Charging System

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:

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.

  1. 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.
  2. 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).
  3. 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.
  4. 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!
  5. 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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