Electrical generation via cored coils and axial flux

[tropes]

Hi Tropes,

Normally, due to Lenz law, an approaching magnet in a coil produces a repel situation (assuming the coil has a heavy electrical load connected to it).

My further notice here is that in case of the coil has a soft iron core, the repel effect is somewhat gets reduced due to the natural attraction between the core and the approaching magnet. But Lenz still affects the operation.

rgds, Gyula

To add to my confusion, I reread some earlier notes and found this quote from
http://www.totallyamped.net/adams/index.html

"the fast rotating magnets that sweep past the coil, also induce an ElectroMotive Force back into the coil which is in the opposite direction to the incoming supply current. This opposing direction of EMF is what is known as Back EMF and happens in all conventional motors regardless of motor type."

If the induced current is in the opposite direction of the incoming supply current, then the coil would be attracting the magnet.
Tropes

[gyulasun]

...
If the induced current is in the opposite direction of the incoming supply current, then the coil would be attracting the magnet.
...

But this attraction is not experimented in practice?

In case of a conventional motor, you may consider the role of back emf as if there was an automatically self-varying voltage source connected in series with the rotor coil, with always an opposite polarity with respect to the input voltage. When motor speeds up, this "voltage source"s amplitude starts increasing from zero to a maximum value (assuming no load on the motor's shaft) but never higher in amplitude than the input voltage feeding the motor. If a load appears on the shaft, rpm tends to decrease, hence back emf also decreases and the motor input current this way is forced to increase to make up for the previous rpm.

IF you feel like reading here are some links:

http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/motorac.html

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/farlaw.html#c2

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/farlaw2.html#c1

If you still have problems, then try to describe a practical setup like moving permanent magnet - coil and consider any action - reaction that happens.

In your example of an approaching magnet to a coil, the current induced by this approach in the coil generates a current whose magnetic field repels the approaching magnet, this Lenz law in full effect.

And your above quoted sentence is not correct because the induced current never gets higher than the incoming current due to copper and some other losses. In order for the coil to attract the magnet in such induction case, the induced current ought to exceed the input current that have caused it. Unfortunately this is not the case in practice.

rgds, Gyula

[tropes]

"... due to Lenz law, an approaching magnet in a coil produces a repel situation..."

Hi Gyula
My interest is with a DC pulse motor which does not use rotating coils.
As illustrated here
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/farlaw.html#c2
the current induced in the coil repels the approaching magnet. That is in the same direction as the supply current in a pulse motor which uses coils in the stator and magnets in the rotor.
Tropes

[capthook]

That is in the same direction as the supply current in a pulse motor which uses coils in the stator and magnets in the rotor.
Tropes

This can be considered almost a 'pre-charging' of the coils, if you will,
with the approaching magnet.
This will create a small field in the coil that when the circuit is opened, will allow the source voltage to flow more easily.
The larger the coil, the larger the 'pre-charge'.
If capturing CEMF (collapsing EMF), this will be slightly boosted as well.

But, it's basically no gain. 
The 'pre-charge' comes at the cost of additional repulsion on approach, slowing the rotor.
And additional drag on exit, slowing the rotor.

[tropes]

This can be considered almost a 'pre-charging' of the coils, if you will,
with the approaching magnet.
This will create a small field in the coil that when the circuit is opened, will allow the source voltage to flow more easily.
The larger the coil, the larger the 'pre-charge'.
If capturing CEMF (collapsing EMF), this will be slightly boosted as well.

But, it's basically no gain. 
The 'pre-charge' comes at the cost of additional repulsion on approach, slowing the rotor.
And additional drag on exit, slowing the rotor.

thanks capthook
I believe this to be the case but I'm not sure how the CEMF is affected.
The  picture of my motor is prior to the addition of coils and power.
Tropes