DRSSTC current transformer....questions
Gregary Boyles, Tue May 02 2017, 03:39PMAfter a bit of research I have the general drift of how these work.
But what sort of ferrite core do they use? The same as GDTs?
And also this schematic is unclear to me:
What is 'RF ground'?
What is 'TS secondary base'
Is the current transformer sampling current through the Tesla coil primary tank circuit or is it sampling current through the tesla secondary coil (surely not)?
Re: DRSSTC current transformer....questions
woodchuck, Tue May 02 2017, 05:45PM
What's uncomfortable about wiring the primary of the current transformer between the bottom of the secondary and ground? The secondary has to be grounded anyway, unless you're making a bipolar Tesla coil.
woodchuck, Tue May 02 2017, 05:45PM
What's uncomfortable about wiring the primary of the current transformer between the bottom of the secondary and ground? The secondary has to be grounded anyway, unless you're making a bipolar Tesla coil.
Re: DRSSTC current transformer....questions
Dr. Slack, Wed May 03 2017, 04:29AM
Let's start with an idealisation. Imagine an infinite sheet of metal, stretching to the horizon in all directions. You set up your TC in the middle of it, and drop a wire from the secondary base to the metal. That's your RF ground.
The RF ground forms the 'other plate' of the capacitor through which the secondary current flows, the 'top plate' being your toroid, and any (conductive) streamers coming from it. I like to think of RF ground being any piece of grounded metal on which 'lines of electric displacement current' can flow to from the top terminal, and return by conductors to the secondary base.
In a less ideal case, you're sitting in a 10th floor apartment. You connect the secondary base to the mains earth at the wall socket. That earth will be bonded to the earth wires all over your flat, capacitively coupled to live and neutral wires buried in the walls, bonded to the wiring in the flat above, and ultimately bonded to that relatively conductive dirt plane stretching out in all directions to the horizon. The main contribution to RF ground will be the wires in the floor, the walls, the ceiling, through which the capacitive displacement current returns to the secondary base. That current is more or less shielded by those conductors from the big earth outside. Which is why if you're operating in that sort of difficult situation, you're advised to put a few 10s of nF earth to live and earth to neutral at the socket where you plug in your TC, to make sure all three wires are officially working as your RF ground.
The current transformer just samples the return current to the base of the TC from the capacitive coupling of the top.
Dr. Slack, Wed May 03 2017, 04:29AM
What's RF ground?
Let's start with an idealisation. Imagine an infinite sheet of metal, stretching to the horizon in all directions. You set up your TC in the middle of it, and drop a wire from the secondary base to the metal. That's your RF ground.
The RF ground forms the 'other plate' of the capacitor through which the secondary current flows, the 'top plate' being your toroid, and any (conductive) streamers coming from it. I like to think of RF ground being any piece of grounded metal on which 'lines of electric displacement current' can flow to from the top terminal, and return by conductors to the secondary base.
In a less ideal case, you're sitting in a 10th floor apartment. You connect the secondary base to the mains earth at the wall socket. That earth will be bonded to the earth wires all over your flat, capacitively coupled to live and neutral wires buried in the walls, bonded to the wiring in the flat above, and ultimately bonded to that relatively conductive dirt plane stretching out in all directions to the horizon. The main contribution to RF ground will be the wires in the floor, the walls, the ceiling, through which the capacitive displacement current returns to the secondary base. That current is more or less shielded by those conductors from the big earth outside. Which is why if you're operating in that sort of difficult situation, you're advised to put a few 10s of nF earth to live and earth to neutral at the socket where you plug in your TC, to make sure all three wires are officially working as your RF ground.
The current transformer just samples the return current to the base of the TC from the capacitive coupling of the top.
Re: DRSSTC current transformer....questions
Gregary Boyles, Wed May 03 2017, 04:17PM
Thanks for that - I have not seen those terms used before so I had no clear idea what they were about.
I take it then you would be better off driving a copper pipe into moist ground and using that as your earth rather than the wall socket earth?
What exactly is the effect on the Tesla coil of the capacitive coupling to the earth wire to the neutral and active wires in the wall cavities? Injecting voltage spikes into the mains supply for tvs etc?
Is a current transformer used in this way likely to result in improvement to the Mini Tesla coil in place of an antenna? Or not really?
Gregary Boyles, Wed May 03 2017, 04:17PM
Dr. Slack wrote ...
Let's start with an idealisation. Imagine an infinite sheet of metal, stretching to the horizon in all directions. You set up your TC in the middle of it, and drop a wire from the secondary base to the metal. That's your RF ground.
The RF ground forms the 'other plate' of the capacitor through which the secondary current flows, the 'top plate' being your toroid, and any (conductive) streamers coming from it. I like to think of RF ground being any piece of grounded metal on which 'lines of electric displacement current' can flow to from the top terminal, and return by conductors to the secondary base.
In a less ideal case, you're sitting in a 10th floor apartment. You connect the secondary base to the mains earth at the wall socket. That earth will be bonded to the earth wires all over your flat, capacitively coupled to live and neutral wires buried in the walls, bonded to the wiring in the flat above, and ultimately bonded to that relatively conductive dirt plane stretching out in all directions to the horizon. The main contribution to RF ground will be the wires in the floor, the walls, the ceiling, through which the capacitive displacement current returns to the secondary base. That current is more or less shielded by those conductors from the big earth outside. Which is why if you're operating in that sort of difficult situation, you're advised to put a few 10s of nF earth to live and earth to neutral at the socket where you plug in your TC, to make sure all three wires are officially working as your RF ground.
The current transformer just samples the return current to the base of the TC from the capacitive coupling of the top.
What's RF ground?
Let's start with an idealisation. Imagine an infinite sheet of metal, stretching to the horizon in all directions. You set up your TC in the middle of it, and drop a wire from the secondary base to the metal. That's your RF ground.
The RF ground forms the 'other plate' of the capacitor through which the secondary current flows, the 'top plate' being your toroid, and any (conductive) streamers coming from it. I like to think of RF ground being any piece of grounded metal on which 'lines of electric displacement current' can flow to from the top terminal, and return by conductors to the secondary base.
In a less ideal case, you're sitting in a 10th floor apartment. You connect the secondary base to the mains earth at the wall socket. That earth will be bonded to the earth wires all over your flat, capacitively coupled to live and neutral wires buried in the walls, bonded to the wiring in the flat above, and ultimately bonded to that relatively conductive dirt plane stretching out in all directions to the horizon. The main contribution to RF ground will be the wires in the floor, the walls, the ceiling, through which the capacitive displacement current returns to the secondary base. That current is more or less shielded by those conductors from the big earth outside. Which is why if you're operating in that sort of difficult situation, you're advised to put a few 10s of nF earth to live and earth to neutral at the socket where you plug in your TC, to make sure all three wires are officially working as your RF ground.
The current transformer just samples the return current to the base of the TC from the capacitive coupling of the top.
Thanks for that - I have not seen those terms used before so I had no clear idea what they were about.
I take it then you would be better off driving a copper pipe into moist ground and using that as your earth rather than the wall socket earth?
What exactly is the effect on the Tesla coil of the capacitive coupling to the earth wire to the neutral and active wires in the wall cavities? Injecting voltage spikes into the mains supply for tvs etc?
Is a current transformer used in this way likely to result in improvement to the Mini Tesla coil in place of an antenna? Or not really?
Re: DRSSTC current transformer....questions
Dr. Slack, Thu May 04 2017, 08:11AM
No, I think you've got hold of the wrong end of the stick. However in your defence, I don't think I demonstrated the stick too clearly.
The RF ground that the TC 'sees' is the conductor around it. There's no choice about this, RF current is flowing into the conductors most local to the TC. If you're in the middle of a field, then the nearest conductor is the earth. If you're in an apartment, then the nearest conductors are the wires in the walls, the plumbing, the HVAC ducting etc.
A circuit (and we all know that current only flows in a complete circuit, don't we) might start at the secondary bottom, through the secondary, topload, capacitance to the nearest conductorsl, some net of impedances which connect them back to what you're calling your RF ground, and the wire from that to the coil bottom, that last wire possibly interrupted by your current transformer.
The key to managing your RF ground, and any interference it causes to your and neighbouring properties, is that phrase 'some net of impedances'.
If you bang a spike in the earth out there somewhere, and run a wire back to your TC secondary bottom, then that 'net of impedances' has got to get RF current from all the wires in your walls, floor and ceiling, into the protective ground maybe at your meter inlet, and back though this long wire. That's a long path, which includes several high inductance long wires, capacitive coupling between live and earth conductors in distribution wiring and any appliances plugged in, and who knows what else.
If you want to minimise interference, you shorten the path current has to take. At the mains inlet to your TC, you connect live, neutral and ground at RF with some X2 filter capacitors, to keep the RF out of the differential between those conductors. Then you connect the TC power supply earth conductor to the secondary bottom. The existing protective earth conductor, grounded at your meter inlet, is just as effective, more so, than a wire to another metal spike in the ground.
If you're in the middle of a field, or a yard, then the RF current will flow from the topload capacitivly to the ground. Rather than taking the long route through the ground, the ground bonding at the meter inlet, the earth conductor tot he TC, in this case you should spike the ground, and connect that to the TC secondary bottom.
In summary, connect all the conductors *nearest to the topload* by as short a connection as reasonable to the secondary bottom, which we then call RF ground.
Dr. Slack, Thu May 04 2017, 08:11AM
No, I think you've got hold of the wrong end of the stick. However in your defence, I don't think I demonstrated the stick too clearly.
The RF ground that the TC 'sees' is the conductor around it. There's no choice about this, RF current is flowing into the conductors most local to the TC. If you're in the middle of a field, then the nearest conductor is the earth. If you're in an apartment, then the nearest conductors are the wires in the walls, the plumbing, the HVAC ducting etc.
A circuit (and we all know that current only flows in a complete circuit, don't we) might start at the secondary bottom, through the secondary, topload, capacitance to the nearest conductorsl, some net of impedances which connect them back to what you're calling your RF ground, and the wire from that to the coil bottom, that last wire possibly interrupted by your current transformer.
The key to managing your RF ground, and any interference it causes to your and neighbouring properties, is that phrase 'some net of impedances'.
If you bang a spike in the earth out there somewhere, and run a wire back to your TC secondary bottom, then that 'net of impedances' has got to get RF current from all the wires in your walls, floor and ceiling, into the protective ground maybe at your meter inlet, and back though this long wire. That's a long path, which includes several high inductance long wires, capacitive coupling between live and earth conductors in distribution wiring and any appliances plugged in, and who knows what else.
If you want to minimise interference, you shorten the path current has to take. At the mains inlet to your TC, you connect live, neutral and ground at RF with some X2 filter capacitors, to keep the RF out of the differential between those conductors. Then you connect the TC power supply earth conductor to the secondary bottom. The existing protective earth conductor, grounded at your meter inlet, is just as effective, more so, than a wire to another metal spike in the ground.
If you're in the middle of a field, or a yard, then the RF current will flow from the topload capacitivly to the ground. Rather than taking the long route through the ground, the ground bonding at the meter inlet, the earth conductor tot he TC, in this case you should spike the ground, and connect that to the TC secondary bottom.
In summary, connect all the conductors *nearest to the topload* by as short a connection as reasonable to the secondary bottom, which we then call RF ground.
Re: DRSSTC current transformer....questions
Gregary Boyles, Thu May 04 2017, 09:36AM
I noted how a transformer affords a high degree of protection against ground loops in your circuit.
But I guess that is not really going to work with a Tesla coil secondary and its open connection at the top load.
I am using 3 x modified MOTs that output 84VAC / 120VDC - the rectifier includes over 1000uF of capacitiance.
Are you talking about X2 caps from mains GND to active and mains GND to NEUTRAL?
If so what would be your suggested uF value?
If so I would assume it would be a low value otherwise it would amount to a short to mains GND?
What do folks generally use to power a 120VDC input Tesla coil if their mains voltage is 250VAC?
SMTP power supplies? Rectified AC transformers?
Oh! I just read something that jogged my memory - Arc Attack create a bit of a Faraday Cage type of thing around their coils and use that as there RF ground.
What if I was to do something similar around my Tesla coil....with some chicken wire or something..... and use that as my RF ground instead?
Surely that is going to be the shortest path possible?
Perhaps if I laid the mesh out on the floor then it might be some what more practical.
Gregary Boyles, Thu May 04 2017, 09:36AM
Dr. Slack wrote ...
No, I think you've got hold of the wrong end of the stick. However in your defence, I don't think I demonstrated the stick too clearly.
The RF ground that the TC 'sees' is the conductor around it. There's no choice about this, RF current is flowing into the conductors most local to the TC. If you're in the middle of a field, then the nearest conductor is the earth. If you're in an apartment, then the nearest conductors are the wires in the walls, the plumbing, the HVAC ducting etc.
A circuit (and we all know that current only flows in a complete circuit, don't we) might start at the secondary bottom, through the secondary, topload, capacitance to the nearest conductorsl, some net of impedances which connect them back to what you're calling your RF ground, and the wire from that to the coil bottom, that last wire possibly interrupted by your current transformer.
The key to managing your RF ground, and any interference it causes to your and neighbouring properties, is that phrase 'some net of impedances'.
If you bang a spike in the earth out there somewhere, and run a wire back to your TC secondary bottom, then that 'net of impedances' has got to get RF current from all the wires in your walls, floor and ceiling, into the protective ground maybe at your meter inlet, and back though this long wire. That's a long path, which includes several high inductance long wires, capacitive coupling between live and earth conductors in distribution wiring and any appliances plugged in, and who knows what else.
If you want to minimise interference, you shorten the path current has to take. At the mains inlet to your TC, you connect live, neutral and ground at RF with some X2 filter capacitors, to keep the RF out of the differential between those conductors. Then you connect the TC power supply earth conductor to the secondary bottom. The existing protective earth conductor, grounded at your meter inlet, is just as effective, more so, than a wire to another metal spike in the ground.
If you're in the middle of a field, or a yard, then the RF current will flow from the topload capacitivly to the ground. Rather than taking the long route through the ground, the ground bonding at the meter inlet, the earth conductor tot he TC, in this case you should spike the ground, and connect that to the TC secondary bottom.
In summary, connect all the conductors *nearest to the topload* by as short a connection as reasonable to the secondary bottom, which we then call RF ground.
I am sort of understanding what you are telling me because I was just reading about ground loops and isolation transformers last night.No, I think you've got hold of the wrong end of the stick. However in your defence, I don't think I demonstrated the stick too clearly.
The RF ground that the TC 'sees' is the conductor around it. There's no choice about this, RF current is flowing into the conductors most local to the TC. If you're in the middle of a field, then the nearest conductor is the earth. If you're in an apartment, then the nearest conductors are the wires in the walls, the plumbing, the HVAC ducting etc.
A circuit (and we all know that current only flows in a complete circuit, don't we) might start at the secondary bottom, through the secondary, topload, capacitance to the nearest conductorsl, some net of impedances which connect them back to what you're calling your RF ground, and the wire from that to the coil bottom, that last wire possibly interrupted by your current transformer.
The key to managing your RF ground, and any interference it causes to your and neighbouring properties, is that phrase 'some net of impedances'.
If you bang a spike in the earth out there somewhere, and run a wire back to your TC secondary bottom, then that 'net of impedances' has got to get RF current from all the wires in your walls, floor and ceiling, into the protective ground maybe at your meter inlet, and back though this long wire. That's a long path, which includes several high inductance long wires, capacitive coupling between live and earth conductors in distribution wiring and any appliances plugged in, and who knows what else.
If you want to minimise interference, you shorten the path current has to take. At the mains inlet to your TC, you connect live, neutral and ground at RF with some X2 filter capacitors, to keep the RF out of the differential between those conductors. Then you connect the TC power supply earth conductor to the secondary bottom. The existing protective earth conductor, grounded at your meter inlet, is just as effective, more so, than a wire to another metal spike in the ground.
If you're in the middle of a field, or a yard, then the RF current will flow from the topload capacitivly to the ground. Rather than taking the long route through the ground, the ground bonding at the meter inlet, the earth conductor tot he TC, in this case you should spike the ground, and connect that to the TC secondary bottom.
In summary, connect all the conductors *nearest to the topload* by as short a connection as reasonable to the secondary bottom, which we then call RF ground.
I noted how a transformer affords a high degree of protection against ground loops in your circuit.
But I guess that is not really going to work with a Tesla coil secondary and its open connection at the top load.
I am using 3 x modified MOTs that output 84VAC / 120VDC - the rectifier includes over 1000uF of capacitiance.
Are you talking about X2 caps from mains GND to active and mains GND to NEUTRAL?
If so what would be your suggested uF value?
If so I would assume it would be a low value otherwise it would amount to a short to mains GND?
What do folks generally use to power a 120VDC input Tesla coil if their mains voltage is 250VAC?
SMTP power supplies? Rectified AC transformers?
Oh! I just read something that jogged my memory - Arc Attack create a bit of a Faraday Cage type of thing around their coils and use that as there RF ground.
What if I was to do something similar around my Tesla coil....with some chicken wire or something..... and use that as my RF ground instead?
Surely that is going to be the shortest path possible?
Perhaps if I laid the mesh out on the floor then it might be some what more practical.
Re: DRSSTC current transformer....questions
Gregary Boyles, Thu May 04 2017, 04:05PM
Just been reading about these: http://jetpropulsion.co.uk/gw0fzy-amateur-radio/tri-band-hf-vertical
I am just now copper plating a steel rod to use as a portable RF GND.
And it would be too hard at all to cut a large circle of builder's plastic and stick some radial lengths of copper tape on to it....solder a copper wire between them at the center before I stick the last bits on to the plastic.
his would make a nice portable GND plate.
After some more reading I also note that you need good coupling between the tesla coil base and earth to get decent streamers.
I am not in an apartment by the way so I could connect my Tesla coil to an external earth with a short path.....although I am in a standard house block.
Gregary Boyles, Thu May 04 2017, 04:05PM
Just been reading about these: http://jetpropulsion.co.uk/gw0fzy-amateur-radio/tri-band-hf-vertical
I am just now copper plating a steel rod to use as a portable RF GND.
And it would be too hard at all to cut a large circle of builder's plastic and stick some radial lengths of copper tape on to it....solder a copper wire between them at the center before I stick the last bits on to the plastic.
his would make a nice portable GND plate.
After some more reading I also note that you need good coupling between the tesla coil base and earth to get decent streamers.
I am not in an apartment by the way so I could connect my Tesla coil to an external earth with a short path.....although I am in a standard house block.
Print this page