FIELD ASSEMBLY
Resistance of Field Circuits at 25C -(77F)
Model
Base Field (Ring #1 to 3)
Control Field (Ring #1 to 2)
FM3V2-B/3
43 to 53 ohms
Less than 1 ohm
FM2V2-B
32 to 42 ohms
Less than 1 ohm
FM4V2-B
43 to 53 ohms
Less than 1 ohm
FM4V2-C
43 to 53 ohms
Less than 1 ohm
FM6V2-C
47 to 57 ohms
Less than 1 ohm
Note: When ordering replacement field assemblies, be sure to include model and serial number from
nameplate on alternator frame.
TESTING A FIELD CIRCUIT
Make sure that all brushes are not in contact with the slip rings. If the alternator has not been disassembled, paper
inserted between the brush and slip ring will serve as insulation. The complete brushholder bracket can be removed if
this procedure is preferred, by removing the screws and nuts at each end of the bracket. The brush gear may use one
bracket or two brackets, depending on the capacity of the alternator. When two are used, both must be insulated or
disconnected.
To measure the resistance of the base field, touch the ohmmeter leads to ring #1 and #3 as shown in the illustration.
Measure from rings #1 and #2 for the control field.
A resistance appreciably lower than shown on the table indicates shorted turns in one or both field coils. The resistance
of less than one ohm on the control field is too low to measure accurately with the average ohmmeter. A complete circuit
between rings should be indicated. A high resistance would indicate a broken connection.
A grounded field circuit can be identified by connecting the meter from the slip rings to the rotor shaft.
NOTE: Occasionally an alternator will lose residual magnetism. It is very unusual unless the alternator has been
disassembled, in which case it will be necessary to "flash the field" on the first start.
(continued)
