Question about Yamaha XJ 650 Motorcycles
First, charge & load test the new battery out of the bike. If it is good, it will stay above 10 volts with a load test. If it is a new battery that has set completely dead, for even a couple of weeks, It isn\'t any good anymore. You will find it won\'t take a charge. It\'s sulfated.
Now put the battery in and connect a DC voltmeter across the battery terminals black to - & red to +. It should be reading 12.6 volts. Now turn on the key, Still 12 volts at least. While cranking, The voltage should stay above 10 volts or the battery is not full charged or in question. When running, the voltage should go up to 14 ~ 15 volts DC but no higher when reved-up. That is charging correctly. If not, It is the voltage regulator/ rectifier ass\'y OR the stator coil. To check the stator coil, Find the Regulator ( aluminum box with fins w/ 3 white wires, a red & a black ground) & pull the plug from it. Put that meter on AC volts & connect to any 2 white wires going into the regulator with it still unplugged. BE CAREFUL OF A GOOD SHOCK IT YOU TOUCH THEM. You should read at least 40 ~ 90 volts AC as you rev-up. Connect the meter between each pair of white input wires (the connections don\'t matter black or red---it\'s AC alternating current-always changing), Just check all pairs of two. They should each be reading approx the same 40 ~ 90. If you have that, Then the stator is good. This model also has a field coil rotor instead of permant magnets. It has generator brushes that wear down & need replacing. If you get no output from the stator coil wires, Pull the generator cover 3 screws just behind the cylinders & below the carbs with the stator wies going in. The brushes are carbon & should not be worn down past the scratched in lines on the side of them. If so, Replace them. While in there, Put your meter on Ohms Test R X 1, & test the Rotor Slip rings with meter wires either way. You should have 4 ~ 10 ohms. Now put a meter lead on one slip-ring (either-it doesn\'t matter which) & the other on Ground anywhere (a screw on the motor case). You should not show any short to ground, Full resistance. If that checks out good & the brushes are good, Then the AC generator is good. There is no way to completely test a voltage regulator other than that 14 ~ 15 output to battery. If you have a good battery,stator, brushes, rotor, & all the wiring connections are clean & tight; Then the regulator is bad if you can\'t get to 14 volts. You can only replace it. Remember that more than one thing could be bad. Bad voltage regulators can short & burn out a stator coil. OR bad brushes can arc & burn out a rotor coil.
Posted on Mar 25, 2014
It is corrected properly, right? + to the wiring harness and - to ground ... right? Are you certain about the rectifier? Is the battery charged at this time?
You know a alternator cannot make power unless you first put power into it ... right? Alternators (unlike most generators) are not self exciting. If your battery is weak or "dead", the alternator cannot make electricity to charge the battery. I don't know what the rating of your alternator is. Your battery should be fully charged before you do any more tests. If you have a 1 amp charger, allow at least 10 hours for a full charge. Don't cook your battery with a big, powerful, fast charging automotive battery charger.
Good luck with your repair ... I hope you find this response helpful.
Thanks for your question @ FixYa.com
Posted on May 02, 2011
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