Generator Light

[electric_monk]

The generator light on my '90 GS has started to glow gently when riding at normal road speed. The light is on fully at start up and idle, I have checked the voltage at the battery with the engine running and at 3000rpm the voltage is reading 14.5 and when I turn the headlight on (at 3000rpm) the voltage drops to about 12.8. The rotor was replaced just over a year ago with an unused replica rotor an old friend had.
I have cleaned the slip rings of the rotor and the brushes but no change. I presume that something is about to fail. Any ideas what the most likely culprit is.

 

[(RIP) Bin Ridin]

Maybe a diode open-circuit?

 

[PW Cymru]

You could try checking the earth straps on the diode board and the condition of their grounding ponts.

You could also try running a seperate earth from the diode board back to the battery via the earths near the coil.

 

[Rob Farmer]

I'd say the rotor is on it's way out but measure the resistance. It's also worth cleaning the brush holder up i've seen them so badly built up with carbon that they track between the brushes.

Quick test at 4.10 below

 

[electric_monk]

Cheers Rob

That looks like exactly what I need. Thanks everyone else for the advice.

steve

 

[(RIP) Bin Ridin]

Frightening to think that if that ikkle bulb blows, bye-bye charging. changing it looks "interesting". FFS.

 

[(RIP) maverick]

Had the same thing last year and even though the rotor read low on resitance in the end it was the voltage regulator.

New rotor
Broken off rotor removal bolt
Price on my face when the light just stayed on after putting everything back together - fekcing priceless

Sometimes it is the small things

 

[DrFarkoff]

Brush length is important too If they aren't making good contact cos they're too short ........
But then again I did mention this !

 

[electric_monk]

Regulator and Rotor checked and showing OK. New brushes fitted and although a bit better the light is showing ever so slightly. Just left to check stator and diode board.