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BMW r60/5 motorcycle--alternator light on when idling?
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Hey everyone:
I am the proud new owner of a 1972 BMW r60/5 toaster. She is running
fine and idling fine but I notice when I let her idle, the red
alternator light comes on. It turns off as soon as I give her gas.
Again, she idles constantly and evenly and doesn't stop. But does
this signify a problem?
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No problem. That is common with slash fives, and newer ones, too.
If you haven't done it yet, be sure to get someone familiar with
airheads to check your points/condenser/timing, valve clearances,
swingarm bearings, and other bits one should do to an airhead. Look into
greasing the output splines soon, too.
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Amanda
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Probably not. Many vehicles of that era didn't put out enough power
from the alternator at idle to operate the lights. It isn't until the
motorcycles (and cars) become high dependent upon electronics that
the alternators are upsized to insure they can provide all of the
needed output even at idle to keep the electronics running.
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My 1980 /7 has done that, on and off, all the time I've owned it
(since 1983). It's never been a problem.
Congrats on the toaster! It's a wonderful bike! Ride it and enjoy
it.
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The alternator light should go off about 1400 RPM.
There are upgrades you can make to the charging
system but they probably aren't needed unless
you run heated grips or clothing. Your bike sounds
like it's fine.
Make sure you see the red alternator light before
you start the engine. If the bulb blows, the bike
won't charge properly because the current that
energizes the alternator flows through that bulb.
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Can you expand on this a little? Obviously all the field current
can't go through the light or it would be glowing all the time.
Are there diodes (other than the rectifier diodes) involved?
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The rotor is an electromagent which is initially energized
by current flowing through the bulb to the points. I believe
you are correct about a diode but haven't delved into all
the gory details and haven't seen a good wiring diagram
that shows this.
At some point, the voltage regulator also gets into the picture,
energizing and de-energizing the points. How it interacts
with the gen light is a mystery to me, but I hypothesize
that it's sort of a bootstrap with the gen light providing
the initial voltage to energize the rotor, which can then
continue to energize itself.
Bottom line among BMW groups though it "don't
let the bulb burn out or you'll drain the battery".
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And of course by "points" I really meant "brushes".
Dohh!!!
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Enjoy a nice bike.
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