Oct 19, 2006
So I've got this bike, it cooked the wires coming out of the stator and the voltage regulator/rectifier. The stator and regulator were replaced with other units, but both the new ones and old ones spec'd out the same. The trouble is, the bike charges at idle but stops charging as engine speed picks up. The stator is still putting out, at 5000 RPM it's putting out over 100 volts. If I disconnect the battery cable at idle, the bike will continue to run just off of the stator voltage. But, if I rev it up and disconnect the cable, the engine will die. Once it drops down to idle speed, the stator will kick in and the bike will start firing cylinders again. The stator wires are still getting hot. Any ideas? We're really stumped on this one.


Oct 19, 2006
I was hoping nobody would ask that, but it's a 99 GSXR750. The regulator gets warm, as expected, but doesn't seem to be getting unreasonably hot. It's the wiring leading up to it that's hot.


Apprentice Goon
Mar 16, 2001
Charlestown, IN
76GMC1500 said:
I was hoping nobody would ask that
I can't imagine why?


Apr 18, 2006
How hot are the stator wires getting? Are they getting hot from the current that is running through them of from the proximity to the engine?

I know nothing of this bike in paticular but I have played around with a couple of outboard motors with charging system. The charging system works a lot differently than on a car. On an auto engine the "rotor" is a winding that the voltage regulator controls the current through. By adjusting the strength of the rotating magnet it can make the alternator put out just what is needed.

On a typical small motor (outboard and motorcycle) the "rotor" is made of permanent magnets. On really small motors the charging circuit simply can't put out enough current to worry about so all it needs is a rectifier and a battery to keep things under control. As the engine gets bigger and they provide more charging capacity a voltage regulator needs to be included.

When the battery needs charging, or the load from the lights and such are putting a demand on the system the regulator has a fairly simple job. As the load gets light, however, the regulator has a problem. The only way the regulator can control the voltage is to provide a variable drop across the regulator. If the load was drawing 10 amps then the stator voltage would probably drop to 18 volts or so and the regulator would have to drop 4 volts, which means that it would have to dissipate 40 watts (4 volts times 10 amps).

If the load drops to 1 amp, and the stator voltage climbs to 100 volts, then the regulator needs to drop 86 volts, which means that it would have to dissipate 86 watts.

This is a guess, but what might be happening is that the regulator sees that the battery is fully charged and the load is light so it simply shuts off the charging circuit so that it doesn't have to dissipate so much heat.

Try turning the lights on and see what happens.

If the stator wires are getting hot while at 100 volts and zero current then I am at a total loss for an explanation.

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