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Uspring can a tesla be over coupled? should there be room for the tesla to vibrate on it's own as its being excited?
"Overcoupling" leads to racing arcs along your secondary annd/or flashovers between the primary and the secondary. I hesitate to believe, though, that this an effect of the coupling coefficient. I think it is due to the increased proximity of the primary to the secondary and the fact, that a secondary inserted farther into the primary puts the secondaries high voltsge parts closer to the primary.
From a theoretical point of view I don't see any disadvantages to an arbitrarily high coupling: The coil would just have to be tuned accordingly.
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
I actually do not use line conditioners, although i'm not saying they aren't necessary.
I simply remove all sensitive electronics from the AC line circuits i'm using for my coils, use proper grounding, and make sure any grounded strike rod is grounded directly to the base of the secondary. This ensures any circulating currents from the secondary through the arcs is returned right back to the source as opposed to having the arcs strike walls and ceilings and having circulating currents go who knows where through your house, etc...
Registered Member #7267
Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407
Just got back from lowes with all the necessities for a separate quality ground. two 8ft ground rods, ground clamps, 6 gauge solid ground wire. All strike targets including strike rail and mesh wire enclosure will be grounded to the base of the secondary and from there to the ground rods. Heatsinks, LV transformer, and that stuff will remain on the house ground line.
Also, I'll note that the base of my secondary, strike rail, and mesh metal enclosure, all meet on a scrap piece of copper clad that is mounted to the base structure (so it is close to the base of the secondary) and from there is where they will be wired to the ground line.
Registered Member #7267
Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407
I was able to get outside tonight and try a higher power test, and I'm still having this problem but now it is just happening at a higher power input. I'm really confused here. The last thing I have to monkey around with is the coupling, so I'm lead to believe that is the issue but I wont know for certain until I try again sometime this week.
Reasons why I don't think its tuning or grounding:
-I buried two 8' ground rods and wired them with 6 gauge solid ground wire 8' apart from each other, had a family friend who's an electrician come and check it out and he said it looked great and its exactly how they install it when their company build's houses. So I'm ruling out the grounding.
-Recall: the resonant frequency of my secondary + toroid is 77kHz measured with scope and signal generator. Doing a few calculations to estimate a tap point to detune for spark capacitance, I tried tapping the primary at 66 kHz to start. With this I had strike rail arcs to secondary again so I tried 73 kHz, then 75 kHz, still with problems.. So I retuned primary to exactly 77 kHz, and at higher power this is giving me an arc from the strike rail to the very top of the secondary, It looked more like racing sparks to me this time. remember the sparks are jumping off the ends of the strike rail, NOT the primary. Some people had suggested lowering the strike rail, which I did also. It is about an inch and a half above the primary. Is it odd that when tuned to 77 kHz I can get a 2' arc to a grounded object at low Vin with no racing sparks, but at high Vin I get racing sparks?
I'll recheck the resonant frequency of my secondary and toroid, but I've already done so twice and got 77.64000 kHz approx. the first time, 77.00000 kHz approx. the second time. coupling coefficient is about .18 which I thought was pretty sufficient, as the secondary windings start at about an 1-1.25" higher than lower most turn of the primary, like mentioned before.
For next testing, I'm tempted to take the strike rail off completely to see what happens, but I think that might be a bad idea. Other than the coupling, I'm stumped. Unless I'm just not tuning the primary low enough, for example Steve Ward's DRSSTC1 had a resonant frequency of about 75 kHz and he tuned his primary to 55kHz.
Registered Member #3964
Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332
if pri-sec is arcing, then it is coupling/ground/torroid problems,, but if it's strike rail to pri, then it is different scenario... also, k=0.18 is high coupling.. some DRSSTCs range from (k=0.12 ~ k=0.17) :mine is 0.12 only, but my coil can manage to produce common 3x the length of my sec, and 3.4x (for its peak),. it is true that you transfer energy from the pri to sec faster when higher K, but the drawback is you cannot maximize the Power input because of the unwanted sparks. not to mention, when you lowered your coupling, (pri-sec) it should also lowered the closeness of Strike rail & primary.
Registered Member #7267
Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407
zzz_julian_zzz wrote ...
if pri-sec is arcing, then it is coupling/ground/torroid problems,, but if it's strike rail to pri, then it is different scenario... also, k=0.18 is high coupling.. some DRSSTCs range from (k=0.12 ~ k=0.17) :mine is 0.12 only, but my coil can manage to produce common 3x the length of my sec, and 3.4x (for its peak),. it is true that you transfer energy from the pri to sec faster when higher K, but the drawback is you cannot maximize the Power input because of the unwanted sparks. not to mention, when you lowered your coupling, (pri-sec) it should also lowered the closeness of Strike rail & primary.
The problem is strike rail to secondary.. forget the primary.. why is your coupling so low? I will try lowering coupling when I test again this week. But also, obviously coupling factor decreases as you tune primary to higher frequency and increases as you tune lower. So should I be setting my coupling coefficient to the resonant point on my primary which is 77kHz? or to where I will detune to? For example, JavaTC tells be that when tuned to resonance, my coupling is about .171 If I increase the height of the secondary by 1" and tune to resonance, coupling is now .14, but if I leave it at the full inductance of the primary then it remains about .17ish So what inductance should I be basing the coupling factor on, the entire L or just L of the tap point?
Registered Member #3964
Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332
Why do you tune in exact or same resonance with the sec? other coilers(incl. me) tune their coils lower by approx ~20% than the known Fres. of the secondary. This is due to the detuning factor that output arcs gives to the system. In my opinion, tuning(inductance point) has nothing to do(or very little tuning effect) with coupling. For the same tapping point(inductance), closing/loosening the coupling of primary to the secondary coil will not change the tuning (inductance) of primary coil. you can design for a high coupling if you want, as long as you are not getting pri-sec arcing(this is good).. your strike rail and sec arcing can be solved by properly designed strike rail (mechanically)..
Registered Member #7267
Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407
zzz_julian_zzz wrote ...
Why do you tune in exact or same resonance with the sec? other coilers(incl. me) tune their coils lower by approx ~20% than the known Fres. of the secondary. This is due to the detuning factor that output arcs gives to the system. In my opinion, tuning(inductance point) has nothing to do(or very little tuning effect) with coupling. For the same tapping point(inductance), closing/loosening the coupling of primary to the secondary coil will not change the tuning (inductance) of primary coil. you can design for a high coupling if you want, as long as you are not getting pri-sec arcing(this is good).. your strike rail and sec arcing can be solved by properly designed strike rail (mechanically)..
I think you might be misunderstanding me or not reading what has already been said in this thread. I know about streamer loading, and detuning of the primary due to added capacitance from the sparks.
Physics Junkie wrote ...
Doing a few calculations to estimate a tap point to detune for spark capacitance, I tried tapping the primary at 66 kHz to start. With this I had strike rail arcs to secondary again so I tried 73 kHz, then 75 kHz, still with problems..
The strike rail is designed just fine:
"The degree of inductive coupling determines the rate at which the energy transfer occurs, the intensity of current, the tuning response, and among other things, the voltage gradients developed along the secondary coil and at the topload. If coupling is too tight, some points along the secondary will have a voltage gradient high enough to cause corona inception and ultimately spark breakout of the secondary winding. Typically, we observe this phenomenon as racing sparks traveling down the length of the secondary. When this occurs, the coupling is too tight and needs to be loosened up (position the coils further away from each other)." -JavaTC
Julian, the equation for coupling coefficient is K = M/sqrt(Lp-Ls) where M is mutual inductance, Lp is primary low frequency inductance, Ls is secondary low frequency inductance. As you change the primary tuning, both Lp and M change greatly. So can you explain why you think coupling and inductance do not effect each other? It's been my experience that coupling changes as tuning changes and its enough kHz to effect the system.
Uspring wrote ...
I don't see any disadvantages to an arbitrarily high coupling: The coil would just have to be tuned accordingly.
Exactly.
Anyways, I raised the secondary 7/8" and tried low power again and thus far I have no racing sparks. Will have to detune and try full power again.
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Strike rail arcs to secondary. -coupling & tuning-
