Inductor with a Magnet

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 -

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).

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Note: Ensure correct polarity prior to connection.

In article , john@Neopha.44in88.net mentioned...

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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It is a horizontal linearity control.

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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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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 , snipped-for-privacy@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.

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.

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Parafeed some DC into it from a larger (mH+) choke?

Tim

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material

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 , snipped-for-privacy@charter.net mentioned...

Which one would it be measuring, then? :-[

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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 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). You'll be glad you did! Just when you thought you had all this figured out, the gov't changed it:

Toroids are out, and pot cores would be difficult.

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.

That could work.. Needs to be DC though, not varying DC like the input to the converter ckt.

the inductance does vary with current density. push the current too far, and the inductance pretty much goes away (saturation)

In article , snipped-for-privacy@cedar.net mentioned...

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.

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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.

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" Gave us:

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" Gave us:

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.

But it doesn't have any adjustment.

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