R80ST, Battery only?

Discussion in 'Old's Cool' started by 110Mike, Mar 2, 2010.

  1. 110Mike

    110Mike Lug in my Kop

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    Hi guys

    Happened tonight.

    When switching my ST off, the ignition light goes ON when turned to park, or turned off! Never had this on any other vehicle.

    I suspect the battery. It went completely flat, won`t hold a charge. Had to jumpstart to get home.

    Is the battery the likely culprit? Or is there something else I should be checking?

    My ignition light always glowed slightly when on the go. Glow only visible in the dark. I read somewhere that this may be due tio alternator brushes?

    Please advise.

    Thanks in advance

    Mike
    #1
  2. bpeckm

    bpeckm Grin!

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    I am not real clear on your question, but from what I think I read: your battery is going flat BECAUSE the red light is staying on, not vice versa.

    Your "light always glowed slightly" when running sounds like it was not charging properly. Could be your alternator brushes... but, in conjunction with what you describe above, I am wondering if you might have a problem with the voltage regulator. Certainly with something in the charging circuit...

    The red gen light should come on, bright, when the ignition is turned "on", before cranking. Then it should stay on, somewhat dimly, until the engine is blipped above idle, and will come back "on, dimly" when the engine is at idle. When you shut off the ignition, that light should go out, completely.

    Describe some more? more hints, more clues......:scratch

    :D
    #2
  3. hardwaregrrl

    hardwaregrrl ignore list

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    uh-oh. yes, more clues please. might want to pick up rick jones' book from motoradd elektrik on the charging system. It could be your brushes, but I suspect your rotor.
    #3
  4. mark1305

    mark1305 Old Enough To Know Better

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    If the GEN light is on in Park and Off, then it sounds like diode board problem or a short internal to the key switch(less likely). The battery is still feeding the system, and the motor is not turning the alternator and producing the voltage to counter the battery voltage which stops flow through the GEN bulb making it go dark.

    I recommend going to Snowbum's site and reviewing GEN light/diode board problems first. Or Moterrad Electrik if Rick has diagnostic info there - I've never checked his site for that, only to buy stuff :D . Edit: I just read through most of Snow Bum's electrical stuff and couldn't find anything specific to the GEN light lighting with the key at Park or Off. He mentions that there have been ignition switch failures and mentions some pinched wire scenarios that cause different weirdness. The range of posibilities looks wide open at this point. Hopefully someone will chime in with some info.

    In the meantime, disconnect the ground cable from the battery (or transmission end) and charge your battery to save it before the plates get permanently sulfated and it won't charge ever again.
    #4
  5. 110Mike

    110Mike Lug in my Kop

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    It is like Mark said in his first paragraph. I will check out the diode board.

    Problem is, it was my only means of transport! I have the R100RS currently stripped to check the shaft.
    4 different cages being fixed at once!

    Could not have been better!

    Mike
    #5
  6. 110Mike

    110Mike Lug in my Kop

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    Will it cause further damage if I simply keep the battery charged and ride like that?
    Till I can get to the root of this?

    The battery was checked and found to be good, a little small though 12A.

    Regards

    Mike
    #6
  7. 110Mike

    110Mike Lug in my Kop

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    Checked, and yes, seems to be the diode board. Molten solder in a couple of places.

    The molten solder probably came from a couple of months ago when I tried to install a better battery:
    While struggling to fit this battery and getting the leads to the terminals I was surprised to get some sparking at the terminals, continued anyway. Kept muttering and thinking "negative earth, negative earth, negative earth.....".
    After tightening up and checking my handiwork I had to ask myself: "negative earth.....negative earth.......why then is that lead that is fastened to the engine casing going to the red + terminal !!??......." :huh

    I am surprised it held as long as it did.

    Hopefully this is all there is to it!

    Mike
    #7
  8. bpeckm

    bpeckm Grin!

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    Aaaaah... true confessions... yep, that would do it!!

    As a temp fix, you could rig up a switch in the negative, turn it off ONLY after you have shut off the engine. Of course, you would be running the ignition with the battery, but that is effectively what you are doing now, and you would have to re-charge the battery every night.

    Or, you could just disconnect the red wire from the diode board (that is the output (normally)) that goes back to the red heavy wire at the starter, which goes to the battery. By disconnecting it, from either end, you would effectively cut the circuit that is discharging the bike.

    For that matter, you could probably pull the wires off the two brushes and do the same thing....just make sure you tape up any loose wires so they cannot swing around and short out.

    Thinking out loud, above... your choice, but any of those should work for you...

    :D
    #8
  9. mark1305

    mark1305 Old Enough To Know Better

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    You can run total loss just off the battery and keep it recharged while the bike is parked. But like bpeckm said, you should disconnect the output from the diode board to avoid feeding any un-rectified, ie., AC current from the alternator to the battery.

    AND, something I learned from OldBMWMaster, the headlight will draw down the battery down very quickly when the battery isn't getting help form the charging system. (I actually learned this on my old Ducati M900 when the VR went out on a 20 mile ride and the 16AH battery went totally flat that quickly.) His opinion, which I buy into, is that all airheads should have a way to turn the headlight off in emergencies and ride the bike with only the 5 watt "city light" on. There are a couple of ways to do it from unplugging the headlight bulb, to switching wires around on the ignition switch or jumpering a wire from the Run position to the Park position behind the switch.

    After you get the diode board fixed, check and see if you still see the faint glow of the GEN bulb when riding above 2000 rpm or more. If so, then you have a separate but minor problem with either worn alternator brushes or dirty slip rings on the commutator they ride on. When the brushes get worn way down, the springs pushing them are near fully extended and don't put enough pressure on the brushes to maintain good contact and alternator output drops allowing the GEN light to glow.

    I did find tons of info on that problem on Snow Bums site. http://bmwmotorcycletech.info/techindex.htm Scroll down to about Article #15 for some in depth info.
    #9
  10. cln

    cln Adventurer

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    Not trying to hi-jack, but what if the red gen light doesn't change intensity? Mine will go off above idle, but stays pretty bright at idle.
    #10
  11. fishkens

    fishkens Long timer

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    That's 100% a-okay. The intensity depends entirely on where the idle is set. What you're really looking for is "on" with the key on but the motor not running and "off" when the engine is running above 1200ish rpm.

    By the way, don't set the idle too low. That results in the oil pump spinning more slowly and not lubing the engine as well as it can be. An idle speed of 900 - 1000 is better than 800 rpm. There's no benefit of idling it below 900 or so-ish. Err on the side of a higher idle speed.
    #11
  12. cln

    cln Adventurer

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    Thanks Fishkens! Will keep this all in mind. My R80st is new to me and I just thought it was weird an idiot light stays on with the engine idling. Glad to know this is "normal".
    #12
  13. Solo Lobo

    Solo Lobo airhead or nothing

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    Well, don't be so quick there. The Gen light turns off completely at idle on my '81 R80G/S. and that's a tick over 1,000
    #13
  14. fishkens

    fishkens Long timer

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    Hmmm, precisely what rpm does the gen lamp need to to go off by to suggest that the charging system is healthy or not? 800? 900? 1000? 1100? 1200?

    My thought is that if it goes off by 1000 - 1200 rpm then that's a crude indicator that the charging system is healthy. But that's crude. I think we really want to put a voltmeter on a healthy battery to see what the charging voltage is at 3,000 rpm. That along with a few other tests give us the full picture. Flickering at idle (depending on the idle speed) does not suggest that something's amiss. Nor does a lamp that's out at idle prove that the charging system is healthy.
    #14