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DRSSTC tuning

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LAN_403

Part Scavenger

Thu Mar 30 2006, 05:06AM

Registered Member #79 Joined: Thu Feb 09 2006, 11:35AM
Location: Arkansas
Posts: 673

I've got my DRSSTC together now, and I was trying to get it going. I played around with it this afternoon, and I can't get it to work properly. At best the "arcs" are like 2mm. That is full power in. Primary current is like 10-20A peak maybe 30. Also, my OCD was triggering when it "power arced"

. I tried to turn the limit up, but then it stayed on all the time.

Thinking my OCD was messing up, I unplugged it and proceeded cautiously. It got just a little better.

Secondly, the toroid almost never gets anything. Any sparks I get are somewhere on the secondary. It's acting like an underpowered SG coil that might need tuning. I've tried all the spots on my primary with no luck. I thought it would be somewhere around T5, which seemed to give better results than the other taps.

Another note, nothing gets even close to hot that I can tell, and I'm pretty sure the bridge saw 300+V at maxV in.

What do I need to check? And what is you guys' normal procedure for breaking in a DRSSTC?

Steve Ward

Thu Mar 30 2006, 05:17AM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

Have you checked the phasing of your feedback CT? Sounds like it might be backwards.

Also, NEVER turn up the voltage higher and higher if it doesnt seem to work! You should verify proper operation at 10-15VAC input. This should be plenty to get it oscillating and proding small sparks of an inch maybe.

Bennem

Thu Mar 30 2006, 06:06AM

Registered Member #154 Joined: Sun Feb 12 2006, 04:28PM
Location: Westmidlands, UK
Posts: 260

Hi Part Scavenger,
I experienced the same symptoms when i first powererd up my DRSSTC,
i then reversed the phase of my feedback CT.
My coil starts operation with about 20volt AC input with appox 2 inch spark, initially i tuned the coils primary to give the highest spark output, then laters as some choose, to tune to the lowest pole for maximum spark.
I usually set the OCD to trigger at ground power arcs.

Part Scavenger

Thu Mar 30 2006, 01:53PM

Registered Member #79 Joined: Thu Feb 09 2006, 11:35AM
Location: Arkansas
Posts: 673

Thanks, I'll go try that right now.

------------------------------------------------ --
It works! It works!
/*dancing around with glee*

Cool. That phasing did the trick! My OCD has the wrong pot in it, and I can't find the right one , so it cuts out badly. I just unplugged it and watched it on the scope. It was striking the strike rail from the secondary something awful, so I raised the secondary about 1.5" At about 50V, I was getting about 1'! Because my OCD was disconected, it eventually died. One of the IGBTs croaked. Oh, well, as soon as I can find myself a new pot, and screw everything down nicely I'll be set and I'll post pics, data, video etc.

Thanks guys, you're awesome! I just can't believe it actually worked.

Steve Conner

Thu Mar 30 2006, 04:54PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Congratulations on getting it to work, looking forward to seeing some pics! Ward is right, if the thing doesn't seem to be behaving properly, don't turn the voltage up, in 99% of cases it just makes things worse.

Dr. Drone

Thu Mar 30 2006, 07:45PM

Registered Member #290 Joined: Mon Mar 06 2006, 08:24PM
Location:
Posts: 1673

Part Scavenger

Fri Mar 31 2006, 12:11AM

Registered Member #79 Joined: Thu Feb 09 2006, 11:35AM
Location: Arkansas
Posts: 673

Geez, now I know why you guys build these things! They are super cool!

You can control the shape and intensity of the streamer, ahh man. The light bulb plasma globe is pretty cool too, they stream outward from the filament and when they hit the glass, they form a snowflake pattern if you get the BPS right. I love this thing already.

I couple of questions, though.

First, I have noticed some ringing in the active region of my gate drive signal. I don't think this is doing my IGBT's any good. I did not happen to get a pic, but I know exactly what it looked like. I posted a GIF of what it's doing.

Secondly, I don't really know what to check for to see if my coil is in tune or if it's hammering my IGBTs. It really seems to like turn 2.5, but that seems a little low to me. Also, I don't know how to estimate what turn it should be on. The cad programs are giving me wierd values I think because they are geared for SG's.

I have a CT that views the current waveform, and I thought that current was supposed to increase during a ground strike, but it decreases.

Up to a certain point, it is a perfect "ringing triangle" and then after a certain power level, it gets messy and goes up and down during the cycle. Usually it looks squareish in the middle. I think this might be beat frequency due to mistuning? I thought at first it was the OCD cutting out the middle of the pulse, but that can't be because it takes out the whole pulse. See gif #1. The first drawing is the lower power, the second, the higher. I had trouble drawing the second one, it is more square in the middle where the current goes down, and the high points are kind of jagged. It gives the general idea though.

Overall, I am happy with my results, and it's alot louder than I first thought, but hey. Is there anything else I need to look for to keep from killing my transistors? BTW, they just quietly die, nothing spectacular, it just stops working. The second time it happened it started drawing power like crazy because both of them went out.

------------------------------------------------ ---------------------
mod edit- combined double post into a single post

GDT ringing

HV Enthusiast

Fri Mar 31 2006, 01:00AM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

wrote ...

First, I have noticed some ringing in the active region of my gate drive signal. I don't think this is doing my IGBT's any good. I did not happen to get a pic, but I know exactly what it looked like. I posted a GIF of what it's doing.

If this ringing is only present during operation (power applied to full-bridge), then it may not be real - you are just picking up noise on the probe. This is especially true if you use a standard oscilloscope probe with the leaded ground clip.

Part Scavenger

Fri Mar 31 2006, 01:30AM

Registered Member #79 Joined: Thu Feb 09 2006, 11:35AM
Location: Arkansas
Posts: 673

It's true that it only happens when it's running, and the only way I could get a connection was with a micro-clip, which is unshielded. Hopefully that's what it is.

HV Enthusiast

Fri Mar 31 2006, 02:23AM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

You really aren't going to be able to get a good measurement with the unit running. That ringing, i suspect as what you are seeing, is normal.

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