DRSSTC frustration / Tesla Coils / Forums

Forums

4hv.org :: Forums :: Tesla Coils

« Previous topic | Next topic »

DRSSTC frustration

first previous 2 3 4 5

Move Thread

LAN_403

Finn Hammer

Wed Oct 03 2007, 05:59AM

Registered Member #205 Joined: Sat Feb 18 2006, 11:59AM
Location: SkÃ¸rping, Denmark
Posts: 741

Steve Ward wrote ...

The tuning for the heterodyning of the primary current is the tuning i always go for.

Excuse my ignorance, but this heterodyning....
Is it a more precise (single word) description of what can also be described as a waveform with notches? 2 frequences beating?

Cheers, Finn Hammer

Bennem

Wed Oct 03 2007, 06:18AM

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

On my feedback type DRSSTC i have noticed two major tuning points.
1: In tune, which produces spark output lineaily as you increase buss voltage,
but you dont seem to get the longest sparks this way.
2: Add more primary inductance (i add another 0.5 - one turn)
I then notice that it takes more buss voltage to produce an output
spark, infact i hardly get much spark perfomance until i reach approx
70% on my variac, then 'whooosh' it snaps out with longer sparks.
The primary current rises quickly whilst under the 70% of variac,
after the 70% the current hardly rises at all
but you have to be carefull not to detune too much as to ring up
too much current that will blow your IGBT's......in my experiance with DRSSTC's

Steve Conner

Wed Oct 03 2007, 09:42AM

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

Hi Marko,

The relationship that Finn and I have observed between operating on the lower resonant mode, and flashovers, only holds true for the PLL driver. There is no evidence that it happens with the self-resonant driver.

The "heterodyning" effect would imply that you have primary and secondary tuned to exactly the same frequency. I think the self-resonant driver can actually generate an output with two frequency components under that condition, exciting both modes equally, whereas the PLL has to choose one or the other.

Marko

Wed Oct 03 2007, 02:05PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Guys, thanks a bunch. I have nothing more to do than try this out.

70% on my variac, then 'whooosh' it snaps out with longer sparks.
The primary current rises quickly whilst under the 70% of variac,
after the 70% the current hardly rises at all
but you have to be carefull not to detune too much as to ring up
too much current that will blow your IGBT's......in my experiance with DRSSTC's

Can this be just the dynamic tuning thing? If that's important for DRSSTC at all...

Marko

Tue Oct 09 2007, 02:27PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Well, this weekend I wasn't able to do much work.
After a day of pondering I still can't find what's wrong with the control board. I found a lot of dead components and replaced nearly all actives from the board (except UCC's and few diodes which test good).

Output is just dead 0. So I'm back on the beginning, and need to revert everything from the garage back into my room which is a terrible mess as of now. So cleaning first.

So the current state of things is, this DRSSTC is dead, and will be enormous pain to repair.

I know it will blow up again on full power so I can't use this bridge design.

New coil needs to be built in order to do any progress, and I don't have money for that.

I'l see if I can at least fix this to give it some 50 or 100V runs and try out higher surge impedance.

How much wasted effort was this

Tom540

Tue Oct 09 2007, 03:20PM

Banned on 3/17/2009.
Registered Member #487 Joined: Sun Jul 09 2006, 01:22AM
Location:
Posts: 617

That's a small tank cap, even for a smallish coil. What frequency/tank impedance were you running at that point?

Now how high is it feasible to go? If I used really high impedance I could pump lots of energy into the coil without actually exceeding IGBT SOA. Spark length/power input efficiency may be worse, but who cares about that as long as sparks are long.

The frequency was around 330KHz. I didn't really pay much attention to impedance but it's around 17 Ohms with a 27nF tank cap and ~8-10uH primary inductance. Tuned slightly lower. I had to do it this way anything over 33nF would blow the IGBT's. In fact 33nF wouldn't work either.

How much wasted effort was this

Not wasted at all. Once you get it working to your satisfaction you'll just want to tweek it more and more and eventually you'll destroy it again. It's all part of the design/learning process. By the way I think your bridge is most likely fixable. You could peel off copper and grounding from the board and maybe add a ton of the thick white RTV to prevent that arcing.

Marko

Tue Oct 09 2007, 09:49PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

I guess I'l have to remove the CT connections completely and somehow solder the cables to CT outputs in air. As it is the thing would be very hard to insulate with silicone, and I guess it's my best try for this bridge.

Yet still it may arc to another CT set and blow through wire insulation. Heck, it may blow my GDT too now.

I'm never safe with these things...

Sulaiman

Tue Oct 09 2007, 11:24PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

Marko,
to arc from the secondary base wire to the CT implies high voltage on your "earth" wire.
If you have a long earth wire or a poor earth this could happen.

I use my TC in the shed or garden with a nearby earth rod,
if you can't get a good earth try several meters of aluminium cooking foil layed on the concrete/ground/floor,
makes a good earth/counterpoise. (with your existing earth for 'safety')

Marko

Wed Oct 10 2007, 12:32PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Sulaiman, my secondary base ground is completely separate from the coil and mains ground, with specific reason to prevent these flashovers.

They happen specifically between positive pole of my bus cap and feedback CT input.

Interestingly they were small never blew anything even though I grounded the - of my low voltage section

Until now, when control board got completely fried.

first previous 2 3 4 5

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob