Question about 1980 Yamaha XJ 650

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Battery not charging

I have a 650 yahama xs, my battery will not charge. How can I check to see if it is the magneto? The battery will take a charge from my charger.
Andy Heffner

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Hi and welcome to FixYa,

Almost always, your described problem could either be a defective rectifier/regulator combo (most likely) or loose, burned or corroded connectors of the 3 yellow wires from the stator to the regulator (likely) or burned/open stator windings (least likely).

You would need a multitester to verify which is faulty by considering:

  • at idle, output of regulator should be around 12.5 volts and go up as the RPM is increased to about 14.5 max;
  • the regulator's output is directly connected to the battery's + terminal;
  • the stator uses 3 coils connected by 3 yellow wires to the regulator. Due to high charging currents, these connectors often gets burned and loose conductivity/connection. Check for burned terminals/connectors or discolored plastic tab;
  • the stator could be checked for continuity. Each yellow wire should measure 0.3 ~ 0.5 ohms to the next yellow wire at any yellow to yellow pairing;
  • in most instances, the yellow wires should not read a connection to ground with the connector to the regulator removed.

Good luck and thank you for using FixYa.

Posted on Jun 24, 2009


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