Topload, effects on efficiency
Linas, Thu Jul 24 2014, 08:58PMHello, since i am redesigning my top-load, one thing does not make sense. Basically, toroid is short turn on top of coil, so it will degrade performance of last secondary windings.
Does any one investigate this ? One simple solution will be to make toroid with a slot, other is to make topload from tube, by winding it on isolator, like this this
Re: Topload, effects on efficiency
Dr. Dark Current, Thu Jul 24 2014, 11:53PM
Yes the topload will divert the magnetic field and cause less induced voltage on the top turns. However from my findings the difference is not that big. Losses in the topload can be a problem with high powers/duty cycles. Making the topload as an incomplete turn could be a good solution but avoid sharp edges which could cause an unwanted break out.
Dr. Dark Current, Thu Jul 24 2014, 11:53PM
Yes the topload will divert the magnetic field and cause less induced voltage on the top turns. However from my findings the difference is not that big. Losses in the topload can be a problem with high powers/duty cycles. Making the topload as an incomplete turn could be a good solution but avoid sharp edges which could cause an unwanted break out.
Re: Topload, effects on efficiency
Dago, Fri Jul 25 2014, 05:44AM
I would assume the coupling from the primary to near the toroid will be near non-existent so the effect is very small.
Dago, Fri Jul 25 2014, 05:44AM
I would assume the coupling from the primary to near the toroid will be near non-existent so the effect is very small.
Re: Topload, effects on efficiency
Steve Conner, Fri Jul 25 2014, 07:06AM
If the toroid is made out of aluminium, that is a highly conductive metal, so instead of absorbing the magnetic energy it will reflect it. The inductance of the secondary will be reduced slightly, but the losses won't increase a great deal.
Steve Conner, Fri Jul 25 2014, 07:06AM
If the toroid is made out of aluminium, that is a highly conductive metal, so instead of absorbing the magnetic energy it will reflect it. The inductance of the secondary will be reduced slightly, but the losses won't increase a great deal.
Re: Topload, effects on efficiency
Mads Barnkob, Fri Jul 25 2014, 08:15AM
Goodchilds and Catons coils uses complete rings for the topload which are all connected to eachother and the secondary coil, so they present the same one turn as a large toroid would. The dics material is only chosen for ease of sourcing/machining/weight.
I also doubt that it absorbs much of the energy directly from the primary as we usually have much else metal in the bridge construction underneath that is closer to the primary.
One thing that could be interesting would be to make a ringed topload where every slot in each ring, to not make complete turns, was connected in series so instead of being one big end terminal it worked like an extension of the secondary coil, I do however have no idea how that would affect the coils performance, just a thought.
Mads Barnkob, Fri Jul 25 2014, 08:15AM
Linas wrote ...
Does any one investigate this ? One simple solution will be to make toroid with a slot, other is to make topload from tube, by winding it on isolator, like this this
Does any one investigate this ? One simple solution will be to make toroid with a slot, other is to make topload from tube, by winding it on isolator, like this this
Goodchilds and Catons coils uses complete rings for the topload which are all connected to eachother and the secondary coil, so they present the same one turn as a large toroid would. The dics material is only chosen for ease of sourcing/machining/weight.
I also doubt that it absorbs much of the energy directly from the primary as we usually have much else metal in the bridge construction underneath that is closer to the primary.
One thing that could be interesting would be to make a ringed topload where every slot in each ring, to not make complete turns, was connected in series so instead of being one big end terminal it worked like an extension of the secondary coil, I do however have no idea how that would affect the coils performance, just a thought.
Re: Topload, effects on efficiency
Linas, Fri Jul 25 2014, 08:53AM
I just point out idea, i know that in linked picture is compleate short.
same apply for electronics, since i have huge metal box, i will redesign my coil frame so that primary will not see any "shorted turns", because this this does effect coil performance, adding any metal below primary in a way, that it can create eddy currents,it will boost power, but that will go to heat, now sparks
And i did test, my aluminum box get warm if i put it below primary, well, it is induction heater, so nothing new that it gets warm.
Linas, Fri Jul 25 2014, 08:53AM
I just point out idea, i know that in linked picture is compleate short.
same apply for electronics, since i have huge metal box, i will redesign my coil frame so that primary will not see any "shorted turns", because this this does effect coil performance, adding any metal below primary in a way, that it can create eddy currents,it will boost power, but that will go to heat, now sparks
And i did test, my aluminum box get warm if i put it below primary, well, it is induction heater, so nothing new that it gets warm.
Re: Topload, effects on efficiency
Dr. Dark Current, Fri Jul 25 2014, 03:53PM
Just put the primary further away from the metal box, or shield only the control electronics into a conductive box (the power electronics will probably be fine with the magnetic field)
OR make the box from a more conductive material, such as aluminium, it will heat less than steel.
Dr. Dark Current, Fri Jul 25 2014, 03:53PM
Just put the primary further away from the metal box, or shield only the control electronics into a conductive box (the power electronics will probably be fine with the magnetic field)
OR make the box from a more conductive material, such as aluminium, it will heat less than steel.
Re: Topload, effects on efficiency
Linas, Fri Jul 25 2014, 06:28PM
it will be standing close to coil, just like in recent Odin DRSSTC testing
But how about capacitors, can i put it below coil, or it should be placed near electronic as well ? so equivalent circuit is capacitors in series creating loop, so not a big deal, i just don't know how metal react to changing magnetic field)
Linas, Fri Jul 25 2014, 06:28PM
Linas wrote ...
And i did test, my aluminum box get warm if i put it below primary, well, it is induction heater, so nothing new that it gets warm.
And i did test, my aluminum box get warm if i put it below primary, well, it is induction heater, so nothing new that it gets warm.
Dr. Dark Current wrote ...
OR make the box from a more conductive material, such as aluminum, it will heat less than steel.
OR make the box from a more conductive material, such as aluminum, it will heat less than steel.
it will be standing close to coil, just like in recent Odin DRSSTC testing
But how about capacitors, can i put it below coil, or it should be placed near electronic as well ? so equivalent circuit is capacitors in series creating loop, so not a big deal, i just don't know how metal react to changing magnetic field)
Re: Topload, effects on efficiency
GrantX, Sun Jul 27 2014, 05:06AM
I was thinking about this topic recently. I also wondered how great of an effect topload material has on performance. I understand that aluminium is the best choice due to weight, but would non-ferritic stainless steel function identically? And at the extreme end, how much would a mild steel toroid degrade performance? I imagine it would be horrible on a small coil, since the primary isn't very far away.
GrantX, Sun Jul 27 2014, 05:06AM
I was thinking about this topic recently. I also wondered how great of an effect topload material has on performance. I understand that aluminium is the best choice due to weight, but would non-ferritic stainless steel function identically? And at the extreme end, how much would a mild steel toroid degrade performance? I imagine it would be horrible on a small coil, since the primary isn't very far away.
Re: Topload, effects on efficiency
Dr. Dark Current, Sun Jul 27 2014, 08:01AM
The heating is mostly due to eddy currents I believe. A stainless steel topload would heat more than aluminum one. The conductivity is the key parameter.
Dr. Dark Current, Sun Jul 27 2014, 08:01AM
The heating is mostly due to eddy currents I believe. A stainless steel topload would heat more than aluminum one. The conductivity is the key parameter.
Re: Topload, effects on efficiency
Linas, Sun Jul 27 2014, 02:24PM
If some one have LCR with Q option, just measure primary Q, add toroid at hight it should be, and do Q measurement again. I believe Q will be lower, but by how much ?
Linas, Sun Jul 27 2014, 02:24PM
Dr. Dark Current wrote ...
The heating is mostly due to eddy currents I believe. A stainless steel topload would heat more than aluminum one. The conductivity is the key parameter.
we don't care about heating, all we care that we have short circuit on top of secondary.The heating is mostly due to eddy currents I believe. A stainless steel topload would heat more than aluminum one. The conductivity is the key parameter.
If some one have LCR with Q option, just measure primary Q, add toroid at hight it should be, and do Q measurement again. I believe Q will be lower, but by how much ?
Re: Topload, effects on efficiency
Dr. Dark Current, Sun Jul 27 2014, 02:30PM
I'd say if the topload is highly conductive, the Q will not drop that much. On my 7kW CW SSTC the toroid made from aluminum ducting got warm, dissipating maybe 20W by guess. On my 1.5kW VTTC the topload made from paint can lid (so some generic steel) gets very hot, but its smaller, again dissipating maybe 20 watts. I believe if it was made from aluminum, it would heat less (and so drop the Q less).
Dr. Dark Current, Sun Jul 27 2014, 02:30PM
I'd say if the topload is highly conductive, the Q will not drop that much. On my 7kW CW SSTC the toroid made from aluminum ducting got warm, dissipating maybe 20W by guess. On my 1.5kW VTTC the topload made from paint can lid (so some generic steel) gets very hot, but its smaller, again dissipating maybe 20 watts. I believe if it was made from aluminum, it would heat less (and so drop the Q less).
Re: Topload, effects on efficiency
Linas, Sun Jul 27 2014, 02:46PM
And answer, use more conductive material to get low heat for me does not make scense, we care about efficiency of energy transfer, not energy transfer for circular currents inside toroid, what does nothing , only degrades performance
Linas, Sun Jul 27 2014, 02:46PM
Dr. Dark Current wrote ...
I'd say if the topload is highly conductive, the Q will not drop that much. On my 7kW CW SSTC the toroid made from aluminum ducting got warm, dissipating maybe 20W by guess. On my 1.5kW VTTC the topload made from paint can lid (so some generic steel) gets very hot, but its smaller, again dissipating maybe 20 watts. I believe if it was made from aluminum, it would heat less (and so drop the Q less).
As far as i understand, it doesn't matter with what you make short, Q will go down. Look, primary is made from 2-6 turns, bus voltage is 300Vdc, so you can expect like 50V, and you don't need low resistance to get it shortedI'd say if the topload is highly conductive, the Q will not drop that much. On my 7kW CW SSTC the toroid made from aluminum ducting got warm, dissipating maybe 20W by guess. On my 1.5kW VTTC the topload made from paint can lid (so some generic steel) gets very hot, but its smaller, again dissipating maybe 20 watts. I believe if it was made from aluminum, it would heat less (and so drop the Q less).
And answer, use more conductive material to get low heat for me does not make scense, we care about efficiency of energy transfer, not energy transfer for circular currents inside toroid, what does nothing , only degrades performance
Re: Topload, effects on efficiency
Dr. Dark Current, Sun Jul 27 2014, 03:02PM
Nope, you don't get it. The topload diverts the magnetic field, you can imagine it as a shorted secondary winding of a transformer with a large leakage inductance.
The current through the topload is given (at a given operating point of your coil). If you increase the resistivity, the dissipation in the topload goes up (P~IIR) and so your Q goes down. If the topload was superconductive, it would not dissipate anything and won't do anything to your Q.
Dr. Dark Current, Sun Jul 27 2014, 03:02PM
Nope, you don't get it. The topload diverts the magnetic field, you can imagine it as a shorted secondary winding of a transformer with a large leakage inductance.
The current through the topload is given (at a given operating point of your coil). If you increase the resistivity, the dissipation in the topload goes up (P~IIR) and so your Q goes down. If the topload was superconductive, it would not dissipate anything and won't do anything to your Q.
Re: Topload, effects on efficiency
Linas, Sun Jul 27 2014, 08:01PM
I have simple idea for test. if some one has DRSSTC without secondary, just hanging top-load where it should be with respect to primary. and simple single turn voltage should be measured as function of distance. Same measurement should be made without topload.
If no one will do this, i will make it myself as soon as i get my bridge working
Linas, Sun Jul 27 2014, 08:01PM
Dr. Dark Current wrote ...
Nope, you don't get it. The topload diverts the magnetic field, you can imagine it as a shorted secondary winding of a transformer with a large leakage inductance.
The current through the topload is given (at a given operating point of your coil). If you increase the resistivity, the dissipation in the topload goes up (P~IIR) and so your Q goes down. If the topload was superconductive, it would not dissipate anything and won't do anything to your Q.
Ok, now i get what you are saying, for me DRSSTC looks more like simple tranformer with load on very long rod.Nope, you don't get it. The topload diverts the magnetic field, you can imagine it as a shorted secondary winding of a transformer with a large leakage inductance.
The current through the topload is given (at a given operating point of your coil). If you increase the resistivity, the dissipation in the topload goes up (P~IIR) and so your Q goes down. If the topload was superconductive, it would not dissipate anything and won't do anything to your Q.
I have simple idea for test. if some one has DRSSTC without secondary, just hanging top-load where it should be with respect to primary. and simple single turn voltage should be measured as function of distance. Same measurement should be made without topload.
If no one will do this, i will make it myself as soon as i get my bridge working
Re: Topload, effects on efficiency
Dr. Dark Current, Sun Jul 27 2014, 08:30PM
Yes that could be an interesting measurement, but I guess it could be modelled as well by some finite element method (maybe the simple FEMM software can do this).
Dr. Dark Current, Sun Jul 27 2014, 08:30PM
Yes that could be an interesting measurement, but I guess it could be modelled as well by some finite element method (maybe the simple FEMM software can do this).
Re: Topload, effects on efficiency
Rod-on, Thu Aug 07 2014, 11:05PM
What is the best shape for the top load? I"m new to this and am doing my research. I've seen round balls, donut shaped ones , ones made from curled copper pipe, slotted ones and some layered on top of others. What is the most efficient shape for the top load?
Rod-on, Thu Aug 07 2014, 11:05PM
What is the best shape for the top load? I"m new to this and am doing my research. I've seen round balls, donut shaped ones , ones made from curled copper pipe, slotted ones and some layered on top of others. What is the most efficient shape for the top load?
Re: Topload, effects on efficiency
Steve Conner, Fri Aug 08 2014, 08:01AM
The donut (toroid) shape is best. It encourages the sparks to travel outwards away from the coil. With a sphere, they tend to go downwards and strike the primary more than you would like.
A large toroid stacked on top of a smaller one is a slight improvement.
From an efficiency point of view it doesn't really seem to matter whether you use a solid metal toroid, or a piece of flexible ducting bent round into a ring, or a skeleton frame made out of pipes, they all work much the same. However, if you are wanting to run the coil without a breakout point, you'll find that a smooth surface gives a single large streamer that wanders around the topload, whereas a rough one can generate several streamers.
Steve Conner, Fri Aug 08 2014, 08:01AM
The donut (toroid) shape is best. It encourages the sparks to travel outwards away from the coil. With a sphere, they tend to go downwards and strike the primary more than you would like.
A large toroid stacked on top of a smaller one is a slight improvement.
From an efficiency point of view it doesn't really seem to matter whether you use a solid metal toroid, or a piece of flexible ducting bent round into a ring, or a skeleton frame made out of pipes, they all work much the same. However, if you are wanting to run the coil without a breakout point, you'll find that a smooth surface gives a single large streamer that wanders around the topload, whereas a rough one can generate several streamers.
Re: Topload, effects on efficiency
Uspring, Fri Aug 08 2014, 09:59AM
I found running a DRSSTC without breakout point adventurous. Nothing happened until the variac was close to max and then suddenly the arc lashed out in an unpredictable direction.
Uspring, Fri Aug 08 2014, 09:59AM
I found running a DRSSTC without breakout point adventurous. Nothing happened until the variac was close to max and then suddenly the arc lashed out in an unpredictable direction.
Re: Topload, effects on efficiency
Steve Conner, Fri Aug 08 2014, 10:34AM
Yes, hardly anyone uses a DRSSTC without a breakout point. You have huge arcs flying around next to sensitive electronics so it is good to have as much control over the direction of them as you can.
When I tried it with Mjollnir, it would break out from the topload in a random direction about half of the time. The other half of the time, it flashed over down the inside of the secondary.
My AG2 coil works happily without a breakout and produces 2 or 3 streamers at once.
Steve Conner, Fri Aug 08 2014, 10:34AM
Yes, hardly anyone uses a DRSSTC without a breakout point. You have huge arcs flying around next to sensitive electronics so it is good to have as much control over the direction of them as you can.
When I tried it with Mjollnir, it would break out from the topload in a random direction about half of the time. The other half of the time, it flashed over down the inside of the secondary.
My AG2 coil works happily without a breakout and produces 2 or 3 streamers at once.
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