Alternator Supply
We offer a range of replacement brand new car alternators.
Alternator units may be factory reconditioned. A core surcharge may be applied to Service exchange alternator units.
Car alternator mobile fitting service available in Shrewsbury and Shropshire local areas.
Depending on location, a car alternator can often be fitted on site saving the cost of vehicle recovery.
A huge range of new or reconditioned car alternators and alternator parts is available. There should be a label on the car alternator stating
- Alternator make and manufacturer part number will identify the exact unit.
- Vehicle manufacturer part number - this is generic and may cover several makes of alternator.
- Voltage and Current Rating (Amps)
- If there are no part numbers on the alternator this may mean strip down is required to compare and get part numbers from individual components.
- A vehicle registration number search will often provide a generic list of alternators which possibly fit the vehicle.
- If no OE part number exist then a visual identification combined with dimensional checks may locate several units that fit but current rating needs to be correct.
The car alternator generates electrical power to recharge the car starter battery and support auto electrical loads such as lights, heating, air conditioning, engine management, fuel injection, electric power steering, and vehicle electronic systems.
Car alternator failure can quickly cause breakdown or sluggish starting by leaving the battery dischrged.
Most car alternators are driven via auxilliary drive belt from engine crankshaft pulley.
Car alternator failure may be indicated by illumination of the dashboard battery charge warning light.
Other dashboard warning lights including ABS, SRS, Airbag, Power Steering, may also illuminate due to low battery voltage.
Fault error codes relating to alternator field circuit, signal, or low battery voltage may be stored in electronic module memory requiring the fault codes to be cleared after the electrical battery charging system fault has been repaired.
A range of car alternator tests can be carried out on the vehicle :
A multimeter can be used to check charging voltage at the alternator B+ terminal and at the battery terminals.
Positive, Negative earth return, and ground connections should be checked for voltage drop under load.
Electrical charge output current (Amps) output can be checked using an ammeter or current clamp with the alternator under load.
The Bosch BAT121 battery tester can be used to check voltage regulator setting and has a fast alternator diode check facility.
Computerised diagnostic equipment can read the serial data stream indicating voltage level at control modules
and carry out an electronic fault code check for stored alternator fault codes.
Oscilloscope signal testing may identify faulty diode waveforms indicating failed diode pack or dropped phase.
Very few local garages have an alternator or generator test bench for stand alone testing of the alternator off the vehicle. Commercial alternator test benches uses motors to drive the car alternator allowing the unit to be run up to various speeds. A load bank enables alternator output load testing off the vehicle. Control over field excitation current and alternator load may be possible to check correct function and output of the alternator. The more modern test benches have the facility to provide computer printouts of test results.
Further alternator strip down investigation may identify worn or faulty components.
Alternator component replacement may be possible providing the original unit manufacturer can be correctly identified from the alternator database.
The alternator brushes (made of a carbon compond) are fitted in a brush holder which may be part of the voltage regulator.
Alternator brushes allow electrical connection between alternator voltage regulator and the slip rings of the alternator rotor.
Fitting new brushes to a worn car alternator may provide a cheap alternator fix when the alternator does not work to get the car back on the road.
Alternator brush renewal usually requires removal of the alternator from the car. When sourcing new brushes you will need the oe manufacturers part number of the alternator
or full dimensions of the brushes required.
The alternator voltage regulator controls alternator output voltage parameters enabling a serviceable car battery to be charged from low voltage to a serviceable level
whilst prevent overcharging of the car battery.
Many alternator voltage regulators are supplied with ignition circuit voltage via wiring from instrument cluster charge warning bulb to D+ terminal of the alternator.
Failure of the charge warning circuit may prevent the alternator from charging and disguise as a failed alternator fault.
Many modern car alternators use the voltage regulator to 'communicate' with electronic modules such as the engine control unit.
An incorrectly specified alternator voltage regulator may cause data communication problems resulting in illumination of the battery charge warning light on the instrument cluster.
Specialist equipment is required to test vehicle alternators having computerised electronic voltage regulator
normally connected to the vehicle computer via Com , DFM, BSS, or LIN, terminal.
The alternator generates alternating current (ac) from the stator which has to be converted or 'rectified' to direct current (dc) to charge the car battery.
The car alternator diode pack acts as a rectifier.
Voltage surges can cause an alternator diode to 'blow', this may be caused by jump starting or welding.
If a car alternator diode fails then the battery charge warning light will glow.
Replacing a faulty alternator diode may cheaply fix the car alternator but other components could be worn meaning the alternator is beyond economical repair.
Alternator diodes signal can be checked with the alternator on the car by using specialist test equipment which monitors the electrical waveform produced by the alternator.
The car alternator may have to be removed and stripped down to test for individual faulty diodes.
Alternator diodes are generally replaced as a complete diode pack matched to the original spec.
The alternator rotor is an integral part of the car alternator which requires removal of the alternator from the vehicle then component strip down to access. The alternator rotor is made up of claw poles, insulated winding of copper wire, pressed on to a central shaft which runs on bearings and is usually pulley driven. Electrical (excitation) current is passed via slip rings through the coil windings of the alternator rotor enabling a magnetic field to be produced. The alternator fan creates a draught of air flowing to cool the alternator windings.
Lack of ventilation may cause the alternator to overheat causing premature failure. Worn alternator bearings will likely result in excessive noise, running hot, with eventual bearing failure causing misalignment and damage to other components. Breakdown of electrical insulation may cause the rotor windings to short circuit or magnetise centre shaft and bearings which will cause overheating.
The stator consists of insulated copper windings. When the alternator rotor is energised and spins, a rotating magnetic field is created causing alternating current electrical output to be produced from the phase windings of the alternator stator.
If the battery charge warning lamp is on this does not automatically mean that the car alternator is faulty.
Loose connections or broken wiring to the car alternator will prevent correct operation of the vehicle charging system.
Checks for voltage drop under load may identify high resistance problems in the car alternator wiring circuit.
The battery charge warning light will light up if there is a low battery voltage fault or charging system problem.
Reasons why a failed car alternator may cause the car battery to drain include:
The failure of an alternator diode(s) may allow electrical current from a charged car battery to drain via the B+ terminal of the alternator
to stator windings emitted as heat.
Parasitic low amp current drains can be difficult to locate and may cause a flat battery
after the car has been stood for a few days.
An electrical charging system fault such as wiring or alternator defect can prevent the battery being recharged.
A defective or old car battery may not hold its charge and will require renewal.
Incorrect car electrical system voltage can cause problems with other electronic control systems which relay on a stable power supply for correct operation.
Too low or too high battery voltage may cause fault codes to be logged in such systems as Airbag module, ABS module, Steering position sensor, . Cars with automatic transmission may suffer from irregular gear shift if alternator failure happens.