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A Hand Cranked MagnetoGenerator

Discussion in 'General Electronics' started by default, Aug 14, 2005.

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  1. default

    default Guest

    I've got one of those. Didn't cost a fortune from "Fair Radio Sales"
    about 10 years ago.

    Mine outputs ~200 volts peak to peak, open circuit @ ~100 hz. It has
    a two pole armature that rotates between the horseshoe pole pieces,
    with a set of slip rings to pull the power off. The waveform is NOT
    sinusoidal. There are a set of brass gears that give a (eyeballing it)
    ~1:3+ speed increase from crank to armature. It will dimly light a 7
    watt 125 VAC lamp. (that is one can see the filament glow, but
    nothing like a full 7 watts).

    I got one of the old, relatively large, horseshoe magnet types. Fair
    Radio also had some compact "field telephone" magnetos - round and
  2. default

    default Guest

    On Sun, 14 Aug 2005 11:12:34 -0700, "Watson A.Name - \"Watt Sun, the


    Interesting links
    I'll bet mine has a set of weak magnets. We were having a contest to
    see who could get the bulb to light the brightest, in the lab - that's
    where the 100 HZ came from. I imagine that they used some iron pole
    pieces for the magnet and it would lose flux over the years.

    Sometime I'll have to hunt for it and see what some rare earth magnets
    can do.
  3. Randy Gross

    Randy Gross Guest


    I'm trying to locate information on the hand crank magneto generator
    used in vintage phones:

    how they were constructed
    what charge was produced and how was it used.

    I tried Google but my query returned little.

  4. You should first look for antique telephones. I know of several dealers
    (yes, dealers) who sell such stuff, and they are members of the ATCA,
    Antique Telephone Collectors Ass'n. The last meeting I went to they had
    old porcelain "Bell System" signs for $400 to $1200, and I asked one guy
    who bought one how those prices were, and he said they were reasonbable.
    So don't expect to get a magneto for cheap. A decent wall telephone
    with a hand crank costs $200 on up, so figure out how much you wanna
    spend. and try the links to member pages. some links to other tel

    Ekkehart Willms website has some amazing items, more than just
    telephones. Like the Art Deco radio for $$$$$! I saw it at the last
    meeting, and it's awesome.(# R7 here Yes, his name is spelled that
    way. I also saw him play the Edison cylinder record player with the big
    tulip horn, and it's amazingly loud for not having an amplifier.

    The generator puts out about 90VAC at about 20 Hz, depending on how fast
    it's cranked. It's bridged across the phone line and when cranked, a
    switch engages and connects the rotor to the line. Just a few magnets
    and a armature with wire and slip rings.
  5. Randy Gross

    Randy Gross Guest

    I see that there is a lot of interest in this device. I was hoping to
    get an illustrated parts breakdown so that I can get a better
    understanding of whats going on when the crank is turned.

    If anyone has one or know where I might view a print, I would
    appreciate the tip.

  6. quietguy

    quietguy Guest

    My cat could give you more information that I can - sadly (and I still
    feel bad about it) I connected one lead from one of these to a metal
    plate, and the other lead to a saucepan of milk - cat stood on the plate
    and started drinking the milk - I wizzed the handle and he jumped

    David - who doesn't feel bad though about all the local kids he talked
    into holding the leads from his genny
  7. default

    default Guest

    Lot of pictures of old magnetos no drawings that I could find.
    Chances are there's an on-line patent or two with the drawings, but
    good luck locating it.

    The magneto is a basic permanent magnet alternator or dynamo. There
    should be a lot of drawings for those - lots of folks wanting to build
    them for small wind or water power plants.
  8. default

    default Guest

    Had this cat that insisted on climbing through the window. It was a
    "city cat" and the owner had just left the window open. When I
    acquired the cat (owner went to work at the CIA) the windows were
    screened and there was no way . . .

    A spark coil with a couple of wires nailed to the sills cured that cat
    - she needed two lessons - to break a lifetime habit.
  9. default

    default Guest

    With a two pole horseshoe magnet that covers (maybe) 120 degrees of
    rotation . . . There's a big bare spot with no generation. That and
    less than optimal pole pieces or armature.

    Wave was sort of like a hemisphere with a spike (like a sine wave)
    superimposed on the first part of the waveform. But that may be unique
    to my magneto.

    If your goal is to raise worms . chances are the waveform isn't all
    that critical. Ring phone bells - ditto.
  10. Randy Gross

    Randy Gross Guest

    It's funny you should mention that. Years ago, I was watching a WWII
    era film and the crank genny was used very effectively in an
    interrogation technique involving the mans' pride and joy. "Ouch!"

  11. Randy Gross

    Randy Gross Guest

    A print for this unit, as far as I'm concerned, is not in cyberspace.
    Schematics abound showing the phone circuits but, keeping in mind the
    fact that this assembly is vintage analog and omitting the phone
    circuitry, I have determined from descriptions by Watson and default
    that what we have left is basically an unorthodox P.M.G.

    What I was trying to uncover was why the waveform is not sineusoidal.
    I'll take a stab at that too.

    I think that the reason is because of the horseshoe magnets providing
    the magnetic field. The highest concentration of flux is at the poles
    of the magnets and does not follow the arc of the rotor coils. When the
    rotor coils are at 90' to the plane of the horseshoe poles, the coils
    aren't cutting lines of flux, they are running with them.

  12. Randy Gross

    Randy Gross Guest

    I agree. I think this unit will remain in the realm of novelty however,
    raising worms is justification enough to keep one handy;-)

    I read that the Military has adapted it, in a handheld version, to
    charging high tech-low voltage DC field equipment such as PDAs', cell
    phones and, If I read correctly, 12 volt batteries.


  13. Rich Grise

    Rich Grise Guest

    It sure seems like it would make more sense to spin one of those
    ultra-strong new magnets between some kind of stator windings.

  14. default

    default Guest

    Doubtless the military has some fancy stuff.

    There was a "survival" radio advertised that was pretty neat. The
    power was stored in a large spring one wound up. The spring powered
    a dynamo and was regulated so that if more power was needed the spring
    unwound faster - if the music, for instance, had a lot of bass the
    spring would spin the dynamo faster.

    Stepper motors make good slow speed, low current, alternators. Good
    for lighting leds as a demonstration. Interesting low speed homemade
    wooden alternator. He could probably more than double the output if
    he mixed some powdered iron in his epoxy on the field coils. Claims
    it can power a 120 volt tube type stereo that dissipates 300 watts,
    powered with an electric drill.
  15. default

    default Guest

    I figure peddling my bicycle I probably generate ~100 watts average
    and can keep that for an hour or two with no problem. I think it
    would take a lot of work to turn a hand crank at that level long
    enough to charge a car battery. Say 9-10 amps into a 60-70 amp hour

    Leg power maybe, but I'd think solar cells or small gas generator
  16. Randy Gross

    Randy Gross Guest

    default wrote:

    I share the curiosity about how modern high power magnets would perform
    instead of the horseshoes. The best application I can think of at this
    time is to boost charge a weak car battery, anywhere! I would have one
    in my trunk dedicated to that function.


  17. I doubt that you would be able to crank one enough to turn over a car
    engine. Have you ever hand cranked an ice cream churn? Think about how
    little electricity it takes to run an electric one. Multiply that times
    the additional energy needed to to turn over a modern high compression
    engine over the efficiency of the charging process.

    Link to my "Computers for disabled Veterans" project website deleted
    after threats were telephoned to my church.

    Michael A. Terrell
    Central Florida
  18. default

    default Guest


    Some related sites with pedal power outputs
    Burst output: 25 amps at 17 volts (425 Watts)
    30 minute average output (back when I was in shape) 150 Watts
    A modestly fit person can expect to
    generate about one tenth horsepower (roughly 70 watts) for a brief
    period. For normal regular use a generator capable of producing
    50 watts or more is quite adequate. If you are a cyclist interested
    in serious training, a generator capable of 100 watts or more is
    desirable, PM generators ranging in size from 60 watts to 200 watts
    are readily available and can be obtained with the bike generator
    options described below.
    Although I have not tested this alternator for exact speed vs output
    information, it seems to start charging 12 volts at approx 80 rpm.
    When coupled to the bike, I was able to generate
    5 amps(60 watts) in a leisurely way, and if I pedaled as fast as I
    could, I'd get about 10 amps(120 watts). This
    seems to be in line with claims we've seen for other peoples plans,
    although it seems clear that with a higher gear
    ratio, one could generate significantly more with this alternator.
  19. I took a hard disk drive apart and removed the platters. I connected a
    red LED the leads of the heads that go to the voice coil. When I
    wiggled the voice coil back and forth in that strong magnetic field, it
    lit the LED, easily. Also, some of the HDD motors are permanent magnet
    and when spun will light the LED.
  20. Forget it. Your arm muscles would give out after a few minutes. 14
    volts output at an amp is 14 watts, figuting 70 percen efficiency, 20
    watts imput to the gen. You can't do that for long; a bicyclist can't
    put out a sustained hundred watts using his legs, only for a short
    burst. The thigh muscles are the largest and most powerful muscles in
    your body.

    At 1 amp, it'll take you an awful long time to charge a car battery.
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