The charging system consists of the alternator
(rotor/stator), rectifier, voltage regulator and the battery.
Problems with the charging system of these older bikes is rare in
bikes of 350cc and less, moderate in bikes from 500-650cc and very
common in bikes of 750cc and over. It will require a manual to do a
good job in this area and if you don't have one anyway, get
one(Clymer is good). Here is a breakdown of what the parts do:
alternator:
produces an alternating current by passing a moving magnetic field
(rotor) through a nonmoving or static (stator) winding of wire.
Gasoline is thus converted from a chemical energy to a mechanical
energy (within the engine) to an electric energy (within the
alternator). This energy is then sent to the
rectifier.
rectifier:
converts alternating current (AC) to direct current (DC). Early
rectifiers simply took half of the energy (single wave), and sent
it to the battery. Since alternating current travels in both
directions, the early rectifiers simply grabbed the energy going
in one direction and set it on. Later rectifiers use a diode group
to grab both directions (full wave) of current and combine them
into one direction and sent this on. Later rectifiers were much
more efficient but more prone to failure.
voltage
regulator: governs the amount of
current coming from the alternator and limits it to about 14-15
volt. This is usually combined with the rectifier to make one
piece of hardware. If too much current is generated, the regulator
sends it to the ground or frame.
battery:
stores energy and is the main place to dispense energy as needed,
to plugs and lights.
A sign of a bad charging system is
when the headlight blinks or strobes at idle or when there is a
marked increase in headlight intensity when you gun the motor. All
bikes show some increase in headlight intensity with higher RPMs but
if it goes from dim to bright, it is probably the charging
system.
I will tell you in advance that finding why your
battery does not charge is a hard thing to do! This is the procedure
I follow to try and solve this problem.
Make sure the battery is good! Use a volt/ohm
meter to see if it is providing near 12 volts. If it reads 10
volts or less, replace it. If it can hardly crank over the engine,
replace it. Motorcycle batteries are not real good providers. They
can go bad even if you take real good care of them. The small thin
lead plates within are not as vigorous as a car battery ones and
can be damaged easily.
Using your manual, read on how to connect your
volt/ohm meter up to your bikes alternator. First check if there
is an electrical leak in the wiring of your stator. The insulation
of the miles of coiled copper wire can deteriorate and cause the
wire to short and thus not provide the extended length of wire
needed to pick up the energy from the magnetic field. If a short
is detected, it must be replaced ($ ouch).
Start the bike and using your volt/ohm meter
test the output of the alternator. It must be within the specs of
your manual. In the 750cc, the alternator portion of the engine is
low and sticks out, just waiting to be smacked when the bike goes
down. If your bike has been dumped or impact has occurred to this
portion of the engine, you may lose your charging power. The rotor
is a magnet and can lose power with an impact.
Using your manual, read on how to connect your
volt/ohm meter to the rectifier. With the bike running, check its
voltage output. It should be within specs (14-15 volts). Now here
is a problem, the rectifier converts AC into DC and this
conversion requires that some of the electrical energy be
converted into heat energy. You can locate the rectifier because
it has heat dissipating fins located near it. Unfortunately this
heat can cause a failure in the unit which can not be detected
except under load (blasting down the road) conditions. So..... the
rectifier may read good at idle or high RPMs in the garage but it
fails on the road! Many shops will swap rectifiers if they are
suspect and test ride to see the result. For us home mechanics
this is not possible!
I have found that the voltage regulator is
rarely at fault. But you can still test it by following the method
outlined in the manual. The test consists of using two batteries
in series and a variable resistor. In effect you try to put over
14 volts across it and see if it stops this too high
voltage.
In my experiences with bad charging systems it is
the rectifier. The exception is the 750 cc engines where the rotor
can easily be bad.
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