The problem occurs during summer conditions in slow traffic and slow bush tracks. The output voltage from the regulator rises with temperature which is called thermal drift. In extreme conditions the regulator can drop out feeding unregulated alternator output to the electrical system.
The increased output voltage from the regulator can lead to overheating and overcharging of the battery. In the case of VRLA batteries it can lead to shorter battery life as these batteries are adversly affected by voltages above 14.2v.
The symptoms can be seen easily with a voltmeter connected. The initial indication is the voltage failing to go down to 12.5 volts when stopping at traffic lights.
The Indication of battery overheating or overcharging is that the inner cells of the battery require greater top up than the outer cells. In hot climates the standard battery requires more frequent checking.The solution is to relocate the regulator to the RHS side of the engine in place of the curved wiring cover as per the XCountry model. The voltage Regulator mount from the XCountry could be used.
105 mm long 50mm wide and 25 mm high with 15mm offset mounts for the engine and Regulator
90mm wide x 80mm high 67.5 mm mounting centers
XCountry Bracket BMW Part No - 62167696798
The XCountry bracket fits the GS but needs to be bent down a little (1 to 1.5cm) to clear the shock adjuster.
The wiring could be moved to the rear of the engine and the VR mounted on the rubber isolators to move it outward a little.
Thanks to Mobius at advrider for the pic and info
FET shunt regulators. The FH020 replaced the FH012. They are used to upgrade many Japanese models and have been used with success on both F650 and F650GS models.
They use Furukawa spade connectors and so are not prone to wire breakage where the wiring leaves the regulator like the F650GS regulator.
Be wary of Counterfeit product at low prices
FET Series regulators. Shindengen have not updated their product web page which only lists the 35 amp SH775 but the 50 amp SH847 regulator is now available. Series pass regulators reduce stator load and temperature.
They use Furukawa spade connectors as per the FH020.
Dimensions are 120 x 120 x 40 mm, 50 C-C mm mounting.
Honda, Polaris and others are using FH775. Polaris part No.4012941
A 50 amp series pass VR from Cycle Electrics. A series pass VR open circuits the stator to regulate. It reduces the load on the engine and the stator runs cooler. The GS should be a little more responsive with this VR.
In the past series pass VR's were prone to high frequency noise, these seem to have it resolved. Tested on F800GS (same stator as 650GS).
Roadstercycle have now discontinued selling the CE650SB and supply the Shindengen SH775/SH847 regulators.
The F650GS has a permanent magnet 3 phase 406 watt alternator. Little is known about the internal circuitry of the regulator but it is an electronic unit and seems to be a shunt type regulator with IC control circuitry.
The regulator is common to the F Series twin cylinder machines and regulates to 13.8 to 14.2v. It was specified at a time BMW batteries were all VRLA batteries and does not suit Unsealed Lead Acid, AGM or Lithium.
Note. The latest models and BMW spares are upgraded VR's which regulate to 14.4v. (marked with SH541SC)