EMI reduction inductor?
dex, Wed Dec 03 2014, 11:35AMYou can see they use a small inductor between top of the DRSSTC and discharging tip:
How long/big should the inductor be to withstand voltage (not to flash over) when sparks hit targets?
Re: EMI reduction inductor?
Polonium210, Thu Dec 04 2014, 03:30AM
I doubt its really an inductor but rather a fancy looking breakout point for show.
Edit: my bad, after watching the video with the sound working I retract my previous statement
Polonium210, Thu Dec 04 2014, 03:30AM
I doubt its really an inductor but rather a fancy looking breakout point for show.
Edit: my bad, after watching the video with the sound working I retract my previous statement
Re: EMI reduction inductor?
Sigurthr, Thu Dec 04 2014, 05:38AM
A nonresonant inductor would simply limit power output. Sure it would affect high order harmonics more than the fundamental, but it would be a significant impedance. A resonant inductor and capacitor would simply be a series resonant LC filter, which would only increase the Q of your resonator further, not much of an EMI reduction, really.
I'd be quite surprised if it did anything at all other than waste power (in the wire resistance).
Sigurthr, Thu Dec 04 2014, 05:38AM
A nonresonant inductor would simply limit power output. Sure it would affect high order harmonics more than the fundamental, but it would be a significant impedance. A resonant inductor and capacitor would simply be a series resonant LC filter, which would only increase the Q of your resonator further, not much of an EMI reduction, really.
I'd be quite surprised if it did anything at all other than waste power (in the wire resistance).
Re: EMI reduction inductor?
Kizmo, Thu Dec 04 2014, 06:49AM
As they say on the video, it limits the rate of current discharging from topload when the streamer hits a grounded target. It is real and it does reduce the EMI problems caused by ground strikes.
Large tesla coil has plenty of topload capacitance and without the breakout inductor the ground strike current can have very high dI/dt and peak at several 100s of amps.
Kizmo, Thu Dec 04 2014, 06:49AM
As they say on the video, it limits the rate of current discharging from topload when the streamer hits a grounded target. It is real and it does reduce the EMI problems caused by ground strikes.
Large tesla coil has plenty of topload capacitance and without the breakout inductor the ground strike current can have very high dI/dt and peak at several 100s of amps.
Re: EMI reduction inductor?
Steve Conner, Thu Dec 04 2014, 10:56AM
It is an inductor and it it is effective in reducing EMI. I have no idea how to size it to avoid flashover. Probably similar to the size in the picture, but with fewer turns than a SSTC secondary would have.
Steve Conner, Thu Dec 04 2014, 10:56AM
It is an inductor and it it is effective in reducing EMI. I have no idea how to size it to avoid flashover. Probably similar to the size in the picture, but with fewer turns than a SSTC secondary would have.
Re: EMI reduction inductor?
dex, Thu Dec 04 2014, 08:23PM
Notice insualtor with big sheds on that inductor. How much does it improve *flashover strenght*?
dex, Thu Dec 04 2014, 08:23PM
Notice insualtor with big sheds on that inductor. How much does it improve *flashover strenght*?
Re: EMI reduction inductor?
Steve Ward, Sun Dec 07 2014, 09:06AM
Wow, such skepticism... I'll have you know i helped engineer that little inductor, and it does make a very notable difference in the intensity of ground arcs (with enough inductance, they look purple like free-air sparks) and a remarkable difference in the measured RF produced from ground arcs.
The resistance is not much, the inductor doesnt really warm up.
The ribs are needed to keep them from flashing over. We submerge the coils in oil or epoxy pot them to survive the HV peaks. You are basically expecting it to withstand a ~1/4 to 1/2 of the TC output voltage for a uS or so (depending on the L of the inductor and C of the topload). The inductance is only a small fraction of the secondary L, so the impedance at Fres is negligible. The whole idea is that it slows down what would be a few 10s of nS discharge time to be much longer (in the uS range, 100X slower), which means that the arc cannot radiate EMI as efficiently due to the wavelength being much longer than the arc.
The inductor in the video is a compromise between best EMI performance and reliability. We tried higher inductance, which helped EMI, but they'd flash over and fail too easily, or would otherwise be too big to be practical.
As people who use Tesla coils professionally, we do make an effort to reduce the EMI so that we can have successful gigs!
Steve Ward, Sun Dec 07 2014, 09:06AM
Wow, such skepticism... I'll have you know i helped engineer that little inductor, and it does make a very notable difference in the intensity of ground arcs (with enough inductance, they look purple like free-air sparks) and a remarkable difference in the measured RF produced from ground arcs.
The resistance is not much, the inductor doesnt really warm up.
The ribs are needed to keep them from flashing over. We submerge the coils in oil or epoxy pot them to survive the HV peaks. You are basically expecting it to withstand a ~1/4 to 1/2 of the TC output voltage for a uS or so (depending on the L of the inductor and C of the topload). The inductance is only a small fraction of the secondary L, so the impedance at Fres is negligible. The whole idea is that it slows down what would be a few 10s of nS discharge time to be much longer (in the uS range, 100X slower), which means that the arc cannot radiate EMI as efficiently due to the wavelength being much longer than the arc.
The inductor in the video is a compromise between best EMI performance and reliability. We tried higher inductance, which helped EMI, but they'd flash over and fail too easily, or would otherwise be too big to be practical.
As people who use Tesla coils professionally, we do make an effort to reduce the EMI so that we can have successful gigs!
Re: EMI reduction inductor?
dex, Sun Dec 07 2014, 11:08AM
dex, Sun Dec 07 2014, 11:08AM
Steve Ward wrote ...
The inductor in the video is a compromise between best EMI performance and reliability. We tried higher inductance, which helped EMI, but they'd flash over and fail too easily, or would otherwise be too big to be practical.
Time of exposure to HV spike is important for a piece of equipment. For instance, transformers can withstand 2-3x higher LI voltage peaks than power frequency (50/60 Hz) peaks. The higher inductance inductor will make discharge oscillations slower. Perhaps, it is stressed by higher voltage surges too?The inductor in the video is a compromise between best EMI performance and reliability. We tried higher inductance, which helped EMI, but they'd flash over and fail too easily, or would otherwise be too big to be practical.
Re: EMI reduction inductor?
Sigurthr, Mon Dec 08 2014, 02:16AM
My apologies for the above skepticism.
I based my comment on my experience with CW coils, where placing an inductor in the breakout path caused significant copper losses and the difference in EMI was negligible for free air streamers. I didn't test ground strikes, just the steady state emissions.
Looking back now, I should have watched the video in entirety to see the intent was ground strike emi reduction.
Sigurthr, Mon Dec 08 2014, 02:16AM
My apologies for the above skepticism.
I based my comment on my experience with CW coils, where placing an inductor in the breakout path caused significant copper losses and the difference in EMI was negligible for free air streamers. I didn't test ground strikes, just the steady state emissions.
Looking back now, I should have watched the video in entirety to see the intent was ground strike emi reduction.
Re: EMI reduction inductor?
Linas, Mon Dec 08 2014, 08:48AM
For me, it's a bit strange. Ok, it does have Xl, but voltage is extremely high, so if i want to limit current, to lets say 1Apeak (i know from CT measurements, my coil peaks at around 2.5A at low to mid power) ?
Xl=2*3.14*L*50k;
1=1MV/Xl=1M/6.28*50k*L
L = 3.18H, it is a bit high
Linas, Mon Dec 08 2014, 08:48AM
For me, it's a bit strange. Ok, it does have Xl, but voltage is extremely high, so if i want to limit current, to lets say 1Apeak (i know from CT measurements, my coil peaks at around 2.5A at low to mid power) ?
Xl=2*3.14*L*50k;
1=1MV/Xl=1M/6.28*50k*L
L = 3.18H, it is a bit high
Re: EMI reduction inductor?
Steve Conner, Mon Dec 08 2014, 10:13AM
Using the fundamental resonant frequency is wrong. You should use the resonant frequency of the ground arc channel with the toroid capacitance, which is something like 50MHz.
If you do this you will see that the peak current in a ground strike can be hundreds of amps and even a small inductance will limit it greatly.
Steve Conner, Mon Dec 08 2014, 10:13AM
Using the fundamental resonant frequency is wrong. You should use the resonant frequency of the ground arc channel with the toroid capacitance, which is something like 50MHz.
If you do this you will see that the peak current in a ground strike can be hundreds of amps and even a small inductance will limit it greatly.
Re: EMI reduction inductor?
dex, Mon Dec 08 2014, 11:39AM
dex, Mon Dec 08 2014, 11:39AM
Steve Ward wrote ...
You are basically expecting it to withstand a ~1/4 to 1/2 of the TC output voltage for a uS or so (depending on the L of the inductor and C of the topload).
How did you come up with these figures? I would expect even a small inductor to be stressed by at least 1/2 of the max TC output voltage when sparks attach to the ground...You are basically expecting it to withstand a ~1/4 to 1/2 of the TC output voltage for a uS or so (depending on the L of the inductor and C of the topload).
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