Two different types of Lucas alternator are used on Mini models; the 11 AC alternator and the later 16 ACR unit, and these can be identified from the illustrations in .
The 11 AC type was used on early models which had positive earth electrical system, but this was superseded by the 16 ACR type coincident with the adoption of negative earth in approximately October 1969. They differ mainly in that the later type has an integral voltage regulator incorporated in the rear end of the unit, whereas the 11 AC type has a separate control unit. The 16 ACR type also has the slip-rings mounted behind the rear rotor shaft bearing outside the slip ring end bracket.
It should be noted that the 16 ACR unit cannot be used on the earlier models with positive earth, as this type of alternator can only be used with a negative earth system.
Most faults allied to the alternator charging system are due either to worn or damaged brushes, or a defective regulator.
Replacement of both the brushes and the regulator unit is detailed under the appropriate headings below. If anything more involved, such as the rectifier diodes, slip rings, bearings, etc., is at fault, it is recommended that the alternator be given to an Electrical Specialist for repair, or an exchange unit obtained. In most cases this will be found to be the most economical and convenient solution rather than attempt to obtain replacement parts and repair it.
It should be noted that the battery should ALWAYS be disconnected before starting work on the charging system to avoid the possibility of damage to the semi-conductor devices in the alternator.