Next, how do we figure out if our charging system is working correctly and how to find out what’s wrong if it isn’t?
(These procedures are basically right out of the service manual)
It’s best to go from the easiest to more difficult tests. You will need a good, digital, Volt Ohmmeter for these tests.
First, make sure your battery is in good condition and fully charged. It should be over 12.8 volts with the bike off.
SYSTEM VOLTAGE CHECK
Connect the voltmeter to the battery and select DC voltage measurement with at least 20 volt full scale.
Start the bike and rev to 5k rpm. You should read 14.0 – 15.5 volts DC. Most bikes seem to be about 14.4 volts, slightly higher at idle.
If the voltage is in the correct range, put the seat back on, nothing to see here.
So what if the voltage is OVER 15.0 volts and keeps going higher if revved higher? Stop the test and replace the R/R before you ride the bike again.
The R/R has failed in the over volt mode (not uncommon with the $39 Ebay/Chinese crap kits) and will boil out the battery(rotten egg, sulfur smell), blow bulbs and then fry expensive electrical components. The R/R is the only part that will cause an over volt condition.
What if the voltage is lower then spec, but higher then the bike off voltage? Otherwise, there is some charge. The R/R rarely, if ever, fails at partial charge. They either go open (no charge), short out (this blows the main fuse and the bike stops) or fail in over volt mode (wide open charging). The reasonable things to check for partial charging are poor connectors or a bad winding in the stator. If the charging voltage is just below spec, the battery could be weak (high current draw) or you might have a cheap voltmeter that is off a couple of tenths of a volt (yes, I’ve seen this happen a few times).
What if there is NO charge? Otherwise the battery voltage goes down when the bike is started and never rises with rpm.
Again, easy stuff first.
WIRING, CONNECTORS CHECK
Check the wiring for obvious damage and or burned parts. This is very rare but it could happen and just takes a minute to look over the harness.
Check the two connectors in and out of the R/R. The one between the R/R and the stator is prone to overheating if it gets loose or corroded.
So the wiring and the connectors are good?
The next test is to see if the stator is functioning correctly. There is no need to open the engine and look at the stator. The electrical tests will tell us what we need to know.
There are three tests to prove the stator is good. You will need to disconnect the plug between the stator and the R/R to gain access to the three wires to the stator windings.
Test #1 Resistance check. Check between each pair of wires (three pairs) for 0.2 to 1.0 ohms resistance. This will check for an open coil or internally shorted coil.
Test #2 Ground check. As the stator diagram showed, all three coils are connected together but they are insulated from the engine. So put one lead of the ohmmeter goes on a good engine ground and then probe each yellow wire in turn. You should not have any continuity. Otherwise infinite resistance or open circuit.
Test #3 No load stator test. Set your voltmeter to measure at least 100v AC. Start the bike and rev to 5k rpm. Check between each pair of wires (three pairs) for 65+ volts AC. Most say they get about 85+ volts, which is fine.
There is a long and complicated process in the service manual to check the R/R. It also seems that many have done the tests, had positive results and yet the R/R was still bad.
This is where the process of elimination come in. Remember there are really only three components to the charging system.
If the wiring/connectors are good and the stator tests good, then it must be the R/R.
It is that simple.
I hope this helps.