Welcome
Username or Email:

Password:


Missing Code




[ ]
[ ]
Online
  • Guests: 28
  • Members: 0
  • Newest Member: omjtest
  • Most ever online: 396
    Guests: 396, Members: 0 on 12 Jan : 12:51
Members Birthdays:
One birthday today, congrats!
uzzors2k (35)


Next birthdays
03/29 GrantX (34)
03/30 Adam Horden (39)
03/30 Mr.Warwickshire (23)
Contact
If you need assistance, please send an email to forum at 4hv dot org. To ensure your email is not marked as spam, please include the phrase "4hv help" in the subject line. You can also find assistance via IRC, at irc.shadowworld.net, room #hvcomm.
Support 4hv.org!
Donate:
4hv.org is hosted on a dedicated server. Unfortunately, this server costs and we rely on the help of site members to keep 4hv.org running. Please consider donating. We will place your name on the thanks list and you'll be helping to keep 4hv.org alive and free for everyone. Members whose names appear in red bold have donated recently. Green bold denotes those who have recently donated to keep the server carbon neutral.


Special Thanks To:
  • Aaron Holmes
  • Aaron Wheeler
  • Adam Horden
  • Alan Scrimgeour
  • Andre
  • Andrew Haynes
  • Anonymous000
  • asabase
  • Austin Weil
  • barney
  • Barry
  • Bert Hickman
  • Bill Kukowski
  • Blitzorn
  • Brandon Paradelas
  • Bruce Bowling
  • BubeeMike
  • Byong Park
  • Cesiumsponge
  • Chris F.
  • Chris Hooper
  • Corey Worthington
  • Derek Woodroffe
  • Dalus
  • Dan Strother
  • Daniel Davis
  • Daniel Uhrenholt
  • datasheetarchive
  • Dave Billington
  • Dave Marshall
  • David F.
  • Dennis Rogers
  • drelectrix
  • Dr. John Gudenas
  • Dr. Spark
  • E.TexasTesla
  • eastvoltresearch
  • Eirik Taylor
  • Erik Dyakov
  • Erlend^SE
  • Finn Hammer
  • Firebug24k
  • GalliumMan
  • Gary Peterson
  • George Slade
  • GhostNull
  • Gordon Mcknight
  • Graham Armitage
  • Grant
  • GreySoul
  • Henry H
  • IamSmooth
  • In memory of Leo Powning
  • Jacob Cash
  • James Howells
  • James Pawson
  • Jeff Greenfield
  • Jeff Thomas
  • Jesse Frost
  • Jim Mitchell
  • jlr134
  • Joe Mastroianni
  • John Forcina
  • John Oberg
  • John Willcutt
  • Jon Newcomb
  • klugesmith
  • Leslie Wright
  • Lutz Hoffman
  • Mads Barnkob
  • Martin King
  • Mats Karlsson
  • Matt Gibson
  • Matthew Guidry
  • mbd
  • Michael D'Angelo
  • Mikkel
  • mileswaldron
  • mister_rf
  • Neil Foster
  • Nick de Smith
  • Nick Soroka
  • nicklenorp
  • Nik
  • Norman Stanley
  • Patrick Coleman
  • Paul Brodie
  • Paul Jordan
  • Paul Montgomery
  • Ped
  • Peter Krogen
  • Peter Terren
  • PhilGood
  • Richard Feldman
  • Robert Bush
  • Royce Bailey
  • Scott Fusare
  • Scott Newman
  • smiffy
  • Stella
  • Steven Busic
  • Steve Conner
  • Steve Jones
  • Steve Ward
  • Sulaiman
  • Thomas Coyle
  • Thomas A. Wallace
  • Thomas W
  • Timo
  • Torch
  • Ulf Jonsson
  • vasil
  • Vaxian
  • vladi mazzilli
  • wastehl
  • Weston
  • William Kim
  • William N.
  • William Stehl
  • Wesley Venis
The aforementioned have contributed financially to the continuing triumph of 4hv.org. They are deserving of my most heartfelt thanks.
Forums
4hv.org :: Forums :: Tesla Coils
« Previous topic | Next topic »   

DR tank impedance, lower vs. upper pole

1 2 
Move Thread LAN_403
Dr. Dark Current
Sun Nov 27 2011, 05:10PM Print
Dr. Dark Current Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Hello,
while experimenting with my non-interrupted DRSSTC running on the lower pole, I noticed that with increasing bridge voltage from zero, the tank current quickly rises but then it kind of "flattens out" and there is not much more increase of output current with higher bridge voltage - the tank impedance increases.
I guess this might have something to do with the spark loading decreasing the secondary resonant frequency and pulling the coil more in tune, decreasing primary Q.

Now my question is - what is the expected behavior on the upper pole?
Applying my spark loading theory, the tank current should be low until a certain voltage, at which the sparks become big enough to detune the secondary coil further away from the primary tank frequency, increasing its Q and current.
Does this sound about right or am I completely off?
Back to top
Steve Conner
Sun Nov 27 2011, 05:45PM
Steve Conner Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
As far as I know, the two poles behave the same with respect to resistive damping.

But detuning by streamer capacitance affects the two poles oppositely. It increases the tank impedance if you're running on the lower pole, and decreases it if you're running on the upper one.

Or maybe I've got that backwards smile The graphs recently posted by Uspring show the effect. Basically the effective transformation ratio changes according to the difference between the primary and secondary resonant frequencies, which is why you can "tune" a DRSSTC by adjusting the primary tap.

I'm not sure which one is better. You can argue that a system running on the lower pole is adjusting itself to better match the spark as it gets bigger, hotter and lower impedance.
Back to top
Dr. Dark Current
Sun Nov 27 2011, 06:08PM
Dr. Dark Current Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Steve, do you think the dynamic tank circuit impedance has an effect on the spark appearance? Assuming the same driving frequency, which pole should be better to get sparks as straight as possible (either by using the ramp up from mains waveform, or QCW modulated supply)?
Back to top
Steve Conner
Sun Nov 27 2011, 06:15PM
Steve Conner Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I don't know! smile And I wouldn't be surprised if my QCW approach, with the current control loop, preferred the opposite pole to Steve Ward's approach, controlling DC bus voltage.

However, the upper pole is still preferred because it lets you achieve a higher operating frequency, and hence straighter sparks, with whatever resonator you had handy. smile This is why Steve and Eric use it.

The upper pole also allows tighter coupling without flashovers, because it has a concave voltage profile: the voltage gradient is lowest at the bottom of the resonator and increases towards the topload. The lower pole has a convex one, making flashovers worse. I worked this out from theory, and Richie B. confirmed it by experiments with a voltage probe.
Back to top
Dr. Dark Current
Sun Nov 27 2011, 06:39PM
Dr. Dark Current Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Interesting smile It would seem that running the lower pole, you can wind the resonator with a thicker wire and push more power into it.
Back to top
Goodchild
Sun Nov 27 2011, 07:49PM
Goodchild Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
Theoretically the lower pole also has the most gain. I have also used the natural resonant freq on my QCW with similar performance to the upper pole.

I plan to wind a higher freq secondary though and try tuning to the lower pole and see how this effects performance. I have a feeling that the capacitive loading of QCW sparks could be a lot higher that a regular DR making lower pole tuning a lot more practical.
Back to top
Dr. Dark Current
Sun Nov 27 2011, 07:57PM
Dr. Dark Current Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Be sure to post the results wink
Back to top
Uspring
Mon Nov 28 2011, 12:22PM
Uspring Registered Member #3988 Joined: Thu Jul 07 2011, 03:25PM
Location:
Posts: 711
Steve McConner wrote:

But detuning by streamer capacitance affects the two poles oppositely. It increases the tank impedance if you're running on the lower pole, and decreases it if you're running on the upper one.

Or maybe I've got that backwards. The graphs recently posted by Uspring show the effect. Basically the effective transformation ratio changes according to the difference between the primary and secondary resonant frequencies, which is why you can "tune" a DRSSTC by adjusting the primary tap.

You got that right. I expect the primary current to rise as a consequence of detuning if running at the upper pole.

Steve also wrote:

The upper pole also allows tighter coupling without flashovers, because it has a concave voltage profile: the voltage gradient is lowest at the bottom of the resonator and increases towards the topload. The lower pole has a convex one, making flashovers worse. I worked this out from theory, and Richie B. confirmed it by experiments with a voltage probe.

You got me thinking on that one. This makes perfect sense to me. At the upper pole the magnetic fields of primary and secondary are in opposite phase so they cancel each other to a certain extent in the region where they overlap i.e. at the bottom of the secondary. Effectively that shortens the secondary coil, so that it has less inductance which makes its (coupled) frequency go up. That is the reason, why the upper pole is above the secondaries uncoupled frequency.

The phase difference between primary and secondary depends on the secondary loading, though. Under heavy loads it will go to 90 degrees, so that the cancellation is reduced.


Back to top
Steve Conner
Mon Nov 28 2011, 01:14PM
Steve Conner Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Yes, I agree. As you showed in that earlier post, I believe that under heavy loading, the coil ends up in the same operating point, no matter which pole it started from.

The question is, do our coils ever get to this "heavy loading" condition? Could we find out by measuring the primary/secondary phase shift on the fly with a DSO?

An observation that might be relevant: Years ago, when a DRSSTC was still called an "ISSTC", everyone used secondary base current feedback. I showed that it couldn't give reliable zero current switching, because the primary-secondary phase shift varied a lot as a function of spark loading, and I tried to persuade everyone to shift to primary current feedback.

So maybe this proves that we do have "heavy loading".
Back to top
Dr. Dark Current
Mon Nov 28 2011, 10:28PM
Dr. Dark Current Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Steve McConner wrote ...

Yes, I agree. As you showed in that earlier post, I believe that under heavy loading, the coil ends up in the same operating point, no matter which pole it started from.

But this is true only when the resonant frequencies of the two individual circuits are the same, right? When we tune for the upper or lower pole, we usually do this by actually detuning the primary tank to one or the other side, so the conclusions might not be true.
Back to top
1 2 

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob

Go to:

Powered by e107 Forum System
 
Legal Information
This site is powered by e107, which is released under the GNU GPL License. All work on this site, except where otherwise noted, is licensed under a Creative Commons Attribution-ShareAlike 2.5 License. By submitting any information to this site, you agree that anything submitted will be so licensed. Please read our Disclaimer and Policies page for information on your rights and responsibilities regarding this site.