Confirming the Delayed Lenz Effect

[TinselKoala]

@Conrad: Now you can put your scope probe "ground" references at the negative rail where they belong, and use a second probe "tip" at the location on the bottom of the load where you now have the first probe's reference attached (mosfet Drain). The voltage difference between the probes will give the drop across the load and can be used to compute the current in the load.
Your gate voltage dropping network is workable I think, but the resistances are kind of low for my liking. You generally don't need such a low value to pull a mosfet gate down when it's supposed to turn off, so you might be wasting some power here. Also, it's sometimes nice to protect the gate with a pair of Zeners from gate to source, back-to-back, at the desired max gate voltage, like 12 or 15 volts. This will limit the max gate voltage and hopefully shunt overvoltage spikes away from the gate and sometimes can save a mosfet that's in severe service. With the optocoupler acting as a sort of "fuse" this shouldn't really be necessary, but who knows until the circuit is built and tested and has had a few failures.

[Farmhand]

Hi all,  I was wondering MileHigh could you look at these scope shots and my drawing and tell me your opinion on what is happening ?

Anyone is welcome to comment.

I'll write what I think here, I'll track the rotor as the different points on the rotor pass the motor coil MC1. The coil MC2 is reverse connected and the coils are placed as shown or thereabouts. The timing is slightly advanced for normal efficient running at around 1800 to 2200 rpm. 

The events are kind of overlapping. As the drawing shows. I neglected the flyback diode, but there is one.

1) At point "A" the mosfet turns on ( I know because the timing is set to do that). This repulses the north magnet above the MC1 coil and continues until just before the next south magnet "engages" the core properly. Also as the south magnet is approaching the MC2 coil it cannot oppose the current. EDIT: Actually I think the south magnet approaching the charging coil does oppose and stop the current in the Charging coil, going by the shots.

2) At about point "B" the current starts in MC2.  This repulses the south magnet as well adding torque to the rotor.

3)  At point "C" the mosfet turns off and the discharge starts. By this point the rotor has turned 45 degrees and the south magnet is above the motor coil MC1 reinforcing the current through it and back to/through the charging coil MC2 via the return circuit. This also is attracting the next South magnet to the MC1 motor coil and the next North magnet to the MC2 coil.

4) From points "C" to "D" the motor coil discharges. This is in time with the approach and departure of the South magnet over the MC1 motor coil and the North magnet passing the MC2 Charging coil. Both reinforcing the current through the coils. And attracting the magnets. At some point the voltage is such that the coils cannot add to it by generation so there is no Lenz effect drag only cogging.

5) THe current in the Charging coil continues towards point "E". If the duty is low there is dead time at the end I guess.

With the scope shot the motor coil current is the yellow trace and is upside down. The points marked on the shots don't necessarily relate to the sketch.
The rise of current in the Motor coil starts at point "A".
The rise of current in the Charging coil starts at point "E" or thereabouts.

EDIT: After some more testing I have determined that the mosfet "on" time (2 mS) is between point "B" and point "C" on the scope shots, and the discharge is the fall of current of course.

To me it looks good,  I just need to get the correct MC2 placement for the delay ect. .

The drawing is a bit off compared to the scope shot but the sketch is what I think I am trying to do.

Cheers

P.S. It does look to me that the motor coil current is rising before the mosfet turns on in those shots. I just took a couple more to study.

It's a resonant push at the right time, just to peak the currents. the next shots show good current in the motor coil and much less in the charging coil but for longer. Sweet.

I will still need to test the all north facing magnets but still only firing on four to see the effect the extra magnets have when they are "N" magnet faces.

OH and one other thing is that I noticed that at efficient running with no load there can be and I took a shot of 900mA RMS current in the motor coil while there was only 700mA RMS current in the charging coil and the circuit was only drawing 400mA from the 12.5 volt battery. Which was turning the 580 gram rotor at about 2200 rpm Whatever that means .  .. 

OK so point "D" on the sketch corresponds to point "F" on the scope shot.





..

[Farmhand]

This generator coil works to speed up the rotor under short circuit.

http://www.youtube.com/watch?v=YpKZw15A41Y

Cheers

[gyulasun]

Dear Farmhand,

Does your generator coil have a ferromagnetic core or it is an air core coil?

If it has a ferromagnetic core, then removing the generator coil completely from your setup, what is the RPM then?

thanks, Gyula

[Farmhand]

Hi Gyula, Yes it has the part from the motor core inside a square laminated one with curved ends. I can check that no problem but I'll need to be a bit  careful so I get a proper result, I'll have to leave it running while I remove the mount with the coil on it, might take a while and I'm about to go do stuff so I might not get it done for a while I think the rpm will be slightly higher without the core there but the input power probably will too also be higher because of the design of the motor, the pulse width will not change but the input power is related to the rpm, so without the core if the motor does spin faster it might consume more energy,  however it didn't seem to in the video, I didn't look that closely though, I do it and post all is shared.  I had that in mind.  See the input current in the video, that is the current out of the battery at 12.5 volts or so.

Umm there is 15.6 uF across the coil though just to be honest.   

I'll do the test it sounds like a good idea.

Cheers