Wondering about the stator problem

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

  1. OFOAM

    OFOAM Been here awhile

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    I'm looking at getting an F7 in the spring. Been doing some research here and the F800 Rider forum. Things sounded pretty good till I read about the stator issues.
    I currently ride an R1200GS so I have lived through the final drive scare. Never had a problem myself. So I know some issues can sound more ominous than they might be. It seems the stator problem exists but doesn't happen to everyone all the time. But, let me get to my point.
    I was recently reading on the StromTrooper forum about a stator issue on the DL650 nearly identical to the one described here. They seemed to have zeroed on a potential cause of the stator frying itself. In there case it's the regulator/rectifier. Has something to do with the stock one being a shunt type. The way it operates causes over heating of the stator due to excess current. Their solution is a series type.
    So, does anyone know which type R/R the F7 has? Has this been considered as part of the cause? Just looking for any info to help me decide if I can do any preventive action should I pull the trigger in May.
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  2. bmwroadsterca

    bmwroadsterca RadioFlyer

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    I am pretty sure that all the F700GSs have the new flywheel with improved venting for cooling the stator.
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  3. ADVwxyz

    ADVwxyz yep

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  4. BygDaddee

    BygDaddee Long timer

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    F7 has the vented flywheel, stator issues are as good as non existent on 2013+ F8/F7 as they are on any bike.
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  5. ADVwxyz

    ADVwxyz yep

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    Be aware the bike is designed "as is" ...and components put on the bike factor into this formula.

    This also means a halogen headlamp bulb pulling X watts /Y amps.

    So, take out 35W halogen headlamp and put in a LED bulb rated 8W for example...... Where does that excess current go?

    Ok- so it has a vented flywheel- it still puts out 400 watts whether you use them or not...

    Hence the RR as stock is under rated if you start to play with changing stock electrical components like the headlamp.
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  6. bmwroadsterca

    bmwroadsterca RadioFlyer

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    While the alternator may put out a goodly amount of current when the regulator shunts it does NOT put out 400 watts. This is because the load consists of the inductance of the stator windings themselves, and the varying resistance of the regulator in parallel with the load of the bike's electrical components. When the resistance is low due to the regulator shunting current the voltage and current go further out of phase and the power factor changes.
    See:
    https://en.m.wikipedia.org/wiki/Power_factor
    The high current during shunting will surely heat the stator but this is not 400W worth.
    There are a huge number of posts in various internet motorcycle fora that perpetuate this myth.
    mike
    #6
  7. ADVwxyz

    ADVwxyz yep

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  8. itsatdm

    itsatdm Long timer

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    BMW changed the flywheel sometime in 2012 by venting it, in order to keep the stator cool. They all put out 400 watts. What is not used is shunted to the frame, it is still putting out 400watts max.
    It takes about 150 watts to run the bike. The rest is available to run all your toys.

    I have seen very little complaints about the stator since they did that. What do you intend to add to it and how may watts does it take?

    Some have put the series type regulator on the older non vented flywheel bikes. That appears to work too. Another option for cheap people like me on an older bike is to buy, a $200 aftermarket stator and hope it last longer than the stock one.
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  9. bmwroadsterca

    bmwroadsterca RadioFlyer

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    The stator + R/R have a capacity of 400W as Joel demonstrated (results in the link in post #7). Power is not "shunted to the frame". Current is shunted to the frame so as to keep the voltage within the specified limits.
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  10. shuswap1

    shuswap1 Long timer

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    What is the difference, I'm trying to understand why this apparently adds heat to the stator. I've read that you are better off running accessories to absorb this extra current than leaving it to be shunted. And, why does the series regulator help?
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  11. bmwroadsterca

    bmwroadsterca RadioFlyer

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    Let's start with a simple explanation.
    The best one I have found comes from here:
    https://www.physicsforums.com/threads/motorcycle-charging-system.839582/

    "Think of the rotor as just a permanent magnet that spins inside stator. That's exactly what it is as you well know, you can feel that when you have the primary chaincase open and can access the rotor just bring a steel tool near it...... as you have doubtless done.

    Now here's where we'll depart from conventional thinking: Think of the stator as an electromagnet, actually an array of them surrounding the rotor. Really it is just that, but it's not usual to describe it so. The array of electromagnets is wound such that current flowing in them cancels out the magnetism from the permanent magnet rotor. Somewhere around ten or twenty or thirty amps will cancel all of it. That's why alternators innately limit their own current. Designers can control maximum current by adjusting strength of rotor magnets and number of turns on stator. They size both to meet the electrical needs of the vehicle. Which means that at probably ten or twenty or thirty amps your alternator's terminal volts will fall to zero. Power (Watts) equals Volts times Amps , so at zero volts alternator power equals zero! Regardless of current. And that ten or twenty or thirty amps is what the alternator will deliver into a short circuit.

    >>>>Here's the key to understanding motorcycle shunt regulators:::<<<<

    So if the alternator is allowed to deliver twenty or thirty amps into a short circuit its power output drops to zero ! That's what the shunt regulator does, it throws a dead short across the alternator stator for a small part of every revolution , causing alternator power to drop to zero for that part of every revolution. It measures battery voltage and adjusts the fraction of time it applies the short to keep battery voltage somewhere around 14 volts . So the common belief is almost right - the regulator dumps not power but current. By dumping current it reduces alternator power output to zero for part of every revolution, making alternator power average just what the vehicle needs. Make that sequence of thoughts work in your mind and there's no need for myths like "storing power in the stator" . "Dump current not power" . That's why the heatsink in your regulator is really small for the amount of power it controls (not dissipates). Compare it to this one that you'd need to dissipate full alternator power.. size of a boot.
    http://www.wakefield-vette.com/Portals/0/resources/datasheets/392.pdf

    The technical term for alternator's self current-limiting is "Armature Reaction", closely related to "Synchronous Impedance". Both are simply the stator behaving as an electromagnet that opposes the magnetism of the rotor."


    Contrast that to the series regulator. The series regulator interrupts the circuit (current goes to zero) if necessary such that the average voltage over time is within the design target range.

    Because the shunt regulator draws more current from the alternator the power dissipation within the stator windings is higher - the coils run hotter and this may deteriorate the insulation over time and failure may ensue.

    The series regulator draws less current so the windings run cooler BUT when the series regulator interrupts the current flow suddenly a high voltage is induced in the windings of the alternator. The series regulator is designed to withstand the voltage however the alternator itself may not be - the insulation could break down and arcing result leading to failure. If the series regulators have been causing this type of failure we seem not to have heard about it in the Parallel Universe so perhaps the stators can tolerate this stress better than they can the heat stress caused by the higher current flow of shunt regulation.

    mike
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  12. TheCowboy

    TheCowboy back in the saddle again

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    Once again - just wrap the damn exhaust pipe with exhaust pipe wrap... the location of the exhaust next to the alternator is the friggin problem... you people are making it WAY to complicated.
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  13. Met n GS

    Met n GS Been here awhile

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    wont the engine run hotter then?
    and what about the muffler?
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  14. Loutre

    Loutre Cosmopolitan Adv Super Moderator

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    stop worrying so much and ride the darn thing. we have reports of +200k miles. those bikes last long. use quality oil and it won't be a problem.
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  15. Met n GS

    Met n GS Been here awhile

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    what oil are u using?

    the other day i decided to go to a different dealer and he said car oil!!!!:eek7
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  16. yaycep

    yaycep Been here awhile

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    He may be too idiot to distinguish an f800 from an air cooled boxer twin, or has a surplus of clutch plates, or you actually own an r-bike which can indeed happily accept car oil.
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  17. Met n GS

    Met n GS Been here awhile

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    oh no, he knew it was a f800gs....he said all the twins can....
    i just said...............ok...........
    what are you using
    #17
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  18. yaycep

    yaycep Been here awhile

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    Usually Castrol Power-1 10W-40.
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  19. Met n GS

    Met n GS Been here awhile

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    not the recommended 15w50?:hide
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  20. yaycep

    yaycep Been here awhile

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    Nope... But I have no logical reason why, except that it's ~20% cheaper. I think it suits the climate here (-5 - +35C) just as good.
    #20