Monster Charging System by Capo

[slob]

S4R Charging System.

The following applies to the electrical charging system fitted to the 996 Desmoquattro S4R, other models may be similar.

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 rotates around the 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 common 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 alternator and RR 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.

Great post - thanks! Would drawing more current (like using higher wattage lamps) put less strain on the reg/rec in terms of heat dissipation? Presumably the more is being used, less needs to be turned into heat?

(yes, I know I should be out riding today.......)

[Stafford]

I did see an item the other day from America that enabled you to reverse the RR so it was not under the seat cooking like a George Foreman grill, but in the air flow above the rear wheel. You did have to change the crankcase vent system at the same time, but there was a kit for that too.

[slob]

http://tpoparts.com/products/?sku_id=S-0193

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