Battery not charging problem

moddy said:

There is a check for resistance and continuity on the alt side, before you do anything else, it's also an easily accessible test, only disconnecting the p-2 and p-3 connectors. Believe me when I tell you, if you go through the hassle of replacing the alternator, only to have the same symptoms isn't worth the time and frustration until the direction you need to go is diagnosed.
Back to the continuity and resistance test, p-2 and p-3 disconnected, voltmeter set to continuity.
It should chirp with any of the 3 leads you combine two of.

It should not chirp from motorcycle ground to any lead, or p-2 connector (field coil wire)
The p-2 connector should chirp between it's two leads, not to any other connection or mc ground.
Now, set to ohms.
Any two leads of the p-3 connector should be less than 1 Ohm.
The p-2 connector no more than 4 Ohms.

Until you see this result the alt won't be ruled out.
Additionally, you could have inconsistent test results because it's most likely a failed solder joint inside the alt that can be shorting or not, while moving things around.
Once you get a reading, see if continuity continues to chirp while moving things around.


Here is the alt disassembly https://www.st-owners.com/forums/showthread.php?155029-I-want-to-repair-this-alternator-for-an-ST1100-and-your-re-invited/page2

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Thanks for the reply, The P3 connector is the 3 yellow wires coming from the Alt. Right? Is the P2 connector the one close to the P3? So I just touch 2 of the yellow wire connectors to hear the chrip correct?

Thanks again for your help.

robertp039 said:

Thanks for the reply, The P3 connector is the 3 yellow wires coming from the Alt. Right? Is the P2 connector the one close to the P3? So I just touch 2 of the yellow wire connectors to hear the chrip correct?

Thanks again for your help.

Click to expand...

The short answer, yes. The reason you will hear a chirp or squeal or beep is because there are 3 separate loops of wire for three phases soldered together, your three leads from the p-3. Make sure any combination of two leads have continuity. The p-2 is and extremely long wire wrapped in a coil, mounted I the center of the alternator. When the regulator requires electrons from the charging system, it completes the circuit at the p-2 connector from battery to create the electrical field within the alternator. The field coil wire, probably 60 to 80 yards (as a guess) of wire is wound around the steel cylinder. Once system voltage is supplied to those two wires it creates an electromagnet at the field coil, completing the chargeability for running the electrical system.
My bench test was trapping the stator in a vice so I could spin the steel inside with a drill, simulating engine running, to test outputs. Without 12v supplied from my RV to the field coil wire, there was no output voltage from the p-3 connector. When I added the 12v to the field coil wire, any two leads from the p-3 connector registered amps, what output you're looking for. I didn't spin the drill too fast doing the amps test. A voltmeter is usually only rated for 10 amps and you can blow the fuse. This changes what people think about there being a constant voltage being produced at the stator, when the vrr behaves like switch to allow battery voltage to field coil wire, to create an electrical field for needed system voltage.... it's a really fast switch.