Also, one should be able to propose some reciprocity of action. Suppose the rotor is free and undriven at any random angular position - with the coil energized would there be a torque on the rotor?

 

Most of the field would be inside the toroid, but some would leak out if it looks like the drawing. Assuming that leakage and the magnet are symmetrical, there will be no torque.

 

Most of the field would be inside the toroid, but some would leak out if it looks like the drawing. Assuming that leakage and the magnet are symmetrical, there will be no torque.

The drawing is just an example, and I drew it in under 3 minutes... I intend to wind it with at least two layers, overlapping them both one wire (tube) diameter out of phase, so as to make sure there are no magnetic field leaks, if possible.
I intend to first coat the tube with polyurethane paint, so as to electrically isolate each turn... leave the tips unconnected, and make tests... then connect the tips, and make more tests.
Since I don't have torque-meter available, I'll use a dc motor to spin the magnet (which will be mounted on ball bearings) and measure current to the motor with the toroid's ends disconnected... and then make more measurements with both ends connected, short-circuiting the toroid... my guess is that there will be more current drawn by the motor if it experiences a change in torque
Also, I'll make another test with a cooper ring with the same mass and inner diameter as the toroid... see how much current is drawn by the motor and compare it to the toroid's performance. If I find there's a significant difference, I'll take out my scope and probe the thing... hell, I think I'll probe it anyway, no matter what happens.
As for reciprocity of action, my guess is that the coil would have to be energized with AC to imitate what the magnet will be doing when it spins... but maybe the current phases inside the toroid will prove to be too difficult to emulate with that method...

But I'm going to do this one step at a time...

Step ONE: find a large diametrically magnetized neodymium magnet... I found a place that sells them but only up to 1 inch in diameter. Does anyone know where I could find larger ones?

 

Step ONE: find a large diametrically magnetized neodymium magnet... I found a place that sells them but only up to 1 inch in diameter. Does anyone know where I could find larger ones?

I saw a magnet makers site a few months ago. Are you willing to buy online?

 

I saw a magnet makers site a few months ago. Are you willing to buy online?

You mean there are other ways to buy something???

 

There it is. First thing up on a google.
K&J Magnetics

http://www.kjmagnetics.com/?gclid=CI7_3sbKpsMCFUto7Aod7zwAmw

Then there is apexmagnets.com

 

There it is. First thing up on a google.
K&J Magnetics

http://www.kjmagnetics.com/?gclid=CI7_3sbKpsMCFUto7Aod7zwAmw

Then there is apexmagnets.com

Thanks, I had already searched K&J, but I only found diamterical magnets of up to one inch in diameter. But I had not heard of apex before... and it seems like they have what I want... for a price, of course...

 

As for reciprocity of action, my guess is that the coil would have to be energized with AC to imitate what the magnet will be doing when it spins...

I must disagree. One merely needs to have a situation where the postulated 'interactive' component of an electrically induced coil field (DC or AC) is not aligned with the rotor pole field. There would then be a torque tending to promote an alignment - transitory perhaps but discernable. A slow hand adjustment of the rotor over the full 360 degrees should disclose that proposed torque.

 

I must disagree. One merely needs to have a situation where the postulated 'interactive' component of an electrically induced coil field (DC or AC) is not aligned with the rotor pole field. There would then be a torque tending to promote an alignment - transitory perhaps but discernable. A slow hand adjustment of the rotor over the full 360 degrees should disclose that proposed torque.

Right... guess we're going to have to wait and see...

 

I've bought from these guys with success. I haven't checked whether they have what you need. Most folks want it polarized on axis.

I love a good experiment, but is there a goal behind this?

 

Yes indeed.
You could also build one of these if you have the time...

http://en.m.wikipedia.org/wiki/Gramme_machine

 

I've bought from these guys with success. I haven't checked whether they have what you need. Most folks want it polarized on axis.

I love a good experiment, but is there a goal behind this?

Thanks wayneh, but I couldn't find diametrical magnets larger than one inch in their website
EDIT: I mentioned my goal in previous posts, to generate a higher amount of heat at the same RPMs

 

Well, why not just pass the electricity through a heating element? No moving parts, nothing to build.

 

I couldn't find diametrical magnets

These are beginning to sound more like diabolical magnets.

(Trying to do word play jokes across a language barrier. )

 

These are beginning to sound more like diabolical magnets.
(Trying to do word play jokes across a language barrier. )

I hadn't thought of that... if my experiment succeeds I might need to call a priest to perform an exorcism, or something...

 

Hi,

The coupling between magnet and coil will have to be very good to see any good results and i think that will be hard to achieve.
Also, there's no core for the coil which means less effect than a motor or generator might have. So the effects of any kind (mechanical, thermal, electrical) will most likely all be quite small, so you will be looking for very small effects. I even have to wonder how much difference you'll see between a rotating magnet in free air and a rotating magnet inside the coil, probably very small, and you'll need a decent speed for the magnet.
Motors and generators have cores which help to increase the transfer of energy.

I think you can use a bar magnet, i dont see why not. Rotating any magnet at high speed though will require careful mounting and balancing.

 

Hi,

The coupling between magnet and coil will have to be very good to see any good results and i think that will be hard to achieve.
Also, there's no core for the coil which means less effect than a motor or generator might have. So the effects of any kind (mechanical, thermal, electrical) will most likely all be quite small, so you will be looking for very small effects. I even have to wonder how much difference you'll see between a rotating magnet in free air and a rotating magnet inside the coil, probably very small, and you'll need a decent speed for the magnet.
Motors and generators have cores which help to increase the transfer of energy.

I think you can use a bar magnet, i dont see why not. Rotating any magnet at high speed though will require careful mounting and balancing.

Some useful comments from MrAl.

To me it seems one would obtain an equivalent or similar outcome by connecting the individual phase windings of a three phase alternator in delta configuration. The vector summation around the closed delta would be close to zero in a well constructed machine approaching ideal behavior, meaning a small or nonexistent circulating current in the delta with the alternator unloaded. The driving motor / turbine has only to overcome the unloaded mechanical and excitation losses to maintain synchronous speed. Only when the delta is connected to an external 3-phase load does the driving torque requirement increase substantially in accordance with load power requirements.

 

Thank you MrAl and t_n_k for your valuable inputs. Now that I think of it, yes, if I want inductive loads in the coil to make a difference, maybe it would be best to wind it around a core. On the other hand, I want to find out how the arrangement I proposed behaves differently, and what you're proposing is that I practically build a three phase motor, and I already know how that will behave... though once I have the magnet, and assemble it with an axis and bearings and a coupled DC motor, building a three-phase winding will probably not be too much extra work... we'll have to wait and see...

 

Didn't Faraday do something like this? Called a 'homopolar generator'. But he rotated the disc not the magnet.

 

Didn't Faraday do something like this? Called a 'homopolar generator'. But he rotated the disc not the magnet.

Faraday's design was based on a flat solid plate of conductive metal