Sorry, but it's hard for me to describe these things in words without some context. If you want to share a schematic of how you think two switches will get it done, I'll be happy to explain the problems in the context of that circuit. You can draw the circuit with simple SPST switches instead of transistors in order to simplify things if you want.

I can't think of any plausible two-switch solution, so I don't have a starting point from which to discuss why it won't work. If you can draw a circuit to show us how you think two switches will work, we can talk through the problems. Or, if you want to start with a diagram of an existing h-bridge circuit and tell us which two switches you think can be omitted, we can talk from there.

As I said before, I think once you actually try to draw it, you'll realize that it doesn't add up.

The only two switch solid state solution I'm aware of would require a bipolar power supply (as mentioned by ebp in post 6.)

Yes, I see now that an H-Bridge configuration is necessary. Even though obviously I'd drawn the 2 circuit diagram I described, I hadn't realised that they can't actually be separated. I do not have even the most rudimentary experience with the subject; and I am grateful for your patience in even replying. Do you agree then that an H-Bridge with MOSFETs is appropriate for this situation: 12 V, around 800 A, very low frequency switching (?with a 555-timer)? And that such a device if constructed for that power rating may be presumed to be capable of handling heat?

What cross-section copper bar are you presently using/planning for the EMs?
I think you should re-design your EMs to have a lot more turns passing a lot less current to achieve the same field strength.
Even a heavy duty 12V car battery will not like having to pass 800A for more than a few seconds at a time.

If you mean the cross-section of the soft iron bar for the EMs, it is 40 mm diameter; and I agree, I'll probably end up rebuilding them at twice that, and twice as many ampere-turns; aiming at 200 A. Still plenty. Also, I only need the apparatus to operate for a few seconds at a time to determine the effect. The problem of inductance sounds difficult, scary even.

What kind of inductance are you talking about in these electromagnets?

If it's more than a very small amount, when you try to switch that current quickly, you will discover that one of the quicker ways to die is open-circuiting an energized electromagnet.

If your current is 800 A and you are cycling at 4 Hz, then even 100 mH of total inductance will require 640 V in order to ramp linearly.

I'm not sure about this, or even the extent to which inductance depends on current in such a situation. It sounds dangerous though, and I'm starting to realise that I will need professional assistance--real technical experience--to go much further. Presuming that the estimation of inductance is correct though--it's probably around that--, and the peak voltage is as you say at 4 Hz, what exactly do you mean by a 'requirement' for that voltage?

 

I'm not sure about this, or even the extent to which inductance depends on current in such a situation. It sounds dangerous though, and I'm starting to realise that I will need professional assistance--real technical experience--to go much further. Presuming that the estimation of inductance is correct though--it's probably around that--, and the peak voltage is as you say at 4 Hz, what exactly do you mean by a 'requirement' for that voltage?

I have no idea what the inductance of your magnets are -- the 100 mH I mentioned was just a number thrown out. But the electromagnets I worked with at NIST had inductances that started at 74 H and went up from there.

The voltage across an inductor is proportional the rate at which the current is changing.

v(t) = L di(t)/dt

So if the current changes (linearly) from 800 A to 0 A in 0.125 seconds, that's a rate of change of 6400 A/s. If the inductions is 0.1 H, the voltage that is required to make that happen will be 640 V. Note that if the inductance is 10 H, the voltage goes to 64 kV.

Furthermore, because the energy in an inductor is a function of the current, the current through inductor MUST be continuous. The effect is that if you open circuit an inductor, it will produce whatever voltage is required to keep the current flowing -- and if the voltage needed is a few million volts, so be it. This is known as "inductive kick". This is how the old-style ignition coils on cars worked. You used a 12 V battery to get some current flowing in a coil of wire and then opened a switch (the points). The inductive kick would then produce enough voltage (typically 30 kV to 50 kV) to create an arc across the spark plug gap for the current to keep flowing.

If you aren't careful, you will be creating arcs that start out with 800 A of current -- not something you want to be anywhere near.

 

If you mean the cross-section of the soft iron bar for the EMs, it is 40 mm diameter

No, I mean what cross-section copper bar/cable will you be winding round the iron, and how many turns? Thin copper wire won't carry 200A for 'a few seconds', yet alone 800A.

 

I have no idea what the inductance of your magnets are -- the 100 mH I mentioned was just a number thrown out. But the electromagnets I worked with at NIST had inductances that started at 74 H and went up from there.

The voltage across an inductor is proportional the rate at which the current is changing.

v(t) = L di(t)/dt

So if the current changes (linearly) from 800 A to 0 A in 0.125 seconds, that's a rate of change of 6400 A/s. If the inductions is 0.1 H, the voltage that is required to make that happen will be 640 V. Note that if the inductance is 10 H, the voltage goes to 64 kV.

Furthermore, because the energy in an inductor is a function of the current, the current through inductor MUST be continuous. The effect is that if you open circuit an inductor, it will produce whatever voltage is required to keep the current flowing -- and if the voltage needed is a few million volts, so be it. This is known as "inductive kick". This is how the old-style ignition coils on cars worked. You used a 12 V battery to get some current flowing in a coil of wire and then opened a switch (the points). The inductive kick would then produce enough voltage (typically 30 kV to 50 kV) to create an arc across the spark plug gap for the current to keep flowing.

If you aren't careful, you will be creating arcs that start out with 800 A of current -- not something you want to be anywhere near.

Calculating Inductance for these coils, I get a similar result of around 100 mH; and 0.125 secs. seems about right. What I neglected to specify properly is that there are 6 EMs in parallel, powered by a 12 V battery, so the current in each one is rather of the order of 120 A (for the Resistance of 0.1 Ohms); which is still a fair bit. The peak voltage--and that's as good an explanation of 'inductive kick' as I've heard (I get it now; my grandfather, who was a motor mechanic and electrician in the 1920s would be proud)--, would therefore be much less, around 100 V.

I am led to believe however that within the circuit as a whole, including transistors, and in order to prevent these burning out, flyback diodes are supposed to modify this effect of arcing in those switches themselves. In any case, one way or another, it's these arcs that must be avoided; and I will be careful to obtain expert technical guidance before I switch anything on. Thank you.

No, I mean what cross-section copper bar/cable will you be winding round the iron, and how many turns? Thin copper wire won't carry 200A for 'a few seconds', yet alone 800A.

Sorry. The wire I'm using is 0.5 mm diameter, about 150 turns, and each EM draws around 120 A (which I neglected to emphasise; if I used twice as many turns, and twice the diameter of the coil, I'd only need 15 A per EM). For 6 EMs in parallel, the total current is around 720 A, which is what the H-bridge has to deal with. I think the existing EMs will suffice, provided there is a switch capable of handling voltage spikes due to inductance as 'WBahn' thankfully has pointed out. The apparatus is already built, and the EMs work well to rotate the core/armature, but only over 135 degrees of rotation due to absence of switch. There isn't much heat either in those EM coils after a few seconds, which as I said, is all I need at a time.

You're making even less sense as you try to explain things. You want to have electromagnets generate a current in permanent magnets??? A helix contained in a sphere??? How old are you, may we ask that? Or what grade in school are you in. Before spending money on this "experiment" you may want to spend some time reading and studying how things work.

I also don't think you have any real idea how high a current 800Amps is, at any voltage. Houses here in the USA are usually only supplied with around 200Amps at 240 volts. I have no idea where you would even find a 800A 12V DC supply for your 'experiment'. Or for that matter there is no wire size chart that goes that high of DC amps, but thewire would be huge if you could find some that would work. But do applaud you for thinking big from the get go.

My apologies. First of all, I am simply assuming a current of those proportions in the EM coils on the basis of a calculation of the resistance: 0.1 Ohm. I hope I haven't made an error there, and believe it or not, I haven't yet measured the actual resistance--I only visit the site of this contraption periodically. Still, when I switch on these EMs using a 12 V battery, there is a nice steady strong magnetic field which actually does propel the 'helical magnetic core' around to the limit of 135 degrees of core rotation at which a switch in EM polarity is required.

Now, if you read carefully, you will appreciate that there is in fact a copper winding wrapped around that ferromagnetic core; and that core is being driven by a rotating magnetic field arising in surrounding EMs powered by a battery. The aim is obviously to generate a current in that winding, not in the magnetic core. That current, if it can be generated, should possess certain properties by virtue of the fact that, although the winding in which it is generated is fixed to the core, it is nonetheless subject to a continuously changing magnetic field at all times arising between the EMs and the rotating core. Alright.

I could send you a picture of the apparatus; but it is not any advice regarding the basis of this experiment which I seek here. My problem is the practical technical one of switching the polarity in these EMs to create a rotating external field. The current in each EM is around 120 A, which is large I know, but quite manageable in such a circumstance. The apparatus is also already constructed, and although I'm only powering the EMs for short periods, they work well. Incidentally, by far the most expensive part of it to date has been the permanent magnets for the core.

Those magnets are arranged to form a helix contained in a sphere. Commencing at the equator of a sphere, move 1 degree of longitude for each degree of latitude, and the curve described on the surface of this imaginary sphere is a form of helix (i.e. a curve such that the angle of elevation from the diameter plane equals the angle of rotation from the diameter). So, using bar magnets of successively diminishing length, and rotating them incrementally one upon the other from the largest diameter component, one may construct a 'magnetic propeller', one side North, one side South, right. (Imagine the Pacific coast of America as magnetised North, and the other curve, up through the Kimberleys and the Andaman trench and the Himalayas and the Urals and so on magnetised South). Incidentally, for a sphere of radius 2r, the plan view of such a 'sphero-helix' will be two semicircles of radius r (the form of the symbol for tao, 'yin-yang').

One then concocts to drive this ideal propeller around on its vertical axis using 12 EMs situated at the midpoints of the edges of a cube with the same centre as the sphere (so, for instance, the EMs oriented at 45 degrees to the horizontal will align periodically with the points on the 'sphero-helix'--and its respective core magnetic components--elevated and rotated by 45 degrees); and of course, since no possible purpose is imaginable for what amounts to some silly motor long since invented..Hmm, well, why not bung a nice long continuous copper winding between these two interacting fields and observe what happens. What kind of winding you wonder? Well, my first inclination, for some peculiar reason, was to try a 'progressive lap-type winding'; by which I mean, one segment down, rotate 90 degrees, one segment up, rotate 90 degrees, next segment down, rotate 90 degrees etc., and after 4 such operations, returning to the first segment, move the first down segment of the next loop one wire width around and repeat, about 300 times. Coil-like isn't it. (If you can't see it, don't worry about it).

If the experiment succeeds in demonstrating a useful output from such a winding, there is an inexhaustible DC supply available from solar cells. Right. I hope all that clarifies things a little; but you must read things very carefully Mr. Shortbus. Once again, my apologies from out here in 'left field'.

 

Yes, I see now that an H-Bridge configuration is necessary. Even though obviously I'd drawn the 2 circuit diagram I described, I hadn't realised that they can't actually be separated. I do not have even the most rudimentary experience with the subject; and I am grateful for your patience in even replying.

No problem at all. I went through this myself a few years ago. It just seemed like too many switches, so I tried to do better. Every time I started to draw a two switch solution, I'd find a problem with it, and eventually I understood why everyone uses the H-bridge configuration.

Do you agree then that an H-Bridge with MOSFETs is appropriate for this situation: 12 V, around 800 A, very low frequency switching (?with a 555-timer)? And that such a device if constructed for that power rating may be presumed to be capable of handling heat?

I agree that an H-bridge configuration seems right, and that MOSFETs are the least likely solid state switch to overheat quickly (assuming you choose wisely with low Rds-on as a high priority.)

The low frequency switching is good news, but with so much power to switch, I imagine your MOSFETs will be large, which tends to mean high gate capacitance, which means it takes longer for the MOSFET to transition out of the linear region (where the worst heating happens.) Even with low switching frequency, you may still want dedicated gate driver circuits for tighter transition times... although maybe that exacerbates the dV/dt concerns WBahn brought up and makes inductive kick problems harder to manage.

I really don't know, just brainstorming at this point. The amperages you're trying to work with are so far out of my league, it's crazy. I've never tried to design circuits for anything beyond about 20A, and the vast, vast majority of my projects are well under 1A total, so my credibility in your 800A realm is low!

I make no presumptions about handling heat. There's a lot of math to do, or a lot of potentially destructive experiments to perform. One thing to keep in mind is that most high amperage devices are only capable of handling their stated limits if they have appropriate heat sinking. Without heat sinks they'll blow up at much lower currents. I can't tell you how many times people get caught off guard by this:

"I bought this 50A SSR, I'm only running 48A through it, and it stopped working! Stupid piece of junk!" But if you read the datasheet, it needs a 2" heat sink for 50A, and it's only good for maybe 5-10 without a heat sink.

So, be very thorough when deciding what various components can handle based on their ratings. At the power levels you're working with, you really need to dig deep into the datasheet and understand it, not just take the front page numbers at face value.

 

The wire I'm using is 0.5 mm diameter, about 150 turns, and each EM draws around 120 A ....

Ummm.... 120A through 0.5mm (24 AWG) wire? I don't think so. The wire would pop like a fuse at that current.

 

Ummm.... 120A through 0.5mm (24 AWG) wire? I don't think so. The wire would pop like a fuse at that current.

For copper wire of that size, fusing is expected at about 60 A in one second for a single conductor in free air. A close-wound coil will fuse at significantly lower current unless something is rapidly removing heat. For 120 A from 12 V with a 150 turn coil, the mean length of turn can only be about 8 mm, which works out to about 2.3 mm inside diameter for a single layer close-wound solenoid winding. No ferromagnetic material that small is going to have much heat capacity.

 

You're making even less sense as you try to explain things. You want to have electromagnets generate a current in permanent magnets??? A helix contained in a sphere??? How old are you, may we ask that? Or what grade in school are you in. Before spending money on this "experiment" you may want to spend some time reading and studying how things work.

I also don't think you have any real idea how high a current 800Amps is, at any voltage. Houses here in the USA are usually only supplied with around 200Amps at 240 volts. I have no idea where you would even find a 800A 12V DC supply for your 'experiment'. Or for that matter there is no wire size chart that goes that high of DC amps, but thewire would be huge if you could find some that would work. But do applaud you for thinking big from the get go.

Actually 800namps at 12 volts is not that difficult to do for a while. One of our products was a battery bank to run a large array of 1KW photo floodlights for filming crash barrier tests. Those battery packs had a 600 amp fuse, since the actual load was only 480 amps once the lamps lit. But the battery pack could deliver over 800 amps into a short circuit for several minutes before things burned out. The big question is: "800 amps for how long??" 20 seconds is no problem, one minute and you are pushing your luck. One thing to know is that there will be a big inductive voltage spike at each turn-off instance, since v=L x dI/dT, meaning voltage equals inductance multiplied by the rate of current change.. For a short term experimental setup a motor spun reversing commutator arrangement with heavy duty brushes could be cheaper than the huge collection of FET devices or transistors. 4 CPS= 120 RPM if you make it a 4-pole setup.

 

The wire I'm using is 0.5 mm diameter

120mA would be more reasonable than 120A for that gauge wire!

 

If the experiment succeeds in demonstrating a useful output from such a winding, there is an inexhaustible DC supply available from solar cells. Right. I hope all that clarifies things a little; but you must read things very carefully Mr. Shortbus. Once again, my apologies from out here in 'left field'.

This is what I thought from the beginning. A form of over unity. None of what you're claiming makes any sense .

 

120mA would be more reasonable than 120A for that gauge wire!

Quite Right!! That is what I get for jumping onto the end of a thread. But the part about a source of energy is confused. All real circuits have losses, only theoretical ones can be lossless, and then you only get theoretical power, not very useful. Yes, ohms law would say 120 amps per 0.1 ohm winding, but an inspection of the current capacity versus wire sizes tells you "no."
BUT you can evaporate that wire very quickly using even just one fresh automobile battery for the supply. A more complete description at the start would have brought reality to the fore much sooner.

 

If I were trying to drive 6 coils, each with 120 A, I would use six separate H-bridges. It would be much easier all round than trying to make one bridge to handle the entire current. I might contemplate 3 bridges.

 

I'll say it again: This thing will NOT be operating with 24AWG wire at 120A, not for more than a second or so.

The power dissipated in the coil - if the resistance is really 0.1Ω - would be I^2•R = 14,400 • 0.1 = 1,440 watts. I don't know the size of the coil but picture in your mind what it takes to cool a 1,000W lightbulb. Not gonna happen!

 

So if the switching the current from the array of photocells spins the sphere, then what? A motor needs to be able to do useful work, and there are available today fully mature brushless motors that are undoubtedly far more efficient, and able to deliver useful work as well. Being aware of what already is available, and understanding how it works, are two keys that help one decide what is not presently available but could be useful. Many useful inventions do actually benefit much of the human race and also reward the inventor with a bit of profit.

 

I agree with shortbus that this now sounds like an over unit idea. At the start of the tread I was thinking the electomagnets where very large like those used in scrap yards. When the TS said the windings were 0.5mm dia (0.2 sq mm CSA) wire I thought they must be superconductor coils but that was ruled out when he said they did not feel very warm. (I only know of superconducters that work near absolute zero.) I also imagined the power source being large lead acid batteries but I now think he must be using some small 12 volt battery with quite a high internal resistance that limits the current to at most a few amps as the wire did not vaporise.

Les.

 

This is what I thought from the beginning. A form of over unity. None of what you're claiming makes any sense .

Look, this is NOT a 'greater-than-unity' device!! Why do you think that? And I an NOT claiming anything. If you are confused by what I have said in response to your curiosity, that is an issue for you.

I added the part about solar cells only to explain how a DC battery might be supplied over a prolonged period. This apparatus is simply intended as a reconfigured AC generator, which aims to produce a type of AC. Probably it will not succeed, but I intend to find out what sort of effect is generated in such a winding.

Quite Right!! That is what I get for jumping onto the end of a thread. But the part about a source of energy is confused. All real circuits have losses, only theoretical ones can be lossless, and then you only get theoretical power, not very useful. Yes, ohms law would say 120 amps per 0.1 ohm winding, but an inspection of the current capacity versus wire sizes tells you "no."
BUT you can evaporate that wire very quickly using even just one fresh automobile battery for the supply. A more complete description at the start would have brought reality to the fore much sooner.

Please ignore the part about the solar cells. At the moment, this device uses a 12 V car battery and to date, applying current to 12 field coils connected in parallel for 5 to 10 seconds only has not resulted in any fusing. As I said earlier, I'm not sure yet what the actual resistance in these EM coils is, but I have calculated it to be 0.1 Ohms, in which case each EM is conducting 120 A. Once again, the problem is not the design of the generator; it is the practical issue of switching polarity in EMs of this sort which was adequately presented at the commencement of the thread.

If I were trying to drive 6 coils, each with 120 A, I would use six separate H-bridges. It would be much easier all round than trying to make one bridge to handle the entire current. I might contemplate 3 bridges.

I think this is probably the most constructive idea yet; and one which I'd not considered. I need to switch polarities in 6 EMs simultaneously at each 180 degrees of core rotation, and the other 6 similarly, but 90 degrees of core rotation later. I should be able to use a 555-timer connected to 6 H-Bridges, right. Also, evidently there is some question about whether the actual current is 120 A (based only on my calculation of resistance), since people doubt that such a current can be conducted through a 0.5 mm gauge copper wire without immediately fusing. As I said, I require this generator to function only for 10 seconds at a time at most in order to demonstrate the effect, hopefully a form of AC with properties I can only conjecture about. Whether this result comes about is, for me, entirely beside the point at this stage; suffice to say that my motives are purely scientific, born of an insatiable curiosity and an indomitable will. 6 separate H-Bridges: of course.

Actually 800namps at 12 volts is not that difficult to do for a while. One of our products was a battery bank to run a large array of 1KW photo floodlights for filming crash barrier tests. Those battery packs had a 600 amp fuse, since the actual load was only 480 amps once the lamps lit. But the battery pack could deliver over 800 amps into a short circuit for several minutes before things burned out. The big question is: "800 amps for how long??" 20 seconds is no problem, one minute and you are pushing your luck. One thing to know is that there will be a big inductive voltage spike at each turn-off instance, since v=L x dI/dT, meaning voltage equals inductance multiplied by the rate of current change.. For a short term experimental setup a motor spun reversing commutator arrangement with heavy duty brushes could be cheaper than the huge collection of FET devices or transistors. 4 CPS= 120 RPM if you make it a 4-pole setup.

This is also possible; and originally I tried to construct a mechanical switch using commutating plates and brushes driven by the rotor itself--but it didn't function properly. I hadn't even investigated the idea of using a separate motor in the way you suggest. Sounds like a good idea. It's either that, or 12 separate H-Bridges connected to 2 timers (or possibly the 'reversing contactor set' mentioned previously by 'Max'). Thanks.

No problem at all. I went through this myself a few years ago. It just seemed like too many switches, so I tried to do better. Every time I started to draw a two switch solution, I'd find a problem with it, and eventually I understood why everyone uses the H-bridge configuration.

I agree that an H-bridge configuration seems right, and that MOSFETs are the least likely solid state switch to overheat quickly (assuming you choose wisely with low Rds-on as a high priority.)

The low frequency switching is good news, but with so much power to switch, I imagine your MOSFETs will be large, which tends to mean high gate capacitance, which means it takes longer for the MOSFET to transition out of the linear region (where the worst heating happens.) Even with low switching frequency, you may still want dedicated gate driver circuits for tighter transition times... although maybe that exacerbates the dV/dt concerns WBahn brought up and makes inductive kick problems harder to manage.

I really don't know, just brainstorming at this point. The amperages you're trying to work with are so far out of my league, it's crazy. I've never tried to design circuits for anything beyond about 20A, and the vast, vast majority of my projects are well under 1A total, so my credibility in your 800A realm is low!

I make no presumptions about handling heat. There's a lot of math to do, or a lot of potentially destructive experiments to perform. One thing to keep in mind is that most high amperage devices are only capable of handling their stated limits if they have appropriate heat sinking. Without heat sinks they'll blow up at much lower currents. I can't tell you how many times people get caught off guard by this:

"I bought this 50A SSR, I'm only running 48A through it, and it stopped working! Stupid piece of junk!" But if you read the datasheet, it needs a 2" heat sink for 50A, and it's only good for maybe 5-10 without a heat sink.

So, be very thorough when deciding what various components can handle based on their ratings. At the power levels you're working with, you really need to dig deep into the datasheet and understand it, not just take the front page numbers at face value.

Very useful advice: Thank you. Presumably the correctly rated H-bridge with MOSFETs may also be equipped with the appropriate heat sink, as long as one checks the fine print. I wish I'd thought to measure the actual resistance in the EM coils; which unfortunately I can't do just at this moment. Possibly the current envisaged is less than 120 A per coil; but I'll certainly be sure about that before proceeding. Thanks again.

 

I'll say it again: This thing will NOT be operating with 24AWG wire at 120A, not for more than a second or so.

The power dissipated in the coil - if the resistance is really 0.1Ω - would be I^2•R = 14,400 • 0.1 = 1,440 watts. I don't know the size of the coil but picture in your mind what it takes to cool a 1,000W lightbulb. Not gonna happen!

Alright, I believe you. This appears to suggest though that the Resistance I've calculated is less than actual, because whatever power is there is clearly not translating to excessive heat, at least over the short periods of ~10 secs. it is operating. I'm still waiting for the actual resistance to be measured; and presumably it will turn out to be greater and the current somewhat less than 120 A at 12 V. I'll let you know.

 

I agree with shortbus that this now sounds like an over unit idea. At the start of the tread I was thinking the electomagnets where very large like those used in scrap yards. When the TS said the windings were 0.5mm dia (0.2 sq mm CSA) wire I thought they must be superconductor coils but that was ruled out when he said they did not feel very warm. (I only know of superconducters that work near absolute zero.) I also imagined the power source being large lead acid batteries but I now think he must be using some small 12 volt battery with quite a high internal resistance that limits the current to at most a few amps as the wire did not vaporise.

Les.

Yes, I'm using a standard lead acid car battery; and since the coils don't even get warm after 5 to 10 seconds, perhaps your suggestion is correct. Thanks. There's nothing very fancy or sophisticated about the apparatus either, nor do I expect any violation of the laws of thermodynamics; just possibly an AC waveform with properties unique to the manner in which it will hopefully be generated. What use it may have if any is obviously contingent on its actuality. It might though conduct itself more efficiently through various media, including the copper conduit itself in which it arises. Or not.

 

Alright, I believe you. This appears to suggest though that the Resistance I've calculated is less than actual, because whatever power is there is clearly not translating to excessive heat, at least over the short periods of ~10 secs. it is operating. I'm still waiting for the actual resistance to be measured; and presumably it will turn out to be greater and the current somewhat less than 120 A at 12 V. I'll let you know.

If you really have 24 gauge magnet wire, it's about 40 feet per ohm. You might even have 26 gauge, which is 24'/Ω. So yeah, the resistance of your coil is probably more than 0.1Ω. You would also have an internal resistance in your power source. These would dramatically reduce the current. You could measure the actual voltage across the coil under load. But don't linger!

 

Look, this is NOT a 'greater-than-unity' device!! Why do you think that? And I an NOT claiming anything. If you are confused by what I have said in response to your curiosity, that is an issue for you.

Why would you think a sphere would work any better for this than the normally used cylinder?

Why do you consider it is going to make AC by pulsing DC into a field made with permanent magnets?

Finally this is why I think you are trying to make some sort of device that will make more volts and current than is put into it. The, "get more out of what is put in" is the description of "over unity". Plain and simple. Do some more reading on how things work.

One then concocts to drive this ideal propeller around on its vertical axis using 12 EMs situated at the midpoints of the edges of a cube with the same centre as the sphere (so, for instance, the EMs oriented at 45 degrees to the horizontal will align periodically with the points on the 'sphero-helix'--and its respective core magnetic components--elevated and rotated by 45 degrees); and of course, since no possible purpose is imaginable for what amounts to some silly motor long since invented..Hmm, well, why not bung a nice long continuous copper winding between these two interacting fields and observe what happens. What kind of winding you wonder? Well, my first inclination, for some peculiar reason, was to try a 'progressive lap-type winding'; by which I mean, one segment down, rotate 90 degrees, one segment up, rotate 90 degrees, next segment down, rotate 90 degrees etc., and after 4 such operations, returning to the first segment, move the first down segment of the next loop one wire width around and repeat, about 300 times. Coil-like isn't it. (If you can't see it, don't worry about it).