Charging problem

[ChrisK]

I have a 1998 M900. Had to jump start it to get it running but after a short while it dies, like the battery isn't getting charged. 8ish volts on the battery when bike isn't running and 10ish volts when the bike is running. Help jog my memory on diagnosing this. Rectifier was brand new last winter.

[koko64]

A couple of things to do while waiting for Howie to reply. 

Check the connections to the regulator you replaced to see if the wires are burned out and hook that poor battery up to a charger you beast! Check the reg itself for signs of over heating and while that battery charges check all your ground connections and check the wires coming out of the alternator case.

If your battery survives give it a pat. Do you have a multimeter and charger?

[ChrisK]

The regulator is grounded still. The three wires from the regulator to alternator cover appear to be fine. All grounds and battery connections are good. Sitting on a trickle charger as I eat late lunch, but I think charging the battery will just be a bad-aid over the real problem.

[ChrisK]

Just started it up again. Trickle charger took it to 13ish volts. Started bike and it dropped to 12.95V. While running the multimeter is usually at 12.95, but every 5 seconds or so it flashes to something really low, like 2, 5, or 7 volts.

[ducpainter]

Since the regulator is fairly new unplug the stator wires and check voltage across the pairs of yellow wires. Single phase alternator will have 2 yellow wires and 3 phase has 3.

IIRC it should be in the 40V AC range.

[ChrisK]

Well I hope I'm doing this right. My three wires between the alternator and rectifier don't have a plug anymore. That melted when the rectifier went bad last year. So I soldered and shrink wrapped them individually.

Anyway, with bike running I put one lead of multimeter on one of three wires and the other lead on another of the three leads. The voltage read 6ish, 5ish, and 3ish for the three paired combinations I could do. Multimeter was set to AC.

Can I take Alternator cover off and inspect behind it?

[ducpainter]

The wires have to be disconnected from the regulator.

Imagine the three wires being numbered 1 2 3

Test 1/2, then 1/3, then 2/3

[ChrisK]

Okay, I'll cut the wires and see what I find.

[ChrisK]

All three combinations were jumping around 10, 11, 12, and 13 volts.

[ducpainter]

From my recollection it seems your stator is fried.

Let me search a little and see what I can find.

Does it change with an increase in rpm?

[ChrisK]

Yes. Holding RPM's steady at roughly 4000 makes the voltage read in the 40's.

[ducpainter]

I think I was wrong...

<snip>

Anyway, to check stator output, follow the three yellow wires from the alternator.  The wires will come out of the left side engine cover.  You will come to a connector that leads to the regulator.  Disconnect the connector.  Each yellow wire is one phase of your 3 phase alternator.  Connect the voltmeter, positive to each stator wire, negative to ground.  You should get 27+10V at 2000 RPM and 78+V at 6000 RPM.  If you are getting  14.5 volts +.5 to the battery at 3000RPM there is no need to perform this test.  One test that is often overlooked by motorcycle shops is battery drain, or the more correct term, parasitic loss.  This is what the bike uses when parked.  Ducati has no spec for this.  A good "anycar" spec would be less than 6 milliamps.  My educated guess would less than 2 for your 696.

Hope this helps
Howie

[ChrisK]

Hovering at 6000 RPM's only got me about 39V.

[ducpainter]

Sounds like a bad stator.

There are resistance tests too, but I didn't search for them.

[ChrisK]

Sounds expensive...