mH] = Lee-Equivalent Energy Inductance
49.329 [mH] = Ldc-Low Frequency Inductance
10.036 [pF] = Ces-Effective Shunt Capacitance
9.245 [pF] = Cee-Equivalent Energy Capacitance
18.272 [pF] = Cdc-Low Frequency Capacitance
0.1473 [mm] = Skin Depth
6.678 [pF] = Topload Effective Capacitance
333.0719 [Ohms] = Effective AC Resistance
203 [Q] = Quality Factor

----------------------------------------------------
Primary Coil Outputs:
----------------------------------------------------
234.12 [kHz] = Primary Resonant Frequency
0 [%] = Percent Detuned
0 [deg °] = Angle of Primary
272.43 [cm] = Length of Wire
1.48 [mOhms] = DC Resistance
0.953 [cm] = Average spacing between turns (edge to edge)
2.207 [ cm] = Proximity between coils
0 [cm] = Recommended minimum proximity between coils
4.652 [µH] = Ldc-Low Frequency Inductance
0.10002 [µF] = Cap size needed with Primary L (reference)
0 [µH] = Lead Length Inductance
74.656 [µH] = Lm-Mutual Inductance
0.156 [k] = Coupling Coefficient
0.128 [k] = Recommended Coupling Coefficient
6.41 [half cycles] = Number of half cycles for energy transfer at K
13.48 [µs] = Time for total energy transfer

----------------------------------------------------
Top Load Inputs:
----------------------------------------------------
Toroid #1: minor=5.1435, major=19.05, height=102, topload




Offline Benjamin Lockhart

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Re: First DRSSTC questions
« Reply #1 on: May 30, 2024, 11:50:06 PM »
Here is the UD2.7 info page. https://www.loneoceans.com/labs/ud27/
Your primary peak current will be way higher than 50A peak because it increases every cycle, adding to the energy stored in the tank circuit until the secondary starts taking some of the energy.

Those IGBTs can handle up to about 300A pulses for short on-times and I'd plan on the coil operating at that current.
You might need a smaller tank capacitor to prevent the current from ringing up too high too quickly. Maybe 50nF?

Also, plan for the primary to have at least 15% lower frequency than the secondary to account for spark loading bringing the secondary frequency down.

You will need a lot more than 4 primary turns because I think the tank cap will be too big given the 300A limit of the IGBTs.

A smaller MMC in the tank circuit will also ring up to a higher voltage, so be aware of that. You can use javadrc to find the maximum voltage there.
« Last Edit: May 31, 2024, 02:58:21 AM by Benjamin Lockhart »

Offline flyingperson23

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Re: First DRSSTC questions
« Reply #2 on: May 30, 2024, 11:57:49 PM »
The calculation for 50A max current is for a SSTC, which doesn't have a resonant capacitor. A drsstc does, so peak current can go much higher, probably on the order of magnitude of 500A. TO-247 coils usually set OCD around 300A. I believe loneoceans' UD2.7 page has a tutorial for setting OCD. It's fine to put 300A peak through these transistors because the overall duty cycle is low and we're doing soft switching/ZCS.

14 gauge wire will work fine. Assuming OCD around 300A, throughout each pulse the current rises from 0 to 300A so the average might be about 150A for each pulse. These pulses are very short and the max duty cycle overall will probably be around 5%, making the average current through the wire 7.5A. Average current is what dictates wire heating and what size wire is needed.

Any pairs of wire, i.e. an input to or output from a GDT, should be twisted together as much as possible. You can find more info about GDT construction here: https://highvoltageforum.net/index.php?topic=1856.0

https://kaizerpowerelectronics.dk/tesla-coils/drsstc-design-guide/  is a great resource as well


Offline davekni

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Re: First DRSSTC questions
« Reply #3 on: May 31, 2024, 01:55:22 AM »
Quote
These pulses are very short and the max duty cycle overall will probably be around 5%, making the average current through the wire 7.5A. Average current is what dictates wire heating and what size wire is needed.
Correction to above:  RMS current dictates wire heating.  5% duty cycle reduces RMS current by sqrt(5%) = 22.4%.
David Knierim

Offline Hi-Deff

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Re: First DRSSTC questions
« Reply #4 on: May 31, 2024, 11:46:20 PM »
I knew I wasn't understanding what I was doing.  Will Mads's MMC calculator tell me what I need to know to build the MMC, the primary, and make sure I don't destroy the IGBT's, or is there something else that I need to consider? 

I was playing around with the MMC calculator and it looks like the RMS current would've been a bit too high.  I bought 9 0.1uF 2kV caps and it's hard to get the MMC down to 0.05 uF without buying a lot more caps.  I may have to go with different caps all together.

Using the MMC calculator, I set the primary peak current to 300A assuming OCD will be set to cut off there and adjusted the frequency (detuned approximately 15%) and primary inductance based on feedback from javatc.  Here are the results I'm getting:

Same for all:
Primary peak current   300 A
On time   200 uS
BPS   200 BPS

3x3 for a MMC capacitance of 0.1uF

Frequency: 193.5 kHz
Primary inductance: 6.764 uH (~ 5 turns)

Advanced results   
Primary impedance    8.2243 Ohm
MMC Xc (reactance)   8.2292 Ohm
MMC Zc (impedance)   8.2292 Ohm
Energy (single cap)   0.0338 Joule
Power dissipation (single cap)   0.7  Watt
Temperature rise (single cap)   7.7 ºC
   
                                 Actual values   MMC Rating
Peak voltage MMC    2468 VDC        6000 VDC
RMS current MMC    30 A                24.9
dV/dt for MMC            80 V/uS           3000 V/uS
Peak current for MMC    300 A              513 A

3x4 for a MMC capacitance of 0.133 uF

Frequency: 197.4 kHz
Primary inductance: 4.887 uH (~4.5 turns)

Advanced results   
Primary impedance    6.0548 Ohm
MMC Xc (reactance)   6.0515 Ohm
MMC Zc (impedance)   6.0515 Ohm
Energy (single cap)   0.0183 Joule
Power dissipation (single cap)   0.39  Watt
Temperature rise (single cap)   4.33 ºC
   
                                 Actual values   MMC Rating
Peak voltage MMC    1815 VDC        6000 VDC
RMS current MMC    30 A                33.4 A
dV/dt for MMC            57 V/uS           2250 V/uS
Peak current for MMC    300 A              684 A

8x4 for a MMC capacitance of 0.05uF

Frequency: 195.48 kHz
Primary inductance: 13.258 uH (~ 7 turns)

Advanced results   
Primary impedance    16.2837 Ohm
MMC Xc (reactance)   16.2917 Ohm
MMC Zc (impedance)   16.2917 Ohm
Energy (single cap)   0.0186 Joule
Power dissipation (single cap)   0.3937  Watt
Temperature rise (single cap)   4.3307 ºC
   
                                 Actual values   MMC Rating
Peak voltage MMC    4887 VDC        16000 VDC
RMS current MMC    30 A                33.2 A
dV/dt for MMC            80 V/uS           6000 V/uS
Peak current for MMC    300 A              684 A


Based on the above, it looks to me like the 3x4 MMC at 0.133 uF would be best, but that's with only 4.5 turns and an impedance of 4.9 uH.  That is the opposite direction of recommendations.  This tells me that I'm not understanding what I'm doing. What do I need to understand about the primary coil impedance to correctly select capacitors and design the primary?

I'm thinking that the caps I bought aren't going to work for me unless I buy a lot more.  So many, that it makes sense to assume I purchased the wrong caps and start over.



Offline Hi-Deff

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Re: First DRSSTC questions
« Reply #5 on: June 03, 2024, 01:25:24 AM »
After some more messing around with javatc I think I'm going to need to go with a 33 nF MMC and that should allow 8.6 turns with a primary inductance of 19.5 uH.  Does this seem more appropriate? Should I be looking to have even more primary turns? 

The design guide discusses high and low primary impedance, but I haven't found where he defines what high and low are.  Also, in the design guide he suggested a capacitance range of 0.15 – 0.45 uF for a coil my size.  That was throwing me off. 

Offline flyingperson23

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Re: First DRSSTC questions
« Reply #6 on: June 03, 2024, 02:23:58 AM »
Typical impedance varies with coil size (this is why a big coil can get thousands of amps of primary current whereas a small coil with the same bus voltage might only get a few hundred), so you can't define high/low impedance exactly. You can generally tell based on the number of primary turns - 8.6 is high impedance, something like 3-4 would be low impedance.

33nF is appropriate for a small coil the size of loneoceans' drsstc 1. 100nF is also fine for that size. His drsstc 2 is considerably bigger with about half the resonant frequency of yours, which is why it needs a bigger MMC. The design guide bases MMC size off secondary size, and your secondary seems unusually large given the rest of your coil.
« Last Edit: June 03, 2024, 02:26:42 AM by flyingperson23 »

Offline Benjamin Lockhart

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Re: First DRSSTC questions
« Reply #7 on: June 03, 2024, 03:47:33 AM »
My DRSSTC1 runs at 200kHz with a 100nF MMC, and rings up to 300A in about 70-90us ish. It also has a really fat secondary and high coupling (0.19), which lowers current some.

BUT that's just a half bridge at 340V DC, so with a full bridge you would need half the MMC value to run at roughly the same primary current. I would think that 33-50nF is about right.

If your coil has lower coupling (skinnier secondary), then the energy transfer is slower so the current will ring up higher.

If the transistors would handle more amps a well performing coil could be designed with a lower primary impedance and large MMC, but pushing large IGBT bricks to 200kHz may not be possible. (you're not going to do it with cm300 for example)
« Last Edit: June 03, 2024, 05:53:34 AM by Benjamin Lockhart »

Offline flyingperson23

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Re: First DRSSTC questions
« Reply #8 on: June 03, 2024, 05:28:44 AM »
My small coil runs at 200khz with 100nF mmc and rings up to 300A in a few hundred us (I run it at 1ms max with pulse skipping). It's so slow because it's on 140Vbus and it's a half bridge, but it still gets decent performance. The half bridge is a BSM150 module, so I can confirm some bricks at least work fine at 200khz.

Offline Hi-Deff

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Re: First DRSSTC questions
« Reply #9 on: June 03, 2024, 05:51:05 PM »
Now I'm thinking I should make a smaller secondary.  Should I just copy the Loneocean DRSSTC1 secondary?  It sounds like Gao was targeting a lower resonant frequency and didn't correctly account for the insulation thickness on the wire.  Are there any changes to the secondary that would make it better suited for running with a full-bridge?

Maybe the best approach at this point is to optimize the primary circuit and make a secondary to work with it.

Also, thank you for your help!
« Last Edit: June 03, 2024, 07:48:38 PM by Hi-Deff »

Offline Benjamin Lockhart

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Re: First DRSSTC questions
« Reply #10 on: June 03, 2024, 10:35:57 PM »
No, I think your secondary is a good size and frequency for a full brige of TO247 IGBTs. It might be capable of 1 meter sparks with a larger toroid, maybe 300mm-400mm in diameter.

I would add another bank of 9 caps in series with the existing 3x3 to make a 50nF MMC with double the voltage rating.
6 series, 3 parallel would probably be fine at 300A.

It looks like 6kV is all you need for a 0.05uF MMC at 200kHz according to javadrc (not javatc). The problem is the RMS current rating of the caps if you don't have enough parallel strings.

I don't think a smaller secondary is a good idea with a full bridge You might be fighting racing spark issues with that much power.

Also I would expect about 100us to be all the on-time it will need to make full size sparks.

High Voltage Forum

Re: First DRSSTC questions
« Reply #10 on: June 03, 2024, 10:35:57 PM »

 


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Hi-Deff
June 03, 2024, 01:25:24 AM
post Re: RDRSSTC - Project Build
[Dual Resonant Solid State Tesla coils (DRSSTC)]
ZakW
June 03, 2024, 01:08:47 AM
post Re: RDRSSTC - Project Build
[Dual Resonant Solid State Tesla coils (DRSSTC)]
davekni
June 02, 2024, 10:29:02 PM
post Re: Steve Ward SSTC5 build
[Solid State Tesla Coils (SSTC)]
Michelle_
June 02, 2024, 10:02:45 PM
post Re: Racing sparks
[Spark Gap Tesla Coils (SGTC)]
davekni
June 02, 2024, 08:25:37 PM
post Re: Steve Ward SSTC5 build
[Solid State Tesla Coils (SSTC)]
Michelle_
June 02, 2024, 04:51:58 PM
post Re: RDRSSTC - Project Build
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Michelle_
June 02, 2024, 04:44:30 PM
post Re: My completed 14-stage Cockroft-Walton voltage multiplier
[Voltage Multipliers]
MRMILSTAR
June 02, 2024, 03:25:11 PM
post APC Smart-UPS 1500VA Teardown
[Electronic Circuits]
Mads Barnkob
June 02, 2024, 01:36:11 PM
post Re: My completed 14-stage Cockroft-Walton voltage multiplier
[Voltage Multipliers]
pete_dl
June 02, 2024, 11:43:40 AM
post Re: RDRSSTC - Project Build
[Dual Resonant Solid State Tesla coils (DRSSTC)]
ZakW
June 02, 2024, 08:49:11 AM
post Re: RDRSSTC - Project Build
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Benjamin Lockhart
June 02, 2024, 08:36:07 AM
post Re: RDRSSTC - Project Build
[Dual Resonant Solid State Tesla coils (DRSSTC)]
ZakW
June 02, 2024, 12:41:50 AM
post Re: Steve Ward SSTC5 build
[Solid State Tesla Coils (SSTC)]
Benjamin Lockhart
June 01, 2024, 08:24:35 PM
post Pearson current monitor model 1330 teardown (100kA)
[Laboratories, Equipment and Tools]
Mads Barnkob
June 01, 2024, 08:22:28 PM
post Re: Steve Ward SSTC5 build
[Solid State Tesla Coils (SSTC)]
Michelle_
June 01, 2024, 03:56:53 AM
post Re: Racing sparks
[Spark Gap Tesla Coils (SGTC)]
Terry
June 01, 2024, 12:03:50 AM
post Re: First DRSSTC questions
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Hi-Deff
May 31, 2024, 11:46:20 PM
post Re: Steve Ward SSTC5 build
[Solid State Tesla Coils (SSTC)]
Michelle_
May 31, 2024, 06:13:59 PM
post Re: First DRSSTC questions
[Dual Resonant Solid State Tesla coils (DRSSTC)]
davekni
May 31, 2024, 01:55:22 AM
post Re: First DRSSTC questions
[Dual Resonant Solid State Tesla coils (DRSSTC)]
flyingperson23
May 30, 2024, 11:57:49 PM
post Re: First DRSSTC questions
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Benjamin Lockhart
May 30, 2024, 11:50:06 PM
post First DRSSTC questions
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Hi-Deff
May 30, 2024, 11:23:35 PM
post Re: Steve Ward SSTC5 build
[Solid State Tesla Coils (SSTC)]
davekni
May 30, 2024, 10:43:06 PM
post Re: Benjamin's DRSSTC3
[Dual Resonant Solid State Tesla coils (DRSSTC)]
davekni
May 30, 2024, 10:24:35 PM
post Re: SSTC tripping circuit breaker
[Solid State Tesla Coils (SSTC)]
NyaaX_X
May 30, 2024, 06:10:04 PM
post Re: SSTC tripping circuit breaker
[Solid State Tesla Coils (SSTC)]
Simranjit
May 30, 2024, 04:56:11 PM
post Re: SSTC tripping circuit breaker
[Solid State Tesla Coils (SSTC)]
Michelle_
May 30, 2024, 04:48:05 PM
post Re: Steve Ward SSTC5 build
[Solid State Tesla Coils (SSTC)]
Michelle_
May 30, 2024, 04:37:22 PM
post Re: SSTC tripping circuit breaker
[Solid State Tesla Coils (SSTC)]
klugesmith
May 30, 2024, 04:16:31 PM
post Re: SSTC tripping circuit breaker
[Solid State Tesla Coils (SSTC)]
NyaaX_X
May 30, 2024, 03:34:10 PM
post Re: SSTC tripping circuit breaker
[Solid State Tesla Coils (SSTC)]
Simranjit
May 30, 2024, 02:53:50 PM
post Re: SSTC tripping circuit breaker
[Solid State Tesla Coils (SSTC)]
NyaaX_X
May 30, 2024, 12:44:47 PM
post SSTC tripping circuit breaker
[Solid State Tesla Coils (SSTC)]
Simranjit
May 30, 2024, 07:52:56 AM
post Re: Steve Ward SSTC5 build
[Solid State Tesla Coils (SSTC)]
NyaaX_X
May 30, 2024, 07:07:53 AM
post Re: Benjamin's DRSSTC3
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Benjamin Lockhart
May 30, 2024, 07:04:40 AM
post Re: Steve Ward SSTC5 build
[Solid State Tesla Coils (SSTC)]
Michelle_
May 30, 2024, 05:16:50 AM
post Re: Steve Ward SSTC5 build
[Solid State Tesla Coils (SSTC)]
Michelle_
May 30, 2024, 05:08:17 AM
post Re: Steve Ward SSTC5 build
[Solid State Tesla Coils (SSTC)]
davekni
May 30, 2024, 04:29:30 AM
post Re: Benjamin's DRSSTC3
[Dual Resonant Solid State Tesla coils (DRSSTC)]
davekni
May 30, 2024, 03:52:36 AM
post Re: Racing sparks
[Spark Gap Tesla Coils (SGTC)]
davekni
May 30, 2024, 03:47:12 AM
post Re: Steve Ward SSTC5 build
[Solid State Tesla Coils (SSTC)]
Benjamin Lockhart
May 30, 2024, 03:41:34 AM

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