Rotax Ducati ignition electrical system, Troubleshooting a Rotax aircraft engine Ducati electrical system.

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Rotax 503 Ducati ignition generator, Rotax 503 magneto generator
Rotax charing system stator unit found behind magneto

The Rotax 447, 503, and 582 Ducati ignition aircraft engines come equipped with a charging system. The system puts out 170 watts AC current at 6,000 rpm or about 12.5 amps. This current has to be converted to DC power via a regulator rectifier which then gives us a constant 12.8 volts DC.

The charging system or stator unit is located on behind the recoil, or electric start and behind the magneto. To get at it you have to remove the recoil, or electric start, recoil cup if hand start, and fan pulley if you engine is a 447 or 503. You will also require a special puller and 30 mm socket to remove the magneto.

With the magneto removed the stator can now be viewed. The stator is a a ring with 12 poles located on it. 4 of these coils are used for ignition while the other 8 are referred to as the "charging system coils." The wiring for both the ignition coils and charging coils exit through a hole in the upper crankcase half on the left hand side as you are looking at the recoil.

You will have two yellow black wires, these are your charging circuit, and a grey wire which is your tachometer wire.


(Note the two black/yellow coming out of the magneto are for charging the two black/yellow coming FROM the coils are for ignition.)

The two red wires coming out of the crankcase will connect to the ignition coils, with the longer going to the farthest coil and the shorter to the closest. These red wires are coming off the trigger coils, two small black boxes located (1 on the 447) located 180 degrees apart on either side of the magneto in the fan tower in the case of air cooled engines and lower crankcase housing on the 582.

For alternator wiring diagram refer to Fig (1).

As mentioned the output is in AC voltage (alternating voltage) and has to be converted to DC (direct current) so that we can run our strobe lights, radios etc. To do this we can use a shunt style regulator. The word "shunt" means that the system moves or shunts "excess power"  to a ground when the voltages output is more than it is suppose to be, thus giving us a constant 13.6 volts.

When a load or a "consumer" is put into the system such as an auxiliary fuel pump, radio, strobe lights, or heater the regulator does not have to "shunt" as much power to ground. In a lightly loaded situation, or where the engine is running with no load the regulator - rectifier will get very hot and thus should be mounted in an air stream and away from fuel lines, wiring etc. and must have a CLEAN solid ground.

This type of system does work well and usually doesn't give us any problems. If there is a problem it will show up in your volt meter readings in either a drop in voltage or an overcharging situation.

Troubleshooting a Rotax Ducati electrical system.

The first thing to check in troubleshooting the system is the battery for good condition and FLUID level. If it is low then refill it with DISTILLED water to the proper level. DO NOT use tap water or any other water any minerals in the water will cause a reaction inside the battery!

A good battery should test out at 12.6 to 12.7 volts DC when the engine is not running. That means if you turn the main power on your voltmeter should be reading 12.6 to 12.7 volts. When running this will then go up to 13.8 to 14.5 volts DC. Anything below or above these values is not good.

A system running constantly above over 14 volts will cause overcharging and "boiling" of the battery requiring constant refilling. This higher than normal voltage can damaged a battery and other electronic components such as radios and strobes.

If the "charging coils"  or stator unit is thought to be the problem disconnect the regulator rectifier and do a voltage check

Normal Volts AC readings are:
16 volts VAC at 1300 RPM,
27 VAC at 2200 RPM
50 VAC at 4000 RPM
77 VAC at 6400 RPM

It is not often that a stator unit will fail, unless you have damaged it by improperly installing bolts that are too long into the electric start or fan pulley, or inadvertently connecting 12 VDC directly to it while boosting your battery. This can be checked easily with a volt meter you are looking for a shorted windings or a ground.

Next check the wiring connections where they connect to the regulator. If either is corroded or not making a connection the system will not work.

Next check the GROUND connection for the regulator-rectifier. If you have a poor ground or NO ground the rectifier will not work.

Wiring Diagrams

Rotax supplies two different regulators, the one RECOMMENDED for use with the Ducati ignition is  264 870. It has a series of fins which aid in dissipating the heat generated by the regulator.

The 866 080 is used with the early model point ignition engines which have a lower output than the Ducati ignition engines. The 866 080 also requires a 1 amp "consumer" to prevent excessive AC voltage from reaching the regulator

This section consists of six wiring diagrams taken from the Rotax manual that show how a given voltage regulator is wired into a given electrical system.

In this sequence of diagrams note the on the Ducati ignition engines the yellow/black wires coming from the stator connect to the two yellow wires on the regulator.

Regulator # 264 870 without a battery.

NOTE: The BLACK wire coming from the regulator is your POSITIVE lead going to the battery, and the case of the rectifier is GROUND!

In this installation a capacitor is used to control the voltage output. The capacitor must be at least 2,000 microfarads and be rated for at least 25 volts.

CAUTION: the capacitor is POLARIZED reversing the leads will short it out, requiring the purchase of a new one!

Regulator 866 080 without a battery
The 866 080 regulator is supplied two ways. One has a black wire which is used to ground the unit. While the other does NOT have a black wire but uses the case to ground out the unit.

When using the 866 080 regulator connect the two yellow wires to your yellow black wires coming from your stator, on DUCATI ignition engines and either ground the black wire or the case.

The red wire is your POSITIVE lead and requires a capacitor to supply constant voltage. This system requires that a 1 amp "consumer" be installed permanently in the system in place of the battery.

Regulator # 264 870 with a battery.
When using the 264 870 regulator with a battery you do not require a capacitor, and all of the "consumers" can be switch on or off without any effect on the charging system.

A 16 amp fuse is hooked up in series on the BLACK output wire from the regulator for system protection.

Regulator # 866 080 with a battery.

When using the 866 080 regulator with a battery a 12 VDC consumer is required to provide the minimum 1 amp draw on the regulator.

Regulator 264 870 using a battery and electric start
This is basically the same system as just connecting a battery to the 264 870 regulator, and it does not require a "consumer."

The added feature is the solenoid. Your main battery cables will connect one on either side of the solenoid. One side coming directly from your battery. The other side going directly to your starter motor.

The third wire is used to activate the solenoid which then supplies power to the starter motor. This can be either a push button or connected directly to a key switch.

CAUTION: When installing an electric start make sure that you have TWO good grounds one coming off the AIRFRAME to the battery and another coming off the ENGINE to the battery.

Most if not all engines are rubber mounted meaning that you will have little or NO ground going to them. Failing to properly ground the engine to the airframe and battery will result in the current looking for a ground. It will generally find it in any small wire that is connected to a ground and will FRY it and anything that is in contact with it!!!!!

Regulator 866 080 using a battery and electric start.
Again note that this system can either have a black ground wire, or be grounded through the regulator case. Also not that it requires a minimum 1 amp constant consumer, and uses a 16 amp fuse.

Otherwise it is the same as the above.

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