Airhead Charging System Secrets

Discussion in 'Airheads' started by StephenB, Apr 17, 2010.

  1. StephenB

    StephenB G(/)S ... what else!

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    It has been said often before, but it is important enough to be stressed over and over again:

    There are no secrets when it comes to the BMW OEM charging system.

    I would argue that the system isn't even error prone when maintained properly.

    The BOSCH components used have decades of heritage and are proven. That is true for the stator, the rotor, the voltage regulator (mech or elec) as well as the rectifier (diodeboard) none of which is complicated nor do they contain advanced technology.

    So why are there reported issues at least once a week?

    Because the implementation BMW choose and because people amongst other things use heated gear and aux lights and are practically wringing the system. Hence, if not perfectly working, it'll not sustain those loads over an extended period of time and exhibit the know problems.

    What can we do preventively:
    • proper grounding (especially of the diodeboard) is absolut key
    • keep contact resistances at a minimum (clean electrical contacts on stator, diodeboard and voltage regulator regularly and use dielectric grease)
    • watch out for oxydation on connectors
    • check alternator brushes and the copper surface of the two sliprings on the rotor regularly
    • (carry know good spares on longer travel)
    It isn't rocket science, just proper maintenance like everything else. It works for me.

    FWIW:
    The one time I helped a fellow rider it was ... the diodeboard.
    The one time my own system failed, it was ... the diodeboard.
    #1
  2. Steverino

    Steverino Arrogant Horse's Ass #1

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    sitting in a hotel room in Palestine, TX 1200 miles from home and your words are little help. But ironic...since my R100GS is not charging. :baldy
    #2
  3. StephenB

    StephenB G(/)S ... what else!

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    I know ... and you don't carry spares!
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  4. Wirespokes

    Wirespokes Beemerholics Anonymous

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    EXACTLY! I agree completely.

    Electrical systems and components last the longest when used well under their maximum capacity. Batteries, for instance. The less it's drained, the better; let it get mostly discharged and its useful life his been shortened dramatically, even though recharged right afterwards.

    The one part I will disagree about is the rotor. On bikes that have been ridden in a very 'sporting' way the rotors will fail. The windings will shift and eventually short out, but replacements from Motorrad Elektric are much more rugged having been beefed up and modified until they don't come back on warranty.

    In the twenty years I've been riding airheads, it's been connections and wear items like brushes I've had to deal with on my bikes. I've carried the smaller replacement items (diode board, rotor, regulator, brush pack) on trips, but only used the rotor for a friend once.

    Just yesterday I helped a friend with a charging problem and it turned out to be the regulator - something I almost never see. We called around to the auto parts houses in the area and no one had one in stock. But they could order one, generally $45 or more. Seems like a lot to me, and for an item that was used on just about every 70s import, surprising there's none in stock. The parts fiche says the bmw item is $55, I think, but the dealer quoted me $80 and $140 (said there were two different ones). I don't think the parts guy knew what he was talking about! I'm going to check the discount import auto (VW guys) and if they can't help me then I'll order one from Rick at Motorrad.
    #4
  5. dduelin

    dduelin Be Thou My Vision, Oh Lord Of My Heart

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    I carry a spare rotor & puller bolt and diode board when traveling. The Bosch system is easy to maintain and cheap to repair compared to newer bikes. They fail from age, of course, but mostly from neglect.
    #5
  6. Steverino

    Steverino Arrogant Horse's Ass #1

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    If riding 3000 miles in 6 days is neglect then guilty
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  7. Joerg

    Joerg Long timer

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    Hi,
    That reminds me of some, uhmmm, human beings ... they only feel good while they are ... filled up to the edge :lol3

    Yup. Of the three electrical failures that I recall on my airheads, two were due to defective rotors. The third was a worn-out insulation.

    Just for the record, you can use any "B-Type" regulator with nominal 14 Volt. Or build one yourself: http://jhau.maliwi.de/mot/voltreg.html
    #7
  8. StephenB

    StephenB G(/)S ... what else!

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    Naa, the neglect happened before ... you're just at the receiving end now!
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  9. StephenB

    StephenB G(/)S ... what else!

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    You're probably right ... and I have two of Ricks rotors.
    #9
  10. stubmw

    stubmw some what aloof

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    If you are stranded, and lack repair parts, I would not hesitate to get a cheapo car battery and charger and use it as a total loss system for extraction to home. IIRC this was a Snowbum approved method from my airlist days. :D
    #10
  11. Steverino

    Steverino Arrogant Horse's Ass #1

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    That is option two and already in place. Locals here in Palestine, TX are marshalling to get it fixed...
    #11
  12. stubmw

    stubmw some what aloof

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    Good luck!!!!! Hope you and the bike are back on the road soon.
    #12
  13. Steverino

    Steverino Arrogant Horse's Ass #1

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    Me too
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  14. StephenB

    StephenB G(/)S ... what else!

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    Yep, did that too at one point! Still a great method to carry on as if nothing had happened:

    http://www.stephenbottcher.net/BMW/misc/P5210073.JPG
    #14
  15. Dolly Sod

    Dolly Sod I want to do right, but not right now

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    How do you neglect a rotor? When a winding opens up what could have been done to prevent it?
    #15
  16. Infracaninophile

    Infracaninophile Finding My Way..

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    Steve:

    Hope you get it back on the road. But if you want to fly home I can PayPal $3000 right now to you in Texas. I'll even eat the fees and add 3%. Just sign the title and leave it under the seat. I'll be down Tue to collect my new bike. :clap

    T.
    #16
  17. The Raven

    The Raven Banned

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    +1, except I don't have a spare 3k now.. and even worse, have no way of getting it out of Texas as I am unable to enter that state again in my lifetime. :lol3
    #17
  18. Wirespokes

    Wirespokes Beemerholics Anonymous

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    Then use someone else's lifetime! Duh
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  19. dduelin

    dduelin Be Thou My Vision, Oh Lord Of My Heart

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    I am sorry I implied that rotors fail from neglect. They are a crap shoot and can go for 100,000 more miles or fail tomorrow.

    I meant that airhead Bosch charging systems in general fail from neglect. The original system is simple but won't last forever if neglected. This means 20-40 year old wiring still in place with the original terminal fittings, corrosion in wires & fittings, never checking output to benchmark the system, failing to renew heat sink paste, leaving batteries chronically undercharged from low revs, lack of riding, add-on loads of lighting/heated gear or a combination of these.

    Aside from an open rotor there are usually signs and symptoms things aren't right for a while before you are stranded.
    #19
  20. StephenB

    StephenB G(/)S ... what else!

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    Strike the heatsink paste, that is ignition related for 1981-on bikes.
    #20