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why do MMC capasitors differ in SSTC and DRSSTC and the SGTC

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teravolt

Tue Mar 28 2006, 05:28AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

I understand that the drsstc is a compleatly resonant system but why shouldn't a mmc be resonant in a sstc? Where does MMC come from? In a drsstc the the tesla secondary capasitance and inductance generate large voltages at resonancs so why shouln't we do this with a sstc. It has been stated that in a sstc the mmc just cupples the power into the pimary. Does this meen that in a sstc transformation takes place from the turns ratio and the Q in the secondary and the fact that the secondary is a 1/4 wavelength antena. In a SGTC the pimary capasitance is siad to play a role in the primary tank circuit and resonance. I have also noticed that in a sgtc if you increase the number NST in parallel the amount of capacitance follows to get a bigger spark. Does this meen that the primary capacitor is only enegy storage in a sgtc or resonant part of the primary circuit or boath? Is there a mystery?

Part Scavenger

Tue Mar 28 2006, 05:57AM

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

q1. There is no MMC in a SSTC.

q2. Multi-Miniature (or Micro) Capacitor.

q3. Nope. In a DRSSTC, the primary generates large voltages at resonance, and just as important because it is resonating, it throughputs alot of current. We don't do that in SSTC's because that's not an SSTC by definition, if we did, it'd be a DRSSTC.

q4. There is no MMC in a SSTC.

q5. Both, if you're asking what I think you're asking. Yes, the capacitor is the only storage in the SGTC. Kind of. Read up on your resonance. What happens is you want to fill your capacitors and discharge them through the primary coil. And you want your primary circuit to resonate at the same frequency that the secondary circuit resonates. Both "systems" will resonate on their own frequency, but if they (frequencies) match, maximum current will flow and the "resonant rise" will begin to occur in the secondary.

When you increase the # of NSTs, you increase the input current to the coil. In turn, you have more power which will fill your cap bank faster. Therefore you can increase the size of the cap bank and pour more power into the coil. Adding more input power without increasing the capacitance is useless. The extra power is either never drawn into the primary circuit, wasted as heat, or other stuff. If you do get increased performance without upping the capacitance, it is because you were not using all of your cap bank to start with.

In a DRSSTC, the MMC doesn't really store anything (well, it does, but not like you think. Again read up on resonant circuits/tanks) It is mainly there to lower the impedance so that massive power can go through the primary circuit. (This would be the resonant effect of a series resonant circuit).

It is important to realize that while SSTCs, DRSSTCs,ISSTCs, and SGTCs are based on similar prinicples, they are completely different animals.

Here's the difference:
An SSTC is basically a transformer that is driven at it's resonant frequency.
A SGTC has a primary cap that drives the primary coil
A DRSSTC has a primary cap that serves to lower the impedance of the primary coil and allows great current flow
An ISSTC is a SSTC that is run with an interruptor but does not have a primary capacitor.
A VTTC is a SSTC that uses tubes instead of semi for switching applications.

DRSSTCs and ISSTCs are both SSTCs. But an SSTC is not necessarily a DRSSTC.

There *are* capacitors in the primary of an SSTC, but they supply power on demand and are not an MMC or tank capacitor.

I hope that clears some things up.

Colin 99

Wed Mar 29 2006, 02:42AM

Registered Member #192 Joined: Fri Feb 17 2006, 03:08AM
Location: Canada
Posts: 44

Just to add to the answers.

In a SSTC there is a small capacitor in series with the primary coil to block any DC that might be present. I have used an MMC (and bypass the small dc blocking cap) on my SSTC to partially resonate the primary coil at the secondary resonance frequency to increase primary current without blowing the breaker.

In a DRSSTC or an ISSTC the current is INTERRUPTED to the power MOSFETs or IGBTs at a rate of 20 to 300 pulses per second usually. If the MOSFETs or IGBTs were running all the time, you'd blow the breaker. They are a solid state version of the classic tesla coil (SGTC) in many ways. A classic tesla coil is interrupted usually at twice the line frequency, 100 or 120 Hz depending on where you live, by the spark gap.

I hope this is clear.

My avatar on the LHS is a picture of my SSTC running near primary resonance. The sparks are 2 1/2 feet into the air.

Part Scavenger

Wed Mar 29 2006, 04:07AM

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

In a SSTC there is a small capacitor in series with the primary coil to block any DC that might be present. I have used an MMC (and bypass the small dc blocking cap) on my SSTC to partially resonate the primary coil at the secondary resonance frequency to increase primary current without blowing the breaker.

Are you sure? I don't think I've ever seen that. I have seen it on the primary of the gate drives but not in series with the TC primary. Having a capacitor there would kill performance I would think, any current going into the primary inductor would have to pass through the blocker cap, and that would not be much. Am I wrong about this?

teravolt

Wed Mar 29 2006, 05:13AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

Thank you Part Scavenger and Colin 99. So in a SSTC the capasitor is for cupling, in a SGTC Cprim. is resnonant and energy storage, and in DRSSTC Cprim. is half of the primary tank. In a SGTC I know that to increase power you can incerase voltage or current or boath and if you increase current primary capasitance must increase and the tesla circuit must or should be retuned in order to get it into its sweet spot. With The DRSSTC the primary tank circuit is resonant with the secondary tank and with the feedback from the secondary and amplification from mosfets you get ocilation as a positive feedback circuit. This I should be efficient. It apears to me that in SGTC's and DRSSTC the primary circuit is a series tank circuit. In a SSTC I know that this can also work. In the SSTC that I built I made the primary resonant with the secondary and I got sparks longer than the seconary, about 1.5 feet. I designed the circuit so I can modulate the output in pulse width and I tune it in by changing the master ocilator. I will try to detune the primary when I get it working again and see if the Cprim. in a SSTC is for cupling only. Has any body tried this? In a series tank circuit at resonance L and C are high Z and voltage is high and current is low witch is determined by the Q or merit of the circuit. to some degree this also aplies the secondary with its toroid capasitance. What do you think. N.B.

Steve Ward

Wed Mar 29 2006, 05:20AM

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

Having a capacitor there would kill performance I would think, any current going into the primary inductor would have to pass through the blocker cap, and that would not be much. Am I wrong about this?

This is very common, and i prefer to use a DC blocking cap on all of my SSTCs. It can actually boost performance a bit as Colin 99 said since you can cancel out some Xl with the caps Xc, allowing for more current than would be allowed with Xl alone. You have to be careful not to get too close to resonance or the current will really take off... but unlike the DRSSTC, the SSTC doesnt have an interrupter or short pulse durations to keep this current under control.

Part Scavenger

Wed Mar 29 2006, 05:47PM

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

Doh!

I stand corrected. Sorry for any confrustication.

Avalanche

Wed Mar 29 2006, 07:03PM

Registered Member #103 Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845

I've never come across using a cap in series with the primary on an SSTC either, none of mine have it

I take it the cap is supposed to be smaller than resonance? Any ways to calculate it?

*gets excited about boosting the spark-age of the maplin special coil*

Marko

Wed Mar 29 2006, 07:25PM

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

DC blocking caps are usually taken very large, 1-2-3 uF, see Steve Ward's SSTC schematics.
You blew your bridge most probably because of overcurrent, try using twice primary turns for twice input vltage.

Check your gate voltages and signal shape, and maybe switch to some othher kind of feedback instead of antenna.

Colin 99

Thu Mar 30 2006, 03:15AM

Registered Member #192 Joined: Fri Feb 17 2006, 03:08AM
Location: Canada
Posts: 44

Yes, I'm cancelling out some of the primary XL with my MMCs Xc. I was lucky When I did this, I was able to use my MMC for my SGTC as the primary capacitor bank for my SSTC. The primary coil is wound over my SGTC secondary with some room to breath (no flash over). I plugged the numbers into Wintesla first and it came out close to resonance on the primary coil, so I tried it.

Using a 220 volt step up transformer on the halfwave recified input of the driver board and I can turn up the variac to about 90 volts ac input before I have to worry about the breaker tripping.

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