Charging problem

Hi people, I'm working on an xj900 1989 that doesn't charge the battery, the regulator rectifier is new and readings are correct but the resistance readings for the stator could and rotor coil are slightly out of spec with .9 ohms on the stator coil( should be .46) and 9.2 ohms on the rotor coil ( should be 4 ohms) is this discrepancy enough to render the alternator faulty. The battery is also new but the xj is a trike and was converted before I was asked to work on it. Would be grateful for any guidance. Thank you.

 

have you looked at the brushes?
touch your meter leads together see what you get for a reading and subtract that from the measurements.
odd that both are 2x what they should be

are the copper rings on the rotor clean?

can you start the bike? what is the output when running?
sometimes new batterys are bad

 

Hi, thanks for the reply, yes the brushes and the battery are good ( did a load test on battery). Bike runs great. The output is almost negligible just a couple of volts ac but will re check the resistance readings, I just assumed ( possibly wrongly) that the meter would read zero resistance with the probes touched together on a digital meter. Yes the bike starts easily but, as I say, will re check resistances. The owner doesn't know how long it hasn't charged for as he only just bought the trike and I noted that the faulty reg rec was relatively new compared with the rest of the electrics.

 

Check the voltage on the two pin input on the harness side that goes to the brushes. Voltage drop caused by dirty connections can lower the input voltage.

 

Just a further thought on the actual output, maybe I'm testing the output incorrectly. DC voltage test across the battery shows no rise in voltage with bike running and obviously a gradual drop. But am I right trying to test for ac voltage at the alternator end of socket eith the reg rec disconnected?

 

Thanks Franz, all suggestions appreciated.

 

Yes l think it will be AC at the alternator end (when the engine is running) of the connector because it has to be converted to DC by the rectifier to charge the battery and run the bike.

My bike was not charging the battery when l got it. The problem was the two pin connector was attached to the wrong harness socket. PO had made a mess of the wiring.

 

According to the Haynes manual brushes can become less efficient with age. There are also wear lines on them which indicate when they should be replaced.

 

On the XJ750 Maxim I recently acquired there was a new, apparently aftermarket, rectifier/regulator but the bike was still not charging. After fixing several poorly done crimp connections to the new fuse box I found the new R/R was bad and the old factory piece was just fine. Just because a piece is new don't be assured that it is good. For what it's worth......
John
ps: I am a fan of soldered connections and shrink tubing vs crimp on connectors.

 

Thank you, Will get back to it in the next couple of days hopefully and yes, soldered joints and heat shrink.

 

Just one more question, should I get battery voltage at the brush wire connector? Thanks again.

 

Yes at the harness side with the ignition on if it is unplugged. Or put your voltmeter across the alternator brushes with the ignition on when harness connector is plugged into brown and green wire to the brushes..

Power goes to the alternator rotor via the brushes and the output from the stator are the three white wires to the regulator/rectifier unit.

 

Have you actually replaced the brushes? Mine looked good but were contaminated with oil and wouldn't put out enough voltage. I'm surprised the bike runs "great" with no voltage output. Mine produced about 12 volts and when the bike was cold hitting the brakes would sometime lower the voltage enough to actually shut to engine down.

 

The brown wire should have 12V switched on it - so with key on and measuring to ground you should read very close to battery voltage. It is usually a bit lower because of some losses along the way in the switches and wiring.

The green wire is the control wire from the regulator and is also measured in respect to chassis ground. The lower the voltage the more current is flowing through the field coil, which increases the magnetic field strength. Consequently, the lower the voltage the higher the output from the stator. The manual directs you to check it with the bike off and the ignition switch set to on and verify it reads less the 1.8V.

Checking for AC voltage is correct, but check phase to phase not phase to ground. With the connector unplugged the voltage should be around 18 VAC at idle and rise to approximately 50 VAC when the motor is revved.

 

Managed to get back to the trike, there is no voltage reading at the brown wire connection in the 2 pin plug with the ign on, there is full battery voltage at the brown wire in the 4 pin ignition switch connector and if I introduce a live from the brown in the 4 pin connector to the brown in the 2 pin brush connector it just blows the main 30 amp fuse. The owner thinks it didn't charge when he bought it, it had been partially rewired, looks like recently by the age of the loom tape.

 

Check the brown wire going to the brushes for resistance to chassis ground with the connector disconnected, it should be open. It's possible the wires going into the AC generator brushes are pinched under the cover, or I think a brush assembly mounting screw can loosen and short the field coil to ground.

 

Thanks Rooster, I think the owner is now going to have the rewired part of the wiring re-rewired ( not by me, I don't do rewires). All the help and suggestions and time are much appreciated.