R65 Charging problems - Need advice

Discussion in 'Airheads' started by CharlesCoonz, Dec 31, 2020.

  1. CharlesCoonz

    CharlesCoonz Adventurer

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    Greetings everyone,

    I need some help with my R65 1988 model since i am not sure where to look for the problem.
    I bought an old neglected crippled bike and restored it as a high end cafe racer.
    While restoring i got a new ignition coil, a new wahrle regulator and installed a lithium battery.
    Everything seem to be working fine until my battery failed with a juice leak.
    I though it was a problem with the battery so i installed a new one and started monitoring the voltage with my motogadget instrumment.
    The voltage seemed fine on my first ride with the new battery but after a few kilometers i noticed some voltage spikes reaching 15 and 16 volts.
    After a few days i repeaded the test and noticed that again after a few minutes of engine running at high revs i got 15 and 16 volts.
    I am trying to see if this is a regulator issue or a bad stator that when warming up causes a problem with the power generation.
    The obvious solution would be that its a bad regulator but the part is brand new.
    A friend of mine said that a bad stator with a bad current generation would cause the regulator to fail so even if i get a new regulator after a while i will have the same problem.
    Is that valid?
    Anyone has any ideas and how to diagnose if its a bad coil in the stator?

    Thanks in advance and happy new years eve.

    Attached Files:

    #1
  2. bmwrench

    bmwrench Long timer Supporter

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    First, confirm your voltage readings with an independent meter. If you're still seeing high voltage, the regulator is faulty-unless you have a bad "exciter" diode. So, confirm the voltage reading, swap in a new voltage regulator, then if he first two steps fail, test the diode board.
    #2
  3. Beemerguru

    Beemerguru Beemerguru...G/S guy

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    Well first it may be a language translation issue but there is no coil in the stator. The stator is just a 3 wire winding that generates current when the energized rotor (big hunk of metal on the end of the crankshaft) spins. The faster the engine spins, the more 3 phase electrons generated by the stator that head up the 3 wires to the diode board. Then the wavy AC current is straightened out to 12V DC and sent to the voltage regulator. That's where spikes in the voltage should be captured..,by the regulator. Usually maxes out somewhere around 13.7 or so but you can get adjustable voltage regulators so you can bump the max limit up a bit to handle the newer gelmat batteries that like around 14.1V to stay fully charged.

    Put a multimeter across the battery terminals and measure there while you vary the engine speed. Let us know what you find.
    #3
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  4. CharlesCoonz

    CharlesCoonz Adventurer

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    If we assume that the regulator was working fine when i got it (its only got 400km installed) is there anything that can burn the regulator and cause it to not filter the spikes?
    I could buy a new one for lithium batteries but i wanna be sure i will not waste a tons of money only to fail again.
    #4
  5. 190e

    190e Long timer

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    It's not really a case of filtering spikes. The regulator works by switching off the current to the rotor and then switching it back on again when the alternator output voltage drops. It does this on/off switching very fast so that it effectively reduces the average rotor current. Without the regulator in the circuit you would get full current through the rotor the whole time and an excessively high charging voltage the whole time. When you see intermittent high voltage readings it's likely because the regulator stopped switching and let full current through to the rotor.
    #5
  6. Beemerguru

    Beemerguru Beemerguru...G/S guy

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    A Lithium battery is big bucks. An adjustable VR is around $20 US from EME or Moto-bins
    #6
    spo123 and nothing like this.
  7. mrclubike

    mrclubike Been here awhile Supporter

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    #1
    I would remove the Lithium battery and check the charging voltage with a normal battery
    You can use some jumper cables and connect it to your car battery
    Just make sure the Lithium battery is disconnected
    The symptoms you describe can be caused by the battery opening
    I would assume that the Lithium battery has electronics in it to properly charge it and that circuitry could be faulty

    #2
    Also check the brown ground wire from the regulator to the brush holder and make sure it also has continuity to ground
    I am not sure if the reg is self grounding thru the mounting or not
    If regulator does not see Battery negative it cant regulate properly

    #3
    Another possibility as the rotor is shorting and causing the contacts in the regulator to weld shut or the switching transistor to short
    Not sure what is in your regulator

    Stator cant cause a over charging condition
    I assume you are calling the "rotor" a "coil"
    #7
  8. Warin

    Warin Retired

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    Using the old voltage regulator for testing will do. Ok the voltage will not be as large as the battery would like, but you will see if the spikes go away, if they do go away then it is the voltage regulator.
    #8
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  9. CharlesCoonz

    CharlesCoonz Adventurer

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    Thanks for your answer. I will check 1 and 2 although i am pretty sure its not a battery thing. The first battery blew up after a few hundred miles and this is a second new one so i assume its something else.

    I will check #2 but regarding #3 would that explain that the problem apears when the engine gets warmed up ? (over voltage apears after 10 of engine running. Do i need a new rotor if thats the case?
    #9
  10. Warin

    Warin Retired

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    Rotors usually go open circuit, meaning the output drops to 0. A rotor going short would still be regulated by the voltage regulator.

    If the rotor going short blows up the voltage regulator then the voltage regulator would remain faulty. engine cold or hot.
    #10
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  11. CharlesCoonz

    CharlesCoonz Adventurer

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    THanks for your reply.
    THanks for the reply. Is there a way to test if the rotor is "bad"?
    #11
  12. 190e

    190e Long timer

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    Measure the resistance which should be approx. 3.5 ohms but the rotor is only able to produce an excess charging voltage if the voltage regulator allows it to. I can't see how the rotor could be the cause of your problem.
    #12
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  13. CharlesCoonz

    CharlesCoonz Adventurer

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    The concept is:

    The regulator was purchased brand new when rebuilding the bike so a bad regulator from factory is kind of a long shot.
    We are trying to see if a bad rotor could burn a regulator that in turn would behave this way.
    The bike had a lot of miles when i purchased it in awful condition so it would not surprise me if there was a problem with the rotor that would in turn cause other problems to the bike.
    When the regulator was installed it was working properly for a while. (100+ miles)
    #13
  14. 190e

    190e Long timer

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    Ok, you need to lift the brushes and slide something insulating under them like thin card then measure the resistance across the slip rings.
    #14
  15. bmwrench

    bmwrench Long timer Supporter

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    The rotor is nothing more than an electromagnet turned on and off by the regulator. If it was shorted to ground, the generator light would protect the rest of the system by remaining lit.
    #15
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  16. Beemerguru

    Beemerguru Beemerguru...G/S guy

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    Maybe just something to check..you said lots of miles..and probably spent time parked outside?

    When you did the rebuild, did you check the 3 wires from the back of the diode board to the stator? Especially if it has the big rubber plug at the diode board..I've taken those off before and found the connectors in the plug corroded and green. Barely making contact.

    and if you keep replacing the lithium with the same model, maybe try an Odyssee PC680 and put some miles on her.
    #16
  17. 190e

    190e Long timer

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    This is what I think the OP is saying:

    If the rotor was a dead short or shorted to ground it it would pull more than the nominal 4 amps through the VR from D+ to DF and that might damage the VR.

    But if the rotor was shorted it would not produce a magnetic field and therefore there would be no output from the alternator which is the opposite of the symptoms being observed. As bmwrench said the gen light would then limit the current that could flow D+ to DF.

    If the rotor was partially shorted to a value less than 3.4 ohms then it's possible a higher than 4 amp current could flow but a partially shorted rotor would also produce less magnetic field and therefore a lower alternator output which would in turn limit the rotor current. What ever output was produced would a least be consistent and not spike in the way that has been observed. Given this is an intermittent fault then perhaps doing a static resistance measure on the rotor is not going to help much. Rotors sometime go open circuit after a period of running but short circuit ?

    It would be a slightly awkward thing to do but the only way to dynamically test the rotor would be to put an ammeter in series with the D+ connection to see if a change in rotor current corresponded with the observed voltage spikes.

    For what it's worth I observed the OP's symptoms in a car getting on for 40 years ago. I'd be driving home from work on the motorway and the headlights would suddenly get very noticeably brighter and then after a while return to normal again. The next day I drove home with a model 8 Avo perched on the dash and when the lights got brighter the voltage shot up to something like 18 volts. I fitted a new VR to the alternator and all was well.


    ChargingSystem3.jpg
    #17
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  18. Warin

    Warin Retired

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    New parts fail. That is why guarantees exist. The new voltage regulator failing is not such a long shot.

    As the fault is not always there, testing at one moment in time may not capture the fault, hence replacing the voltage regulator with the old one is suggested.
    #18
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  19. mrclubike

    mrclubike Been here awhile Supporter

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    Yes new parts fail everyday
    Reinstall the old reg and verify the Brown wire between REG and rotor brush is good and grounded
    While you are in there make sure the black wire from the brush to the REG isn't rubbing against the POSITIVE heat sink on the Diode board

    If the REG isn't seeing the Battery Negative it cant regulate properly
    We know it is seeing battery positive because it is charging

    We have an over voltage issue here
    This is a very rare condition and indicates that most of the charging system is good

    I have been following this forum religiously and cant remember this problem ever coming up before
    As a mater of fact out of the 40 years I have been a mechanic I remember seeing this 2 times
    Last time it was incorrect wiring between the reg and alternator
    I am also suspicious of that LITH battery
    #19
  20. Beemerguru

    Beemerguru Beemerguru...G/S guy

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    I had a couple builds that suddenly steadied out at 15v. One for a few hundred miles (long trip), and it really ballooned the PC680. Thing looked 7 months pregnant

    But I was also running the 800 watt alternator kit. So I got very good tracking down the problem.. Both times the VR popped its cap. Replaced and has always read 13.8V with both set of driving lights, heated jacket, heated seat, GPS, and phone charger.

    Overkill for most builds now but nice to know I could add an inverter to power a small microwave and cook popcorn at Death Valley Rendezvous!!
    #20
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