Bad XJ700 Alternator?

I'm fairly certain my alternator is bad. I've been through 2 batteries in less than a year. Got a brand new AGM replacement yesterday at 12.7 volts and rode for less than an hour. Checked the battery after and it's now resting at 12 volts. With they key in the ignition it drops to 11.58. So is the battery screwed now? Do I need a special AGM battery tender?

Last question. I would be super appreciative if someone could dumb this down for me



If you suspect alternator issues, first check the resistance on the wires to the rotor. Dirty rotor commutator rings, corroded connections, etc.----all of these problems will reduce the available rotor field voltage. Next, check the condition of the connectors from the alternator to the rectifier (the 3 white wires). There's usually 2 connectors -- one from the alternator, often hidden behind the battery box, and the other near the regulator. Corrosion in these spots will reduce the stator's outputted current (bad corrosion will often melt the connector, as the outputted current turns into heat rather than being delivered to the battery). Third, with the engine running, back-probe each of those 3 white wires at a connector to ensure voltage is being generated on each leg. Finally, using a multi-meter and following the directions in the manual, check the function of each of the 6 diodes in the rectifier to make sure the power is being properly rectified from AC to DC

 

I know where the alternator is so I take off the cover with the coiled wires and do a resistance check with the positive end on the wires and the negative on the metal cover the wires are in?

 

Start by checking the voltage at the battery with the engine idling, then at 2,500 RPM, than at 4,000 RPM. I think that you'll find the voltage is low at all RPMs.
Then remove the alternator cover and inspect the brushes. I think that you'll find them to be worn out.
Replace the brushes and clean the copper traces on the alternator with an eraser.

 

Stator and coil are in spec. Bought replacement brushes just to be safe because they were down to 10mm. So I checked the regulator rectifier against the manual and got all kinds of crazy numbers. There's a used parts store in town that has a bucket of regulator rectifiers. As long as the wires match and the 12R-A0 decal is on it, it's a match?

 

Also unrelated question:

My right side front turn signal light is constantly on. When I use the right side blinker it stays on but you can see it getting brighter as it blinks. Any ideas?

 

I think 11 mm is the min spec on brushes
from xj4ever catalog
NOTE: Alternator brushes should be replaced whenever they are less than 11mm in overall length.....

does the rear blink and front not?is this a newly happening thing and it worked once?


check for 27 watt bulbs in holders, check bottom of bulb for bad contact points , pop cover on flasher and clean contacts.

disconnect canceler unit.
check for proper connection in headlight bucket

 

Ok bike still isn't charging. The rotor is at 5.5 ohms. I rubbed the rings with an eraser and wiped the whole rotor but it didn't change anything. What should I try next?

 

How about the left side is bad? The XJ700 utilizes running lights on the front combined with the blinker so if working properly the running light will always be on and the flasher on time will make it brighter as you described.

The 3 wire 3 phase stator (stationary) should read .46 ohms between each leg. Also, no leg should have continuity to ground. If you get the correct reading on the stator (usually reads a bit high because of the DMM lead resistance and not a perfect contact with the terminals), then it should be OK and just needs a rotating magnetic field from the field coil to produce a voltage. The AC voltage output from the stator is rectified by Rect section of the Rect / Reg and applied to the battery to charge it.

The field coil (rotor / electro magnet) should be 4 ohms +/- 10% when measuring at the copper rings. Theoretically, it should be the same at the two pin connector for the brushes, but will often read a bit higher, like in the 10 to 15 ohm range. Current through the rotor that travels via the brushes is controlled by the Reg section of the Rect / Reg. When you turn the key on the regulator should provide maximum current through the rotor as the motor is not spinning and thus there is no output voltage. You can do a quick check of the magnetic field by holding a thin feeler gauge about a 1/8 inch from the AC Generator cover and turn on the key. If a magnetic field is being produced ( Reg sinking current through the rotor/ brushes), then the feeler gauge will be pulled toward the cover. Doing this is simplifying the V2 test from the service manual.

Crazy numbers don't mean much, they should be consistent with the chart, although using a DMM you will get different readings and also won't be working with a meter that has the polarity reversed. Point is, for each diode using a DMM on the diode scale you should get approximately 540 ohms in one direction and open in the other.

Troubleshooting per the service manual is pretty easy, but if you have a particular issue getting through it just ask.

 

Thanks for the quick reply rooster.

The left front turn signal is off always except when blinking when turning left. So maybe the right one is SUPPOSED to always be on and the left one is the one broken.

The stator is in spec and I replaced the reg/rec but the bike still isn't charging so I figure it had to be the rotor. What do I do to get the rotor in spec? I already changed the surface of it, bought new brushes and a new reg/rec

 

Is that directly across the copper rings or at the connector through the brushes? If directly across the copper rings and you have confidence in the meter and feel you had a good point of contact with the copper rings then not much else you can do but replace it. If you were measuring at the 2 pin connector for the brushes that's a pretty good reading.

I would still try the test with a thin feeler gauge about 1/8 inch away, and also check the V2 voltage at the green wire.