Lucas CFR2 cutout

This is the device used on many pre war cars to control current in the charging system and also to prevent the battery being discharged through the dynamo at low speeds where the voltage achieved is less than battery voltage. This is the system used on my 1938 Morris 8 series 2. The Dynamo used in conjunction with this is a three brush dynamo where the third brush is 2.5mm thick its job is to hold the voltage to 6.5 volts therefore the cutout is just switching in at 6.3volts and out at about 6.0.

The resistors shown on the back is really one piece of resistance wire with a centre tap or connection. The terminals above from left are _______ A F1 A1 E D F2

The resistance is switched in by the PCL light switch which has Half Charge and Full Charge position then sidelights and headlights. In the Half Charge position full resistance of 2.4 ohms is placed in series with the field windings limiting current output to about 4 amps. On Full Charge the resistance between F1 and F2 is shorted out so now the resistance in series with the field coils is 1.2ohms and the current output is 8 amps. When the sidelights are turned on the resistance remains at full charge and the current output is still 8 amps. when the headlights are turned on all resistances in series with field coils are shorted out which allows the dynamo to produce maximum current about 12 amps maybe 13 amps which is what this dynamo namely C45YV3 was rated as. I have seen CFR2 cutouts used on Austins which had higher resistances used in field circuit and the only reason I can think for this is that the Morris used an Electric fuel pump where austin and others used mechanical engine driven fuel pumps. When checking a charging circuit which is not operational on these old cars it usually comes down to poor electrical connections. At a fast idle the dynamo should give about 2 volts with all connections removed. When D and F are connected together the voltage can rise to 20 volts but will only provide a very small curent (bright charging lamp). This has happened to me I had sidelights on and had to use stoplights but had no blown bulbs. If this is experienced check the third brush ( mine had broken and dissiintegrated) and the connections to it. Check connections at rear of cutout remove the three screws, this will release the resistance wire and the insulating material behind it this will expose the terminals for cleaning. Remeber this insulating material is real asbestos. The resistance readings you get should be as follows.

D to E 40 0hms

D o F1 1.2 ohms

D to F2 2.4 ohms

F1 to F2 1.2 ohms

A to A1 is through the fuse on the left which is 25 amps and 25mm long, it controls the horn and wiper.

Fuse on right is the field fuse it protects field coils from excessive current is rated at 6 amps and is 20mm long. These connections need to be clean as well or charging can be upset.