low voltage at idle (1100 rpm)

I have been having an issue with the charging system on my XJ750RH Seca. The voltage drops low enough to be using the battery when idling. I have checked the grounding between the frame and engine and the battery seems to be good. I still need to check with a hydrometer. The rotor resistance is 5.5 ohm (hot engine, not 20c). The stator reads about .5 ohm. The diodes are working, but I'm not sure about the regulator. The problem seems to be worse after a long run. The flashers are slow to respond or don't work at all and the headlight is not as bright at idle. So annoying...

 

Have you checked the brush length and cleaned the rotor traces?

 

could be bad battery or brushes

all XJ-series models, the maximum available charging output VOLTAGE should be as follows (all values are approximate):

* approximately 500-2000 rpms: 1.8 volts gradually increasing to 14.2 volts
* 2000+ rpms: 14.2 volts up to about 14.8 volts, with a maximum of 14.8 volts (all models except XJ700-X and XJ750-X)

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.

stator
0.46 ohms +/- 10% for all XJ650, all XJ700, all XJ750, and XJ900RK models.
(white1 to white2, white1 to white3, and white2 to white3)


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):

 

the brushes are like new and I have cleaned up the copper contact rings. I may have to get a battery then. It is 3 years old and it needed a top up last week (was below plates). It seems to start the bike just fine and holds a charge.

 

did you use distilled water to top it off?
starting voltage drop?

 

I used distilled water. I don't know what the voltage drop is yet. I will have to check it out in a couple days.

 

I charged the battery and had it tested the next day. The rated CCA is 190 (136 CCA tested at 12.53V) I need a new battery for sure. It's 3 years old anyway.

 

Sorry for the late update. I found the issue causing the low voltage problem. I had to shave of some of the new powdercoating between the frame and ignation coils. I used a length of wire to diagnose. The bike lights up like a christmas tree now :-D

 

Check the R/R connector for corrosion. I'm betting on a bad ground or a bad power wire to the batt.

 

It's all good now. the whole system has been checked and it's been fixed.