TECHNICAL INFO  

 ELECTRICS 

Dynamo to Alternator Conv. Notes 

Keith, 
Just to finish off on this an explanation of what is going on. Back to basics it's quite simple really. 
Aside from all the letters on the regulator box the connections are simple. 
The box is merely acting as a terminal box so that the existing wiring can be used without modification. 
 
The cables A & A1 are power connections to the ignition switched electrical components and those fed without the ignition being on. 
The main feed from the alternator - the thick cable - needs to be connected directly to these - D in this case using the the links in the modified regulator box, though it could be achieved without the box being there, provided that this connection is sound and will carry the higher current generated by the alternator. It's easier as a modification to use a modified regulator box for this purpose. 
 
On an a car built with an alternator these connections are usually on the starter solenoid either as a separate item or piggy backed on the starter itself. The alternator then connects to this point directly and so does the battery cable. 
 
The other connection - the small one on the alternator - connects to the ignition warning light. Hence the F to E connection. Again this could be achieved without the box. 
The ignition warning light is fed with 12V when the ignition is switched on and earths back through the alternator to make it glow. 
As the alternator speeds up then the voltage rises on this connection and the warning light goes out as it has 12V on both sides of the lamp and no current can flow. 
 
When the dynamo was in use this F connection was to the field of the dynamo. This energised the dynamo field coils from the battery to allow current to be generated. As the output from the dynamo increased this then operated a coil in the regulator box was energised cutting off the earth connection to the ignition warning light so it went out. This was called the cut-out. This also prevented the battery from discharging itself through the dynamo when the engine wasn't running. Early cars just had this cut-out feature and could overcharge their batteries on long journeys. 
 
The regulator box also acted as a regulator ( that's it called that )to ensure the battery could not be overcharged, damaging it - basically boiling it dry. When regulator boxes went wrong this could happen. So the regulator box sensed the battery voltage and as it got higher reduced the amount of current being sent to the battery. This is adjustable inside the box by adjusting some screws and I have set this in the past. When everything was on lights - wipers - heater the dynamo could not keep up with only 22Amp output but the regulator box would see the voltage drop and deliver full output and if this wasn't enough then the battery would supply the extra. Early cars and even some motorbikes had ammeters so that the driver could keep an eye on this. Later, battery condition voltmeters could be used to keep an eye on the state of charge of the battery. This is indicated by the voltage usually 13.6V if fully charged. The voltage at which the cut-out operates is also adjustable but be warned dragons lurk here because you need to know what are doing and have the right equipment. It was always easier to replace the box with one set up by Lucas in the factory. Some cars, the 1100/1300 comes to mind, had different 3 bobbin regulators which were a bit more accurate. I've never seen one of these on a Mini and I don't think they were ever fitted. 
 
The diode package in the alternator does all this electronically without all the "mechanical" bits and contacts that need adjusting and get dirty. They give better outputs at lower speeds and are theefore more reliable than the dynamo and regulator box set up. 
Alternators were fitted to Minis when they started to have heated rear windows because these took so much current. The existing dynamo set up could not cope. Then of course when all the other modern stuff got fitted - brighter and more lights etc - more and more current was needed so bigger and bigger alternators were fitted.