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Thread: 85 R80 charging

  1. #1
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    85 R80 charging

    We have gotten the R80 running good and decided to check the charging voltage.
    The warning light goes off just above idle, but when a multimeter is hooked to the battery, the voltage is only 12.7. If the RPM is raised to 3000, within a few seconds the voltage tops out at 13.2

    The battery is new and cranks fast. The owner and I rode 150 miles yesterday with his heated liner on and the battery seems to have been charged.
    We started troubleshootng and followed Chiltons advice to scrape the paint away from the rectifier mounting bolts. That made the rise to 13.2 a little faster. We then cleaned the connector on the voltage reg. That made the rise to 13.2 even faster.

    Is the regulator doing it's job of not over charging, or should the voltage rise to 14V or so?
    Ron

    91 K75RT ABS

  2. #2
    On the Road
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    Charging

    13.2 is not a bad level for the charging circuit, but 13.7 would be alot better. I would definitely try a new regulator on the bike or maybe compare yours to another airhead & see what theirs reads on the same meter. There is a wiring kit available from BMW that runs seperate ground wires to your diode board from a engine grounding point under the front cover. You might also check the spring tension on the brushes at the alternator.

    Good Luck


    Quote Originally Posted by roncooper View Post
    We have gotten the R80 running good and decided to check the charging voltage.
    The warning light goes off just above idle, but when a multimeter is hooked to the battery, the voltage is only 12.7. If the RPM is raised to 3000, within a few seconds the voltage tops out at 13.2

    The battery is new and cranks fast. The owner and I rode 150 miles yesterday with his heated liner on and the battery seems to have been charged.
    We started troubleshootng and followed Chiltons advice to scrape the paint away from the rectifier mounting bolts. That made the rise to 13.2 a little faster. We then cleaned the connector on the voltage reg. That made the rise to 13.2 even faster.

    Is the regulator doing it's job of not over charging, or should the voltage rise to 14V or so?

  3. #3
    Liaison 20774's Avatar
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    Be sure you can trust the multimeter...try another one or find a known voltage and compare to that.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  4. #4
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    Question about the grounding wire for the rectifier. When I run a continuity check between a mounting screw for the rectifier and the engine, I get no resistance.
    Does this mean that a grounding wire is not needed?
    Ron

    91 K75RT ABS

  5. #5
    James.A
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    Quote Originally Posted by roncooper View Post
    Question about the grounding wire for the rectifier. When I run a continuity check between a mounting screw for the rectifier and the engine, I get no resistance.
    Does this mean that a grounding wire is not needed?
    Ron , you probably need the grounding wire. I'll assume you are not describing the voltage regulator here, but the rectifier under the front cover. If by "no resistance", you mean infinite resistance (open circuit), then you need it for sure. If the 1985 R80 has the diode rectifier mounted on rubber mounts, you should consider changing those to solid mounts for better heat transfer. I'm not sure what year the rubber mounts were introduced, but they isolate the body of the rectifier from the motor, hence the need for a ground wire.

  6. #6
    Registered User lkchris's Avatar
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    Quote Originally Posted by hp1bmw View Post
    There is a wiring kit available from BMW that runs seperate ground wires to your diode board from a engine grounding point under the front cover.

    There is indeed and it's specifically for R100 engines with rubber-mounted diode boards. Pretty sure R80 engines have direct-to-metal mounted diode boards.
    Kent Christensen
    21482
    '12 R1200RT, '02 R1100S

  7. #7
    Registered User beemerguru's Avatar
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    Some engine timing covers had metal bosses for mounting the diode board,,other relied on the rubber mounts. If you have one with the metal posts, make sure the paint is scraped off for a solid ground.

    If you have rubber mounts, replace with solid metal for heat dissipation and a good ground. You only need the ground spider harness if you have the rubber mounts.

    I would guess either voltage regulator or worn down brushes..but first, pull all the charging circuit connections and replug like you started ...you can sometimes pick up half a volt just doing this..especially the 3 wire harness into the back of the diode board...ever seen a green corroded connection? That's where it will be.
    Greg Hutchinson
    R80G/S (4) 633CSi with 450K mile
    '68 R60/2 '88 K100RS Special Edition
    http://gregsgssite.shutterfly.com/

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