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Help, any gurus with alternator experience or knowledge?

Discussion in 'Electronic Repair' started by default, Jul 8, 2006.

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  1. jasen

    jasen Guest

    only if you can increase the voltage to compensate for the resistance
    which increases twice - due to greater length and reduced cross-section
    of the conductor. the extra turn compensate for only one of those increases.

    annealed, and oxygen free, copper wire will have slightly loer resistance
    but I don't think it'll be enough.

  2. Guest

    Guest Guest

    I have to point out (since I am a mechanic in an electronic newsgroup) that
    you are taking the electronic approach to solving your problem. The
    mechanics approach would be to adapt a longer lived, less expensive, more
    popular alternator form another brand of car onto your engine.

  3. default

    default Guest

    Sure that's what a mechanic would do with a car - where one has lots
    of room and can make a mount or switch pulley sizes etc to make it

    I, on the other hand, have a crankshaft mounted alternator that must
    fit in a certain space to keep it out of the rain - and I'd much
    rather put in permanent magnets and redesign the regulator than rewind
    the rotor - but I don't own a metal lathe, and I'm not too sure if
    wood would work - not to mention the hassle of getting the inside
    taper on the rotor right with the tools I have. This seems like the
    best option to me.

    I have thought of just putting a sheave on the end of the crankshaft,
    kludging in a mount to hold a John Deere permanent magnet alternator
    out there in the elements - but there ain't no good way to do it.
  4. default

    default Guest

    Well I calculated for three sizes of wire, in the same physical space.
    The coil resistance in going to larger gauges went from 5 ohm to 1
    ohm, Power dissipation went from 28 watts to 144 watts. Magnetic
    force went from 1,415 Gilbert's to 1,417 Gilbert's.

    Always the chance I made a mistake somewhere.
  5. jasen

    jasen Guest

    I think so... if you show your working I might be able to spot it.

  6. default

    default Guest

    I don't have my data - it was from the original winding five years
    ago. The formula to get from ampere turns to Gilbert's is simple
    (current *number of turns*1.257).

    If my memory serves, I used something like the number of turns that
    could fit in a cross sectional area times the mean length per turn to
    get wire length and resistance, from a 1914 book on solenoid
    construction . . . .

    But logically I see your point and it seems likely I went wrong
    somewhere in there . . . For the sake of argument:

    If each turn of wire has one ohm resistance, and I have a four turn
    coil and 8 volts to drive it I have a current of 2 amps and 8 ampere
    turns dissipating 16 watts total.

    If I halve the diameter of the wire the cross section drops by a
    factor of four so the resistance should increase by a factor of four.
    So now I have 16 turns fitting where 4 where, and the resistance is 64
    ohms. Four times the turns, with four times the resistance per turn.
    With the same 8 volt supply that's 0.125 amps for 2 ampere turns
    dissipating 1 watt.

    Conclusion: I was full of shit to state that wire size didn't matter.

    Efficiency: To produce the same 8 ampere turns with a 1/2 size wire
    will take only 4 watts - so it becomes four times more efficient to
    decrease the wire size by one half (keeping the volume the same), or I
    could produce 32 amp/turns of field strength for the same 16 watts
    that produced 8 A/T with larger wire. (if the volume were to

    Practically speaking there's something like a theoretical increase of
    7% or so when wires lay in the interstices created by the layer below.
    Increase the turns by a factor of four and that 7% becomes significant

    See any flaws in the logic?

    I'm glad we had this chat.
  7. Chuck Harris

    Chuck Harris Guest

    Huh? It comes out exactly the same either way:

    8V, 4 ohm, 4T = 16W, 8A-T
    32V, 64 ohm, 16T = 16W, 8A-T

    The only issues as far as efficiency goes are the insulation thickness
    as a percentage of the winding, and the wasted space due to the imperfect
    packing between the wires. You can write equations for each, and calculate
    the best wire size for an 8A-T coil, if you want.

  8. default

    default Guest

    If a single coil will give me two ampere turns with 1 watt of
    dissipation won't four parallel coils give me the equivalent of 8
    ampere turns at 4 watts dissipation? All running at 8 volts in
  9. Chuck Harris

    Chuck Harris Guest

    Of course, but you will have twice as much wire volume as the original


  10. Jason D.

    Jason D. Guest

    Please cut to one newsgroup forum, you're cross posting to many
    newgroups. Thanks.

    Reason those wires breaking off is that crankshaft have firing
    impulses on the crank, even with flywheel and damper crankshaft still
    vibrate in rotation plane. Whack whack whack, those poor wires from
    the winding to the slip rings vibrating like twanged bow string and
    evenually come apart.

    Is the winding throughly SECURE? Also you may want to redesign the
    eyelets to be MORE close to the winding. Always fabric sleeve these
    flying wires and use cotton twine wetted with varnish and bed it then
    lay the wires across it and bury the wires with more twine. Let set.
    This is what old school motors were done this way to stop wires from

    Especially look at the old vacuum motors, They had to be built to
    survive 10,000 rpm from dead stop, same with engine starters.

    Cheers, Wizard
  11. default

    default Guest

    Yeah was hoping to find a person who's done a rewind himself. The
    repair group is too busy, figured I'd drop off the screen in a day or
    My latest plan is to try a self-supporting coil. I found some 22
    gauge wire I could afford. Rather than make a bobbin, I put some
    polyethylene facings to my mandrel and plan to spray it with silicone
    as a mold release agent. I'm serving some small braided wire to the
    ends of the magnet wire and bringing those up through fabric sleeves
    and anchoring the ends in wraps of cotton twine.
    I'm using the same epoxy that worked last time for this winding. The
    stuff I ordered didn't get here and won't until Friday. I may still
    do a second coil with vinyl ester resin since I have more than enough
    wire now.

    There's no doubt the wire and sleeves I used were anchored well enough
    the last time - but I think it was a mistake to use Teflon sleeves -
    the wire had about .5 millimeter of play in the sleeve and it was 1.5
    centimeters long embedded in epoxy - but epoxy can't penetrate the

    Fabric sleeve (called spaghetti in the repair trade here) has been
    supplanted with Teflon and heat-shrink tubing. I have some Military
    type, small diameter (2.5mm), silver plated coaxial cable with a
    fabric braid. Probably used for airframe applications from sensors to
    cockpit. I'm using the braid and fabric and discarding the Teflon
    center conductor.

    Thanks for the ideas
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