Inductor with a Magnet

  • Thread starter Watson A.Name - "Watt Sun
  • Start date
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Watson A.Name - "Watt Sun

Guest
I pulled some ferrite core chokes out of a Compaq monitor and one had
a magnet on the top, held on by heat shrink tubing. I measured the
inductance with the magnet on, and it measured 8.2 uH. I cut off the
HST and removed the magnet, and the inductance shot up to 35 uH. I
think this has something to do with varying the permeability.

I don't remember seeing anything about this kind of choke in any
electronics manuals, so I thought I'd do a web search but I came up
with nothing. I tried magnetically polarized inductor and magnetic
core inductor, but neither gave any info that I could find. Do you
know what they call these devices? Thank you.


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Just when you thought you had all this figured out, the gov't
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@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@
 
Try magnetically biased. Placing the magnet on the inductor really is
shifting the saturation point so that in one direction of current flow, it will
saturate easily but in the other, it will not.

Cheers!

Chip Shults
My robotics, space and CGI web page - http://home.cfl.rr.com/aichip
 
On Mon, 10 Nov 2003 05:02:09 -0800, Watson A.Name
- "Watt Sun, Dark Remover" <alondra101@hotmail.com> wrote:
I pulled some ferrite core chokes out of a Compaq monitor and one had
a magnet on the top, held on by heat shrink tubing. I measured the
inductance with the magnet on, and it measured 8.2 uH. I cut off the
HST and removed the magnet, and the inductance shot up to 35 uH. I
think this has something to do with varying the permeability.

I don't remember seeing anything about this kind of choke in any
electronics manuals, so I thought I'd do a web search but I came up
with nothing. I tried magnetically polarized inductor and magnetic
core inductor, but neither gave any info that I could find. Do you
know what they call these devices? Thank you.
Click to expand...
Wow! A new 'field' of interest!
Using "flux biased inductor" gave one link to
a NASA paper, using a magnet in the air gap.
Sorry, the tiny browser I used doesn't have cut/paste (dillo).



--
_______________________________________
John E. Todd <> jtodd@island.net

Note: Ensure correct polarity prior to connection.
 
In article <slrnbqva7j.n6.john@Neopha.44in88.net>,
john@Neopha.44in88.net mentioned...
On Mon, 10 Nov 2003 05:02:09 -0800, Watson A.Name
- "Watt Sun, Dark Remover" <alondra101@hotmail.com> wrote:

I pulled some ferrite core chokes out of a Compaq monitor and one had
a magnet on the top, held on by heat shrink tubing. I measured the
inductance with the magnet on, and it measured 8.2 uH. I cut off the
HST and removed the magnet, and the inductance shot up to 35 uH. I
think this has something to do with varying the permeability.

I don't remember seeing anything about this kind of choke in any
electronics manuals, so I thought I'd do a web search but I came up
with nothing. I tried magnetically polarized inductor and magnetic
core inductor, but neither gave any info that I could find. Do you
know what they call these devices? Thank you.


Wow! A new 'field' of interest!
Using "flux biased inductor" gave one link to
a NASA paper, using a magnet in the air gap.
Sorry, the tiny browser I used doesn't have cut/paste (dillo).
Click to expand...
I didn't see that when I googled on flux biased inductor, but I did
see a bunch of weird stuff like SQUIDs, Josephson junctions, and even
a flux capacitor(!)

You should be able to highlight the text, do a Ctrl-C for copy, and
then in the other prog, do a Ctrl-V for paste.

--
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###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@
 
Watson A.Name - Watt Sun, Dark Remover wrote:
I pulled some ferrite core chokes out of a Compaq monitor and one had
a magnet on the top, held on by heat shrink tubing. I measured the
inductance with the magnet on, and it measured 8.2 uH. I cut off the
HST and removed the magnet, and the inductance shot up to 35 uH. I
think this has something to do with varying the permeability.

I don't remember seeing anything about this kind of choke in any
electronics manuals, so I thought I'd do a web search but I came up
with nothing. I tried magnetically polarized inductor and magnetic
core inductor, but neither gave any info that I could find. Do you
know what they call these devices? Thank you.
Click to expand...
It is a horizontal linearity control.


--
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Change 'news' to 'sewn' in my Reply address to avoid my spam filter.
 
On Mon, 10 Nov 2003 05:02:09 -0800, Watson A.Name - "Watt Sun, Dark
Remover" <alondra101@hotmail.com> wrote:

I pulled some ferrite core chokes out of a Compaq monitor and one had
a magnet on the top, held on by heat shrink tubing. I measured the
inductance with the magnet on, and it measured 8.2 uH. I cut off the
HST and removed the magnet, and the inductance shot up to 35 uH. I
think this has something to do with varying the permeability.

I don't remember seeing anything about this kind of choke in any
electronics manuals, so I thought I'd do a web search but I came up
with nothing. I tried magnetically polarized inductor and magnetic
core inductor, but neither gave any info that I could find. Do you
know what they call these devices? Thank you.
Click to expand...
Useful where you anticipate a steady current flowing but still want
the inductance there (without saturating the inductor) should the
current rise more.

Measuring inductance may have kicked it over into saturation or the
magnet is acting as a shorted turn on the end of the ferrite -
lowering inductance for measuring purposes. Just a theory.



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I pulled some ferrite core chokes out of a Compaq monitor and one had
a magnet on the top, held on by heat shrink tubing. I measured the
inductance with the magnet on, and it measured 8.2 uH. I cut off the
HST and removed the magnet, and the inductance shot up to 35 uH. I
think this has something to do with varying the permeability.
Click to expand...
These are used where you are going to have a really large DC current, like
in a horizontal sweep section, or boost converter. The magnet biases the
core "negative", allowing the current to use the full area from "negative"
to "positive" instead of just from zero to "positive".

You could just use a larger core, but then the inductance goes up, material
gets expensive etc.
 
In article <46Odnd_i8dieWTKiRVn-iw@comcast.com>, dvanhorn@cedar.net
mentioned...
I pulled some ferrite core chokes out of a Compaq monitor and one had
a magnet on the top, held on by heat shrink tubing. I measured the
inductance with the magnet on, and it measured 8.2 uH. I cut off the
HST and removed the magnet, and the inductance shot up to 35 uH. I
think this has something to do with varying the permeability.

These are used where you are going to have a really large DC current, like
in a horizontal sweep section, or boost converter. The magnet biases the
core "negative", allowing the current to use the full area from "negative"
to "positive" instead of just from zero to "positive".

You could just use a larger core, but then the inductance goes up, material
gets expensive etc.
Click to expand...
I've been using toroids and pot core inductors for the LED V boost
converters I've been making. Looks like I can't put a magnet on
those.

So I took the magnet off, and the inductance went up from 8.2 uHy to
35 uHy. It would stand to reason that if I put enough current thru
the coil to balance out the magnet's field, then the inductance would
also be 35 uHy. There's no way I can do that, because the LC meter
doesn't allow DC, to my knowledge. So I can't test out my theory.


--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@
 
"Watson A.Name - Watt Sun, Dark Remover" <alondra101@hotmail.com> wrote in
message news:MPG.1a19665bba94f2cf9898e8@news.dslextreme.com...
There's no way I can do that, because the LC meter
doesn't allow DC, to my knowledge. So I can't test out my theory.
Click to expand...
Parafeed some DC into it from a larger (mH+) choke?

Tim

--
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Website @ http://webpages.charter.net/dawill/tmoranwms
 
"Dave VanHorn" <dvanhorn@cedar.net> wrote in message
news:46Odnd_i8dieWTKiRVn-iw@comcast.com...
I pulled some ferrite core chokes out of a Compaq monitor and one had
a magnet on the top, held on by heat shrink tubing. I measured the
inductance with the magnet on, and it measured 8.2 uH. I cut off the
HST and removed the magnet, and the inductance shot up to 35 uH. I
think this has something to do with varying the permeability.

These are used where you are going to have a really large DC current, like
in a horizontal sweep section, or boost converter. The magnet biases the
core "negative", allowing the current to use the full area from "negative"
to "positive" instead of just from zero to "positive".

You could just use a larger core, but then the inductance goes up,
material
gets expensive etc.
Click to expand...
Also good for some signal shaping - when current goes one way it's at full
inductance, when it goes the other way it has almost no inductance.

>
 
In article <vqvm847i8p5be0@corp.supernews.com>, tmoranwms@charter.net
mentioned...
"Watson A.Name - Watt Sun, Dark Remover" <alondra101@hotmail.com> wrote in
message news:MPG.1a19665bba94f2cf9898e8@news.dslextreme.com...
There's no way I can do that, because the LC meter
doesn't allow DC, to my knowledge. So I can't test out my theory.

Parafeed some DC into it from a larger (mH+) choke?
Click to expand...
Which one would it be measuring, then? :-[

Tim

--
Click to expand...
--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@
 
I've been using toroids and pot core inductors for the LED V boost
converters I've been making. Looks like I can't put a magnet on
those.
Click to expand...
Toroids are out, and pot cores would be difficult.

So I took the magnet off, and the inductance went up from 8.2 uHy to
35 uHy. It would stand to reason that if I put enough current thru
the coil to balance out the magnet's field, then the inductance would
also be 35 uHy. There's no way I can do that, because the LC meter
doesn't allow DC, to my knowledge. So I can't test out my theory.
Click to expand...
For this, you need a rod core.
At least if you don't want to get into machining neodymium magnets.
It can be done, find yourself a lapidary, with experience working opals.
 
"Tim Williams" <tmoranwms@charter.net> wrote in message
news:vqvm847i8p5be0@corp.supernews.com...
"Watson A.Name - Watt Sun, Dark Remover" <alondra101@hotmail.com> wrote in
message news:MPG.1a19665bba94f2cf9898e8@news.dslextreme.com...
There's no way I can do that, because the LC meter
doesn't allow DC, to my knowledge. So I can't test out my theory.

Parafeed some DC into it from a larger (mH+) choke?
Click to expand...
That could work..
Needs to be DC though, not varying DC like the input to the converter ckt.
 
Parafeed some DC into it from a larger (mH+) choke?

Which one would it be measuring, then? :-[
Click to expand...
the inductance does vary with current density.
push the current too far, and the inductance pretty much goes away
(saturation)
 
In article <ZLKdnQ2aG8FjYzKiRVn-uw@comcast.com>, dvanhorn@cedar.net
mentioned...
I've been using toroids and pot core inductors for the LED V boost
converters I've been making. Looks like I can't put a magnet on
those.

Toroids are out, and pot cores would be difficult.

So I took the magnet off, and the inductance went up from 8.2 uHy to
35 uHy. It would stand to reason that if I put enough current thru
the coil to balance out the magnet's field, then the inductance would
also be 35 uHy. There's no way I can do that, because the LC meter
doesn't allow DC, to my knowledge. So I can't test out my theory.

For this, you need a rod core.
At least if you don't want to get into machining neodymium magnets.
It can be done, find yourself a lapidary, with experience working opals.
Click to expand...
I took some old .5 GB HDs apart at work and used the neodymium magnets
to hold some pics to the file cabinet. Well, someone came over and
took one off, and let it snap into the steel so hard that it broke
into fragments, and the guilty party slinked off, never to admit his
bad behavior. So there are some fragments holding one corner up, and
it looks like the magnet is made of sintered particles, similar to
ferrite. I'd say it's probably very difficult to machine this
material, it'll just fracture if it's stressed.

I'm taking a huge 5.25" full-height 8-platter Priam HD apart. It has
a true linear motor for the heads, uses four BUZ71s to drive it in H-
bridge, I believe. Really quite a mechanical marvel, but it holds only
150 MB. Probably cost a couple thou back in early 1988, which is the
date code on many of the chips.


--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@
 
I took some old .5 GB HDs apart at work and used the neodymium magnets
to hold some pics to the file cabinet. Well, someone came over and
took one off, and let it snap into the steel so hard that it broke
into fragments, and the guilty party slinked off, never to admit his
bad behavior. So there are some fragments holding one corner up, and
it looks like the magnet is made of sintered particles, similar to
ferrite. I'd say it's probably very difficult to machine this
material, it'll just fracture if it's stressed.
Click to expand...
Like most rocks.
Lapidaries are skilled in cutting and shaping rocks.
The reason that I suggest someone with experience in opals, is that they are
similar to Neodymium magnets, they die if they get too warm. Best cut in a
stream of water.
I've had NIB magnets machined this way, to exact sizes, while I was waiting
on prototypes.
The machined pieces had almost exactly the strength of the protos, when they
finally arrived.
At least as good a match, as I would normally get between batches.

In the normal method, the magnet material is cut before charging, then they
are loaded in the zapper, and charged all together, so if the material is
decent, you'll get about 5% variation in a lot.
 
On Mon, 10 Nov 2003 05:02:09 -0800, Watson A.Name - "Watt Sun, Dark
Remover" <alondra101@hotmail.com> wrote:

I don't remember seeing anything about this kind of choke in any
electronics manuals, so I thought I'd do a web search but I came up
with nothing. I tried magnetically polarized inductor and magnetic
core inductor, but neither gave any info that I could find. Do you
know what they call these devices? Thank you.
Click to expand...
Try saturable core reactor. It's an old technique that relies on the
fact that any magnetic core will have a value of flux that saturate
and at that point the inductance will be far lower due the diminished
influence of the core.

I did some work about 35 years ago before veractors were common and
cheap using a powered iron cored inductor that had a secondary winding
to push DC through. Gave better tuning range than simple LC tuning
with practical parts.

More recently it was QEX or QST (brain fade) had a design for a loop
antenna using a saturable core to vary the loading inductor for remote
tuning.

Allison
 
On Mon, 10 Nov 2003 15:39:58 -0000, "Graham W"
<graham@his.com.puterINVALID> Gave us:

Watson A.Name - Watt Sun, Dark Remover wrote:
I pulled some ferrite core chokes out of a Compaq monitor and one had
a magnet on the top, held on by heat shrink tubing. I measured the
inductance with the magnet on, and it measured 8.2 uH. I cut off the
HST and removed the magnet, and the inductance shot up to 35 uH. I
think this has something to do with varying the permeability.

I don't remember seeing anything about this kind of choke in any
electronics manuals, so I thought I'd do a web search but I came up
with nothing. I tried magnetically polarized inductor and magnetic
core inductor, but neither gave any info that I could find. Do you
know what they call these devices? Thank you.

It is a horizontal linearity control.
Click to expand...

There ya go. Nearly all CRT type monitors have one.
 
On Mon, 10 Nov 2003 13:26:06 -0800, Watson A.Name - "Watt Sun, Dark
Remover" <alondra101@hotmail.com> Gave us:

. I'd say it's probably very difficult to machine this
material, it'll just fracture if it's stressed.
Click to expand...

One thing would be a cut off wheel on a Dremel tool. It would
abrade the surface as opposed to trying to cut at it. Just like
ferrites, not machinable.

There are hard drive grave yards out there where working drives can
be bought for a few bucks each.

I have an old full height 5.25" ESDI drive that I took apart. The
head mech is a huge linear motor, several head pairs. Absolutely no
slew at all. Straight passes! Huge rare earth magnets, and big
copper bars. Good inch and a half stroke.

One of the most interesting little motors I've ever seen. As soon
as I find it, I'll post some photos in alt.binaries.misc.
 
Graham W wrote:

Watson A.Name - Watt Sun, Dark Remover wrote:

I pulled some ferrite core chokes out of a Compaq monitor and one had
a magnet on the top, held on by heat shrink tubing. I measured the
inductance with the magnet on, and it measured 8.2 uH. I cut off the
HST and removed the magnet, and the inductance shot up to 35 uH. I
think this has something to do with varying the permeability.

I don't remember seeing anything about this kind of choke in any
electronics manuals, so I thought I'd do a web search but I came up
with nothing. I tried magnetically polarized inductor and magnetic
core inductor, but neither gave any info that I could find. Do you
know what they call these devices? Thank you.


It is a horizontal linearity control.
Click to expand...
But it doesn't have any adjustment.



--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@
F
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