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Registered Member #7267
Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407
zzz_julian_zzz wrote ...
2nd Generation DRSSTC from Dan, I have the book, but uhh... the feedbacking circuit samples the signal from the Secondary isn't??? if this is the case, then detuning the Pri will not work properly for the system. It must be sampled from the primary.
As for the 2 circuits, EVR's utilize the soft cut of the interrupter signal when D-FF is on a negative edge, S.wards, utilizes a positively edge triggered.
using a full bridge of this IGBTs could give sparks up to 5ft (if system is properly configured) Thanks.
The 2nd generation is not a secondary feeback system, it is a primary feedback system lol trust me i would not make a mistake like that !! If we are talking about the same book (DRSSTC: Building the Modern Day Tesla Coil, Electrical and Mechanical Design) look on page 209, that is the schematic I am using.
mine is a mix between wards drsstc1 and mccauleys drsstc2
Your coil seems quite similar to Wards last version of his DRSSTC1 wrt to the primary and secondary tank parameters. You have a somewhat lower MMC capacitance, which should help lowering the pri current and also a lower coupling due to your measures against racing sparks. It is really puzzling that Ward could utilize the full voltage of his full bridge, which is twice the amount of your half bridge, and still didn't get excessive primary currents. Note that in his scope shots you can observe a flattening of the pri current to the end of the burst, while in your shots the rise of the current seems just to be limited by the length of the burst.
Registered Member #3964
Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332
ow heheh :) sorry i doubted :) hehe! if you go to "un doubled" mains, uhmm i think the performance would differ, haven't you noticed anything that is heating on your bridge when operating the coil?
Registered Member #3964
Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332
Uspring wrote ...
Physics Junkie wrote:
mine is a mix between wards drsstc1 and mccauleys drsstc2
Your coil seems quite similar to Wards last version of his DRSSTC1 wrt to the primary and secondary tank parameters. You have a somewhat lower MMC capacitance, which should help lowering the pri current and also a lower coupling due to your measures against racing sparks. It is really puzzling that Ward could utilize the full voltage of his full bridge, which is twice the amount of your half bridge, and still didn't get excessive primary currents. Note that in his scope shots you can observe a flattening of the pri current to the end of the burst, while in your shots the rise of the current seems just to be limited by the length of the burst.
Ward's Secret is tuning.. :) that's what came to my mind first..
Registered Member #154
Joined: Sun Feb 12 2006, 04:28PM
Location: Westmidlands, UK
Posts: 260
Hi there, So you are using Dan McCauleys H-bridge circuit which according to his Schematic, he uses a 0.1uf cap on the output of his bridge? try removing that cap and test again to see if it makes a difference. leave the caps that bypass from either or both + and - to ground as they help bypass primary strikes.
Registered Member #7267
Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407
Bennem wrote ...
Hi there, So you are using Dan McCauleys H-bridge circuit which according to his Schematic, he uses a 0.1uf cap on the output of his bridge? try removing that cap and test again to see if it makes a difference. leave the caps that bypass from either or both + and - to ground as they help bypass primary strikes.
Just my tuppence worth.
Mel.
That crossed my mind. I guess I will try that. But do you know of any reason why that would be causing an issue?
@Uspring. I etched EVR's half bridge boards and use two of them. I wonder if it has anything to do with the specs of the IGBTs. Back in those days everyone used the 40N60. I wonder how performance would change if I switched to a 600V 200A or similar, like the IXGN320N60A3 (staying with SOT-227 package). I might get away with the higher currents perhaps?
@julian. To be honest I dont check much for heating. But I have sufficient cooling so I dont worry much about it.
I've got a question for all of you. I was thinking about the possibility that my toroid has poor conductivity, which would cause current to ramp up high in the bridge. The toroid is all aluminum tape, just a single layer, and there is a lot of resistance between the pieces that overlap each other. Sound plausible? (Trying to think of many possible issues and eliminate them one by one). I dont know much about how an aluminum spun toroid would differ from a DIY toroid with aluminum tape where surface conductivity is poor until voltage is great enough, making it an insufficient capacitor
Registered Member #3964
Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332
mine is DIY too.. the important thing there is the conductivity(but as long you get contacts from any point of the torroid, then its good) Remove all sharp edges.
Registered Member #7267
Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407
zzz_julian_zzz wrote ...
mine is DIY too.. the important thing there is the conductivity(but as long you get contacts from any point of the torroid, then its good) Remove all sharp edges.
It is very smooth. It's actually pretty nice toroid. By contacts from any point on the toroid, do you mean continuity? Because basically thats a slight issue. The adhesive side of the aluminum tape does not have continuity through to the other side, therefor each piece of tape does not have good conductivity to the next piece of tape. I can measure anywhere from a few hundred Kohms to Meg Ohms of resistance between pieces.
I started fine tuning the primary by going every 1/8th turn instead of quarter turn. Tonight I got nice 41" arcs
Above: PW is about 40uS. a few 41" strikes to grounded target. OCD does not trip
Above: PW is about 75uS. more frequent 41" arcs to grounded target. OCD still does not trip until I increase PW to about 90-100uS as seen in the video
Notice the current is not as high as I have been experiencing in earlier tests. I also increased the OCD to 800A or about there. I really dont know exactly what the OCD is set to because it hardly tripped at all, just a few times here or there at right about 8V on the scope.
I think that the problems I am having could be a multiple of things, such as fine tuning the primary and coupling, finding the perfect tank capacitance, and possibly the toroid could be made a little better. But my thoughts on the toroid are: if I am getting 41" arcs, then its probably not a big deal. Maybe a layer of aluminum foil will make the conductivity superb.
But my thoughts on the toroid are: if I am getting 41" arcs, then its probably not a big deal. Maybe a layer of aluminum foil will make the conductivity superb.
Although currents in the toroid easily reach a few amps, the corresponding voltage drop has to be seen in relation to the voltage up there. So a bit of resistance doesn't matter.
So basically, lower K=higher Ipri and higher K=lower Ipri? I have somewhat noticed this in my data, but only a slight increase. It is much more clear at high power levels. I have raised my secondary even more to k=.136 and I'm noticing that current is higher already.
I've been looking at this from the perspective of the equation describing the input impedance. It is the product of 2 terms: a) k^2. It increases with coupling b) A term describing the dependence on the frequency the coil runs at. It gets largest, when the operating frequency is closest to the secondary resonance. The operating frequency depends on your primary taps _and_ the coupling. A large coupling will shift the operating frequency away form the secondary resonance, so this term will become smaller, when coupling is increased.
Put together you have the product of 2 terms, one getting bigger with coupling, the other one smaller. The net effect is, that they can mostly cancel each other. For large arc loads on the secondary the frequency shift due to coupling as described in b) will vanish. so you'll get a strong effect of coupling on the input impedance. What you see is much as expected, i.e. little effect of coupling with light loads and stronger ones with heavy loads.
Registered Member #7267
Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407
Uspring wrote ...
Put together you have the product of 2 terms, one getting bigger with coupling, the other one smaller. The net effect is, that they can mostly cancel each other. For large arc loads on the secondary the frequency shift due to coupling as described in b) will vanish. so you'll get a strong effect of coupling on the input impedance. What you see is much as expected, i.e. little effect of coupling with light loads and stronger ones with heavy loads.
That is very interesting. Makes sense the way you so eloquently describe it As I detune the primary resonant frequency with low K of ≤.15, the current increases as a result of the "stronger effect with heavy loads". But as the primary resonant frequency gets closer to that of the natural frequency of the secondary, it decreases because the arc load is much weaker/does not have as strong of an effect. On the flipside, then if I raise the coupling again, current increases slightly at the 'weaker arc load'.
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Strike rail arcs to secondary. -coupling & tuning-
!! If we are talking about the same book (
