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38 Posts
Discussion Starter #1 (Edited)
Got my bike running again yesterday.
Dead this morning.

I performed a leak test and it showed 0.76mA. Which is waaay high and suggests a short circuit.

However, I've also been having all the symptoms of a bad regulator (electrolyte drain, dimming lights, etc.) I fully charged the battery today and at idle it was showing 13.3 and at 3K it was showing 13.5. Seems like charging might be working....

I took her out for about 20 minutes and came home and checked again.
Idle was about 12.2
3K was about 13.5

A. I'm puzzled as the post ride readings sort of contradict themselves and I don't really know what to make of them. (In terms of a faulty regulator)

B. If the regulator is bad, is it likely it's the culprit for the leak as well?

Premium Member
1,966 Posts
This should help

Charging System.
Electrical power is generated by a 3 phase 520W (43A) permanent magnet alternator driven directly at engine speed from the left hand end of the crank shaft. The magnetic rotor is bolted to the flywheel and round outside the stator which is fixed to the left hand engine cover (the alternator cover). The alternating current voltage output is proportional to engine speed producing a regulated DC output of 14.5V at 3000 RPM. The frequency of the alternating current also varies with the engine speed,
The maximum system load is well within the capacity of the alternator, up to 28A being available for battery charging at normal loads.

Engine RPM 2000 6000
Output Voltage (Phase/Phase) 27±10 78 ±10

Alternating Current (AC) is rectified to Direct Current (DC) and regulated according to the battery voltage,
AC flows alternately in one direction then the other in cycles that are dependant on the speed of the alternator rotor but typically could be hundreds of times per second. Diodes rectify the AC into DC, which flows in only one direction. Three pairs of diodes rectify both directions of the AC output of each phase.
The regulator' reduces the average current through the rectifier to the amount that is necessary to satisfy the operating loads at any given time, the regulator senses the battery voltage and regulates the output voltage to 14.5Vdc by shorting the alternator phase outputs to ground, limiting the power input to the rectifier. A 40A fuse is fitted in series with the regulator DC output to the battery. Ducati specs the output at 14.5V @ 3000 RPM. When the load is in excess of the alternator output, the battery is discharging to maintain the load.
The ground in the charging system is the negative output from the rectifier. The AC-part of the three phase system is floating from ground, measurement of the AC-output should be from phase to phase, and not from one phase to ground..
In this system, the alternator is producing full power all of the time, the excess power is converted to heat which is dissipated by a finned heat sink surrounding the Rectifier/Regulator (RR).

Charging System Schematic.

Operational Issues.

Heat is main cause of RR failures, as noted the alternator produces full power at all times, excess power being shorted to ground, with a fully charged battery over 330W of excess power is converted into heat, additional heat is generated from the rectifier. A flow of cool air over the RR heat sink is essential if problems are to be avoided.

Loose and corroded connections are another source of failures, with up to 40A flowing through the alternator wires, high resistance connections will heat up and have been known to melt the insulation on the wires. All connections should be periodically checked to ensure they are clean and secure. A coating of Corrosion Block Grease (A Lear product) is recommended.

Extensive city use where engine speeds are lower than 3K, will cause the battery to discharge, in such cases the battery should be charged overnight to ensure adequate power availability.

It is recommended that a battery tender be used to maintain the battery charge during periods of no use.

38 Posts
Discussion Starter #3 (Edited)
Thanks a lot! Thanks some great information.

Unfortunately, I've figured out that that isn't the problem.

I started tracing the leak by pulling fuses. The leak stopped when I pulled the 5A injection fuse which goes straight into the ECU. I put the fuse back in and unplugged the ECU and sure enough, no leak. Unless anyone has a further explanation, I think it'll be awhile before my bike runs again since I'm a student and not really in the position for a $1000 ECU.

Of course, I'm always open to suggestions.

Since it isn't keeping the bike from running I guess I could just wire in a battery kill switch. I'd just have to remember to flip it whenever I park the bike.
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