Custom Airhead without a GEN lamp, blowing rotors??

Discussion in 'Airheads' started by Ron Seida, May 15, 2010.

  1. Ron Seida

    Ron Seida Adventman

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    I have had the pleasure of working in the local BMW shop for the last few months and have lately come accross an interesting problem. We're working on a custom /6 with custom wiring. There is no GEN lamp, it has been removed and i suspect that the wires are possibly shorted together, or the resistor mod was done. We will find out more on Tuesday when we look deeper into the issue but would like to prepare mentally before we tear into it. The question is this: lets asume that you remove the GEN light and short the wires together. What will happen, what symptoms should i expect? The bike is currently not charging, but it did before. We replaced the rotor a few weeks ago as the old one had no continuity. The replacement now shows no continuity, bad luck maybe :dunno. We replaced it with another good rotor, still not charging. End of the day so we went home, we'll continue it on Tuesday, starting with ruling out the regulator, diode board and brushes. Thing is without an actual GEN light, i smell a rat. Your thoughts?
    #1
  2. Lornce

    Lornce Lost In Place

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    If the light's missing (assume you mean the bulb) there must be a connection if it was charging earlier. An exciter current passes through the bulb enroute to the alternator. It won't charge without it.

    Two bad rotors isn't unheard of, especially if they're old rotors. :dunno

    How's the rectifier?

    :ear
    #2
  3. caponerd

    caponerd Kickstart Enthusiast

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    I think he said the wires from the generator light are shorted together.

    I'd start by putting some kind of light back in the circuit, or at least a resistor to emulate the light.
    #3
  4. sparkymoto

    sparkymoto Learning a lot here

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    I too have a modded /6 with the dash removed. I'll be adding an aftermarket speedo but in the meantime will install this...on my to-do list today actually.

    Product description on link explains what it does. Hope that helps.
    http://www.motoelekt.com/genlightacc.htm
    #4
  5. Ron Seida

    Ron Seida Adventman

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    The light is indeed missing, but i have yet to discover if there is a resistor wired into the circuit to take its place. My understanding is that the circuit excites, or energises the rotor making it magnetic, but the rotor will work without it if it already has a magnetic charge?? Sorry, electronics are not my strong point :puke1 , just trying to arm myself with a better understanding of the system to more efficiently diagnose the problem on Tuesday. By rectifier, you mean the diode board, visually it looks good, but we will check it out closer on Tues. along with the regulator and also make sure the brushes are making proper contact. The two bad rotors were used rotors, but a good, tested used rotor from a shop bike was installed on Friday and, much to our dismay, still no charge. Thanx for the input.
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  6. Ron Seida

    Ron Seida Adventman

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    If i may make a sugestion :norton . The light is good to have as it helps to diagnose problems like the one that i'm having. Without it you are left in the dark, literally :lol3 .
    #6
  7. sparkymoto

    sparkymoto Learning a lot here

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    yeah, the new speedo will have the indicator light but in the meantime, I'll rely on the auxillary doo-dad to do it's job. fingers crossed that the bad stuff doesn't happen in the rotor, rectifier, board or dirty brushes dept :puke1

    Good luck on Tuesday. Hope the problem presents itself.
    #7
  8. caponerd

    caponerd Kickstart Enthusiast

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    I don't think those have permanet magnet rotors (which is why they need the "exciter"), so if the exciter isn't exciting, the generator won't generate.
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  9. Ron Seida

    Ron Seida Adventman

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    I read in a Snobaum article last night that the rotor, if it has some residual megnetism, could start charging without the exciter. Anyways, we'll find out more on Tuesday when we dealve deeper into the issue. The owner says he has a wiring diagram, that should help. Thanx for your thoughts!
    #9
  10. Lornce

    Lornce Lost In Place

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    'xactly.

    :nod

    Hey Ron, really enjoyed your DR650ADV thread.
    Great fabrication and travel skills/attitudes.
    :thumb :thumb
    #10
  11. Lornce

    Lornce Lost In Place

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    Snowbum's forgotten more about electronic esoterica than most mortals will ever comprehend. Might want to e-mail him and get a clarification on that? It might have been a special case or circumstance?

    :dunno

    snowbum@bmwmotorcycletech.info

    He actually welcomes the technical discourse. He's quite a character.

    :thumb
    #11
  12. Ron Seida

    Ron Seida Adventman

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    Thanx Lornce. I'll wait until i have a better diagnosis of the problem, maybe its a simple diode board or brush problem. It's not having the light and not knowing how he modded the electrical system thats throwing me off. I'll let you guy's know how it works out.
    Thanx for reading my thread, glad you enjoyed it :thumb.
    #12
  13. Ron Seida

    Ron Seida Adventman

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    So the guy rode his bike over to the shop this afternoon and the boss continued to diagnose the problem. Rotor, good. Brushes, good. Noticable wiring, good. Diode board, swapped with a Thunderchild, good. Regulator, swapped with a new one, good. Charging...... nope! At this point he handed the bike over to me and i started tracing wires, a blue one to be exact. As i had first suspected, the light has been removed from the system, cut between the regulator and the bulb and taped up with some black electrical tape :becca (i hate that stuff, amature!) Tomorrow i'm going to wire in a 3w. bulb and see where it gets us. The bike was charging, intermitantly, without the exciter circuit :huh . Your thoughts? :ear
    #13
  14. bmwrench

    bmwrench Long timer

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    I have seen these charging systems work without a bulb. The rotor is something that can remain magnetic, but it first must have had a magnetic field generated in it. The original rotor would have, of course, a bulb connected to it originally, which would magnetize it. This worked until the rotor failed. You could do the same thing with a new rotor by installing it, starting the motor and charging the rotor via the positive brush.

    You're on the right track-Install a proper charge light.
    #14
  15. Ron Seida

    Ron Seida Adventman

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    Today i wired in the exciter circuit and the bike is charging like it should. This means that the bike was charging with the previous rotor until it died. Then it was charging with the second rotor until it died :huh . When we put in the third rotor, it would not charge, meaning the two previous rotors were magnetised and the third one wasn't? Wierd, huh...
    All's good now :freaky
    #15
  16. azcycle

    azcycle Chihuahua Wrangler

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    This is slightly related to this topic, so I'm going to ask here instead of starting a new thread. History: My r65 had the speedo/tach removed by the previous owner (my father in law who passed away in November). He didn't replace the speedo at all, and wired in some sort of other-bmw model "dashboard" (see pic).
    [​IMG]
    Yes, that is gum stuck to the high-beam light. My FIL was a character, for sure.

    Now, despite how it looks, everything does work, and the system charges, etc. But I am planning on installing a TrailTech Vapor (with idiot lights) or an Acewell gauge that has all included... speedo, tach and idiot lights.

    Here's the question: If the Vapor and/or Acewell lights are LED's, which I believe they are, will they allow the charging system to work? I read somewhere (maybe here) that an LED won't allow the charging system to work like it should, and I need to use a filament-type bulb.

    Anyone know an answer to this? If it's true, I'll have to fabricate some sort of separate light just for the charging idiot light.
    #16
  17. caponerd

    caponerd Kickstart Enthusiast

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    Based on what the final resolution of the original question turned out to be, I'd say you do need a filament bulb in there.
    LED lights do not behave the same in a circuit as filament lights do. This is why you have to add resistors to a system when you install LED turn signals. The lack of resistance makes them flicker instead of flash on and off.
    #17
  18. anonny

    anonny What could go wrong?

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    Ron, usually I do all my own work.... BUT... if I ever have to take my BMW to a shop I hope you are the guy working on my bike, nice show of integrity. :freaky
    #18
  19. Middleweightboxer

    Middleweightboxer Middleweightboxer

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    Remember the way the system works is that the alternator spinning up offsets the 12v coming from the charge light and thus turns the charge light off. Without some load on that wire you have a short. So as least put a resistor on the line or better yet a bulb. The bulb actually tells you everything you need to know about the charging systems health.

    And yes, an alternator will spin up a charge if it has enough residual magnetism in the rotor. I had a bad instrument board that prevented the charge light from lighting but kept the battery up for several days and thousands of miles.
    #19
  20. bmwhacker

    bmwhacker Still on 3 wheels

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    I simply added a small LED unit in the headlamp shell when I installed this Acewell Computer...works good. The Acewell wiring does not fit the criteria for the BMW charging system.

    [​IMG]

    [​IMG]
    #20