Results of alternator testing - help??

[tri650]

I went to the tips and troubleshooting tips and followed the instructions for testing the alternator. I tested off of the two wiring connectors as they recommend -the white wires and the green and brown. My results:

Resistance between each white wire was between .8-1. Guide says 0.4 +/-10%
Resistance between brown and green wires was 3.9. Guide says 3.5 +/-10%
Put the connectors back together and turned on ignition - measured 11.5 volts between brown wire and bike frame - guide says 12.
Tested green wire and it was at about .5 - guide says less than 1.8
Started the bike and revved the engine. Green voltage would only register at .1-.3 Guide says should be between 9-11.
According to this the regulator is bad. Is this correct?

[3Phase]

Tri650, it depends! I know, that's not exactly helpful.

The voltage measured at the Brown wire should read battery voltage.

If the voltage measured directly at the battery is 12 Volts or higher but you're only getting 11.5 volts on the Brown wire it means there is a voltage drop somewhere. It's most likely a bad ignition switch or dirty/burned ignition switch connector in the headlight shell.

The voltage regulator varies the ground from the field coil to control the charging current. The Brown wire is the Positive feed from the ignition switch and it runs down to the field coil. The Green wire is the return to ground so the voltage at the Green wire is inversely proportional to the amount of current going to the battery. In other words, it works 'backwards'!


The voltage measured at the Green wire will only rise when the battery is charged and the voltage regulator starts to limit the charging current to the battery. That's why you can only do the tests when the battery is fully charged. If the battery is discharged the alternator may have to work for a while, sometimes many, many, miles or hours to recharge the battery.

Green wire voltage:

Less than 1 Volt = battery is discharged and the regulator is allowing full field current to go to ground to maintain the system voltage and charge the battery.

1 or 2 Volts and continues to rise steadily to ~12 Volts = the battery is charging and the regulator is maintaining the system voltage without running the alternator at full capacity.

[tri650]

Thanks. I think I get what you are saying. I need to check the ignition switch. I have a spare regulator coming also. I will check this out and provide an update.

[3Phase]

Tri, what is the voltage at the battery when the engine is running? The XS11 doesn't charge well, if at all, at idle so you have to run it at 2,000 RPM to test the charging system.

According to your test there is nothing immediately obvious that is wrong with the alternator or the voltage regulator but you never quite got around to mentioning what the system voltage was with the engine running. If the battery was discharged (or bad) the voltage on the Green wire will stay low until the battery starts to recover its charge.

1) Check the battery voltage and the Brown wire voltage. The two readings should be identical or very close to each other. If they are not the same it is most likely that the ignition switch or its connector are bad/corroded/dirty/burned/dropping voltage/no good.

2) Full-field the voltage regulator. With the regulator/rectifier connected, ground the Green wire and start the engine.

3) Run the engine at about 2,000 RPM and measure the voltage at the battery. If the voltage goes up when the Green wire is grounded then you may have a bad regulator. If the battery voltage doesn't start to rise then the rectifier may be bad.

4) While the engine is running, check the voltage at the Brown wire again. If it's lower than the voltage at the battery then the ignition switch or its connector is bad/corroded/dirty/dropping voltage/no good.

[tri650]

Thanks for the tips. I will check it out tonight. As I recall I was running about 11.5-12 volts when the engine was on - and it did not change as I revved it up to 2000 or higher.

[3Phase]

Ah, that's a completely different kettle of fried diodes: the rectifier is probably toast, good thing you have another one on the way.

[tri650]

Got a spare regulator and just put it in. Ran the rev test and it performed as expected - voltage increased when i gave it gas. This was not the case with the other two regulators I had (one on the bike and one spare). Hopefully this solved the problem.

[3Phase]

Right on, it's working!