[CallMeSnake]

Alternators need a minimum speed to turn their output on. A loose belt could do this, though short of someone installing the incorrect size or overstretching the belt on install that shouldn't be possible. Maybe a broken cord inside the belt or a loosening pulley. After that the only other possibility would be a dead rectifier, so one of the 3 phases is producing no output, which would make the alternator not have enough current output at lower speeds.

Check the belt and pulleys. If they are OK, the alternator may need to be replaced or serviced. The rectifiers are trivial to replace and cheap, but almost nobody does that anymore. You will need to find an alternator shop that is willing to open the alternator to replace it. Given that your charge voltage is correct at higher engine speeds, the regulator is probably fine.

Might be a loose connection or ground, but given how the voltage always falls when the engine comes to idle I'd bet on the two items above. Your alternator produces more current as it's speed increases. They are sized to make just enough power to run everything on the bike at idle and keep the voltage high enough to prevent battery discharge, which would be 12.8-12.9V.

 

[CallMeSnake]

Gak. Missed that it was a water cooled bike. At least that means the diodes are external to the stator and can be checked, as can the stator. Hopefully it's not a bad stator.

 

[CallMeSnake]

To test the resistance of the stator windings you need an accurate meter capable of measuring such low values. Many cheap meters won't give you valid readings at low resistance values. Seems unlikely that all 3 windings have failed in exactly the same way.

When measuring the voltage on the disconnected stator windings, the voltage should rise as the motor speed increases, could get as high as 50-60V with no load applied. 13v at idle seems low.

All that said, the fact that you get 0 volts on pins 1-2 means that 2 of the windings out of 3 are shorted since you get continuity between all pin combinations. If you are absolutely certain that there is no output on pins 1-2, the stator needs to be replaced.

This would match your symptoms, in that the stator is only producing 1/3 the output it's rated at, so at idle it cannot keep the voltage high enough. When the motor spins faster, the remaining winding is making enough power to push the voltage up into the acceptable range even with the load the bikes electronics present.

Oil leaking out of the stator electrical connector indicates that the seal on the wire end inside the motor has failed and engine oil is being pushed through the wire out to the connector. That in and of itself isn't a big deal since oil is a good insulator, though the sealed connector at the regulator means that the regulator may start to fill with oil over time as it's connector isn't hermetically sealed at the pins to circuit board.

If you go to replace the stator, be aware that the service manual indicates that the M6 bolts that hold it on have Loctite 270 (red), which may require heat to get them removed.

Also, be aware that you are one winding away from zero stator output and that last winding is now being run much harder that it normally would.

 

[CallMeSnake]

Motorcycle charging system - Page 1

Motorcycle charging system - Page 1

www.eevblog.com

Take a look at this diagram. It's shows how a typical 3 phase stator is wired. If you look at the Y configuration the coils are connected in, to get 0 volts across two of the pins, the two coils you are measuring across both would need to be shorted. When you measure across any two pins, you are actually measuring across 2 coils in series. If one is shorted, the other coil still has output. The voltage would be 1/2 of normal, but you would not see 0.

As to why you see 0.8 ohms across any 3 pins, it's entirely possible that there is a low grade short in all the coils. Basically like a fine wire shorting across the coil. The meter probes with a very low current and reads voltage drop when measuring resistance. Such a low current will not appreciably heat up something with a very small cross section, so it reads it as a short. When the stator is running and making power, it makes enough current that it heats up the short, raising it's resistance and turning it into a much higher value while under power. Same principle as a light bulb. Measure that with a meter and you see less than an ohm. Measure the current and voltage while it's on and it works out to 20-100 ohms or more.

I suspect the stator failure is a bunch of burned up insulation and oil creating low resistance paths between the wires that make up the windings. It's a common failure mode in transformers and motors as well. Once a single spot has an insulation failure, it creates heat or even an arc, leading to further insulation failure until the entire winding is shorted between all the wires or the core.