Author Topic: Mid-sized DRSSTC build with freewheeling  (Read 1297 times)

Offline markus

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Mid-sized DRSSTC build with freewheeling
« on: February 23, 2024, 08:43:42 AM »
Hello everyone,

after some time away from my projects I now find myself with the time to continue with various stuff, including the DRSSTC I had started planning. This will be my second DRSSTC after a small-ish coil reaching 66cm spark length.

The goal is a mid-sized coil that is not too much of a burden storing / transporting, since storage is somewhat limited, and I need to move the coil whenever I want to run it.
After seeing various freewheeling coils, I definitely want to build a coil that allows me to experiment with that.
Right now I have parts for mostly everything except the topload and the MMC, but still need to do a fair bit of the construction.
Before starting with that I wanted to ask if there are any comments on my planned build. Here the details:

Driver (currently in another project for testing purposes):
  • UD+ with 24V 2A supply adjusted to ~21V (built and tested)
  • GDT 2x N30 CAT5 UTP 14/13 turns (I accidentally put one less winding on the first core than I had intended)
  • Gates: 5.6Ω (for now) with 1N5189 reverse schottky diode, P6KE30CA 30V TVS. It seems like I need to reduce the gate resistance though
  • Feedback / OCD: 40 to 2x 25 turns on N30 core for 1:1000 each



Bridge:
  • 2x eupec BSM150GB120DL half bridge IGBT modules in full bridge configuration, rated at 300A / 25°C each (might upgrade to BSM200GB120DLC modules, or CM200DY-24H which I recently found on ebay for the incredible price of 7€/pcs).
  • 2x (used) 4700uF 450V Kendeil electrolytic caps in parallel for 9400uF in total
  • 2x B32656-S0105-K500 MKP Snubber 1.0uF 1000V (13A RMS / 6mΩ ESR / 450V dV/dt)
  • 20x4 mm copper bus bar
  • 2x 1.5KE4400CA TVS across C/E
  • 10kΩ 11W resistor across bridge output
  • 2x 22kΩ 9W bleeder resistors (one for each bus cap)





Rectifier:
Rectified 230V mains => 325V (might add three phase for more power if needed)
  • KBPC5010 single phase full bridge rectifier (50A / 1kV)
  • 20A single phase EMI filter
  • Precharge: 10 Ohm 50W resistor with a RC delayed relay
  • For three phase I have some full bridge rectifier modules lying around, which will give me 325V if I use them as half wave rectifier (connect minus to N instead of the rectifier module)

Secondary:
  • Wire diameter 0.3mm (I have a 2kg reel)
  • 120mm diameter pipe (actually 126mm OD) at 65cm length, reaching 1:5 ratio and 100kHz f_res

Primary circuit:
  • 8mm copper pipe, tapped at ~6 Turns
  • Total of ~7.5 turns
  • MMC of 130x R76UN23905050J in 5s26p configuration for a rating of 10kV and 146Arms. At 90kHz this gives a peak voltage of 5860V (at 700A) / 5022V (at 600A). Arms should be fairly high so I do not get limited by my MMC when experimenting with freewheeling. Assuming a worst case of 600A at 20% duty cycle results in a 25.8 °C temperature rise which is still a bit high (with the kaizer MMC calculator), but I intend to run on 500A for now and will pretty sure have a lower duty cycle too. If necessary, I can still add a few more parallel strings to get more Arms - at 0.234uF I get 168Arms and more reasonable 14.3 °C, at ~5.6 turns primary.


What are your thoughts on my planned design? Does everything make sense?

Some additional questions:
  • MMC:   
    • Is my planned MMC suitable? Is it perhaps a bit oversized for this coil?
    • Is there a rule of thumb as to how much of a safety margin I should factor in compared to the DC ratings?
    • Do I connect my MMC as parallel series strings, or as a set of parallel caps in series that results in a grid-like structure?
    • Do I need bleeder / balancing resistors for my MMC and if yes, what values / rating / type? Or is the 10k resistor across the bridge output enough?
  • Are the TVS useful, or do they increase risk for blowing my bridge in the case they overload and fail short? I saw conflicting information while looking around. Is it better to put two in series for 880V?
  • Is it an issue that one GDT ended up with one turn less than the other? I guess I will just have to scope the gate waveforms to check if there is a difference.
  • I am thinking of cutting my heat sink into two parts since it seems a bit oversized, and I would end up with another heatsink for a future project. Do you think it is better to leave it as is? In that case I would put some stuff like the drivers etc on the free part.
  • There is also the option of winding my secondary on a 160mm pipe instead of a 120mm one (same 0.3mm wire, same length). This would give me an aspect ratio of 1:4 and lower the frequency to ~80kHz, which would allow me to upgrade the IGBTs if I ever wanted (300A bricks). However looking at Mad's website, the resulting reactance of 65kOhm seems rather high compared to the recommended 50k-ish, and of course requires more space. Do you think it would be preferrable to go into that direction instead?

Thanks a lot!
« Last Edit: February 23, 2024, 01:02:00 PM by markus »

Offline AstRii

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Re: Mid-sized DRSSTC build with freewheeling
« Reply #1 on: February 23, 2024, 09:58:10 AM »
That's a very nice and clean build, good job!

I will try my best to answer your questions (more experienced coilers feel free to correct me):
Quote
Is my planned MMC suitable? Is it perhaps a bit oversized for this coil?
Is there a rule of thumb as to how much of a safety margin I should factor in compared to the DC ratings?

Both of these questions come down to how reliable you want your system to be.
If you want to show your coil to your friends once in a while, you can stick with DC rating. However if you want your coil to run reliably many times per month, I would at least go with the AC rating of the caps and perhaps even factor in some 30% safety margin.
The same goes for the Irms rating. I would say 146Arms is quite a lot for your coil, but hey, the more the better. Also with UD+ driver I assume you want to run longer on-times resulting in higher RMS current.

Quote
Do I connect my MMC as parallel series strings, or as a set of parallel caps in series that results in a grid-like structure?

Parallel series strings is the most often used configuration that is proven to work, I'd stick with that.

Quote
Do I need bleeder / balancing resistors for my MMC and if yes, what values / rating / type? Or is the 10k resistor across the bridge output enough?

It is known that UD1.3b driver was causing issues during the startup of each pulse due to residual charge on the MMC. This behaviour can be seen here:

I'm not sure if this problem persists with UD+ driver. However if you're going to use bleeder resistor, I would strongly advice to use resistors across MMC.
In case the resistors fails short circuit, it will destroy your bridge. If it's across MMC, it will only short out the MMC, and the bridge (nor anything else) should not be damaged.

Quote
Are the TVS useful, or do they increase risk for blowing my bridge in the case they overload and fail short? I saw conflicting information while looking around. Is it better to put two in series for 880V?

This question has been discussed a few times here already, I would say most people on this forum would agree that placing TVS diodes on the bridge only increases the risk of blowing up the bridge as it already happened to me.
The thing is that the bridge is very low impedance source and if TVS start to conduct, there will be high current flowing. Combined with the 880V of voltage drop, this is a huge power loss which will blow them up. And as semiconductors often fail short-circuit, they will short your bridge and destroy it. It's fine to place TVS on the Gates, as there certainly won't be potential kiloAmperes of current flowing and the voltage drop is only 30V. The bridge is a different story.

Also let's face it, if you're having 880V+ peaks on your bridge, chances are your coil is not well tuned and clamping those spikes is not the correct solution.

Quote
Is it an issue that one GDT ended up with one turn less than the other? I guess I will just have to scope the gate waveforms to check if there is a difference.

Most likely not, with 21V Gate drive, it should not matter that much. But scoping everything and testing for possible transistor heating is a good idea before you run it at full power.

Quote
I am thinking of cutting my heat sink into two parts since it seems a bit oversized, and I would end up with another heatsink for a future project. Do you think it is better to leave it as is? In that case I would put some stuff like the drivers etc on the free part.
Seems like you could be fine with half of your heatsink (if you're going to active cool it). However this depends on the power levels you want your coil to reach.

Quote
There is also the option of winding my secondary on a 160mm pipe instead of a 120mm one (same 0.3mm wire, same length). This would give me an aspect ratio of 1:4 and lower the frequency to ~80kHz, which would allow me to upgrade the IGBTs if I ever wanted (300A bricks). However looking at Mad's website, the resulting reactance of 65kOhm seems rather high compared to the recommended 50k-ish, and of course requires more space. Do you think it would be preferrable to go into that direction instead?

I think this 50k impedance doesn't matter really. I've seen coils running very well at much more off than 65k. Just make sure your coupling stays in the acceptable boundaries and that the distance between primary and secondary is enough to shield against primary strikes.
 





« Last Edit: February 23, 2024, 10:11:52 AM by AstRii »
Bc. Marek Novotny
Czech Republic, Czech Technical University in Prague
www.uhvlab.org

Offline davekni

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Re: Mid-sized DRSSTC build with freewheeling
« Reply #2 on: February 24, 2024, 05:33:49 AM »
Quote
That's a very nice and clean build, good job!
Yes, looks great.

Quote
2x eupec BSM150GB120DL half bridge IGBT modules in full bridge configuration,
Long on-times of freewheeling designs can't survive quite as high peak current as for shorter on-times of typical DRSSTCs.  Also, unlike many bricks, diode thermal resistance is 2.5x higher than IGBT thermal resistance.  If using freewheeling extensively, diodes may limit current before IGBTs do.  I don't have any good info on how much current would be safe.  Hopefully you'll get other thoughts on this.

Quote
Are the TVS useful, or do they increase risk for blowing my bridge in the case they overload and fail short? I saw conflicting information while looking around. Is it better to put two in series for 880V?
Images suggest your TVS diode pairs are across Vbulk (high-side collector to low-side emitter).  If that is accurate, will not cause problems.  Not useful either as your bulk caps won't survive 880V.  Your bulk caps are plenty large enough to absorb energy from ring-down without over-voltage.

Quote
Is it an issue that one GDT ended up with one turn less than the other? I guess I will just have to scope the gate waveforms to check if there is a difference.
No issue.

Quote
Do I connect my MMC as parallel series strings, or as a set of parallel caps in series that results in a grid-like structure?
Quote
Parallel series strings is the most often used configuration that is proven to work, I'd stick with that.
Yes, more common, but either works.  My DRSSTC is half way between, grid within each section, but sections paralleled.  (I tune by changing MMC, so need to easily add or remove smaller sections.)

Quote
Do I need bleeder / balancing resistors for my MMC and if yes, what values / rating / type? Or is the 10k resistor across the bridge output enough?
Quote
It is known that UD1.3b driver was causing issues during the startup of each pulse due to residual charge on the MMC. This behaviour can be seen here:
I don't think that is an issue with newer drivers.  10kΩ 11W resistor across bridge output should help if it still is there to some degree.

Quote
However if you're going to use bleeder resistor, I would strongly advice to use resistors across MMC.  In case the resistors fails short circuit, it will destroy your bridge.
Power resistors rarely fail shorted.  AFAIK, carbon film resistors are the only type likely to fail towards low resistance.  Also, if resistors across MMC experience higher voltage, so must be higher value.  Useful for balancing MMC series strings, but not for discharging bridge output between enable pulses.

Quote
Do I need bleeder / balancing resistors for my MMC and if yes, what values / rating / type? Or is the 10k resistor across the bridge output enough?
My DRSSTC has ~470k resistors across each MMC capacitors, one for each parallel set of caps in grid configuration, just as a precaution.  Probably not necessary.  MMCs see AC, no intentional DC.  Only possible need I can dream up is if corona discharge from MMC internal connections has some DC component, such as one connection point emitting electrons into air better than it does positive ions.  I expect such an effect is too tiny to matter if it exists at all.

Quote
There is also the option of winding my secondary on a 160mm pipe instead of a 120mm one (same 0.3mm wire, same length). This would give me an aspect ratio of 1:4 and lower the frequency to ~80kHz, which would allow me to upgrade the IGBTs if I ever wanted (300A bricks). However looking at Mad's website, the resulting reactance of 65kOhm seems rather high compared to the recommended 50k-ish, and of course requires more space. Do you think it would be preferrable to go into that direction instead?
No personal experience here.  I have the impression from reading on this forum and a bit theoretical thinking that higher-impedance coils are better for freewheeling.

Have fun with your beautiful build!
David Knierim

Offline markus

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Re: Mid-sized DRSSTC build with freewheeling
« Reply #3 on: February 26, 2024, 11:11:14 AM »
Thanks for the feedback so far!
I guess I can just omit the TVS then. By the way reading davekni's reply made me wonder if the usual place for TVS is actually across the bridge output instead of where I put mine (across CE / the bus)?

Regarding the IGBT modules:
You are right about the diodes and smaller die size! At first I thought a 2x smaller die size should be fine, since in freewheeling mode one out of four diodes is used alternatingly, which would be half as often as the IGBTs in a full bridge inverter. But after thinking about this a bit more I realized that of course during freewheeling the IGBTs are used the same way as the diodes, which is why both actually see the same stress!
The BSM150 IGBTs are more for testing purposes, since I have a bunch of these. Once everything works fine I had planned to swap for my pair of eupec BSM200GB120DLC which have the same footprint. Unfortunately the diodes are proportioned mostly the same (2.25x smaller), same with my Mitsubishi CM200DU-24F.
But looking at similar bricks like the Powerex CM200DU-24F that have diode and IGBT dies of the same size, it seems like the diodes they have are not actually larger. Instead the IGBT dies are just smaller (0.15 °C/W instead of 0.08 °C/W)! Does this mean my bricks are actually not that bad after all (at least not worse than a Powerex CM200 for example)?

Meanwhile I finished building the enclosure for my UD+:

Offline AstRii

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Re: Mid-sized DRSSTC build with freewheeling
« Reply #4 on: February 26, 2024, 01:09:51 PM »
I guess I can just omit the TVS then. By the way reading davekni's reply made me wonder if the usual place for TVS is actually across the bridge output instead of where I put mine (across CE / the bus)?

TVS diodes are usually put across each individual transistor C-E.
Bc. Marek Novotny
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Offline davekni

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Re: Mid-sized DRSSTC build with freewheeling
« Reply #5 on: February 27, 2024, 03:48:05 AM »
Quote
Does this mean my bricks are actually not that bad after all (at least not worse than a Powerex CM200 for example)?
Also depends on diode Vf and IGBT Vce, switching losses, and max allowed temperature (sometimes 150C and sometimes 175C).  Vf and Vce and other losses matter at max temperature.  Transient thermal impedance is important too unless duty cycle is very high.
David Knierim

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Re: Mid-sized DRSSTC build with freewheeling
« Reply #5 on: February 27, 2024, 03:48:05 AM »

 


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post Re: IKY150N65EH7, is it good for DRSSTC
[Dual Resonant Solid State Tesla coils (DRSSTC)]
davekni
April 19, 2024, 03:09:29 AM
post Re: IKY150N65EH7, is it good for DRSSTC
[Dual Resonant Solid State Tesla coils (DRSSTC)]
unrealcrafter2
April 19, 2024, 01:47:37 AM
post Re: How to get a GE Yokogawa AB40 Sync Scope to rotate without a powerplant.
[Laboratories, Equipment and Tools]
Bobakman
April 19, 2024, 12:19:21 AM
post Re: How to get a GE Yokogawa AB40 Sync Scope to rotate without a powerplant.
[Laboratories, Equipment and Tools]
klugesmith
April 18, 2024, 11:33:01 PM
post Re: How to get a GE Yokogawa AB40 Sync Scope to rotate without a powerplant.
[Laboratories, Equipment and Tools]
Bobakman
April 18, 2024, 11:15:15 PM
post Re: Small-ish 3D printed SGTC via cheap ZVS flyback build, humbly asking a couple ?s
[Spark Gap Tesla Coils (SGTC)]
davekni
April 18, 2024, 10:59:36 PM
post Re: What actually kills MOSFETs?
[Beginners]
unrealcrafter2
April 18, 2024, 10:03:48 PM
post Re: How to get a GE Yokogawa AB40 Sync Scope to rotate without a powerplant.
[Laboratories, Equipment and Tools]
klugesmith
April 18, 2024, 09:53:25 PM
post Re: Welcome new members, come say hello and tell a little about yourself :)
[General Chat]
unrealcrafter2
April 18, 2024, 09:50:09 PM
post Re: Small-ish 3D printed SGTC via cheap ZVS flyback build, humbly asking a couple ?s
[Spark Gap Tesla Coils (SGTC)]
Michelle_
April 18, 2024, 09:15:55 PM
post Re: 100kHz CM300 gate resistor choice
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Mads Barnkob
April 18, 2024, 08:50:49 PM
post Re: 100kHz CM300 gate resistor choice
[Dual Resonant Solid State Tesla coils (DRSSTC)]
unrealcrafter2
April 18, 2024, 08:11:27 PM
post Re: Small-ish 3D printed SGTC via cheap ZVS flyback build, humbly asking a couple ?s
[Spark Gap Tesla Coils (SGTC)]
davekni
April 18, 2024, 07:28:05 PM
post Re: How to get a GE Yokogawa AB40 Sync Scope to rotate without a powerplant.
[Laboratories, Equipment and Tools]
Bobakman
April 18, 2024, 06:30:30 PM
post Re: Small-ish 3D printed SGTC via cheap ZVS flyback build, humbly asking a couple ?s
[Spark Gap Tesla Coils (SGTC)]
Michelle_
April 18, 2024, 06:03:57 PM
post Re: Small-ish 3D printed SGTC via cheap ZVS flyback build, humbly asking a couple ?s
[Spark Gap Tesla Coils (SGTC)]
Michelle_
April 18, 2024, 05:26:13 PM
post Re: Small-ish 3D printed SGTC via cheap ZVS flyback build, humbly asking a couple ?s
[Spark Gap Tesla Coils (SGTC)]
NyaaX_X
April 18, 2024, 04:03:38 PM
post Re: Small-ish 3D printed SGTC via cheap ZVS flyback build, humbly asking a couple ?s
[Spark Gap Tesla Coils (SGTC)]
Michelle_
April 18, 2024, 02:56:40 PM
post Re: DIY induction guns? (warning:long)
[Induction Launchers, Coil Guns and Rails guns]
Benbmw
April 18, 2024, 06:17:15 AM
post Re: Small-ish 3D printed SGTC via cheap ZVS flyback build, humbly asking a couple ?s
[Spark Gap Tesla Coils (SGTC)]
Michelle_
April 18, 2024, 05:46:07 AM
post Re: Small-ish 3D printed SGTC via cheap ZVS flyback build, humbly asking a couple ?s
[Spark Gap Tesla Coils (SGTC)]
MRMILSTAR
April 18, 2024, 05:18:31 AM
post Re: IKY150N65EH7, is it good for DRSSTC
[Dual Resonant Solid State Tesla coils (DRSSTC)]
davekni
April 18, 2024, 04:34:52 AM
post Re: How to get a GE Yokogawa AB40 Sync Scope to rotate without a powerplant.
[Laboratories, Equipment and Tools]
klugesmith
April 18, 2024, 04:11:53 AM
post Re: Small-ish 3D printed SGTC via cheap ZVS flyback build, humbly asking a couple ?s
[Spark Gap Tesla Coils (SGTC)]
Michelle_
April 18, 2024, 04:02:44 AM
post Re: 100kHz CM300 gate resistor choice
[Dual Resonant Solid State Tesla coils (DRSSTC)]
davekni
April 18, 2024, 03:35:52 AM
post Re: How to get a GE Yokogawa AB40 Sync Scope to rotate without a powerplant.
[Laboratories, Equipment and Tools]
MRMILSTAR
April 17, 2024, 11:54:05 PM
post 100kHz CM300 gate resistor choice
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Benjamin Lockhart
April 17, 2024, 11:37:16 PM
post Re: Has anyone tried to build a TMT (extra coil) Tesla coil?
[General Chat]
Michelle_
April 17, 2024, 02:29:30 AM
post Re: Has anyone tried to build a TMT (extra coil) Tesla coil?
[General Chat]
MRMILSTAR
April 16, 2024, 11:56:12 PM
post Re: How to get a GE Yokogawa AB40 Sync Scope to rotate without a powerplant.
[Laboratories, Equipment and Tools]
klugesmith
April 16, 2024, 11:46:57 PM
post Re: How to get a GE Yokogawa AB40 Sync Scope to rotate without a powerplant.
[Laboratories, Equipment and Tools]
Bobakman
April 16, 2024, 10:40:11 PM
post Has anyone tried to build a TMT (extra coil) Tesla coil?
[General Chat]
Michelle_
April 16, 2024, 09:21:39 PM
post Re: Medium Drsstc question
[Dual Resonant Solid State Tesla coils (DRSSTC)]
flyingperson23
April 16, 2024, 08:04:16 PM
post Re: First DRSSTC SKM100
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Benjamin Lockhart
April 16, 2024, 06:48:05 PM
post Re: Game changing tesla coil secondary winding suggestions
[General Chat]
Michelle_
April 16, 2024, 06:18:40 PM
post Re: Small-ish 3D printed SGTC via cheap ZVS flyback build, humbly asking a couple ?s
[Spark Gap Tesla Coils (SGTC)]
Michelle_
April 16, 2024, 06:14:53 PM
post Re: 3D printed mini-slayer: world's weakest tesla coil
[Solid State Tesla Coils (SSTC)]
unrealcrafter2
April 16, 2024, 05:44:44 PM

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