how to detect eddy currents and measure their negative impact

[brandnewb]

I am not sure what you meant Matt

But anyway. I will make a few test coils and add the powder. And observe what happens.
I think an experiment says more than a hunch I might have which might be wrong.

How often do you want readings?

[Mary B]

do you mean cog as in a magnet wants to stay attracted to the coil and it is difficult for it to move to the next one?

Because if that is what you meant then that is also my definition of cogging.

But can you please show me examples where each phase was so close together that it would be surprising that cogging still occurred?

{1}i.e if stacking coils in an axial arrangement has been around for ages then I will admit that I have not done my homework right. I will blame youtube!! {1}

{2}cogging always occurs to a certain degree. I mean coil wires under load will also be a part of it. Especially when one uses field enhancing additives. I mean to explore where it becomes an issue. I am almost certain that when spacing coils apart like traditional then yes cogging will become an issue.

But when we go for a continues loop then those matters are dealt with aren't they?

Please just someone help me out of my misery.

{2}

{3}And no I will not start introducing Ai again for now as it is rather expense and the answers are usually still garbage{3}

Lost me at continuous loop...

[brandnewb]

understood Mary!,

Let us break this down into smaller bits so we can zero in on the point I am trying to make.

First let us see if we can find a common agreeable defninition of cogging.

Like I said earlier in my books it is when magnets like to stick to ferromagnetic enhanced coils. Causing resistance for the magnets to move and then when they do it is in a shock like manner rather than a smooth rotation.

If we can agree on that then I will take it to the next step.

[Bruce S]

do you mean cog as in a magnet wants to stay attracted to the coil and it is difficult for it to move to the next one?

Because if that is what you meant then that is also my definition of cogging.

But can you please show me examples where each phase was so close together that it would be surprising that cogging still occurred?

{1}i.e if stacking coils in an axial arrangement has been around for ages then I will admit that I have not done my homework right. I will blame youtube!! {1}

{2}cogging always occurs to a certain degree. I mean coil wires under load will also be a part of it. Especially when one uses field enhancing additives. I mean to explore where it becomes an issue. I am almost certain that when spacing coils apart like traditional then yes cogging will become an issue.

But when we go for a continues loop then those matters are dealt with aren't they?

Please just someone help me out of my misery.

{2}

{3}And no I will not start introducing Ai again for now as it is rather expense and the answers are usually still garbage{3}

Lost me at continuous loop...

Mary B;
If I read it right, it would be similar to Ed Lenz's Wave winding or something of one coil wound in an "S" fashion, so the magnets break the wire's field at certain intervals.
I've built one of Ed's Wave winds mini-mills a decade or so ago when our daughter has to do a science project . Very nice plans and package he sold. worked just like he said it would.
There's more then one continuous loop gen (Or Axial Flux gen setup with serpentine windings)  out on U-tube. Keep thinking about using a 3-D printer to put one together just to give it a try, but work keeps getting in the way

Cheers
Bruce S

[brandnewb]

Thank you Bruce,

After a quick search regarding the stuff you mentioned I still do not think I have been able to get my point across.
So I would still like it if we could take this step by step.

Step one is first establish a commonly agreed upon definition of cogging.

Once we have that I will most likely be able to get my point across.

[Mary B]

understood Mary!,

Let us break this down into smaller bits so we can zero in on the point I am trying to make.

First let us see if we can find a common agreeable defninition of cogging.

Like I said earlier in my books it is when magnets like to stick to ferromagnetic enhanced coils. Causing resistance for the magnets to move and then when they do it is in a shock like manner rather than a smooth rotation.

If we can agree on that then I will take it to the next step.

Generally accepted version of cogging but it doesn't require iron, as a magnet passes a coil providing a lot of current it will slow down some... not as bad as an iron core coil but still there.

[brandnewb]

ok great.

Now what I am hoping for is that I can get the coils so close to each other that this effect will be negligible. That is what I meant with continues. Although technically there are still gaps between the coils making it not continues I am hoping I can get close enough that it starts behaving like that.

I will let you know how far I get with that.

[Mary B]

Close together iron core coils, magnets go around the outside edge. I can tell you it WILL cog! I put one on my exercise bike...

[brandnewb]

yes of course Mary!

Coils under load will behave like magnets and start cogging magnets. Especially when field enhanced like with iron powder.

But since my coils are stacked that should theoretically mean that there are no spots of no attraction. i.e no points where cogging becomes an issue.

The continues loop I introduce

But I will fall back to an experiment as it will make debating so much less opinionated.

I will keep one posted.

[joestue]

so yes the coils under load produce a force on the magnet, that's how you get mechanical power into or out of the machine.

the extent to which this is a problem is called torque ripple and its usually expressed as a percentage of the torque. so, 1-5%.

mitigation can be in many forms, but one of them is to make the current flowing through the coil match the back emf of the coil, so if your 3 phase machine is a sinusoidal machine, then you need an active power factor controlled rectifier.

Or you can get pretty close with a 12 pulse rectifier, which requires a minimum investment of a 3 phase auto transformer with 6 separate secondaries connected in a certain way, rated for 21% of the total power. unfortunately most folks here have wind turbines that are too slow to make transformers viable. the volts per hz is too high, which makes the transformers large and expensive.

the second way to make a 3 phase machine have a low torque ripple is to make it produce a trapezoidal waveform, and then feed it into a standard 6 diode rectifier with a battery as a load. adding an inductor may also smooth things out.

if your coils are really badly designed.. then even a resistive load won't produce constant torque.

a constant current boost converter setup such that the power draw out of the turbine is constant, can be used after the 6 diode rectifier, and the torque will be constant, because the power drawn by the boost converter will be constant. -this won't be easy to build and nobody does this, because the constant current converter has to modulate its power draw faster than 12 times the frequency of the generator.  it will also need a global controller to do MPPT and monitor the turbine rpm so your blades don't blow up.

 (it still wont be perfect because as the voltage at the turbine drops and the current increases, the I^2R losses in the generator also increase.)

[brandnewb]

"trapezoidal waveform"

That is what Mary's earlier side by side stacking suggestion will bring us!! interesting. I still do not believe it will result in a higher voltage though for the same Hz.

But if torque ripple becomes an issue rather than reaching a certain voltage level then that might be it!!

But an experiment will do more than a thousand hunches.

Thank you Joestue for not giving up on me just yet by keeping the information coming!!

so yes the coils under load produce a force on the magnet, that's how you get mechanical power into or out of the machine.

the extent to which this is a problem is called torque ripple and its usually expressed as a percentage of the torque. so, 1-5%.

mitigation can be in many forms, but one of them is to make the current flowing through the coil match the back emf of the coil, so if your 3 phase machine is a sinusoidal machine, then you need an active power factor controlled rectifier.

Or you can get pretty close with a 12 pulse rectifier, which requires a minimum investment of a 3 phase auto transformer with 6 separate secondaries connected in a certain way, rated for 21% of the total power. unfortunately most folks here have wind turbines that are too slow to make transformers viable. the volts per hz is too high, which makes the transformers large and expensive.

the second way to make a 3 phase machine have a low torque ripple is to make it produce a trapezoidal waveform, and then feed it into a standard 6 diode rectifier with a battery as a load. adding an inductor may also smooth things out.

if your coils are really badly designed.. then even a resistive load won't produce constant torque.

a constant current boost converter setup such that the power draw out of the turbine is constant, can be used after the 6 diode rectifier, and the torque will be constant, because the power drawn by the boost converter will be constant. -this won't be easy to build and nobody does this, because the constant current converter has to modulate its power draw faster than 12 times the frequency of the generator.  it will also need a global controller to do MPPT and monitor the turbine rpm so your blades don't blow up.

 (it still wont be perfect because as the voltage at the turbine drops and the current increases, the I^2R losses in the generator also increase.)

[joestue]

torque ripple is the least of my concerns to be honest.

just figure out how to get the highest mechanical resistance, with the coils shorted together, for a given torque on the magnet disk.

you don't need to wind all the coils to do this experiment, you just have to wind a complete set of 3 phase coils, however many are necessary, taking up their sector of the disk. voltage and turns count doesn't matter, so long as the total volume of the copper test coil is the same between various tests.

wrap a rope around the shaft, hang a weight on it, and the slower it falls, the more power you'll get out of that coil group.

[brandnewb]

thank you joestue,

I am already working on the test coils and test magnet holders.

But I also plan to try various additives to pure resin.

The idea is to have a pure epoxy resin cast coil as a base line. And several other variations to see what the effects of those additives are.

I really like that I do not have to wind real full sized coils that will save a bunch of time and material.

Anyway here comes my question. I also plan to blow up a few coils by overloading them with just simply too much power input.

Would it be ok for me to use a variable speed motor with a known wattage output to drive the alternator test bench? And then crank up the speed and document when things start overheating?

It will also address Mary's earlier (might not have been in this thread) mention that without a controlled RPM, result accuracy will be sub optimal. Which in essence I agree with.

{1}To drive a variable speed motor. I can supply a continues power of 11 KW. spread over 3 phases. I am assuming this will enable me to supply the power needed to start seeking the limits of a coil magnet configuration. In case that is not enough I can temporary bypass the my circuit breakers in the part of the electrical breaker cabinet that is my responsibility and for short bursts supply a bit below 19.83 KW before the main breakers ( that are not part of my electrical breaker cabinet) trip.

I am hoping that this will enable enough power to start seeking limits.

If no objections then I am going to try this route to add to the alternator test bench{1}
{2} oops here I go again poluting public threads. I will create a new one{2}