charging system test reults

I would love an extra set of eyes. The bike is an 81 xj650 maxim. It has a somewhat minimal wiring setup done by previous owner and trust me he was no expert.

When I purchased the bike a year ago it had a janky headlight set up. The headlights were wired to a 2 way toggle switch direct wired to battery. there is no stock instrument cluster and the hi lo switch on the handle bars were not wired up. The blinkers worked as well as the aftermarket brake/tail light set up. a month or so ago I decided to rewire the hi lo beam switch so I removed the toggle and got the headlight working properly again. Now the light only turns on once the motor is running which is I believe how it is supposed to work. everything worked fine for a month or so.

about a week and a half ago I started blowing fuses in the headlight. There are inline fuses and not the old style fuse box. Only the headlight fuse was blowing. Everything else seemed to be working. So I suspected a short somewhere. I would change the fuse and try to find shorts to no avail. I tried physically moving every single wire in the bike trying to get a fuse to blow. No good. But when I would rev the engine or go for a short ride it would blow. So I suspected a rectifier problem I have been to the Ultimate Relay forum and read and re read the thing numerous times. I have scoured this forum looking for as much info as I can about all the stator, rectifier and battery testing that I can find. So i have tested everything and I think I have the answer but someone tell me if I should be looking at anything else. I suspect that the stator is not charging properly. Here are my test results

Rectifier diodes:
0-0-0
643-641-641

0-0-0
682-695-642

Stator:
.6-.7-.7-.7 resistance, nothing to ground

When the bike was at idle it was around 9.5 to 10v at the connector between stator and rectifier when revving engine it never got over 12.7 or 12.8 volts. This why I assume that the stator is bad as the voltage should increase significantly. Also I did not have a new fuse in the headlight circuit. Should I have replaced that fuse when testing? Any ideas or other tests? bike fires right up.

The battery is brand new and tested at 12.8 at start up.

 

this link has a good read on the charging system
The Ultimate Relay, Switch, Sensor, and Diodes Guide
If your charging voltages are too low, suspect the alternator brushes first, then perform the alternator stator and rotor checks as described in the Alternator Section.
Checking Alternator Rotors:
Measure the resistance across the two lead wires (usually brown and green) at the connector; the specifications should be:.

4.0 ohms +/- 10% for all XJ650, all XJ700, all XJ750, XJ900RK, and XJ1100 models.
Note that worn, dirty, or damaged alternator brushes can affect these readings, as can "dirty" copper commutator rings on the rotor face (where the brushes contact the rotor):

 

NOTE: Alternator brushes should be replaced whenever they are less than 11mm in overall length......the factory maintenance interval indicates that you should expect to replace these brushes every 8-10,000 miles. Factory brushes have "wear marks" (scribed lines) on the brush to indicate their wear limit; these aftermarket brushes also have the scribed wear line. Overall length of these brushes are 17.10mm, with 9mm of length from the wear bars to the contact end of the brushes:

 

I did pull the cover off alternator and the brushes were both long and even. I will do it again and snap pics

 

Resistance at the rotor with bike off is 12.3 at the connector.
Picture of brushes attached. I believe they are at 7/16" so just over 11mm.

Possibly just the brushes?

 

So did you check the voltage at the battery with the bike running to see if you had the 14.5 +/- .3V at 2K rpm and up?

Not that unusual to read on the high side at the connector, doesn't mean you are not passing current through the brushes to the field coil. Worry about that after checking voltage at the battery with the bike running.

Does it have the stock headlight bulb 55/60W? Are you running a 10 amp fuse? Anything non stock added to the headlight circuit such as running lights, etc.

Measuring AC phase to phase or phase to ground? Once again, start at the battery and see what your charging voltage is. In order to blow fuses, it would have to be nearly double the normal output, and certainly not lower.

 

yes you need new brushes. when they are new at 17mm with 9mm of usable lenght

 

Hi guys still dont have the problem resolved. The bike will not put out more than 12 volts at 2k to 3k rpm. It is not charging the battery. voltage runs about 11.8 to 12.4 volts at higher rpms. I did get a used brush set up that had longer usable brush length. The stator resistance check at the connector are within spec. However when I test the rotator at the green and black wires at the 2 pin connector it is about 52 ohms, Spec is 4 ohms. So I need a new stator it looks like. I am hoping If I can get a replacement for it I wii l fix it. Should I test anything else?

 

your rotor is dirty and needs to be cleaned use electric spray cleaner crocus cloth or a hard art eraser to make them shine.

also used brushes are not the best Idea the brushes wear to the face of the rotor

http://www.xjbikes.com/forums/threads/the-ultimate-relay-switch-sensor-and-diodes-guide.27543/
from above link
Note that worn, dirty, or damaged alternator brushes can affect these readings, as can "dirty" copper commutator rings on the rotor face (where the brushes contact the rotor):

 

Ok I will try to get everything shined up. I will report back to see if that affects anything. would you recommend getting new brushes only or the whole brush plate and wiring assembly?

 

Just new brushes.

The #1 cause of low output voltage is worn brushes and dirty/scored rotor traces.

 

You freaking wizards are right again. Cleaned up the rotor face and the brushes and the voltage is charging again. I wish I could buy you guys a beer. Good call, again, you all have kept me rolling. Voltage rises at it should when the bike is given throttle. Thanks again-Dustin