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.
My question is regarding C7 and C8 in the FET part of the circuit.
Is the sum of the value of these two capacitors meant to form a resonant circuit with the primary coil, with a resonant frequency the same as (or roughly the same) as the oscillation frequency of the 555.
The reason that I ask is that I set this part of the circuit up in the java circuit simulator and observed that, unless the resonant frequency of C7, C8, L1 matches the frequency of the square wave input to the FET gates, then you get bugger all current going through L1. Which means poor power transfer from L1 to L2.
And how would you apply audio modulation to this circuit?
C7 and C8 are the half-bridge dc-blocking capacitors. They take the place of the other half of the bridge. Since the output is an AC square wave the current passes through the capacitors, but it is influenced by the impedance presented by the capacitors at the drive frequency. I've built the circuit as shown, but found better performance by increasing the value as much as possible for the build on hand.
Registered Member #1403
Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968
A SSTC does not rely on resonant energy transfer, it is only the secondary circuit that resonates. What we do is pump energy into the secondary circuit with help from the antenna feedback to hit it at the right frequency.
I used a simple AM modulation circuit that Sync once had on his site:
Registered Member #9039
Joined: Wed Dec 26 2012, 03:31PM
Location: Epping, Victoria, Australia
Posts: 117
Sigurthr wrote ...
[Not Steve, but answering anyway] but found better performance by increasing the value as much as possible for the build on hand.
Could you elaborate on that matey? What size capacitors did you end up using? And what happened when you increased their value further?
Sigurthr wrote ...
[Not Steve, but answering anyway] C7 and C8 are the half-bridge dc-blocking capacitors. They take the place of the other half of the bridge. Since the output is an AC square wave the current passes through the capacitors, but it is influenced by the impedance presented by the capacitors at the drive frequency.
OK so what I as observing in that Java circuit simulator was the fact that the two caps had very high impedance at the square wave frequency I was inputting to my FET gates.
As a result I was only getting uAs through the inductor that I was using as a simulated primary coil.
If I changed the square wave frequency or cap values I got more or less amps going through my simulated primary coil.
Can I also ask what sort of peak current you got through your primary when you run your setup.
I am just trying to work out fuse values and cable amp ratings etc so I don't melt down my power supply etc.
By the way, do you guys have any idea how bloody hard it is to find anyone in Australia who is interested in this sort of stuff.
I have read that you guys have Teslathons etc in the states.
There is nothing, zero, zilch in Aus.
It's is OK if you like sport - plenty of events and clubs to choose from. But it is a 'desert' down under if you like science. Paul Keating's 'banana republic'....here we come!
Increasing the capacitance of series capacitors lowers the impedance presented to an AC signal. Increasing the DC blocking capacitors sizes will allow higher currents through the bridge.
The primary inductance forms a low pass filter, blocking the harmonics of the drive signal, which is why primary current appears sinusoidal or triangular instead of square. So, if your sim isn't focused on the f0 and next harmonic it will report a very high impedance and low current flow.
In a SSTC (not DR) primary current is determined by the impedance presented by the primary inductance at the drive frequency. So, you can effectively dial in a desired primary current by adding or removing primary turns. Coupling factor plays a tremendous role in current draw as well, but given that SSTCs perform best with very high coupling and as far as build construction goes it is a "static" value, one focuses on the inductance of the primary as the means of setting current draw.
My 400W Hi-Fi Audio SSTC draws about 4.8Apk. My 3kW SSTC draws 17.3Apk.
Oh, there's a few aussie TCers, just not a ton. Fiddy is one (and a good friend of mine) that has quite an impressive TC collection. There's a lot of TCers here in the states but very few in the midwest and east coast. All of the Teslathons I've heard of are on the west cost. I live in the northern midwest and It would cost me over $1000 in air-faire alone to attend one, which would preclude me bringing any of my coils of course. To drive would take a little under a week and probably just as much money. So don't feel too left out, plenty of us here in the states unable to enjoy those festivals.
Registered Member #9039
Joined: Wed Dec 26 2012, 03:31PM
Location: Epping, Victoria, Australia
Posts: 117
Sigurthr wrote ...
Increasing the capacitance of series capacitors lowers the impedance presented to an AC signal. Increasing the DC blocking capacitors sizes will allow higher currents through the bridge.
So then frequency and capacitive impedance must be inversely proportional. I am going to make a capacitor sub-point in my setup so I can change those H bridge capacitors easily if I want.
Sigurthr wrote ...
The primary inductance forms a low pass filter, blocking the harmonics of the drive signal, which is why primary current appears sinusoidal or triangular instead of square. So, if your sim isn't focused on the f0 and next harmonic it will report a very high impedance and low current flow.
In a SSTC (not DR) primary current is determined by the impedance presented by the primary inductance at the drive frequency. So, you can effectively dial in a desired primary current by adding or removing primary turns. Coupling factor plays a tremendous role in current draw as well, but given that SSTCs perform best with very high coupling and as far as build construction goes it is a "static" value, one focuses on the inductance of the primary as the means of setting current draw.
Yeah of course, I sort of forgot about the inductive impedance thing. I should have realized because I am playing around with a microwave transformer to create a power source.
I angle grinded the weld joints and replaced the high voltage secondary with my own 84V secondary. After rectification it will give me about 120V DC.
I was wondering whether or not there would be enough impedance in the primary coil of my modified MOT to not blow a house fuse. But, as it turned out, my fears were misplaced.
The only problem is that, with block of 'I' pieces separated from the block of 'E' pieces, it makes one hell of a racket. I hope I can clamp it together tight enough to stop most of the noise.
A modified MOTwould be a hell of a lot easier to deal with than 10 x 12V car batteries.
I have completed my control circuit but yet to do my drive circuits. I am creating twin stereo TCs.
I have setup my control circuit so I can switch between an audio modulated square wave and a square wave from an extended duty cycle astable 555 with a cap sub-point so I can switch caps and change the frequency easily and a double gang pot so I can vary the duty cycle.
I have done the audio modulated square wave as follows:
Audio source => LM358 non-inverting amplifier with a gain of x11 + Triangle wave from an XR-2209 (timing cap and resistor sub-points so I can easily change the frequency as needed) => LM393 based comparator => audio modulated square wave.
I have also done the antenna part a bit differently. I made a Schmitt trigger inverter from an LM358 so I don't have to worry about the dual supply voltages (5V and 12V). I used a calculator I found to select component values that would match the trigger voltages specified in the datasheet for SN74HC14.
Registered Member #33
Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971
Gregary Boyles wrote ...
Sigurthr wrote ...
Increasing the capacitance of series capacitors lowers the impedance presented to an AC signal. Increasing the DC blocking capacitors sizes will allow higher currents through the bridge.
So then frequency and capacitive impedance must be inversely proportional. I am going to make a capacitor sub-point in my setup so I can change those H bridge capacitors easily if I want.
Correct, capacitive impedance (often called reactance) is inversely proportional to frequency. Zc = 1/(2*pi*F*C). The frequency here is the TC operating frequency. The capacitors are effectively in parallel as the TC primary sees them, so the capacitance to use in the formula is (C7 + C8). Even a single microfarad will be less than an ohm at 250 kHz, so they don't need to be huge in capacitance. It's important to make sure that they can handle the RMS current that you expect in the primary, each cap will take half of this current.
There's not really a need to change the caps out during regular use, if they are properly sized to begin with, they won't negatively affect performance. They only make a difference if they are too small, then they will negatively affect performance. I used 2x 1 µF in my SSTC when running at several kilowatts, and they never negatively affected the performance.
Your MOT based isolation transformer is a good idea. This should both make the setup safer, and limit the damage potential in case of faults by limiting the possible fault current. It can be hard to eliminate vibration after splitting the core, I prefer to saw off the old secondary while leaving the core intact. Welding the core edges would be ideal in your case, but a solid clamp should help as well.
The MOT will probably run hot, as they are designed for constant fan cooling and for the lowest possible cost. Adding a few extra turns to the core and putting them in series with the primary will greatly lower the idle power draw.
Your audio modulation method is interesting, I think some members here have tried it before. One thing that might be a challenge is that the coil can take some time (microseconds to milliseconds) to start up after you pull the enable line high. This might lead to some distortion if the PWM carrier frequency is too high.
Registered Member #9039
Joined: Wed Dec 26 2012, 03:31PM
Location: Epping, Victoria, Australia
Posts: 117
Wolfram wrote ...
Gregary Boyles wrote ...
Sigurthr wrote ...
Increasing the capacitance of series capacitors lowers the impedance presented to an AC signal. Increasing the DC blocking capacitors sizes will allow higher currents through the bridge.
So then frequency and capacitive impedance must be inversely proportional. I am going to make a capacitor sub-point in my setup so I can change those H bridge capacitors easily if I want.
Correct, capacitive impedance (often called reactance) is inversely proportional to frequency. Zc = 1/(2*pi*F*C). The frequency here is the TC operating frequency. The capacitors are effectively in parallel as the TC primary sees them, so the capacitance to use in the formula is (C7 + C8). Even a single microfarad will be less than an ohm at 250 kHz, so they don't need to be huge in capacitance. It's important to make sure that they can handle the RMS current that you expect in the primary, each cap will take half of this current.
There's not really a need to change the caps out during regular use, if they are properly sized to begin with, they won't negatively affect performance. They only make a difference if they are too small, then they will negatively affect performance. I used 2x 1 µF in my SSTC when running at several kilowatts, and they never negatively affected the performance.
Your MOT based isolation transformer is a good idea. This should both make the setup safer, and limit the damage potential in case of faults by limiting the possible fault current. It can be hard to eliminate vibration after splitting the core, I prefer to saw off the old secondary while leaving the core intact. Welding the core edges would be ideal in your case, but a solid clamp should help as well.
The MOT will probably run hot, as they are designed for constant fan cooling and for the lowest possible cost. Adding a few extra turns to the core and putting them in series with the primary will greatly lower the idle power draw.
Your audio modulation method is interesting, I think some members here have tried it before. One thing that might be a challenge is that the coil can take some time (microseconds to milliseconds) to start up after you pull the enable line high. This might lead to some distortion if the PWM carrier frequency is too high.
Good luck with the project.
Despite the antenna business, I was going to try and set the frequency of the triangle wave as close to the resonant frequency of the secondary plus top load as possible. I would presume that this will help.
I have purchased an XR-8038 from ebay hong kong (still waiting for it to arrive). This chip outputs square, triangle and sine waves but it also has a frequency modulation input. Not sure whether or not the FM affects the square wave output though but, if it does, I might give that a try if my current audio modulation scheme does not work that well.
Can you point me in the direction of schematics detailing how others in here have done audio modulation?
I'm terrible with worded descriptions of schematics, so I won't comment on your audio modulation scheme other than to say driving at or near resonance is always a good thing.
I will caution you to stay away from the capacitive region when using a half bridge, as they prefer inductive or resistive impedance on their outputs. This equates to driving at or above resonance, and never below. When using FM modulation take care that the delta-f stays where the lower frequency bound is at or above resonance.
I wrote a treatise on audio modulation a while back and invite you to read it:
It certainly isn't all encompassing, but it accurately reflects my experiences in the field.
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.
Question for Steve Ward re his mini SSTC
