Question for Steve Ward re his mini SSTC
Gregary Boyles, Tue Feb 10 2015, 01:11AMhttp://www.stevehv.4hv.org/SSTC5/miniSSTCfnlsch.JPG
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?
Re: Question for Steve Ward re his mini SSTC
Sigurthr, Tue Feb 10 2015, 04:19AM
[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. I've built the circuit as shown, but found better performance by increasing the value as much as possible for the build on hand.
Sigurthr, Tue Feb 10 2015, 04:19AM
[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. I've built the circuit as shown, but found better performance by increasing the value as much as possible for the build on hand.
Re: Question for Steve Ward re his mini SSTC
Mads Barnkob, Tue Feb 10 2015, 06:53AM
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:
Mads Barnkob, Tue Feb 10 2015, 06:53AM
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:
Re: Question for Steve Ward re his mini SSTC
Sigurthr, Tue Feb 10 2015, 06:58AM
And I use a VCO to FM modulate the drive signal, relying on the bandwidth of the resonator to perform slope detection.
Sigurthr, Tue Feb 10 2015, 06:58AM
And I use a VCO to FM modulate the drive signal, relying on the bandwidth of the resonator to perform slope detection.
Re: Question for Steve Ward re his mini SSTC
Gregary Boyles, Tue Feb 10 2015, 10:34AM
Could you elaborate on that matey?
What size capacitors did you end up using?
And what happened when you increased their value further?
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!
Gregary Boyles, Tue Feb 10 2015, 10:34AM
Sigurthr wrote ...
[Not Steve, but answering anyway]
but found better performance by increasing the value as much as possible for the build on hand.
[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.
[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!
Re: Question for Steve Ward re his mini SSTC
Sigurthr, Wed Feb 11 2015, 01:31AM
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.
Sigurthr, Wed Feb 11 2015, 01:31AM
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.
Re: Question for Steve Ward re his mini SSTC
Gregary Boyles, Wed Feb 11 2015, 03:24PM
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.
Gregary Boyles, Wed Feb 11 2015, 03:24PM
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.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.
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.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.
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.
Re: Question for Steve Ward re his mini SSTC
Wolfram, Wed Feb 11 2015, 09:09PM
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.
Wolfram, Wed Feb 11 2015, 09:09PM
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.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.
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.
Re: Question for Steve Ward re his mini SSTC
Gregary Boyles, Thu Feb 12 2015, 12:32AM
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?
Gregary Boyles, Thu Feb 12 2015, 12:32AM
Wolfram wrote ...
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.
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.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.
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?
Re: Question for Steve Ward re his mini SSTC
Sigurthr, Thu Feb 12 2015, 12:44AM
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.
Sigurthr, Thu Feb 12 2015, 12:44AM
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.
Re: Question for Steve Ward re his mini SSTC
Kolas, Sat Feb 14 2015, 07:52PM
Erm, Iam no expert but I do know that driving above resonant frequency will cause the secondary to go into 90 degree phase difference with the primary. Which will entirely disagree with the feedback method used by most tesla coils. And phase leading by the secondary can cause failure in the mosfet/igbt stage amplification via over voltage. this is at least what i have read in the past, it is not my personal experience to my knowledge.
Kolas, Sat Feb 14 2015, 07:52PM
Erm, Iam no expert but I do know that driving above resonant frequency will cause the secondary to go into 90 degree phase difference with the primary. Which will entirely disagree with the feedback method used by most tesla coils. And phase leading by the secondary can cause failure in the mosfet/igbt stage amplification via over voltage. this is at least what i have read in the past, it is not my personal experience to my knowledge.
Re: Question for Steve Ward re his mini SSTC
Sigurthr, Sat Feb 14 2015, 11:14PM
I believe this only occurs in DRSSTCs where primary feedback is used. Using secondary base or antenna feedback, or running open loop doesn't have this problem.
Any FM modulation of the drive signal will have capacitive and inductive going excursions by the nature of FM. Setting the bias point so that the frequency lowering excursions stay above resonance prevents a capacitive impedance being reflected to the bridge, thus preventing high peak currents from flowing as a result of current leading.
Sigurthr, Sat Feb 14 2015, 11:14PM
Kolas wrote ...
Which will entirely disagree with the feedback method used by most tesla coils. And phase leading by the secondary can cause failure in the mosfet/igbt stage amplification via over voltage. this is at least what i have read in the past, it is not my personal experience to my knowledge.
Which will entirely disagree with the feedback method used by most tesla coils. And phase leading by the secondary can cause failure in the mosfet/igbt stage amplification via over voltage. this is at least what i have read in the past, it is not my personal experience to my knowledge.
I believe this only occurs in DRSSTCs where primary feedback is used. Using secondary base or antenna feedback, or running open loop doesn't have this problem.
Any FM modulation of the drive signal will have capacitive and inductive going excursions by the nature of FM. Setting the bias point so that the frequency lowering excursions stay above resonance prevents a capacitive impedance being reflected to the bridge, thus preventing high peak currents from flowing as a result of current leading.
Re: Question for Steve Ward re his mini SSTC
GrantX, Sun Feb 15 2015, 05:38AM
Welcome to the forum, always good to see another Aussie (greetings from the Yarra Valley).
I'm also in the middle of designing a small SSTC (albeit very slowly, not much time on my hands recently and I'm dividing it between a bunch of projects). I'm probably going to use a CT over the secondary's ground lead for feedback rather than an antenna. It looks neater and I have a bunch of Epcos N30 cores sitting around. Apart from that and the use of IGBT's, the bridge itself is very similar to Steve's Mini SSTC design. My secondary is around 465 kHz (50mm x 285mm coil with a 150mm x 40mm toroid) and I'm using 0.68 uF DC blocking caps, which gives an effective impedance of around 0.25 Ohms. With a 325 VDC bus this is negligible. The DC blocking caps are the flat terminal snubber types rated at 20A RMS and the IGBT's are FGH40N60SMD's (600V 80A, 137 nanosecond total switching delays), which is probably excessive for the power level I hope to achieve.
I haven't yet decided what feedback scheme to use, I've been looking at both the simple Schmitt trigger design as seen in the Mini SSTC, and a PLL design based on a 4046 IC.
Looking forward to seeing how your design progresses. Hopefully one day there will be enough of us for an Aussie Teslathon :)
GrantX, Sun Feb 15 2015, 05:38AM
Welcome to the forum, always good to see another Aussie (greetings from the Yarra Valley).
I'm also in the middle of designing a small SSTC (albeit very slowly, not much time on my hands recently and I'm dividing it between a bunch of projects). I'm probably going to use a CT over the secondary's ground lead for feedback rather than an antenna. It looks neater and I have a bunch of Epcos N30 cores sitting around. Apart from that and the use of IGBT's, the bridge itself is very similar to Steve's Mini SSTC design. My secondary is around 465 kHz (50mm x 285mm coil with a 150mm x 40mm toroid) and I'm using 0.68 uF DC blocking caps, which gives an effective impedance of around 0.25 Ohms. With a 325 VDC bus this is negligible. The DC blocking caps are the flat terminal snubber types rated at 20A RMS and the IGBT's are FGH40N60SMD's (600V 80A, 137 nanosecond total switching delays), which is probably excessive for the power level I hope to achieve.
I haven't yet decided what feedback scheme to use, I've been looking at both the simple Schmitt trigger design as seen in the Mini SSTC, and a PLL design based on a 4046 IC.
Looking forward to seeing how your design progresses. Hopefully one day there will be enough of us for an Aussie Teslathon :)
Re: Question for Steve Ward re his mini SSTC
Sigurthr, Sun Feb 15 2015, 05:56AM
GrantX, if you do decide to use the 4046 be sure to read up here on the forum about the problems related to the phase comparators (type 1 vs type 2) intrinsic to the 4046. Long story short it is a pain in the arse to get right unless you get lucky. I made four TCs with that ic, and only one ever ran right, even though there were no deviations in design other than secondary size and resultant frequency. I eventually moved on to other drive topologies.
That high of DC bus does indeed negate the impedance of the dc blocking caps, but do remember that a half bridge only sees half the bus voltage at its output. Running off 177V bus like we do here in the states, that quarter ohm is more important.
Sigurthr, Sun Feb 15 2015, 05:56AM
GrantX, if you do decide to use the 4046 be sure to read up here on the forum about the problems related to the phase comparators (type 1 vs type 2) intrinsic to the 4046. Long story short it is a pain in the arse to get right unless you get lucky. I made four TCs with that ic, and only one ever ran right, even though there were no deviations in design other than secondary size and resultant frequency. I eventually moved on to other drive topologies.
That high of DC bus does indeed negate the impedance of the dc blocking caps, but do remember that a half bridge only sees half the bus voltage at its output. Running off 177V bus like we do here in the states, that quarter ohm is more important.
Re: Question for Steve Ward re his mini SSTC
GrantX, Sun Feb 15 2015, 06:23AM
Thank you for the reply Sig, that helps a lot. I do understand that a half bridge will only give me +/- ~160 VDC across the primary, but I got lucky and scored a huge box of snubber capacitors. Since the snubbers are all screw terminal, I can increase or decrease capacitance without having to change any of the layout.
I was considering the 4046 scheme because I foolishly assumed it would be more reliable and stable than the Schmitt trigger, but I see now that people have had some serious difficulties with those IC's. Thanks for the warning, I'll start looking into some alternatives.
I don't want to clutter up Greg's thread, so I'll make a new thread soon to continue procrastinating about the feedback circuit ;)
GrantX, Sun Feb 15 2015, 06:23AM
Sigurthr wrote ...
GrantX, if you do decide to use the 4046 be sure to read up here on the forum about the problems related to the phase comparators (type 1 vs type 2) intrinsic to the 4046. Long story short it is a pain in the arse to get right unless you get lucky. I made four TCs with that ic, and only one ever ran right, even though there were no deviations in design other than secondary size and resultant frequency. I eventually moved on to other drive topologies.
That high of DC bus does indeed negate the impedance of the dc blocking caps, but do remember that a half bridge only sees half the bus voltage at its output. Running off 177V bus like we do here in the states, that quarter ohm is more important.
GrantX, if you do decide to use the 4046 be sure to read up here on the forum about the problems related to the phase comparators (type 1 vs type 2) intrinsic to the 4046. Long story short it is a pain in the arse to get right unless you get lucky. I made four TCs with that ic, and only one ever ran right, even though there were no deviations in design other than secondary size and resultant frequency. I eventually moved on to other drive topologies.
That high of DC bus does indeed negate the impedance of the dc blocking caps, but do remember that a half bridge only sees half the bus voltage at its output. Running off 177V bus like we do here in the states, that quarter ohm is more important.
Thank you for the reply Sig, that helps a lot. I do understand that a half bridge will only give me +/- ~160 VDC across the primary, but I got lucky and scored a huge box of snubber capacitors. Since the snubbers are all screw terminal, I can increase or decrease capacitance without having to change any of the layout.
I was considering the 4046 scheme because I foolishly assumed it would be more reliable and stable than the Schmitt trigger, but I see now that people have had some serious difficulties with those IC's. Thanks for the warning, I'll start looking into some alternatives.
I don't want to clutter up Greg's thread, so I'll make a new thread soon to continue procrastinating about the feedback circuit ;)
Re: Question for Steve Ward re his mini SSTC
Gregary Boyles, Sun Feb 15 2015, 06:42AM
I am a volunteer for the Science Talent Search run by the Science Teachers Association of Victoria. If I can get my SSTC working, plus a few other devices, I was going to see if they would let me demo them on their presentation day at Latrobe Uni.
I was also toying with the idea of displaying them as alternative Christmas lights one year.
Perhaps even a display at Epping Plaza or Westfield South Morang if they let me.
I am currently doing a kitchen renovation, as well as run my landscaping and mail order nursery business and maintain my business website. So my time is also some what divided.
Gregary Boyles, Sun Feb 15 2015, 06:42AM
GrantX wrote ...
Welcome to the forum, always good to see another Aussie (greetings from the Yarra Valley).
I'm also in the middle of designing a small SSTC (albeit very slowly, not much time on my hands recently and I'm dividing it between a bunch of projects). I'm probably going to use a CT over the secondary's ground lead for feedback rather than an antenna. It looks neater and I have a bunch of Epcos N30 cores sitting around. Apart from that and the use of IGBT's, the bridge itself is very similar to Steve's Mini SSTC design. My secondary is around 465 kHz (50mm x 285mm coil with a 150mm x 40mm toroid) and I'm using 0.68 uF DC blocking caps, which gives an effective impedance of around 0.25 Ohms. With a 325 VDC bus this is negligible. The DC blocking caps are the flat terminal snubber types rated at 20A RMS and the IGBT's are FGH40N60SMD's (600V 80A, 137 nanosecond total switching delays), which is probably excessive for the power level I hope to achieve.
I haven't yet decided what feedback scheme to use, I've been looking at both the simple Schmitt trigger design as seen in the Mini SSTC, and a PLL design based on a 4046 IC.
Looking forward to seeing how your design progresses. Hopefully one day there will be enough of us for an Aussie Teslathon :)
Gidday Grant. You don't live all that far way from me then.Welcome to the forum, always good to see another Aussie (greetings from the Yarra Valley).
I'm also in the middle of designing a small SSTC (albeit very slowly, not much time on my hands recently and I'm dividing it between a bunch of projects). I'm probably going to use a CT over the secondary's ground lead for feedback rather than an antenna. It looks neater and I have a bunch of Epcos N30 cores sitting around. Apart from that and the use of IGBT's, the bridge itself is very similar to Steve's Mini SSTC design. My secondary is around 465 kHz (50mm x 285mm coil with a 150mm x 40mm toroid) and I'm using 0.68 uF DC blocking caps, which gives an effective impedance of around 0.25 Ohms. With a 325 VDC bus this is negligible. The DC blocking caps are the flat terminal snubber types rated at 20A RMS and the IGBT's are FGH40N60SMD's (600V 80A, 137 nanosecond total switching delays), which is probably excessive for the power level I hope to achieve.
I haven't yet decided what feedback scheme to use, I've been looking at both the simple Schmitt trigger design as seen in the Mini SSTC, and a PLL design based on a 4046 IC.
Looking forward to seeing how your design progresses. Hopefully one day there will be enough of us for an Aussie Teslathon :)
I am a volunteer for the Science Talent Search run by the Science Teachers Association of Victoria. If I can get my SSTC working, plus a few other devices, I was going to see if they would let me demo them on their presentation day at Latrobe Uni.
I was also toying with the idea of displaying them as alternative Christmas lights one year.
Perhaps even a display at Epping Plaza or Westfield South Morang if they let me.
I am currently doing a kitchen renovation, as well as run my landscaping and mail order nursery business and maintain my business website. So my time is also some what divided.
Re: Question for Steve Ward re his mini SSTC
GrantX, Mon Feb 16 2015, 10:00AM
I'm often in Melbourne's northern suburbs since most of my friends live in that area, seems to be a nice place.
What's involved in volunteering for the Science Talent Search? Seems like it could be entertaining. Once I have a few projects finished to a high enough quality I'd love to take part in some kind of science/tech demonstrations.
GrantX, Mon Feb 16 2015, 10:00AM
Gregary Boyles wrote ...
Gidday Grant. You don't live all that far way from me then.
I am a volunteer for the Science Talent Search run by the Science Teachers Association of Victoria. If I can get my SSTC working, plus a few other devices, I was going to see if they would let me demo them on their presentation day at Latrobe Uni.
I was also toying with the idea of displaying them as alternative Christmas lights one year.
Perhaps even a display at Epping Plaza or Westfield South Morang if they let me.
I am currently doing a kitchen renovation, as well as run my landscaping and mail order nursery business and maintain my business website. So my time is also some what divided.
Gidday Grant. You don't live all that far way from me then.
I am a volunteer for the Science Talent Search run by the Science Teachers Association of Victoria. If I can get my SSTC working, plus a few other devices, I was going to see if they would let me demo them on their presentation day at Latrobe Uni.
I was also toying with the idea of displaying them as alternative Christmas lights one year.
Perhaps even a display at Epping Plaza or Westfield South Morang if they let me.
I am currently doing a kitchen renovation, as well as run my landscaping and mail order nursery business and maintain my business website. So my time is also some what divided.
I'm often in Melbourne's northern suburbs since most of my friends live in that area, seems to be a nice place.
What's involved in volunteering for the Science Talent Search? Seems like it could be entertaining. Once I have a few projects finished to a high enough quality I'd love to take part in some kind of science/tech demonstrations.
Re: Question for Steve Ward re his mini SSTC
Gregary Boyles, Mon Feb 16 2015, 01:54PM
I attend the STS meetings, do what I can to help with their judging day and presentation day - for models specifically. It is a lot of fund playing with the in models and inventions the kids come up with.
The first year one kid created a small high voltage coil gun - it was very well done. Last year another kid made a model of 3D laser scanner. I.E. He manually and randomly scans a 3D object with a small laser and then he used a standard USB webcam, and some software he wrote, to construct a 3D model on his laptop.
If you are interested in getting involved then check this out:
Call Janice in the office and let hew know you want to be involved.
Gregary Boyles, Mon Feb 16 2015, 01:54PM
GrantX wrote ...
I'm often in Melbourne's northern suburbs since most of my friends live in that area, seems to be a nice place.
What's involved in volunteering for the Science Talent Search? Seems like it could be entertaining. Once I have a few projects finished to a high enough quality I'd love to take part in some kind of science/tech demonstrations.
Gregary Boyles wrote ...
Gidday Grant. You don't live all that far way from me then.
I am a volunteer for the Science Talent Search run by the Science Teachers Association of Victoria. If I can get my SSTC working, plus a few other devices, I was going to see if they would let me demo them on their presentation day at Latrobe Uni.
I was also toying with the idea of displaying them as alternative Christmas lights one year.
Perhaps even a display at Epping Plaza or Westfield South Morang if they let me.
I am currently doing a kitchen renovation, as well as run my landscaping and mail order nursery business and maintain my business website. So my time is also some what divided.
Gidday Grant. You don't live all that far way from me then.
I am a volunteer for the Science Talent Search run by the Science Teachers Association of Victoria. If I can get my SSTC working, plus a few other devices, I was going to see if they would let me demo them on their presentation day at Latrobe Uni.
I was also toying with the idea of displaying them as alternative Christmas lights one year.
Perhaps even a display at Epping Plaza or Westfield South Morang if they let me.
I am currently doing a kitchen renovation, as well as run my landscaping and mail order nursery business and maintain my business website. So my time is also some what divided.
I'm often in Melbourne's northern suburbs since most of my friends live in that area, seems to be a nice place.
What's involved in volunteering for the Science Talent Search? Seems like it could be entertaining. Once I have a few projects finished to a high enough quality I'd love to take part in some kind of science/tech demonstrations.
I attend the STS meetings, do what I can to help with their judging day and presentation day - for models specifically. It is a lot of fund playing with the in models and inventions the kids come up with.
The first year one kid created a small high voltage coil gun - it was very well done. Last year another kid made a model of 3D laser scanner. I.E. He manually and randomly scans a 3D object with a small laser and then he used a standard USB webcam, and some software he wrote, to construct a 3D model on his laptop.
If you are interested in getting involved then check this out:
Call Janice in the office and let hew know you want to be involved.
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