I've got a 2012 Yamaha WR450F motorcycle which has a 3 phase alternator with a regulator/rectifier. Currently the battery is not charging when the bike is running and testing the voltage when running reports 12.2 volts (12.67 as rest)

I've tested the alternator by doing a resistance check by probing the 3 wires, each pair read .7 ohms, the manual specifies .58 to .78 ohms. I've also tested that each wire was not earthed. Each wire read 0L on the multimeter when testing against the negative pole on the battery terminal.

I also tested the alternator AC voltage by probing each of the wires. Each pair of wires reported about 20 volts at idle and increased by about 20 volts per 1000 rpm.

I also tested the DC voltage coming out of the regulator by disconnecting the DC side and measuring the output voltage whilst the bike was running, it only read .7 volts, the manual specifies 14.

After this I performed positive and reverse bias test of the rectifier which passed. Not sure what else to do I assumed the regulator had failed and replaced the regulator/rectifier with a new unit from Yamaha.

I've installed the new regulator but the battery is still not charging, I've performed all the same tests with the same results, including the .7 volts coming from the regulator.

Any ideas on what else I could be missing?

1 Answer 1


Where did you test the AC voltage? In the leads coming out of the stator? Or the leads coming into the regulator?

It's possible there's a short/bad wire on the AC wires between the stator and the regulator.

Where did you test the DC voltage? In the leads directly coming out of the regulator? Perhaps there is a short somewhere there.

Was the regulator new and OEM? If not, it's possible you have a bad replacement regulator.

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