M201 - régulateur électronique SOCOMEL
When the last M201 rolled off the Hotchkiss-Brandt production line at Stains in 1966 I doubt anybody would have seriously envisaged that jeeps would remain in active service well into the 1990s. One effect of this was that the army had to continue to hold a significant stock of spares for both the jeeps actually in service and those held in reserve storage.
This prolonged service life resulted in some interesting new parts for the jeep which included a roll cage or 'arceau de sécurité' and even an electronic regulator to replace the aging Paris-Rhone and Marchal electro-mechanical types. It is difficult to say who designed the electronic regulator but they were manufactured by a small company called Socomel SA in France. I have only ever seen two examples of these so my guess would be that they were only produced as a small batch for evaluation purposes on jeeps and other vehicles like the SUMB which used the same Marchal dynamo and regulator.
The size comparison between the Socomel and original Paris-Rhone regulator can be seen below. There is evidence on the case of the Socomel regulator (below) that it once had a label on the front which has obviously become detached.
Based on the information found inside one of the examples I have taken apart, they were made in 1990 and even given a NATO / OTAN reference code though not a full NATO stock number. The schematic gives a clear indication of how the regulator works (if you are electronically minded) though not the full circuit diagram.
The three adjustment pots (from left to right in the diagram) are equivalent to adjusting the original three regulator coils and control the voltage at which the cut-out operates (Re), the current limit (I), and the voltage limit (U).
(Click to enlarge / Cliquez pour agrandir le schéma).
For some reason the design included a relay to connect the dynamo to the battery when charging was possible even though there were certainly diodes available at the time capable of replacing this.
Both the examples I've seen had ceased to work having blown the main safety fuse, indicating an internal fault, so my guess would be that they were not judged to be a success during trials and no more were manufactured.
The blown fuse link can be seen just below the thick red cable on the right.
Socomel regulator on M201 no. 14017 (photo Baz Davis)