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Alternator supply

Car Alternators, Van Alternators, Motorhome Alternators ,4x4 Alternators HGV Commercial Vehicle Alternators, Quarry & Construction plant Alternators
Tractor & Combine Alternators, Industrial Engine Alternators, Canal boat & Marine Alternators


*Vehicle breakdown callout  alternator supply  & fitting service (on site where possible)
available to Telford, Shrewsbury, & Local Shropshire areas.

Supplier of 12v or 24v automotive alternators brand new outright with a full 12 month warranty*
or factory service exchange alternators rebuilt to manufacturers specification carrying manufacturer standard warranty*
Please use the enquiry form below for replacement alternator mail order prices
for alternator component parts go to
Alternator Parts page:

Vehicle Make Vehicle Model
Engine CC Fuel type  
Year of Mfr Reg no
Air conditioning fitted Power steering
Your Name Email address
Message Please include Part Numbers from Alternator label Solution Graphics

Completion of all form fields is not mandatory but all information helps.
Please include any part numbers to assist alternator identification
eg Bosch alternators usually have a 10 digit part no.

On Site Fitting
The majority of 12v and 24 volt automotive alternator removal and replacement can be carried out on site .
We operate a rotating electrics supply and fitting service in Shropshire areas.

Battery test and vehicle charging system testing available.
Troubleshooting of alternator charging circuit problems
Auto electrical diagnostics  wiring faultfinding and repair.

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 FAQ list

Alternator function :

The automotive alternator is an electricity generation plant  which provides power to recharge the vehicle starter battery and also supply electricity for other vehicle electrical systems such as lighting, wipers, heater motor, car audio ,sat nav, etc whilst the vehicle engine is running.

Alternators generate AC ( alternating current ) which is converted to DC ( direct current) by a rectifier (diode pack)

Alternators , Dynamos , and Starter Motors are often referred to as ROTATING ELECTRICS .

Where is my alternator located ?
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.

How is the Alternator driven
Normally belt driven from a drive 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. Broken or loose mounting brackets can result in loss of drive belt tension and subsequent loss of alternator performance.

How long does an alternator last ?
Alternator lifespan
Usual life expectancy of a motor car alternator is 100,000 to 200,000 miles, though this depends on the operating conditions of the vehicle such as environment, temperature, driving cycle, maintenance, etc.  Premature alternator failure can be caused by engine oil and fluids leaking on to the unit.

I have fitted extra electrical accessories such as amplifiers and driving lamps do I need a higher output alternator for more amps ?
The vehicle manufacturer calculates the power output of the alternator required for each vehicle with regard to original equipment fitment. Increasing the load on a vehicles electrical system may require an alternator system upgrade including cable. Some special purpose vehicles with split charge dual battery systems may be fitted with an additional alternator or battery charging management system.

How does an Alternator work ?
The alternator generates electricity by "electromagnetic induction". When a conductor such as a wire moves through the lines of force of a magnetic field a voltage is induced in the conductor. Whether the conductor moves in relation to the magnetic field or vice versa the principle is the same.

Alternator Rotor

The basic vehicle alternator consists of a ROTOR with magnetic poles and an 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
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.

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

Alternator Voltage Regulation

By controlling the excitation current of the rotor the magnetic field strength is proportionally controlled. This excitation control is used to regulate the alternator output by means of the Voltage regulator.
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).

Rectifier Diodes

The initial current produced by the alternator is as its name suggests alternating (AC) .
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. The 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 DC voltage level produced by the alternator must be slightly higher than battery voltage to allow the battery to charge.

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.

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 .


Have the vehicle battery tested.

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 .

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 for a 12 volt system would be :

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

Alternator Noise possible causes:
Excess drive belt tension
Insufficient drive belt tension
Bearing failure
Stator winding fault

What causes  Alternator output to fail ?
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.

Water leaks on to the alternator : Water entering an air cooled alternator can cause problems particularly in Winter when at freezing temperatures the water turns to ice and causes internal component damage .

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