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First attempt at DRSSTC! Please help a newb...

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Andri

Tue Jun 02 2009, 04:06AM

Registered Member #1533 Joined: Wed Jun 11 2008, 02:13PM
Location: ReykjavÃk, Iceland
Posts: 46

MOTVolt wrote ...

Arrgh!, so I need to do more research! Ok so the CW coil is basically like driving a flyback... With the DRSSTC what exactly happens when the primary tank starts to resonate? I was under in impression that the current increased, what does the voltage do? I was thinking of having PWM driving the primary with current feeback to reduce the drive significantly, just enough maintain resonance... Instead of using an interupter, which has OCD anyway.

PWM will limit the peak current through your primary. An interrupter only limits the average current.
Thus, PWM is a bad idea for a TC if you want big sparks.

LithiumLord

Tue Jun 02 2009, 12:46PM

Registered Member #1739 Joined: Fri Oct 03 2008, 10:05AM
Location: Moscow, Russia
Posts: 261

The goal of DRSSTCs is driving significant (read: >100A) currents through the system without having any reflected power, which allows for high peak power and reduced stress on the switches due to the ZCS removing the high switching loss. A generic DRSSTC in order to both clamp the current and limit the input power (you are not running 100+A off-wall, right ;) ) uses strobed operation mode, with the strobe length limited by timing and OCD operation. There is, however, a way to make a DR coil running CW, but this will require a tough design in order to make the energy stored in the primary LC to be driven away into the secondary output fast enough by means of a lot of messing with the coupling and L-C balance.
There is an easyer way however - in a non-resonant drive topology, the primary gets some magnetizing current flowing in both directions, triangular in shape, and the additional sine component induced by the secondary ringing. As the triangular wave represents purely reactive load, it never draws any power off the power supply, and the only power consumed is stored in the secondary LC circuit oscillations alone. This allows for the system to run within the desired limits independent of the pump time as the secondary ringup is clamped by the breakout voltage, thus tweaking those systems only involves balancing the coupling and mag current in order to achieve the desired primary to secondary energy transfer, think of it as a CWDR topology with a fewer things to keep an eye on, this comes at a cost however as with the triangular current component flowing through the bridge you are no longer free of the switching loss.

The PWM is not a way to go. In single-resonance systems, it will do nothing but reducing the power, but it will not be as efficient as just increasing the primary tap number to reduce both the mag current and the step-up ratio. In DR systems, it's also a big step back, as the switches will be forced in quenching a high current, thus no ZCS any longer and the system will no longer have any advantage over a generic ISSTC speaking efficiency-wise, however will be less efficient as in ISSTC the switches only quench the magnetizing current, but here it will be forced to quench the current driving the actual power transfer which is much higher in a properly balanced system.

MOTVolt

Tue Jun 02 2009, 10:46PM

Registered Member #1996 Joined: Wed Feb 25 2009, 03:56AM
Location: Blackburn South, Melbourne, Australia
Posts: 10

Wow, Ok that covers the primary side of things, what I still don't understand is the secondary values. I have used the online calculators and they all give different answers which leads me to believe they are all wrong... Wouldn't the most energy be transferred if both primary and secondary are tuned to the same frequency? Or are the arcs bigger if everything is out of tune... How can there be all these high frequency, tall secondary's with huge toploads when it doesn't make sense according to:

syntroniks

Wed Jun 03 2009, 12:07AM

Registered Member #1530 Joined: Tue Jun 10 2008, 03:34PM
Location:
Posts: 32

I always thought the reason of adding the series cap (SSTC to DRSSTC) was to be able to, as LithiumLord stated, push large amounts of currents through the primary. When you drive at the resonant frequency of the primary, all of the power you put into the primary is stored (except for resistive losses).

Lower frequency is usually nice.

but for 5000 uH (I hope this is 500 mH)
100 mm diameter
900 mm height
700 turns gives ~~

I am not too sure how those numbers look in real life but it beats the voltage you might get out of 95 turns.

(I know 900 mm is very tall.)

HV Enthusiast

Wed Jun 03 2009, 12:12AM

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

MOTVolt wrote ...

Wow, Ok that covers the primary side of things, what I still don't understand is the secondary values. I have used the online calculators and they all give different answers which leads me to believe they are all wrong... Wouldn't the most energy be transferred if both primary and secondary are tuned to the same frequency? Or are the arcs bigger if everything is out of tune... How can there be all these high frequency, tall secondary's with huge toploads when it doesn't make sense according to:
1243982807 1996 FT70510 Tank

In a nutshell, yes, the primary is tuned to the secondary frequency. Tall secondaries and huge toploads usually give low frequency, not high frequency. Small secondaries and small toploads are high frequency.

LithiumLord

Wed Jun 03 2009, 12:24AM

Registered Member #1739 Joined: Fri Oct 03 2008, 10:05AM
Location: Moscow, Russia
Posts: 261

Hmm, and what exactly doesn't make a sence here? Apparently the pump current should be of the same frequency as the secondary resonator runs at, however what's wrong with the formula? As for the different calculators, they all use different algorithms, some primitive ones just calculate the secondary capacity as the one of a cylinder, the more advanced use the proper distributed network calculation and the best ones take the coupling, intercoil capacity and environmental conditions in account.

MOTVolt

Wed Jun 03 2009, 02:56AM

Registered Member #1996 Joined: Wed Feb 25 2009, 03:56AM
Location: Blackburn South, Melbourne, Australia
Posts: 10

So my best bet is to build a secondary based purely on asthetics, then tune the primary to it. I will start with an SSTC then move to DRSSTC! Thanks for all your advice, it's just hard to know where to start...

HV Enthusiast

Wed Jun 03 2009, 02:42PM

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

MOTVolt wrote ...

So my best bet is to build a secondary based purely on asthetics, then tune the primary to it. I will start with an SSTC then move to DRSSTC! Thanks for all your advice, it's just hard to know where to start...

No, no, no, no, no.

1. Determine your resonant frequency (target between 100-200kHz for example)
2. Find what available wire you have
3. Find what available coil form you have
4. Find what available toroid you have
5. Use Tesla calculator to design secondary to meet these requirements.

Its a very straightforward process.

Here is a paper I wrote showing how I do this:

http://www.easternvoltageresearch.com/designfiles/paper_howto.pdf

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