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Triggered SISG

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Finn Hammer

Tue Oct 31 2006, 09:41PM

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

All,

When I saw the SISG coil, I saw an IGBT stack with a safety gap across it. A basic building block that needed a trigger mechanism to really appeal to me. It should be triggerable even when using DC-Resonant charging, and it should be elegant.

I built a 2 section SISG because it would enable me to find out all the elemental things that I needed to know, and decided to start out with a transformer trigged SCR.
I selected the gate trigger toroid according to the TLAR criterium (That Looks About Right)

and so that the center would hold the insulation from RG214 antenna lead, because the toroids will be parked at elevated potentials.
The trigger wire is passed down the center of the toroids, and current from a 25ÂµF cap is dumped down that wire controlled by an IGBT and a couple of triple5`s.

At the present moment, the circuitry looks like this:

There are 4 250V sidacs in series, and the SCR bridges the bottom 3. Therefore I can trigger from 250Volts and up, and the top SIDAC will turn off the current in the string, in case the SCR should be unable to do so.
Suppose that I connect this gap to a resonant DC supply, which has from 250 to 499 volts on it. I can trigger it. After the ringdown the capacitor will be charged up to 998volts. The gap can hold it off untill I trigger it.
The way I wanted it.

It works great, although I am unable to get the fast charging times that you get, Terry:

Yellow is main cap
cyan is pri. current
magenta is gate
Anyway, the final scope check without breakout:

Before first light @ 988V off a single CD 150nF 942/2000 and about 3 inches

Nothing like a first light, particularly not when it is a real "first"

Cheers, Finn Hammer

Terry Fritz

Wed Nov 01 2006, 06:35PM

Registered Member #393 Joined: Tue Apr 18 2006, 12:30AM
Location:
Posts: 297

Hi Finn,

Cool Stuff!

You might only have to trigger just one section. Assume there are three sections at 1000V each for a total normal firing voltage of 3000V. If the voltage is at say 2500V, then just firing one section will fire the other two as well.

It depends on the charging circuit timing, but if the voltage is close to the firing voltage, just triggering one section will bring the whole array into conduction.

Cheers,

Terry

Finn Hammer

Wed Nov 01 2006, 09:36PM

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

Terry Fritz wrote ...

You might only have to trigger just one section. Assume there are three sections at 1000V each for a total normal firing voltage of 3000V. If the voltage is at say 2500V, then just firing one section will fire the other two as well.

I don`t agree. The DC resonant supply is the well known "Radar Supply" . with a charging choke and a de"Q`ing"diode in series with the transformer and rectifier.
I am sure you know it well
This supply is special because it initially charges the capacitor to the rectified voltage of the transformer(s).
Let`s say ~5000volts.
(3MOT`s in wye: sqrt2*sqrt3*2100V = 5143V
So the very first ringdown happens from ~5000 volts.
However, the 2nd. time, the cap is charged to ~10000volts
To get to the 2nd. charging cycle I have to be able to trigger at the initial voltage ~5000V.
But the Sidac`s have to hold of the the ~10000 volts as well because if not, then the breakrate will increase without controll.

For these reasons, I need to be able to trigger the gap at less than the initial voltage (half of the totalstandoff voltage of the gap. and the gap has to be able to stand off the full charging voltage from the second recharge and on.
The gap has to be triggered every time in order to be able to run from a DC resonant supply.

However, it would be neat to be able to start the coil up on a variac, and this would require that the top sidac is a low voltage type, the lowest there is would do fine.

I am using a sidac at the top, because it stops to conduct when the voltage across it is removed, unlike the SCR, which only stops conducting when the current through it drops to zero. I am not sure it would ever do that if not for the top sidac.

Terry Fritz wrote ...

It depends on the charging circuit timing, but if the voltage is close to the firing voltage, just triggering one section will bring the whole array into conduction.

Cheers,

Terry

I hope that the only charging circuit timing I will need to worry about is the size of the charging choke: it should be small enough to allow the primary capacitor to fully charge in the time between ringdowns at the highest breakrate, yet big enough to allow the IGBT`s to turn off safely at the level the current has risen to, during the ringdown, where the supply is shorted.

Cheers, Finn Hammer

Steve Conner

Wed Nov 01 2006, 11:01PM

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

Wow, neat work Finn!

Terry Fritz

Thu Nov 02 2006, 03:40AM

Registered Member #393 Joined: Tue Apr 18 2006, 12:30AM
Location:
Posts: 297

Hi Finn,

You and I are thinking of completly different charging systems. It's all cool

Charge on!!

Cheers,

Terry

Daniel Uhrenholt

Thu Nov 02 2006, 03:13PM

Registered Member #125 Joined: Fri Feb 10 2006, 01:52PM
Location: Aalborg, Denmark
Posts: 155

Yearh, i cant wait to see this thing in action!

Finn Hammer

Fri Nov 03 2006, 10:47PM

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

Terry Fritz wrote ...

Charge on!!

Charging the triggeed SISG

Tonight I got the fiber optic trigger transfer link adapted to the SISG`s SCR gate trigger driver, and also, added a bare secondary from a MOT as a charging choke, so that I could try the resonant charging system at various breakrates, 60 to 1200 BPS.

This first picture shows the voltage across the primary capacitor (yellow) during the first 3 ringdowns of a 1000BPS burst.
(Magenta is the gate voltage on the IGBT that fires the current pulse down the trigger transformers. Soft recovery to avoid spikes!

Cursor 1 refers to the initial voltage on the primary cap, which is 352V (200x differential probe)
After the ringdown, the voltage jumps up to 816 volts, as pointed out by cursor2. This is more than double, so I suppose that is "good".

Next picture shows one ringdown,

revealing that the quench happens after 400Âµs. This could probably be shortened down a bit and I just now realize that a look at the charging current here is needed. I`l take that tomorrow. It will probably bring clues to the high recharge level on the primary cap.

This trigger stuff removes the super repeatability of the original SISG coil, but boy is it cool to have a coil that changes breakrate at the twist of a knob.
This coil is such great fun, It feels just like getting back to playing with a.....a _real_ Tesla Coil again.

Cheers, Finn Hammer

Terry Fritz

Sat Nov 04 2006, 06:30AM

Registered Member #393 Joined: Tue Apr 18 2006, 12:30AM
Location:
Posts: 297

Hi fine Finn ram,

revealing that the quench happens after 400Âµs. This could probably be shortened down a bit

It looks like the SISG is stying in conduction way too long (cool scope BTW

)... Once the primary energy is gone - plus a little, you might as well turn it off so it can start recharging again. Of course, there are all kinds of timing issues now with this triggered stuff

This trigger stuff removes the super repeatability of the original SISG coil, but boy is it cool to have a coil that changes breakrate at the twist of a knob.

The SISG is sort of "chaotic" anyway... But now the firing voltage is varying too... COOL!!!

I just figure the coil "knows what it is doing"

The sparks seem to love it!!!

For the PIRANHA drive circuit, I am posting a big "WARNING" tonight...

"""
Now that others are interested in the PIRANHA SISG design, be VERY aware that the PIRANHA primary circuitry is VERY DANGEROUS!!! There is NO ballast or current limiting for the MOT which pretty much directly connects and drives everything on the primary!!! The 165nF caps hold 4 joules at 8000V and can recharge at 500BPS!!! It is an easy and simple design, but it packs a LOT of "serious killing power"!!! They are "very different" than any other coils...
""""

Cheers,

Terry

Finn Hammer

Sat Nov 04 2006, 09:53AM

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

Just changed the Gate drain resistor to 900 ohm, for a nice 184ÂµS quench, which takes place while the current out of the charging reactor has risen to 2 amps.

Well, this is low power testing with just one SISG section and low voltages.

I guess it`s time to wrap the stuff up on a soldered board and add some power.

Cheers, Finn Hammer

Finn Hammer

Thu Nov 09 2006, 09:57PM

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

I am building a board with 10 SISG sections, all triggered.
I forgot to buy 33 Volt TVZ`s to protect the gates of the IGBT`s.

Can I use BZV85 zeners back to back instead. They are 1.3W types, and allow a non repititive peak reverse curent of 1.2A @100ÂµS

I hope they will do, so that I can test the board during this week-end

Cheers, Finn Hammer

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