Alternator supply - Shropshire UK - Tel: 01743 884888


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

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

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 - information helps.
Please include any part numbers to assist alternator identification eg Bosch alternators usually have a 10 digit part no.

On Site Alternator Fitting in Shropshire and Mid Wales


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

Many 12v and 24 volt automotive alternator removals and replacements can be carried out on site.

Rotating electrics fitting service operated 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 one or more vehicle batteries as well as supplying electricity for 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 ) converted to DC (direct current) by the alternator rectifier (diode pack)


The term Rotating Electrics refers to Alternators, Dynamos, and Starter Motors

The Alternator is generally engine driven by drive belt connected to the crankshaft pulley , or coupling to shaft drive or gear drive. If drive belt driven correct belt tension is essential. 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 charging performance.

Alternator lifespan -

Alternator lifespan of a motor car alternator is 100,000 to 200,000 miles, dependant upon operating conditions such as environment, temperature, driving cycle, maintenance, etc.

Alternator premature failure causes

Engine oil and fluids leaking on to the unit.

Incorrect or poor electrical connection

Voltage Spikes eg from jump starting


A higher output alternator may be required when additional accessories are fitted

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. Special purpose vehicles with split charge dual battery systems may be fitted with an additional alternator or battery charging management system.

Alternator operating priciple

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 Alternator Rotor has magnetic poles and an excitation winding which rotates as it is driven from the engine.
The ROTOR becomes an electromagnet which when energised creating a magnetic field.

Alternator Stator

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

Alternator Excitation : Power is supplied to EXCITE the rotor to create a magnetic field. (excitation current is required to create a magnetic field unless permanent magnets are used ) 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. Excitation power control is used to regulate 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 vehicle batteries 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.

Symptoms of a faulty alternator

The first sign of  alternator charging system  fault is often indicated to the driver by illumination of the battery charge warning light on the dash whilst the engine is running followed by gradual loss of electrical power until the engine cuts out and fails. Low battery voltage may mean the starter motor clicks or does not operate preventing 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 using a voltmeter. Voltage reading 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 :

Alternator Noise possible causes:

Excess drive belt tension
Insufficient drive belt tension
Bearing failure
Stator winding fault causing phase imbalance

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 causing internal component damage .

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

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