dynamo rotor test

Discussion in 'Motorbike Technical Discussion' started by jseely13, Aug 23, 2004.

  1. jseely13

    jseely13 Guest

    so i'm having this electrical non-charging problem... after buying a
    stator on ebay, i got bored waiting for it to get here and decided to
    use my head and check the rotor...

    the screwdriver wouldn't stick and hold to it.... i could feel a
    little force, but not much. should the screwdriver actually stick and
    hold on it's own? is this my problem? will my stator be back on ebay
    in a week?


    -- john
    jseely13, Aug 23, 2004
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  2. jseely13

    jseely13 Guest

    75 kz400D
    jseely13, Aug 25, 2004
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  3. jseely13

    Mark Olson Guest

    The 1975 KZ400D did not use a permanent magnet rotor. It used a fairly
    unique design of an excited field style system with a fixed field coil
    that supplied the magnetic field to a moveable rotor, which in turn
    induces a changing magnetic field in the stator. I would not expect
    the rotor or the field coil to have a strong magnetic field without
    the field coil being connected to the regulator. My KZ650B1 worked the
    same way, distinctly different from the typical exicted field design
    which uses slip rings to supply field current to a moving rotor, as in
    the DOHC CB750/900/1000.

    Did you perform any electrical tests of the various components before
    buying the stator? What, if any, were your results?
    Mark Olson, Aug 25, 2004
  4. jseely13

    jseely13 Guest

    hehe... wellll...

    i tested my rectifier according to the manual, and it checked out.
    the regulator is a new used part, and the previous owner had replaced
    the field coil w/ a new used part in an attempt to solve the
    electrical problem. i tried to test for voltage coming off the three
    yellow wires from the stator (w/ + and - to pins, and w/ + to a pin
    and - to ground) and was unable to see voltage, but did see a spark or
    two while attempting to test.

    i sorta assumed the new used parts were working and deduced that
    between the rotor and stator, it was probably the stator... since a
    magnet wouldn't just up and lose it's charge.... something i now
    understand can happen...

    anyway, the stator was NOS on ebay for $40 after shipping, so i jumped
    at the chance... perhaps a waste of money...

    my local bike shop and a bike mechanic friend told me a screwdriver
    should just stick to the rotor if it's good. are they confused b/c my
    bike is different?

    do you have suggestions on electrical tests i should perform to track
    this down/test my parts? the only other dynamo test in my manual
    involves a variable resistor, which i don't have and looks expensive.
    i couldn't test the regulator b/c i haven't had a working tach until
    recently, but can perform that test now...
    jseely13, Aug 27, 2004

  5. I'm glad to see someone else buys brand new parts they don't actually
    need, on the grounds that they're cheap and one might as well....

    I'm building up a stock of components for the Honda 400 Four that way.

    Best Ebay item was a NOS master cylinder repair kit. Genuine Honda item,
    all the components.... something you *will* need, one day.
    The Older Gentleman, Aug 27, 2004
  6. jseely13

    Mark Olson Guest

    No comment.
    Never assume *any* part is working. That will waste more time than
    any other mistake you can make. Always proceed from the assumption
    that nothing is 'trusted', everything has to be tested, directly
    or indirectly.
    Not a bad idea to keep one as a spare, if nothing else.
    I believe so, yes. If it wasn't clear from what I wrote before,
    your bike does not use a permanent magnet rotor. Neither does it use
    a rotating field coil as the '79- Honda DOHC CB750 did. Your bike's
    rotor is more of a pole piece that directs an externally applied field
    (from the stationary field coil) to the pole pieces of the stator.
    It is not a magnet. It probably will have some residual magnetism,
    but nothing compared to what a permanent magnet rotor has, which is
    what your bike mechanic buddy is used to seeing nearly 100% of the
    time nowadays.
    At least you can test the stator for shorts to ground, and
    winding-to-winding resistance. The resistance of any stator wire
    to ground should be infinity (no connection) and the resistance of
    any one yellow wire to any other yellow wire should be the same, and
    roughly an ohm or two, but not a dead short. I can't give you the
    exact numbers because I don't have my genuine Kawasaki manuals here
    at work. You would be well served to buy the genuine Kawasaki shop
    manual for this bike. Next, check the field coil the same way, with
    the regulator disconnected from the field coil wires, neither field
    coil wire should have any connection to ground, and the resistance
    between the two wires should be a few ohms, not open, not a dead short.

    Assuming the resistance tests pass, measure the AC, not DC, voltage
    from the three stator wires to each other, with the yellow stator
    wires disconnected from the regulator. Note that you still have to
    have the field coil wires connected to the regulator or there won't
    be any magnetic field present. You should see roughly 50V AC, again,
    not DC, when measuring the open circuit voltage on the stator wires
    at 3000 rpm or so.

    If all the resistance measurements check out, but there is no AC
    voltage or low AC voltage measured with the stator disconnected from
    the regulator, then you can *briefly* connect 12V directly to the
    field coil (with the regulator disconnected), and measure the AC
    voltage from the stator again. If the coils are good, you should
    see AC on the stator. If you do, but you didn't get any AC output
    when the regulator was driving the field coil, it is pretty likely
    that the regulator is the culprit.

    Get busy with that meter and get back to the group.
    Mark Olson, Aug 27, 2004
  7. jseely13

    jseely13 Guest

    thanks much for the help/advice... had a friend moving this weekend,
    so no time yet, but i'll get the meter goin and let you know what i

    thanks again,

    -- john
    jseely13, Aug 29, 2004
  8. jseely13

    jseely13 Guest

    Wire to wire was 0.5ohms for all three wires, manual says 0.4-0.6 is
    right. Wire to ground was infinity at Rx10K.
    4.4-4.5 ohms on the field coil wires (manual says "about 4.8", less is
    short, more is open). no reading on either wire to ground.
    ok, ran this test. plz forgive me, i'm not sure how to read the
    multimeter. i ran the test at 4000rpm, w/ my multimeter set on ACV60
    (i have AC6, 30, 60, 300, & 600). here's what my meter looked like:

    [DC] ^
    0 20 40 60 80 | 100 120
    0 10 20 30 40 | 50 60
    0 5 10 15 20 | 25 30
    [AC] | [30V UP]
    0 1 2 3 4 | 5 6
    [AC] | [6V ONLY]

    so i assume i'm reading the 10,20,30 line, which puts me at around 45
    [email protected] rpm. this is lower than you expected. perhaps i'll rerun the
    test at 3000 as you suggested (it was late at night ;).

    does my reading qualify as low and warrent proceeding to the next test
    i don't think i'll ever leave the group at this rate... three new
    problems cropped up last night... will it ever end? i just want to
    ride :-\

    -- john
    jseely13, Sep 4, 2004
  9. jseely13

    Mark Olson Guest

    It doesn't sound way low, I just pulled 50V out of my hat, so to
    speak. It might be a little low. Yes, I think you should test
    the AC output across all combinations of the three stator wires
    with a full 12V going into the field coil winding.

    According to section 'D' of the very good fault finding chart at:


    you should see at least 50V when running at 5000 rpm with the field
    coil 'full-fielded'. If you don't, the stator is probably bad.
    If you do, but you're still having low output, and all your previous
    resistance checks pass (and they did), the regulator is the problem.

    The full field test: disconnect the field coil winding and the stator
    windings from the regulator. Apply 12V across the field coil while
    running the engine at 5000 rpm, and measure AC volts across all three
    combinations of the three stator wires. The voltage should be
    fairly close to the same number for all three winding combinations.
    If any of them are less than 50V or if there is a marked difference
    between any of the readings (more than a couple of volts, I'd guess)
    then the stator is faulty.

    Good luck.
    Mark Olson, Sep 4, 2004
  10. jseely13

    jseely13 Guest

    thanks very much for the advice, although i'm not 100% that i
    understood your suggestion.

    looking at the chart, i first rev'd to 5k and checked the dcv on the
    batt, and had approx 14.5-14.8 dcv (14.8 being what it expects). then
    i unplugged the stator wires and checked voltage on them at 5k (i
    didn't unplug the field coil wires or the regulator, b/c i'm unsure
    what should be plugged to what if i did so) and saw 60+ acv.

    so unless i made a mistake, at this point it sounds like the regulator
    or that i don't have a discharge problem at all. i only mention the
    latter b/c i've ridden the bike 20 miles or so (and i really need my
    permit, and tags, and insurance... sigh...) and haven't yet noticed a
    decrease in batt voltage.

    if i tested wrong, i'd appriciate any further pointers. otherwise, i
    think i'm going to keep riding it for now (and get legal about it) and
    test the voltage after every trip to see if i'm getting a discharge.
    but i'm a computer person, and one of my favorite sayings is:
    "problems that go away on their own can come back on their own"...

    thanks again for all the help!

    -- john
    jseely13, Sep 6, 2004
  11. jseely13

    Mark Olson Guest

    It sounds like the charging system is working fine, at least
    when the engine is running. I was under the impression that
    it was not, from your previous posts.
    You can have a system where the alternator charges the battery
    yet the battery runs down and loses charge, either because the
    battery itself self-discharges at a high rate, or there is
    some parasitic load on the battery that causes it to discharge.
    It is relatively simple to determine if there is such a parasitic
    load, disconnect the positive battery lead and measure how much
    DC current is flowing with the ignition key in the 'off' position.
    If there is more than a very small amount (in your case, I'd
    expect to see less than 1 milliamp), there is a defective
    component or a 'short' somewhere in the system that needs to be
    replaced or fixed.

    If there is no excessive parasitic current drain, yet the
    battery discharges over a short time (less than a month or
    two) then the battery is defective.

    Again, good luck.
    Mark Olson, Sep 6, 2004
  12. jseely13

    jseely13 Guest

    so was i :( i rode it for two nights a while ago and the batt drained
    while riding to where the lights dimmed and it died and couldn't kick
    over. waited 5-10 min, drove halfway home, repeat... voltage was
    10.5-ish.... that was pre carb tuning, when the bike idled around
    3-4k rpm, but w/ the same (new) batt as right now....?
    i'd only owned the battery for a day or two, and the drain took place
    over two days of short riding at night after working on it (using the
    elec starter i/o kickstarting as i do now). no major electrical
    changes have been made since that time. once there was a sudden short
    outta nowhere that burned out a fuse and got the rectifier white wire
    very hot (melting the plastic fuse holder). last night after 10 miles
    of riding, my bike idled low and died twice in a short period (lights
    not dim) while i was holding in the clutch coasting, but starting
    right back up on the first kick. it died again as i pulled in the
    driveway about a mile away (after a couple stop signs).

    my wife says i have gremlins... i'm gonna get it legal and then just
    ride it and see what comes up. thanks very much for all the
    assistance, it taught me some good stuff. i've got some odds and ends
    to do in the meanwhile... :)

    -- john
    jseely13, Sep 8, 2004
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