Technical 19 www.aftermarketonline.net MAY 2025 Silver Lady’s double design secret revealed Autoelectro shares what the firm says is a rare find, as its technicians reveal a double alternator discovery in a passenger car engine Engineer Sir Henry Royce, one of the founders of the luxury car brand, is credited with saying: “Take the best that exists and make it better and when it does not exist, design it.” That focus on innovation for the vehicle best known for its iconic Spirit of Ecstasy, aka the ‘Silver Lady’, has been brought into sharp focus by technicians at Autoelectro, a leading independent remanufacturer and supplier of starter motors and alternators in the UK. The firm said the technicians’ discovery involves the Rolls-Royce 6.7 V12 engine, found in the latest Cullinan, Phantom and Ghost models (2018-onwards), which requires two alternators. While some heavy-duty trucks, commercial vehicles and public service vehicles have required two alternators for some time, for a standard passenger car, one alternator is usually enough. However, for the latest Rolls-Royce 6.7 V12 engines that is not the case. During a routine newto-range exercise, which results in at least two new part numbers being released every week, AEG1647 was introduced. But Autoelectro’s production and cataloguing team later identified another OE number with identical vehicle details but differing specifications. Curious about the discrepancy, the firm procured an OE version of the alternator and conducted a detailed reverse-engineering process. This investigation revealed the design feature. One of the alternators is mounted on the left-hand side and the other ion the right. That led Autoelectro to develop the new AEG1689 part number. Why are there two alternators? After further investigation, it transpired that there are also two batteries fitted to the same engine. It was discovered that one is used for traditional vehicle electrical systems, while the other is for specialised equipment. Autoelectro believes the latter is likely tailored to the unique requirements of highend Rolls-Royce technology — such as those luxury ‘essentials’ including the fridge, wine cooler, heated and cooled seats, televisions and ambient lighting. Notably, during the same investigation, Autoelectro’s experts spotted that older Rolls-Royce 6.7 V12 engines — fitted only to 2003-2017 Phantom models — also have two alternators. However, those are both water-cooled. Autoelectro’s data shows that they are the same AEK2864 alternator, but because there’s such a high electrical load, two alternators are needed to manage it. In contrast, the alternators mounted onto the older Phantom line up on top of each other, while on the newer 6.7 V12 engines, AEG1647 and AEG1689 are fitted on opposite sides of the engine and are not water cooled. Instead, they are aircooled and have vast air ducts attached to the rear to help with cooling and ventilation for heat dissipation. Evolution of RollsRoyce alternators Interestingly, Autoelectro’s experts also uncovered that a different Rolls-Royce 6.6 V12 engine from 2009, used in models like the Wraith, Ghost and Dawn, was fitted with an air-cooled 220A alternator, AEK3692. This led engineers to conclude that the latest 6.7 V12 engine design took the best parts from both the previous 6.7 and 6.6 V12 engines. By using two air-cooled 180A alternators, AEG1647 and AEG1689, it is possible that Rolls-Royce developed a solution to ensure optimal performance and efficient ventilation, eliminating the need for water-cooling systems. While the automotive aftermarket may not see many Rolls-Royce 6.7 V12 engines with two alternators fitted, this example is a fascinating insight. www.autoelectro.co.uk alternator test equipment Photo: Jean-Marc-Bonnel / Pexels
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