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Wanted to get the inductance right, and know I can make a simple wound coil of magnet wire for a search coil using the coil calculators, but I want to wrap around a soft iron ferrite rod. Is there a different calculation for that? Could I just use a couple fixed inductors at the right total inductance and resistance? They are small and cheap, but would inter-wire capacitance cause them to be unusable?
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How to build Pin pointer coil for surf pi? Anybody? -
We had some discussions of this matter some years ago. Unfortunately Geotech1's search feature does not work so well, making Google or other search engine often better to locate desired archives.
Yes, ferrite rods can be used to form cores on which to wind coils. The ferrite concentrates the lines of force, which yields more inductance in a smaller space, using less wire.
No, you don't want to use fixed inductors that you can purchase off-the-shelf.
One problem that you will encounter using ferrite rods is that it is usually impossible to calculate in advance the inductance for a given number of turns. Even if you find specifications for the rod's material, the rod's AL (inductance index) depends on the rod's dimensions. -Good luck- finding specifications for a specific rod of specific dimensions. You would generally need an inductance meter or some other tools to determine the final product's inductance. Also, beware that the wrong material can result in excessive flyback time.
And, why use magnet wire? you will generally have less interwinding capacitance with PVC, polyethylene, or Teflon insulated wire. The enamel used in magnet wire is quite thin, meaning that the wires lie closer together, thereby adding capacitance.
I have read that soft ferrite is desired but I really can't tell from experience which ferrite material will be best. Just what, constitutes "soft"?? My recommendation is to find various rods and do some experimentation.
You can arrange more than one core an an array which will allow greater inductance for a fewer number of turns, but I have a feeling that there is a point of diminishing returns in regard to detection range.
I seem to remember a bbsailor's recommendation for using (ICH) ROD7.5/50 (currently available from Surplussales.com) but that was a long time ago and my memory is often faulty.
Alltronics, Allelectronics, BGmicro, and goldmineelectronics (dot.coms) are some other surplus dealers that may have some usable materials.Comment
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Thanks Porkluvr!
From what (little) I understand, I think "soft" in this case is in terms of magnetic coercivity.
http://en.m.wikipedia.org/wiki/Coercivity.
From Wikipedia:"Ferromagnetic materials with high coercivity are called magnetically hard materials, and are used to make permanent magnets. Permanent magnets find application in electric motors, magnetic recording media (e.g. hard drives, floppy disks, or magnetic tape) and magnetic separation.
Materials with low coercivity are said to be magnetically soft. They are used in transformer and inductor cores, recording heads, microwave devices, and magnetic shielding."
As for "why magnet wire", it was what I had on hand. Will look for some Teflon or pvc coated wire on your advice.
Probably won't make myself the pinpointer until I find a friend with an inductance meter.
Cheers,
GSComment
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rod core inductors
Here's something I just found at http://download.ebooks6.com/download.php?id=12550
From the title, if this won't shed some light on the subject there is no light.
edit: Here's another place to look. Buried down about halfway on this page are some good tips about determining Al value (but they're calling it by another name, uh-oh).Comment
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no hard work
http://www.youtube.com/watch?v=oaCyVGAuYX0
i put some turns of 0,25 litz wire around a 10mm ferrite rod
start with 120 turns + and see what you et for a result
the specs are other like a simple monocoil (wire + ferrite rod gave a higher inductance than normal)
monocoil best under 300mH, ferrit core coil over 500mH
you can make the induction (L) variable by winding the wire on a tube (for exaple 12mm round cable channel) with double side adhesive tape
put the ferrit rod into the tube and move it within the coil until you get good results
i mine case i got really easy 12cm for a 2€ coin in air (best pointer ever since a long time)Comment
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