Wondering about the stator problem

Discussion in 'Parallel Universe' started by OFOAM, Oct 17, 2016.

  1. bmwroadsterca

    bmwroadsterca RadioFlyer

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    If you have a look at the link in post #7 you will see that the measured output was 378W at anything over 4500 RPM. Joel's choice of a voltage could be different from whatever BMW uses when it rated the thing at 400W. No way to know.

    The voltage induced in a conductor crossing a magnetic field is directly proportional to the speed at which the conductor crosses the field so the voltage output of the alternator increases with increasing RPM. On the other hand the current output of PMA remains fairly constant over a wide range of RPM and one of the advantages of a PMA is the ability to deliver current at low RPM. Since whatever the PMA puts out gets rectified and then voltage regulated the output power of the alternator is mostly a function of its ability to deliver current.

    Lenz's Law states that an induced current will oppose the change that caused it. This gives rise to the phenomena quoted in my post #11 where the current tends to level off once there is enough of it to generate a magnetic field that cancels out the field of the rotating magnets. The power generated by the alternator when being shunted momentarily is a function of that current and the combined resistance of the windings and shunt (plus miscellaneous losses internal to the PMA). Generally speaking this will NOT be the full power output capacity of the PMA and why it is erroneous to think that the PMA is always putting out its 400W.

    What is "ELI5"?

    mike
    #41
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  2. TheCowboy

    TheCowboy back in the saddle again

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    look, my stator failed at 35,000 miles... I looked at it (I am an aircraft mechanic for 50 years) - I determined the damn exhaust was way too close to the alternator case (where the stator lives) - I put a new stator from Ricks in - I wrapped the exhaust like hot rods do... I now have 95,000 miles with no problems... I'm telling you these other folks are overthinking things... Keep it simple... it's not astrophysics...
    #42
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  3. RBMann

    RBMann Been here awhile

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    Okay Cowboy, I don't have any numbers for wrapping the exhaust as I have not done that. I did however measure the temperature of the stator cover with the stock stator installed and on my bike it was almost 100 F. hotter than the clutch cover or the rest of the engine. I opened the stator cover and found my stator black/charred. I decided to replace the stator before it failed with an Electrosport model. I also installed a series regulator at that time. After the upgrade the stator cover ran the same temperature as the rest of the engine.

    So I think everyone agrees that heat is the problem. Will a series regulator reduce the temperature of the stator, yes. Will wrapping the exhaust do the same and the amount, I don't know. How about doing some measurements to see?
    #43
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  4. TheCowboy

    TheCowboy back in the saddle again

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    Did that years ago... 70 F difference between wrapped and not wrapped... I used a thermal gun aimed at the cover... not real scientific but was good enough for me. BTW, opened up the alternator cover yesterday on a whim... the stators still look pretty good... not like new, but still pretty good.
    #44
  5. ADVwxyz

    ADVwxyz yep

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    So it is a blended solution then... the best it seems would be Wrapping and a Series... or, second best one or the other... to each their own... post #41 is most interesting... thanks.
    #45
  6. benkenobi

    benkenobi n00b

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    Cowboy, could you post some pictures of your wrapped exhaust?
    #46
  7. RBMann

    RBMann Been here awhile

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    Thanks for the numbers Cowboy.

    Now for fun. If we use a series regulator -100F., wrap the heaters -70F. and install a vented stator lets say another -30F. then we could make ice or cool drinks on the side cover.:D
    #47
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  8. Tewster2

    Tewster2 Long timer Supporter

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    Exactly :lol3
    #48