An Anti-Cogging Core??

[Randy Gross]

This web site, http://www.otherpower.com/pmg2.html , came up in another
discussion. The author built a wooden alternator with air core coils to
eliminate the cogging effect in the PMG.

Could stainless steel, or other alloy, be used in this situation to
boost inductance in the coil but not cog the magnet?

The stainless I work with has a slight magnetic attraction. The magnet
will not stick but, you can feel the tug when the magnet is close.

This brings up another question:

Is there a non-ferrous metal ( alloy ) that can be wrapped in a coil of
wire and utilized as an electromagnet?

Curiosity is a good thing!

rg

 

[John Popelish]

Randy Gross wrote:

This web site, http://www.otherpower.com/pmg2.html , came up in another
discussion. The author built a wooden alternator with air core coils to
eliminate the cogging effect in the PMG.

Could stainless steel, or other alloy, be used in this situation to
boost inductance in the coil but not cog the magnet?

No. The magnetic attraction is caused by the sudden increase of flux
as the magnet gets near. That same, sudden increase in flux is what
makes the voltage generation so large and efficient.

The stainless I work with has a slight magnetic attraction. The magnet
will not stick but, you can feel the tug when the magnet is close.

If it is attracted, it will help, but if it is attracted less than
iron, it will work less well than iron.

This brings up another question:

Is there a non-ferrous metal ( alloy ) that can be wrapped in a coil of
wire and utilized as an electromagnet?

There are lots of ferromagnetic alloys, including some that contain
little or no iron (especially those containing nickel), but you aren't
likely to run across many of them in your basement or junkyard.

Curiosity is a good thing!

You can retain much of the gain of an iron core without producing
cogging, if the iron closes most of the flux path, but does not have
what are called salient poles (protruding bits that concentrate the
flux at specific angular locations).

For instance, if you have a rotating two pole magnet structure and a
pair of stationary coils on opposite sides of the rotating magnet, you
have a very long path for the flux from one pole of the magnet,
through the coil, through the air,around the outside to the back side
of the other coil, through that coil and back to the other magnet
pole. All that air really weakens the amount of flux taking that path.

Now, if you place a smooth ring of iron around the coils (and make
them as flat and thin as possible, to get that ring as close to the
magnet as possible) you have provided a much easier path for the flux
between the outsides of the coils, so that the only air in the path is
from the magnet poles to the coils (the rotational air gap) and the
thickness of the coils. So the peak flux passing through the coils
will be much increased. But there are no chunks of iron sticking out
toward the magnet (salient poles) at any particular angles, so there
will be no cogging.

 

[Randy Gross]

John Popelish wrote:

Randy Gross wrote:
This web site, http://www.otherpower.com/pmg2.html , came up in
another discussion. The author built a wooden alternator with air
core coils to eliminate the cogging effect in the PMG.

Could stainless steel, or other alloy, be used in this situation to
boost inductance in the coil but not cog the magnet?

No. The magnetic attraction is caused by the sudden increase of flux
as the magnet gets near. That same, sudden increase in flux is what
makes the voltage generation so large and efficient.

The stainless I work with has a slight magnetic attraction. The
magnet will not stick but, you can feel the tug when the magnet is
close.

If it is attracted, it will help, but if it is attracted less than
iron, it will work less well than iron.

This brings up another question:

Is there a non-ferrous metal ( alloy ) that can be wrapped in a
coil of wire and utilized as an electromagnet?

There are lots of ferromagnetic alloys, including some that contain
little or no iron (especially those containing nickel), but you
aren't likely to run across many of them in your basement or junkyard.

Curiosity is a good thing!

You can retain much of the gain of an iron core without producing
cogging, if the iron closes most of the flux path, but does not have
what are called salient poles (protruding bits that concentrate the
flux at specific angular locations).

For instance, if you have a rotating two pole magnet structure and a
pair of stationary coils on opposite sides of the rotating magnet,
you have a very long path for the flux from one pole of the magnet,
through the coil, through the air,around the outside to the back side
of the other coil, through that coil and back to the other magnet
pole. All that air really weakens the amount of flux taking that
path.

Now, if you place a smooth ring of iron around the coils (and make
them as flat and thin as possible, to get that ring as close to the
magnet as possible) you have provided a much easier path for the flux
between the outsides of the coils, so that the only air in the path
is from the magnet poles to the coils (the rotational air gap) and
the thickness of the coils. So the peak flux passing through the
coils will be much increased. But there are no chunks of iron
sticking out toward the magnet (salient poles) at any particular
angles, so there will be no cogging.
jpopelish@rica.net

I think I understand. I read at

http://www.tpub.com/neets/book1/chapter1/1j.htm

where a process for magnetic shielding is described. The author placed
short lengths of Iron rod, in a box configuration, around the object
that he intended to "shield" from the flux. The Iron provided a
positive path for the flux.

Should the rings around the coils touch creating a complete path or,
should they "halo" the coils?

rg

 

[John Popelish]

Randy Gross wrote:

I think I understand. I read at

http://www.tpub.com/neets/book1/chapter1/1j.htm

The shielding analogy is good, except that the magnet is inside the
shield. The ring contains the flux to mostly inside the ring.

where a process for magnetic shielding is described. The author placed
short lengths of Iron rod, in a box configuration, around the object
that he intended to "shield" from the flux. The Iron provided a
positive path for the flux.

The electrical analogy is that the iron represents a low resistance
path for current. The permanent magnet produces some amount of
magneto motive force that is analogous to DC voltage. The air gaps
represent high resistance material. The less air the flux has to pass
through and the more or the path that can be in iron, the higher the
current (flux).

Should the rings around the coils touch creating a complete path or,
should they "halo" the coils?

The iron outside the coils should be one complete ring (a slice of
iron pipe or a stack of washers). The coils are slipped between the
ring and the rotating magnet. The space needed for the coils is what
forces there to be a minimum magnetic gap at each end of the magnet.
The ring collects the flux from one pole of the magnet, splits it in
half, and brings each half to the other pole of the magnet through
each half of the ring. Since this process is independent of the
angular position of the magnet, there is no cogging. In the absence
of any coil current, the total flux is constant, independent of position.

 

[Randy Gross]

John Popelish wrote:

Randy Gross wrote:

I think I understand. I read at
http://www.tpub.com/neets/book1/chapter1/1j.htm

The shielding analogy is good, except that the magnet is inside the
shield. The ring contains the flux to mostly inside the ring.

where a process for magnetic shielding is described. The author
placed short lengths of Iron rod, in a box configuration, around
the object that he intended to "shield" from the flux. The Iron
provided a positive path for the flux.

The electrical analogy is that the iron represents a low resistance
path for current. The permanent magnet produces some amount of
magneto motive force that is analogous to DC voltage. The air gaps
represent high resistance material. The less air the flux has to
pass through and the more or the path that can be in iron, the higher
the current (flux).

Should the rings around the coils touch creating a complete path or,
should they "halo" the coils?

The iron outside the coils should be one complete ring (a slice of
iron pipe or a stack of washers). The coils are slipped between the
ring and the rotating magnet. The space needed for the coils is what
forces there to be a minimum magnetic gap at each end of the magnet.
The ring collects the flux from one pole of the magnet, splits it in
half, and brings each half to the other pole of the magnet through
each half of the ring. Since this process is independent of the
angular position of the magnet, there is no cogging. In the absence
of any coil current, the total flux is constant, independent of
position.
jpopelish@rica.net

This is an interesting approach, it's like a venturi, a flux venturi! I
almost wish I could "see" this process in operation. I see what you
mean about efficiency too, the flux is gathered and then targeted.
Fascinating!

rg

 

[Jasen Betts]

In article <xn0e6551x3xjk4000@news.east.earthlink.net>, Randy Gross wrote:

Should the rings around the coils touch creating a complete path or,
should they "halo" the coils?

as I understand it he's decribing a setup where there's a magnet rotating
inside a freomagnetic ring and in the gaps between the ring asn the magnet
is wound the output coils

it seems to me that you could use a single continouas coil wound around the
core like in a way similar to a toroidial transformer but with the ends
shorted (to make it continuous) and tapped at equal spacing for however
many phases you want.

Bye.
Jasen

 

[John Popelish]

Jasen Betts wrote:

In article <xn0e6551x3xjk4000@news.east.earthlink.net>, Randy Gross wrote:


Should the rings around the coils touch creating a complete path or,
should they "halo" the coils?




as I understand it he's decribing a setup where there's a magnet rotating
inside a freomagnetic ring and in the gaps between the ring asn the magnet
is wound the output coils

it seems to me that you could use a single continouas coil wound around the
core like in a way similar to a toroidial transformer but with the ends
shorted (to make it continuous) and tapped at equal spacing for however
many phases you want.

I agree.