Connect with us

Ferrite Rods (or work alikes)

Discussion in 'Electronic Basics' started by phaeton, May 5, 2007.

Scroll to continue with content
  1. phaeton

    phaeton Guest

    This looks like a pretty cool circuit:

    However, where would I purchase a set of ferrite rods? I checked
    Jameco and Radio Shack, but no dice.


    Would any ferrous metal rod work similarly? I.e. a simple steel nail
    or bolt?


    Anyone ever build this? Would increasing the voltage increase the

  2. Phil Allison

    Phil Allison Guest


    ** No, must be ferrite.

    Get then nothing out of any discarded transistor radio, cassette radio or
    clock radio.

    ......... Phil
  3. default

    default Guest

    A bolt probably won't work. Eddy currents in the bolt would eat up a
    lot of the energy making the range low assuming the transmitter
    portion oscillated at all.

    You do have some options however. Assuming you can't find some
    ferrite rod material, you can stack a series of toroids or ferrite
    beads together and treat it like a rod (use a dowel or nonconductive
    center or just glue them together)

    It oscillates at 35 KHZ which is relatively low and you could probably
    get by with a bunch of thin iron wire. The iron should not conduct
    well, so allow it to rust a little before packing the core.

    I use steel fence (agricultural electric fence) wire for wire cores
    since it is readily available and cheap. It is zinc coated to prevent
    rusting and is very conductive. I cut the wires to the length I need
    for my core then put them in a jar of vinegar for a few days - that
    causes the zinc to oxidize and insulates the wires. I neutralize the
    acid with a rinse of baking soda.

    Craft stores are another source of thinner steel wire - but they can
    be costly if you need a large core.

    Alternatively you can just chuck them in a fire and burn the coating
    off - the zinc vapor may be toxic so you'd want to avoid doing it
    where you breath or under the chicken in the BBQ grill . . . Burning
    it will or may cause it to anneal and that is desirable in a magnetic
    core (easier to bend or straighten too)

    You can make your own powdered iron cores that will work really well.
    I started fooling with steel wool in an attempt to make a high
    frequency core - it actually worked pretty well.

    You can make a core to rival commercial ones by buying fine iron
    powder - stay away from science shops, it costs too much - it is for
    sale on line for pyrotechnic purposes in different sieve numbers
    (particle sizes). Stuff is used to make bright white star burst
    fireworks shells and roman candles.

    My technique is to mix the powdered iron with epoxy thinned with a
    smidgen of acetone (or get thin boat builders epoxy or polyester
    resin) then pour it into a short length of PVC or CPVC pipe that has
    been waxed inside with a coating of silicon grease as a mold release.

    Pour it and cap it on both ends with greased PVC end caps pushed on,
    store it vertically while the epoxy sets - or you will regret it - one
    end cap will leave a shoulder in the molded product - it won't come
    out from that side. Let harden for a day or two then push the iron
    out (a dip in a pan of boiling water will help if it doesn't just
    slide out - most won't with PVC, CPVC is smoother inside).

    Voilà! a powdered iron core that didn't cost a mint.

    A further refinement is to stack ring type ferrite magnets around the
    mold while it hardens (stack has to be full length and you may have to
    grind off the shoulder on top before you push it out)

    I have a lot of old speaker magnets that work well for that - but
    winding a coil and passing current through it may also work.

    Magnets increase the permeability of the core by aligning the
    particles of iron while it sets up. They also tend to cause the
    mixture inside to try to walk out of the tube - so be sure to use two
    end caps pushed on hard.

    It may work to just stuff a tube with iron powder and glue the caps on
    - I don't know. The wall thickness of the tube may work against you
    for leakage inductance and the particles may move around while being
    excited by the driver - I assume that would be a bad thing but I
    haven't tried it.

    cool circuit - haven't built it
  4. jasen

    jasen Guest

    Fence wire is high-tensile, I'd expect softer wire, like tie wire to
    work better.

    pre-rusted tie wire can be had cheap at places that sell steel for
    concrete reinforcing.

    a coating of lacquer may work better than just trusting the rust to
    insulate it.

    To straigtten short lengths of wire roll them between two flat MDF boards.

  5. Buy cheap radios from Wal-Mart and rob parts from them.
  6. default

    default Guest

    Yeah, annealed (soft) wire is better for transformer hysteresis.
    Leaving it in the charcoal grill and shutting the vents to kill the
    fire works like a champ to anneal, remove the zinc, and oxidize it .

    Easier to work with the stiff wire if one is stuffing a tube to
    capacity. Likewise, uncoated or oiled wire is easier to pack than
    varnished wire.

    Tie wire sounds good, I have to check that out. Bailing wire is
    pre-rusted or has a black oxide coating from the factory - but who
    needs 80 pound coils of the stuff? Fence wire is only $5 for a 1/4
    mile and there must be ten-fifteen pounds on the spools. Really handy
    around the house too.

    Back when I was experimenting with induction coil cores, I stretched
    the wire between trees with a come-along (cable hoist) and ran a
    series of offset pulleys up and down the wire - that straightened it
    pretty well. You can also buy wire for suspended ceiling "T" bar in
    bundles of straight lengths 10 feet long.

    My first attempt at powdered iron was to feed steel wool through a
    hammer mill style garden leaf shredder. What a fiasco! It worked
    but tended to "pill" clumps of compressed wool. You wouldn't believe
    how far the stuff travels - the next day the clothes I wore and side
    of the house and deck had rust stains.
  7. phaeton

    phaeton Guest

    Excellent, you guys.

    As far as using wire to make an inductor, how about putting pieces in
    a plastic drinking straw for insulation? Work? No?

    As far as epoxying a bunch of beads together, does there need to be
    anything in the middle of them? Maybe just a plastic bolt to mount
    them somewhere with?

    Now (the big question)

    Which has a higher effect on the 'coarse tuning' of the inductor:

    1) Number of turns of wire.
    2) Length of ferrite core.
    3) Diameter of ferrite core.
    4) Other

    I realize that radios are 'fine tuned' with a variable capacitor. I
    know this is also not a very simple answer, so pointers to data is

    Also, the transmitter circuit calls for 3V-9V operation. If I were to
    modify the circuit for 18V-24V operation, would that increase its


  8. Sure, but not really needed. The ferrite is not a very good
    conductor. and the signal voltage is low, so the wire
    insulation is plenty.
    Nothing needed, but almost anything will work. Even a metal
    bolt, since most of the flux will pass parallel to it
    through the ferrite.
    Proportional to almost turns squared, for turns in the
    middle third of the rod.
    Almost proportional to length.
    Less than proportional.
    Location of turns on rod. Higher inductance for turns near
    center of rod, so fine adjustment by sliding the rod off center.
    If nothing burned up, probably. I would go with a longer
    rod, though.
  9. Phil Allison

    Phil Allison Guest

    "John Popelish"

    ** You have completely misconstrued the OP's words.

    Tell the PITA troll to get his ferrite rods from old radio and shut the
    **** up.

    ........ Phil
  10. Sorry to hear about the pain in your ass.

    Mine feels just fine.
  11. Phil Allison

    Phil Allison Guest

    "John Popelish"

    ** Misconstruing is your only forte.

    Piss head.

    ......... Phil
  12. At least I'm good at something.

    By the way, do you care to tell why you are so angry so much
    of the time? Are you here to because you are angry, or in
    spite of being angry?
  13. Phil Allison

    Phil Allison Guest

    "John Popelish"

    ** Misconstruing is your only forte.

    Piss head.

    ** Misconstruing is your only forte.

    Piss head.

    ** Misconstruing is your only forte.

    Piss head.

    So fuuuuck the hell off.

    ........ Phil
  14. Phil Allison wrote:
    Get used to disappointment.
  15. Phil Allison

    Phil Allison Guest

    "John Popelish"

    ** Misconstruing is your only forte.

    Piss head.

    You'll be dead soon.

    ........ Phil
  16. Of course, as shall we all.
  17. Lord Garth

    Lord Garth Guest

    I'm surprised you haven't placed Phil in your ignore list John....

    I never see anything from him unless it's copied.
  18. I can't turn away from train wrecks, either.
  19. Phil Allison

    Phil Allison Guest

    "Lord Garth"

    ** Bugger off - you worthless tenth wit.

    ....... Phil
  20. Lord Garth

    Lord Garth Guest

    You do well not letting him pull you down to his level.

    The guy tried to tell me what I had found inside of a no name
    wall wart in 1979! It was then I added him to my short list of
    ignores. Funny thing is, that wall wart and the digital clock it's
    attached too, are still operating today. The chip is a Mostek 50250.
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day