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Thread: Alternator check

  1. #31
    Registered User lmo1131's Avatar
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    Thanks for that info Paul.

    I'm going to run what I've got for a while and see how it goes. The battery is a generic lead/acid. The PC680, mentioned by Barron, is a probable upgrade I will keep in mind.
    "It is what you discover, after you know it all, that counts." _ John Wooden

    Lew Morris
    1973 R75/5 - original owner

  2. #32
    Registered User lmo1131's Avatar
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    Awwwww crap. That didn't last long...

    Took a little 200 miler today; up to Big Sur and back; foggy at the start and cleared by 10, one of God's perfect riding days. Several starts and stops, with no problems. Got back to the shop and checked voltage just for the helluvit.

    12.2V @ idle.

    12.9V @ 3000.

    It remains to be seen how the starter does in the morning. I suspect it will be it's same-o same-o reluctant self.

    I give up, that's what I was getting with the 39 year old OEM regulator... .. . at least I'm only out $30.

    Thoughts?
    "It is what you discover, after you know it all, that counts." _ John Wooden

    Lew Morris
    1973 R75/5 - original owner

  3. #33
    Monza Blue 1974 R90/6
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    I think the $30 for the regulator was probably money well spent. It was time.

    How old is the battery and who manufactured it?

    Barron

  4. #34
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    Replacing the stock rotor with one providing more power is the only real solution. Based on articles about the /5 charging systems, the alternator (when new) puts out 180 watts. That amount of power is marginal. Add 35+ years of age considering corrosion and decomposition of winding insulation with mechanical wear and the alternator probably puts out less than 180 watts.

    New rotor: http://www.euromotoelectrics.com/pro...t-rotor642.htm

    A new battery will also help but not fix the problem.

    Edit: here is snowbum's page link for the alternator describing the /5 180 watt system: http://bmwmotorcycletech.info/trbleshootALT.htm It appears that altering the stator is needed to increase the output. So, just replacing the rotor may not be the solution.
    Last edited by Stan_R80/7; 06-04-2012 at 12:52 AM.
    Stan

    AH# 13238

  5. #35
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    There is no reason why a STOCK /5 with 180 watt system in proper working order will not start reliably at 40deg - something missing in this discussion.

    Is the bike STOCK - headlight orig or 60watt max H4?

    Are there other loads you have not mentioned?

    Do not turn the light on till started

    Does the bike have aftermarket electronic ignition - this is a cold weather nightmare since cranking draws voltage below trigger threshhold for some systems- if so use kick starter when cold

    What other loads are there that are not stock?

    If starting/runnig at 40deg use oil 10w40 or 15w40 - NOT XXw50

    I have absolutely no trouble starting old /5s with small 10LA2 lead acid battery if the bike is properly tuned and making a 10 mile ride at 45mph or more with 55/60 watt H4 and 40watt electric vest on full.

    Till you figure it out suggest you use the kick pedal before cold start

    Ignition off - gas on - choke on - prime the bike by stroking through one compression per cyl to get fresh charge of fuel/air (save your battery making this effort)

    Ignition on - kick or hit the starter should fire on first revolution
    Kick is better since it leaves max voltage for ignition system

    The original system is adequate - you really need to keep searching till you find what is wrong before just throwing a bunch of expensive aftermarket parts at this bike.

    There should be no reason to need to keep a charger on the bike every night if the battery is good - this might be killing or has already killed the battery

    There is no reason the bike (with points) should crank more than 2 or 3 revolutions before starting - not tuned properly if cranks more

  6. #36
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    "But there is still a slight hesitation when the starter engages (and has been since the bike was new); and the starter has never really shown any "authority" when turning over the engine."
    =====================================
    This is the case on one of my junkers known to have PO installed too small diameter wire for ground and feed to starter. I should fix it but usually just kick it.

  7. #37
    Registered User lmo1131's Avatar
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    Update

    The original system is adequate - you really need to keep searching till you find what is wrong before just throwing a bunch of expensive aftermarket parts at this bike.
    Load-tested the battery yesterday: it had one weak cell (so much for "it's only six months old"). Replaced with generic lead/acid wet cell; charged for ~12 hours.

    I made a extender cable for my digital multimeter, plugged it into the remote battery tender pig tail, tucked the meter under the map window on my tank bag and went for a ride:

    voltage @ battery before start; 13.8
    voltage @ 1000 13.9 - 14.1 (fluctuates)
    voltage @ 2000 14.1
    voltage @ 4000 14.16 (sustained highway speed; all lights off)
    voltage @ 4000 13.85 (headlight on (60/55W H4; low beam))
    when the head light is turned off voltage returns to 14.1+ almost instantaneously.

    The bike started right up this morning after being left outside in the fog all night, off the battery tender. Turn signals cycle faster. Horn is louder.

    I've never had instrumentation on this bike and have to say I like it. Now I'm thinking I'd like to permanently install that Datel digital voltmeter; $50 seems kind of steep but it is small, and waterproof...

    So this would seem to mark the end of the quest for increased voltage. In the future I will suspect the battery when/if a voltage drop is observed.
    "It is what you discover, after you know it all, that counts." _ John Wooden

    Lew Morris
    1973 R75/5 - original owner

  8. #38
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    Good to know - it was the battery. As a note, a battery hydrometer is always reliable to check the condition of a standard lead acid battery. I don't think most people own one - and one for a motorcycle battery is generally smaller than for a car battery so not as readily available in auto parts stores. Plus, they don't work for gel-cell or sealed lead acid batteries.

    I bet the stock voltage regulator is still good.
    Stan

    AH# 13238

  9. #39
    Grammarian no, Rider yes ISAMEMON's Avatar
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    glad its sorted out,
    so another spare part for your collection ( the old regulator)

  10. #40
    Registered User lmo1131's Avatar
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    so another spare part for your collection ( the old regulator)
    Well that, and my multimeter.

    Note to self: Next time, do not leave multimeter under tank bag map window, in direct sunlight, until the middle of the afternoon ...
    "It is what you discover, after you know it all, that counts." _ John Wooden

    Lew Morris
    1973 R75/5 - original owner

  11. #41
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    battery

    Lew, glad you have resolved the problem(s). Can you tell us the brand of the battery you just replaced?

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