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1

Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC low power testing killing IGBTs

« on: December 03, 2023, 06:50:36 AM »

So far so good. Up past 24” arcs now.

I’ve noticed that the OCD trips (set for 400A) yet the scope doesn’t show current going above 320A. What gives? Would this be transients that are too fast for the scope, but somehow long enough for the OCD circuit? Or, is the EVR OCD design up to some shenanigans? Should I set the OCD per the scope shots or stick to EVR settings chart?

-Matt

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Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC low power testing killing IGBTs

« on: December 01, 2023, 02:03:32 PM »

Looking at previous scope shots, the undershoot looks to be close to or the same as these do, and slightly more than the overshoot. Maybe just a coincidence?

The gate resistance is 5.4ohm (measured). If diodes were shorted, I should see a short across the gate resistance, no? I guess they could be open…

Guess it’s clear to let it rip? I’ll see if I can push higher peak amps this time.

-Matt

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Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC low power testing killing IGBTs

« on: December 01, 2023, 05:07:24 AM »

Rewound the GDT for 10 turns on the secondary and 7 turns on the primary.

Look okay? It boosted the voltage up a few volts but also has a little more overshoot.

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Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC low power testing killing IGBTs

« on: November 30, 2023, 06:10:34 PM »

I’ll wind another GDT (less than 1:2:2 since I’m only needing another 5v or so) tonight to see what the waveforms look like. This would be much easier than reworking the EVR design.

My planned upgrade (ud2.7 with a cm300 half bridge) won’t have this problem. Just need a few more parts to make the swap.

-Matt

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Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC low power testing killing IGBTs

« on: November 30, 2023, 12:03:30 AM »

Managed to kill another IGBT. At least this time, I was pushing the coil near the max. No explosion, just sudden silence. I was near 400A, which seems low for these IGBTs. I’m thinking that this might be due to running 15v on the gates instead of something closer to 20v since the max pulsed rating is 300A.

Any reason not to modify the GDT to output 20v instead of 15v? I could wrap a 10 turn primary directly over the existing windings without much hassle…

-Matt

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Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC low power testing killing IGBTs

« on: November 27, 2023, 03:12:43 PM »

Thanks again, David. That’s two of EVRs products that needed outside help and modifications to make them work.

-Matt

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Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC low power testing killing IGBTs

« on: November 26, 2023, 08:04:56 PM »

Quote from: thedoc298 on November 26, 2023, 05:14:20 AM

Quote from: Mads Barnkob on November 18, 2023, 09:15:32 AM
Quote from: FonziDaytona on November 17, 2023, 11:40:01 PM
I see the on board MMC has bleeder resistors and my upgraded MMC doesn’t. Maybe startup IS the issue after all?

-Matt

This is what is tried to be fixed with a 10K resistor across the inverter output, to get rid of any residual charge that could confuse the logic at start of a pulse, not just start-up, but it would sound sputtering and unstable.

Did you take a look at all gate driver resistors, TVS and diodes from GDT to IGBTs? Many components can fail "half" at IGBT failures, like gate resistors going from 10R to 100R-10K and you get all these weird behaviours from differently damaged components in the drive chain.

Hello all, enjoying the chat, where (and I looked) would I find more info about the 10k resisitor and what problem it might fix. I know it's not necessary 10k.

It fixed issues where my coil wouldn’t oscillate at low power or act “weird” and then kill a IGBT. Lost a lot of them…

After adding a 7kohm resistor across the half bridge outputs, the coil starts up at very low input voltage to the bridge. No weirdness either.

Now back to tuning and seeing if I can push my IGBTs higher :-)

Here it is hitting around 21”

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Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC low power testing killing IGBTs

« on: November 24, 2023, 11:26:04 PM »

Got my new IGBTs in (the C2D1) version which can handle another 100A.

Added a 7k resistor across the bridge output, and now I’m able to get things going with barely any voltage in from the variac. Here is a screen shot of current and voltage across the bridge. I am testing at very low BPS and on time with just the primary in place.

Edit: Excuse the scaling. I swapped my Pearson 110 CT for a triad CT (easier to fit in there) and forgot to change scaling around.

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Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC low power testing killing IGBTs

« on: November 21, 2023, 02:02:52 PM »

While I keep waiting for my replacement IGBTs, I had another question about the voltage drop and calculation for half bridges…Should bus voltage (400v approximately from voltage doubler) be half (200v)? So the calculation for energy in capacitor vs MMC energy would be (BUS/2)^2 instead of BUS^2?

-Matt

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Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC low power testing killing IGBTs

« on: November 19, 2023, 05:32:49 AM »

I put the hv power supply leads directly on each set of TVS diodes and then reversed the leads.

-Matt

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Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC low power testing killing IGBTs

« on: November 19, 2023, 12:01:31 AM »

I hooked up my Bertan to the board and applied +500v (gradually) to each set of TVS diodes. Set one clamped at 435v and set two clamped at 425v. Guess they can be ruled out?

-Matt

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Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC low power testing killing IGBTs

« on: November 18, 2023, 06:24:23 PM »

Here’s a picture of the setup. It’s a pretty standard design…

As for TVS testing, I’ve tested for short circuit and none are shorted. To test open, I’d need to remove and connect to my hv power supply, right? Any other way to guess?

Zener diodes all test 0.6v, so guess they’re good. Gate resistors are 5.5ohms, so those should be good.

I’m itching to tweak something (easy that is) while I wait for replacement IGBTs :-) Should I remove some turns from the GDT? Or, should the bridge resistor negate any shenanigans from it having higher inductance?

Another thought that I had was voltage sag caused by smallish bus capacitors (1000uF each) and a much higher MMC (.165uF vs .075uF) than designed?

-Matt

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Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC low power testing killing IGBTs

« on: November 17, 2023, 11:40:01 PM »

I see the on board MMC has bleeder resistors and my upgraded MMC doesn’t. Maybe startup IS the issue after all?

-Matt

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Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC low power testing killing IGBTs

« on: November 17, 2023, 08:49:25 PM »

I think I read that this would go from the CE connection (half bridge) to either positive or negative rail depending on which IGBT comes on first, right? So if positive rail IGBT comes on first, then resistor goes to negative rail?

-Matt

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Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC low power testing killing IGBTs

« on: November 17, 2023, 02:22:29 PM »

I’ve noticed at times that startup requires a much longer on time than I usually run. I usually keep on time below 100uS, but have to start up near 250uS (from time to time) to get it to start. The first set of IGBTs were lost at low power and I could hear a thumping from my variac. OCD was set to 150A, so it wasn’t that.

Second set was lost very inexplicably since they had been going strong for many runs.

Last two sets lost at low power, too low to see any discharge. (Last set was with secondary removed).

Maybe startup is somehow killing them?

What size/type resistor should I use for start up?

-Matt

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Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC low power testing killing IGBTs

« on: November 17, 2023, 04:45:57 AM »

Current was measured with a Pearson 110. I do have the OCD set and it did trigger a few times during tuning, but failures all occurred well below the limit. After I had things tuned and hitting around 23-24”, no more OCD triggering.

I guess the next thing is going to be getting new IGBTs installed and managing some scope shots with power applied to the bridge?

If all else fails, I do have a UD2.7 driving a cm300dy-12nF for my fusor power supply. I’ll probably duplicate that setup and use for this coil.

EVRs stuff seems very finicky and expensive to own.

-Matt

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Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC low power testing killing IGBTs

« on: November 17, 2023, 01:29:51 AM »

Here is the VGE with ground clip on emitter.

Forgot to mention that I’m not using the onboard MMC. I upgraded to a larger one…Having said that, my first blown IGBT was with the on board MMC, so I’m leaning towards something else. I’m also using a different primary and secondary (much larger and robust than what was called for).

Any chance the upgraded MMC is the problem? It’s 0.165uF rated for 6400v.

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Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC low power testing killing IGBTs

« on: November 17, 2023, 01:22:03 AM »

My GDT is 1:1:1 and I see is supposed to have 10 turns. I actually have 15 since that’s how many fit. Could that be a problem? The capacitor is two 1uF in parallel, so 2uF total.

I swapped both driver ICs and same result with diff probe.

Previous measurements, I actually had ground clip tied to board ground. I can clip to emitter to see if that makes a difference. No power to bridge during any measurements.

-Matt

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Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC low power testing killing IGBTs

« on: November 17, 2023, 01:08:41 AM »

I decided to use my diff probe to see how VGE looks. Looks perfect to me?

20

Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC low power testing killing IGBTs

« on: November 17, 2023, 12:32:28 AM »

Here is the measurement from the GDT secondary (in purple). Yellow is VGE on the good IGBT.

Messages - FonziDaytona

Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC low power testing killing IGBTs

Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC low power testing killing IGBTs

Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC low power testing killing IGBTs

Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC low power testing killing IGBTs

Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC low power testing killing IGBTs

Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC low power testing killing IGBTs

Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC low power testing killing IGBTs

Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC low power testing killing IGBTs

Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC low power testing killing IGBTs

Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC low power testing killing IGBTs

Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC low power testing killing IGBTs

Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC low power testing killing IGBTs

Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC low power testing killing IGBTs

Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC low power testing killing IGBTs

Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC low power testing killing IGBTs

Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC low power testing killing IGBTs

Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC low power testing killing IGBTs

Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC low power testing killing IGBTs

Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC low power testing killing IGBTs

Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC low power testing killing IGBTs

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