Magnet Inductance Boost with Finemet nanocrystaline core

[Kator01]

Hi Luc,

unfortunately I have not so much time to go into great length of explanation. But I will try to make it understandable.
You have to somehow find some literature to understand the BH-diagram. because It is essential for further understanding what is going on.

First:    comparison of areas of both curves
Your coil is running idle in both cases. This does not show a real situation. It will be different under load that is current draw by a secondary coil or physical movement towards a pm  or away from it.

Second:  you do not know where the zero-line is in the second curve because you have the static pre-magnetization left in the core ( after puls off ) due to your pm attached to it. I am sure the curve is above the zero-line, meaning in the positive area of induced voltage. It must be so. If you would remove the pm from your coil after switching off the puls, only then will you see the whole picture.
But this is impossible to to.

If you look at the pic I attached to my post , the full BH diagram is the dynamic path of sinuswave-current flowing in the coil. For a DC-Puls - as you have applied it - only that part of the curve is valid which is above the horizontal zero-line ( Middle diagram)  As the fieldstrength rises ( Ampere Turns per Meter ) while the puls increases the current in the coil so does the induced Voltage per second = B. It rises steep first and enters the saturation-area where the curve gets more flat.
If puls is cut off the the upper left part of the BH-curve is valid. At that time current from your puls-generator  stops and the magnetic field collapses creating the negative spike. So the current you had to spent is 230 mA as you stated.  You have not spent current for reversal of magnetization because you just stopped the current  while an ac-current would continue to demagnetize to zero and further on to the negative side consuming more power

Now if you magnetize your core with a permanent-magnet the BH-curve starts at the level of the arrows either in the positive side ( above the horizontal level) or the negative side depending on the  pm-pole facing your coil. Lets assume your pre-magnetization has shifted the level above zero. Then this means your puls-current starts here and does not have to magnetize up to this arrow- level in the first place thus not using so much current. You reach the saturation level with less current.
As I said before symmetric pre-magnetization like you did in a torus-core will bring about a different behavior than in a solenoid which is magnetized along its axis. It can not be compared.

For any valid test you have to repeat this pre-magnetization and pulsing using a solenoid which is at the same time moving by another magnet, as in the muller device
It does not make sense this way â€" of course depending if you like to find something out about muller-principle or some basics about  torus-core-coils with different materials.

Regards

Kator01

[firlight]

Hi Dave, thanks for posting your additional comments and new test results.

I'll try again to see if I can get a small Inductance change in the FERROXCUBE.

Concerning the current drop when the core is biased. You believe there is an inductance gain! ... how interesting. Kator01 says there is no Inductance gain. I don't know what an Inductance gain would look like on the scope. So I started this topic to see if anyone has the answers. So far we have a split.

Not sure why you ask "does the inductance remain high when you remove the bias magnet?"

I think the answer is no but I show the differences in the video (with and without magnet)

Thanks for sharing

Luc

Hi Luc
          Will try and explain again what is happening which causes a reduction in current.It is called Inductive Reactance.I suggest you study this ,read the bit inductive reactance.http://www.ndt-ed.org/EducationResources/CommunityCollege/EddyCurrents/Physics/selfinductance.htm
With your core you are increasing the permability  which increases the inductance.
You can test this with a Air coil.Take one Air coil connect to a function generator  use some frequency and connect in series with a current meter,note the current then insert a piece of
ferrite rod and you will see a current reduction Caused by more reactive current.
Lenz`s Law ,or "For every action there is a equal and opposite reaction" Which opposes the primary current.

Regards Dave

[gotoluc]

Hi Luc,

unfortunately I have not so much time to go into great length of explanation. But I will try to make it understandable.
You have to somehow find some literature to understand the BH-diagram. because It is essential for further understanding what is going on.

First:    comparison of areas of both curves
Your coil is running idle in both cases. This does not show a real situation. It will be different under load that is current draw by a secondary coil or physical movement towards a pm  or away from it.

Second:  you do not know where the zero-line is in the second curve because you have the static pre-magnetization left in the core ( after puls off ) due to your pm attached to it. I am sure the curve is above the zero-line, meaning in the positive area of induced voltage. It must be so. If you would remove the pm from your coil after switching off the puls, only then will you see the whole picture.
But this is impossible to to.

If you look at the pic I attached to my post , the full BH diagram is the dynamic path of sinuswave-current flowing in the coil. For a DC-Puls - as you have applied it - only that part of the curve is valid which is above the horizontal zero-line ( Middle diagram)  As the fieldstrength rises ( Ampere Turns per Meter ) while the puls increases the current in the coil so does the induced Voltage per second = B. It rises steep first and enters the saturation-area where the curve gets more flat.
If puls is cut off the the upper left part of the BH-curve is valid. At that time current from your puls-generator  stops and the magnetic field collapses creating the negative spike. So the current you had to spent is 230 mA as you stated.  You have not spent current for reversal of magnetization because you just stopped the current  while an ac-current would continue to demagnetize to zero and further on to the negative side consuming more power

Now if you magnetize your core with a permanent-magnet the BH-curve starts at the level of the arrows either in the positive side ( above the horizontal level) or the negative side depending on the  pm-pole facing your coil. Lets assume your pre-magnetization has shifted the level above zero. Then this means your puls-current starts here and does not have to magnetize up to this arrow- level in the first place thus not using so much current. You reach the saturation level with less current.
As I said before symmetric pre-magnetization like you did in a torus-core will bring about a different behavior than in a solenoid which is magnetized along its axis. It can not be compared.

For any valid test you have to repeat this pre-magnetization and pulsing using a solenoid which is at the same time moving by another magnet, as in the muller device
It does not make sense this way â€" of course depending if you like to find something out about muller-principle or some basics about  torus-core-coils with different materials.

Regards

Kator01

Thanks Kator01 for taking the time to better explain this.

It is beginning to make more sense! I'll let it digest for some time and reread again later.

Thanks for sharing

Luc

[gotoluc]

Hi Luc
          Will try and explain again what is happening which causes a reduction in current.It is called Inductive Reactance.I suggest you study this ,read the bit inductive reactance.http://www.ndt-ed.org/EducationResources/CommunityCollege/EddyCurrents/Physics/selfinductance.htm
With your core you are increasing the permability  which increases the inductance.
You can test this with a Air coil.Take one Air coil connect to a function generator  use some frequency and connect in series with a current meter,note the current then insert a piece of
ferrite rod and you will see a current reduction Caused by more reactive current.
Lenz`s Law ,or "For every action there is a equal and opposite reaction" Which opposes the primary current.

Regards Dave

Hi Dave, thanks for posting your explanation.

It is very simple. I don't need to test an air core coil and adding a core to see the effect as I know the current will drop. However, I find it interesting that you seem to be saying the PM is raising the cores permeability therefore we have a drop in current.

Kator01 explanation seems to be quite different!

Interesting

Thanks for sharing

Luc

[Magluvin]

Hey Luc

I think the answer as to how and why is more complicated than just saying it increases inductance.  To test, run a slow freq sweep to the coil, no magnet , then sweep with the mag, and watch the scope. There may be differences at different freq than just measuring a larger inductor.

Have you tried the magnet to the outside of the core, like I did on the orbonbon? I even had multiple mags on the outer core that gave it an advantage for different configs.

Good to see ya back in action. ;]

Mags