Autoelectrics tech pages

Alternator Parts Supply


Supplier of automotive alternator components

Alternator Parts supply for Car, Van, Motorhome ,4x4,
HGV Commercial Vehicle,
Quarry & Construction plant,
Agricultural Tractor, Combine
Canal boat , Industrial Generator engine

Please use the enquiry form below for replacement alternator mail order prices: Part Numbers from your alternator label are always required.

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


Service Tel No Shrewsbury 01743 872222 *Vehicle breakdown callout  alternator supply  & fitting service (on site where possible) available to Telford, Shrewsbury, & Local Shropshire areas.

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.

Typical Part No format by mamufacturer

OEM names used for reference only

Bosch  - ten digit typically starting 0 123 or 0 986 0124
Delco DRA...
Hitachi LR...
Lucas LRA... or LRB...
Mitsubishi A2T... or A5T... Valeo A..VI... or A..(letter)...

Alternator Removal

Always follow vehicle manufacturers recommended procedure

The engine driven alternator will be located in the engine bay of the vehicle and normally bracket mounted to the engine block. Not always accessible. Sometimes other components may have to be removed before the alternator can be accessed.

Disconnect Battery

Ensure engine is stopped and ignition key off.

Disconnect battery chassis ground terminal first avoiding sparks before attempting alternator removal

Remove Alternator Drive Belt or coupler

Usually the alternator is belt driven via a v belt or ribbed  belt connected to the crankshaft pulley . In a few instances the alternator may be shaft driven or gear drive. The alternator must be mounted securely to enable it to be driven efficiently.

Remove Cables

Take careful note of where cables are connected to ; follow safe disconnection procedure only.

Remove mountings

Broken or loose mounting brackets can result in loss of drive belt tension and subsequent loss of alternator performance.

Identify Failure Cause and Rectify

Premature alternator failure can be caused by engine oil and fluids leaking on to the unit. Trace the source of any fluid leaks and repair prior to fitment of reconditioned alternator. Water leaking on to the unit can enter and freeze in cold climate causing failure

Component function

Alternator Rotor

The basic vehicle alternator consists of a ROTOR with magnetic poles and Copper excitation winding which spins as it is driven from the engine. The ROTOR is an electromagnet which when energised creates a magnetic field.

Alternator Stator

The housing of the Alternator consists of Stationary wires forming a "winding" of coils of wire known as a STATOR.

The stator normally consists of a soft iron laminated core around which reasonably heavy gauge copper wire is wound to form usually three windings connected in Star or delta formation. Charging voltage output of the alternator is generated in the stator.

Alternator Excitation Current

Power is supplied to EXCITE the rotor to create the magnetic field . (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 retain excitation and power generation in progress whilst the rotor is spinning.

Brush Pack

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

Voltage Regulator

Alternator Voltage Regulation is done by controlling the excitation current of the rotor which in proportionally controls magnetic field strength. This excitation control is used to regulate the alternator output by means of on/off switching of the Voltage regulator.

ECU feedback

In 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).

Charging Voltage

The DC voltage level produced by the alternator must be slightly higher than battery voltage to allow the battery to charge. Bad connections at wiring terminals and breaks in wiring looms can cause charging problems.

Rectifier Diodes

Alternating Current(AC) is produced from the alternator stator . Unfortunately AC cannot be used to recharge the vehicle battery so has to be converted to DC . The process of converting AC power to DC power is known as rectification. Rectification is done by the Diode pack (a diode acts like a one way valve in an electrical circuit).

Car alternators are Three Phase AC generators with rectification to DC.

The Diode pack has a secondary function when the ignition key is off to prevent the power draining from the battery via the alternator windings causing the battery to discharge. This is often a cause of charge warning light staying illuminated on dash.

Alternator fault symptoms

What are the symptoms of a faulty alternator ?

The first sign of  alternator charging system  fault is often indicated to the driver by the battery charge warning light on the dash illuminating 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 .


Battery test

Have the vehicle battery tested. We can test batteries using Bosch or Midtronics battery test equipment

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.

Visual check

A visual check with the engine stopped should be carried out to ensure the alternator is secure and drive belt correctly tensioned. Also check for oil ,fuel or coolant leaks which may have caused the alternator to fail.

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

Check all heat shields are in place .

Voltage tests

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 for a 12 volt system would be :

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 special equipment to test and verify as output varies according to demand.


Alternator Noise with engine running ;possible causes:

Alternator Output failure causes

Common causes of alternator failure are:

Broken or defective wiring to the alternator.

Wear and tear ; Worn out brushes ,sliprings, bearing failure, diode pack failure.

Excessive drive belt tension causing premature bearing failure.

Insecure mounting bolts / bracket causing insufficient drive belt tension.

Poor electrical connection causing high resistance and leading to overheating.

Electrical overload due to a defective battery or fitment of vehicle accessories, or vehicle wiring faults.

Inadequate ventilation and cooling possibly caused by fitment of vehicle body kits.

Voltage surge caused by boost starting using jump leads without surge protection. (Diode failure)

Oil, fuel or coolant leaks onto the alternator.

On modern alternators controlled by an electronic control unit an incorrect battery type may cause problems.

Alternator test and repair facilities

We have facilities to test and fault find vehicle alternators on site or remove from site for bench testing and repairs.

Alternator supply

We can also supply outright brand new or service exchange alternators for most makes of vehicle.


Can my old alternator be remanufactured ?

We offer a service exchange unit policy on most alternator , dynamo , dynastarter and starter motor units.


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

Alternator Repair,Recondition , Supply, Fitting

We can supply & fit many makes of vehicle alternator to suit your automotive charging system including replacements for Alfa romeo,AMC,Audi,AVF,BMW,Bosch,Butec,Cajavec,Carrier,Caterpillar,
CAV,Chrysler,Citroen,Cummins,Daihatsu,Delco remy,Ducellier,Efel,Elmot,Femsa,Fer,Fiat,Ford,GM,Halla,Hella,Hitachi,

Honda,Hyundai,Iskra,Isuzu,Iveco,John Deere,Kia,Komatsu,Kubota,Lada,Lucas,Magneti Marelli,A127,Magneton,

MAN,Mando,Massey Ferguson,Mazda,Mercedes Benz,MGF,Mitsuba,Mitsubishi,Monark,Motorola,Nikko,Nippondenso,

Nissan,OMC,Opel,Paris Rhone,Perkins,Peugeot,Poong sung,Prestolite,Real,Renault,Rover,214,Saab,Scania,SEV,SJCE,Skoda,Subaru,


Please quote any reference numbers to help identify parts you may require.