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Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I don't think it would make a huge difference. Coupling is coupling. The flat primary is maybe slightly better, but I'm not sure if the improvement is worth the hassle of rebuilding it, compared to just raising the secondary.
The last coil I made had a 45 degree conical primary, which is kind of a compromise.
Also, NACOLIAKNSSTC (Nowadays Any Combination Of Letters Is A Kewl New SSTC)
Registered Member #1643
Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039
Sounds good, raising will def. be better than lowering. Right now the first turn on my primary matches the first turn on my secondary, roughly 1" off the ground. I have 8 turns to find my resonance, so, reality it climbs about 5 inches up my secondary. 24awg wire, so you can do the math to estimate how many turns.
When people refur to the tank cap in an DR do they mean the large input filter cap (as I have always thought) or do they mean the cap in seirise with the primary
They mean the cap in series with the primary as this forms the "tank" circuit. It does cause confusion for non native english speakers or people new to electronics from time to time. Filter caps are also called "energy storage" caps. What does a tank of fuel do? Store liquid energy, so don't feel bad about the confusion.
Aah now it all makes sense the reason I was confused is because most Sstc's also have a series cap on the primary but don't often have a large fillter cap so then I guess the difference between an Sstc and a Dr is just that in a Dr the tank circuit is tuned to the same frez as the primary
A SSTC doesn't need any capacitor in the primary circuit... you're "hard" driving the pulses going in to the primary at the frequency the secondary is resonant to, a kind of forced systemic resonance (the primary is never in resonance at all).
A DRSSTC is a SSTC where you add capacitance to the Primary so that it forms its own LC circuit which you set the resonance point to be the same (or close to, in reality) as the secondary's self-resonance frequency. The DR in DRSSTC means "dual (or double) Resonant" since there are now two resonant circuits; 1) the primary + tank cap, and 2) the Secondary.
In an ideal theoretical (not real world!) Tesla Coil you would choose components so that one resonant circuit feeds another, which then feeds another. With a simple SGTC this would be descibed as where the first circuit is the input transformer and the primary capacitor, the next would be the tank capacitor and the primary, and then it is coupled to the secondary, which is its own resonant circuit. Everything would be operating at the same frequency. This of course doesn't work in real life as resonant rise would destroy real world components. The DRSSTC is just a "chip off the block" so to speak in that it strives to achieve resonance in every viable subsystem of the device.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
The story goes that in the first radio transmitters, around the turn of the 20th century, the tuning capacitor consisted of a stack of metal plates immersed in a tank of oil. Hence the name tank capacitor, and tank circuit for the LC resonant circuit.
Later on, Tesla coil builders borrowed the term from radio hams.
Actually, All of my SSTC's (full bridges) feature a 1.36uF in series with the primary...
So do just about every Sstc h bridge circuit I have ever found including mine so I guess most of the Sstc's out there are actually DRSSTC's that gust need a tune up (it think they use it as current limiting)
I am far from an expert or pioneer who coined the terms but it seems to me that it is not the case that a SSTC cannot have a capacitor in the primary circuit, just that the primary circuit is by definition NOT RESONANT. As soon as the primary circuit enters resonance with the secondary it becomes a DRSSTC.
So it seems it would be more correct to say a SSTC doesn't need a primary circuit capacitor but a DRSSTC does and it must be selected for resonance.
Though if you're going to put a capacitor in the primary circuit why not go all the way and make it a DRSSTC? I suppose you would need to implement a controller/interupter since DRSSTCs cannot run CW mode, but they're not that hard to do, a simple PWM 555 into an enable pin is all it takes. It seems to me that a nonresonant tank capacitor is just going to hurt performance by creating parasitic oscillations at the primary LC's Fres, which depending on the feedback method used could get in to the drive circuitry and compete against the secondary's feedback.
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Medium size DRSSTC - Primary Flat or Helical
