Replace stator, flywheel rotor magnet and regulator with belt driven alternator

Jabiru aircraft use a stator to produce an alternating electric current. The stator is fixed to the engine casing and a magnet fixed to the flywheel rotates over it. As the magnetic field cuts across the winding, a current is produced. The stator on the Jabiru aircraft output rises as RPM increases reaching a maximum of 44VAC with a maximum current of 10AMP at 3100 RPM.

The output of the stator is fed to a SCR regulator. The regulator is a Kubota part number RP201-53710, RP501-7211 or 15531-64603 (there are different models) of the kind used on small tractors.

SCR regulators powered from AC power circuits use silicon controlled rectifiers (SCRs). Whenever the output voltage is below the desired value, the SCR is triggered, allowing electricity to flow into the load until the AC mains voltage passes through zero (ending the half cycle). SCR regulators have the advantages of being both very efficient and very simple, but because they can not terminate an on-going half cycle of conduction, they are not capable of very accurate voltage regulation in response to rapidly-changing loads.

Disadvantages of current setup

Due to itís location within the firewall and inadequate cooling, the regulator is prone to overheating and failure.

 Loads on flywheel are higher due to weight of magnet and may cause dynamic imbalances that cannot be corrected unless significant weights are added to flywheel.

 Maximum output voltage and current is reached at high RPM and can be too low to change battery in high power demand conditions. This can lead to a gradual battery drainage and deterioration if aircraft is operated at low RPM with lots of electronics and ancillary electrics (fuel pump, position and navigation lights, radio and transponder) on. It can be precipitated by the occasional difficulties in starting that Jabiru engines are prone to.  

There are further concerns relating to the total power produced by the stator as many aircraft have much higher demands on power due to many electronic devices, such as Electronic Flight Information Systems (EFIS) and Engine Management Systems (EMS) and Global Positioning System GPS systems that are now fitted as standard.

 Proposed Modification

The modification is a standard kit that is available from CAMit (builders of Jabiru aircraft engines and accessories).

 The kit shall replace the stator, magnet and regulator with a small automotive alternator that is driven a pulley that is fixed to the flywheel. The existing Stator, magnet and regulator can be removed or kept in place as a backup power system should it be required for IFR aircraft operation.

The kit contains all of the parts, accessories and fasteners that are required to complete the modification as is accompanied with detailed fitting instructions.  

The kit has a voltage and power rating that is much higher and can produce a steady current at lower Revolutions per Minute (RPM). Power output is rated at 10 AMP at 750 RPM (idling speed) and gradually increases to a maximum of 40A at 75% of operating RPM.

 The kit is compatible on all Jabiru engines (2200 and 3300 and 5300).