Rotating Magnetic Field's and Inductors.

[poynt99]

Brad,

If your hypothesis is that the drive coil's inductance is being increased by the passing magnets, could you devise a test setup to verify your hypothesis?

[poynt99]

There is one way I can think of that might increase the inductance of a cored inductor, but only momentarily during the ON time, which of course is what we are dealing with here.

If we think of the core polarization as a pendulum, where zero polarization is when the pendulum is at a neutral low position, and full polarization (in either direction) when the pendulum is at 90 degrees to one side or the other, it is possible that an apparent increase in inductance might occur if the pendulum (core) is pre-set at 90 degrees (or anything between 0 and 90) to one side, and the firing of the coil is in the direction or polarity which pulls the pendulum in the opposite direction, causing the pendulum to pass through zero.

I think we know that the converse is true, i.e. the momentary inductance would be decreased if the firing of the coil was in the same polarization that the core was already in.

This would not be too difficult to test, and I think could be done in a sim quite easily as well. I will give it a try.

[tinman]

Brad,

If your hypothesis is that the drive coil's inductance is being increased by the passing magnets, could you devise a test setup to verify your hypothesis?

Is the information and test results not enough to confirm this?
How else can you increase the output current(while maintaining the same output voltage),when the input current has been decreased. The decrease of input current obviously did not decrease the magnitude of the magnetic field being built around the inductor,as if it did,then we would see what your results showed,and that being a reduction in output current. If the core of the coil is biased by a PM's field that is opposite to the one to be induced when current starts to flow through the coil-dose that not increase the effective inductance during the point of current flow through the coil--as MH stated ?.

As you know(or should know),with my DUT,a south field is approaching the core of the coil,and this field is induced into the core before the ON time. Once the current starts to flow,this induced field from the PM now has to be flipped to the opposite field,and the magnet is pulled the rest of the way toward the core of the coil.

If i was to make a test setup to verify this,how would i go about it,other than the way i already have? I think with your sim setup,the opposite field that the tank circuit provide's(the simulated rotor),is happening at the same time as the field that is being produced by what would be your coil,where as in my DUT,the field from the magnet on the rotor is already building in the core of the coil before the current starts to flow in the coil.


Brad

[tinman]

OK-just finished the test with the ring magnet on a string--cotton thread used for sewing.

I started with the magnet 2mm off the wooden floor. When started,the magnet once again(as all the other test done showed)spun in a CCW direction. After 7 minutes the magnet touched the floor.
Two things tell us that it is the string/thread unwinding.
1- All thread around the world(or most there off) is wound in the same direction--something to do with a world standard,so as it suits all sewing machines around the world,and the way the bobins spin in those machines. I guess if it was wound in the opposite direction,the spin direction of the bobins in sewing machines may unwind the thread?.
Anyway,this is why we all get the same CCW spin,no matter where in the world we are.

2- The simple fact that my thread got longer,and not shorter,is telling us that the thread is unwinding.

Ah well,it was a quick,easy and fun test,and as far as i can see--problem solved.


Brad

[wopwops]

About the magnet and thread experiment: I replicated this and really thought it was incredible, but it must be caused by the tension in the thread. I eliminated the thread by placing my magnet in a plastic lid and floating the lid in a plastic bowl full of water. The attraction to north was very strong. The magnet was easily able to swing the lid around. Sadly, it cogs as one would expect. No rotation in either direction.