Auto Electrics Mobile Product Services Shropshire

Tel 01743 884888


Alternator voltage regulator supply

Repair and Rebuild components for Vehicle Alternators

Alternator Parts Supply UK Mail Order

Supplier of  automotive alternator components

Please  use the enquiry form below for replacement alternator mail order prices:

Alternator Manufacturer Alternator Unit Part No
Component Required Component part  ref  
Component Required Component part  ref  
Component Required Component part  ref  
Component Required Component part  ref  
Component Required Component part  ref  
Your Name Email address
(Completion of all form fields is not mandatory but all information helps. Please include any part numbers to assist alternator identification)

Common Alternator Wiring Terminal Letter Designations
B+ , 30, Battery Positive
S, M, 2, Battery Voltage Sense
B- , 31, D-,GRD Battery Negative
F, DF , 67 , FLD , EXC, Field/Rotor
D+, 61 , L , IND, Charge Warning Lamp
IG, 15 , R , Ignition
N, C, Central Point
W, P, STA, Tachograph rev counter (stator single phase tap AC output)
D Dummy
DFM , FR, SIG, C, M, Digital Field Monitor duty cycle output for computer control unit monitoring.
LIN Local Interconnect Network bi-directional control to control module
COM bi-directional digital communication with control module
Please Check the manufacturers instructions for specific application of wiring terminal designation.

Alternator Voltage Regulator function

A Voltage regulator controls the excitation current of the alternator rotor therefore the magnetic field strength is proportionally controlled. This excitation control is used to regulate the alternator output by means of the Voltage regulator.

DFM: Digital Field Monitor terminal

With ECU regulated systems, the duty cycle of the excitation current can be reflected as a feedback signal to measure the amount of alternator capacity being used via the DFM signal terminal (DF Monitor).

Alternator Excitation

Power is supplied to EXCITE the rotor so the magnetic field is created. (Without excitation current there will not be a magnetic field) some alternators are SELF-EXCITED, this means after the rotor is initially excited a wire connected to the stator taps some of the power generated to keep the rotor excited and power generation in progress whilst the rotor is spinning.

Brushes : Brush pack

The brush pack or brushes form the means of connecting the spinning rotor to the  excitation power source.

Symptoms of a faulty alternator voltage regulator

Possible signs include illumination of vehicle battery charge warning light on dashboard whilst the engine is running followed by gradual loss of electrical power until the engine cuts out and fails. The discharged battery can prevent the vehicle engine from being started.


Check all connections are tight and wires are in good condition.

A quick check for a failed alternator is to measure battery voltage with the engine off using a voltmeter. Start the engine and run at around 2000rpm whilst monitoring battery voltage which should have increased slightly if the alternator is charging the battery. B+ terminal voltage at the alternator should also be checked.

Incorrect alternator output voltage ( alternator overcharging or undercharging ) can affect sensitive vehicle computer systems and related systems.

Typical battery voltage readings for a 12 volt system :

  • Engine off  : 12.5 volts
  • Engine running at 2000 rpm : 13.2 to 14.6 volts at battery
  • (regulated voltage)
  • A battery voltage indicated above 15 volts with the engine running on a standard 12v charging system often indicates a fault though vehicle manufacturers specification should be checked to verify.

  • Some modern vehicles have alternators with dynamic electronically controlled output which is affected by the embedded software in the vehicle engine control computer. These require specialist equipment to test and verify as output varies with demand.

    Voltage Regulator part number Fits Unit   Typical Application
    F00M145225 0124315001, 0124315005   VW ,Audi, Skoda ,SEAT


    Unit warranty is subject to original suppliers standard terms & conditions.

    Alternator Repair , Recondition , Supply, Fitting.

    Shrewsbury 01743 884888

    Alternator Identification

    Alternator units are identified by alternator manufacturers part number eg Bosch 10 digit part no 0 120 ....., Hitachi LR....., Valeo A...V... , Lucas LRA...., Mitsubishi A..T..., Nikko ..., Nippondenso part no...,

    Vehicle manufacturers part no may also be labelled.

    Alternator voltage and current output  rating may also be stated.