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Registered Member #1799
Joined: Thu Nov 06 2008, 02:20AM
Location:
Posts: 23
I don't like all of the rotary gap stuff because you have to use a synchronous motor that gets out of line with the frequency and you have to adjust the phase alignment and mess with this and that and turn a left hand threaded screw 5 times backwards so that Jupiter's moons aren't angry. I don't like the asynchronous stuff for an AC tesla coil because you get the ineffecient low voltage firings. The idea of a constant voltage switch seems very attractive to me, but it seems like static gaps don't work very well in application because of overheating, clogging, and build up of conductive ionized gasses.
I came up with this idea and threw something together in Inventor. Something would also be added for forced air, this is just a very basic representation of the idea. The copper plate is stationary (i'm thinking it could be replaced by ice water-cooled copper pipe) and the polycarbonate electrode discs are spinning.
Has anyone tried something like this before?
How far can you push NSTs? I'm deciding on what size tank capacitor to use with the resonant circuit formed by the leakage inductance and tank capacitor in mind. I have a 15kv 30mA Franceformer (14.8k secondary resistance, 1591.5H calculated inductance). When I'm messing with the capacitance value in Microsim what kind of voltage and current outputs will I be able to get on the "resonance curve" before it's dangerous to the transformer?
Registered Member #477
Joined: Tue Jun 20 2006, 11:51PM
Location: Seattle, WA
Posts: 546
Hi Nick, welcome aboard!
Interesting. I'm not sure I understand your idea completely, though. You are moving the electrodes to aid gap deionization alone? I would think a simple air blast gap (e.g., leaf blower gap) would do just as well for that, if not better; the motion seems superfluous to me, since the proximity of the electrodes is not varied. Perhaps you could expand on the benefits you expect?
"Low voltage firings" misinterprets the problem with asynchronous RSGs. I would characterize most of the problems as being poor construction practices, although the incidence of these and the inherent tendency of asynchronous gaps to misfire when not built or operated properly makes them a special problem for NST coils, since misfiring can lead to resonant overvoltages in the primary tank which will quickly destroy wimply NST secondaries.
Asyncronous RSGs need to be built with large rotors having many electrodes, and need to be run at high speed. This guarantees many viable electrode presentations per AC cycle, at which point setting the gap is reduced to much the same process one uses to set a static gap. The advantage of well-designed and operated async gap is that you can easily vary the coil power (to a point) by simply increasing the power availability, which naturally increases the gap break rate. The same advantage exists for actively quenched static gaps. However, with a NST, one is not usually able to capitalize on this advantage, which is another reason ARSGs and NSTs are not a great mix.
Syncronous RSGs are advantageous from an efficiency standpoint not because they fire reliably at higher voltages, but because you know the electrodes will be in the right place only when the voltage is at its peak, so you can set the electrodes very close together. This reduces the resistance of the gap (I*I*R losses), so your gap isn't wasting as much power in heat.
Registered Member #1799
Joined: Thu Nov 06 2008, 02:20AM
Location:
Posts: 23
J. Aaron Holmes wrote ...
Hi Nick, welcome aboard!
Interesting. I'm not sure I understand your idea completely, though. You are moving the electrodes to aid gap deionization alone? I would think a simple air blast gap (e.g., leaf blower gap) would do just as well for that, if not better; the motion seems superfluous to me, since the proximity of the electrodes is not varied. Perhaps you could expand on the benefits you expect?
"Low voltage firings" misinterprets the problem with asynchronous RSGs. I would characterize most of the problems as being poor construction practices, although the incidence of these and the inherent tendency of asynchronous gaps to misfire when not built or operated properly makes them a special problem for NST coils, since misfiring can lead to resonant overvoltages in the primary tank which will quickly destroy wimply NST secondaries.
Asyncronous RSGs need to be built with large rotors having many electrodes, and need to be run at high speed. This guarantees many viable electrode presentations per AC cycle, at which point setting the gap is reduced to much the same process one uses to set a static gap. The advantage of well-designed and operated async gap is that you can easily vary the coil power (to a point) by simply increasing the power availability, which naturally increases the gap break rate. The same advantage exists for actively quenched static gaps. However, with a NST, one is not usually able to capitalize on this advantage, which is another reason ARSGs and NSTs are not a great mix.
Syncronous RSGs are advantageous from an efficiency standpoint not because they fire reliably at higher voltages, but because you know the electrodes will be in the right place only when the voltage is at its peak, so you can set the electrodes very close together. This reduces the resistance of the gap (I*I*R losses), so your gap isn't wasting as much power in heat.
Hope that helps!
Cheers, Aaron, N7OE
I thought the electrode spacing had something to do with the improved efficiency. I couldn't find much quantified data about it though.
There would be forced air incorporated into this design, the drawings are very basic. The motion of the electrodes is to aid in the distributive heating of the spark gap. If the gap stays cool it can handle more power and hold a more consistent firing voltage. In function it's like an ARSG operating at an infinitely high speed.
Registered Member #477
Joined: Tue Jun 20 2006, 11:51PM
Location: Seattle, WA
Posts: 546
NickCesar wrote ...
I thought the electrode spacing had something to do with the improved efficiency. I couldn't find much quantified data about it though.
There would be forced air incorporated into this design, the drawings are very basic. The motion of the electrodes is to aid in the distributive heating of the spark gap. If the gap stays cool it can handle more power and hold a more consistent firing voltage. In function it's like an ARSG operating at an infinitely high speed.
Well-known coiler John Couture did some research on gap spacing a while back which he published in his Tesla Coil Design Manual (I think it was called that). The problem is that close spacing slows deionization. This can be aided with an air blast. Some people use an air-blast static gap, closely spaced, in series with their RSGs to help with quenching, too.
I think you'd be surprised at how effective eletrode cooling is in a simple air-blast gap consisting of copper or brass pipes pointed directly at each other. I have built a couple of such gaps, and they were immediately cool to the touch upon being powered off, even when operated up into the multi-kW range. In such a design, the heat is literally blasted away from the gap itself. I think you'll be hard-pressed to compete with that, but it's worth a shot. If you do give this a try, I think we'll all be very interested to see how it goes!
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Rotating "static" gap idea and some NST questions
