How to recondition an alternator

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How to recondition an alternator
How to recondition an alternator

An alternator is an electrical machine capable of transforming mechanical energy into electrical energy in the form of alternating current through the use of the phenomenon of electromagnetic induction. They work according to the principle that an induced electrical voltage is created in a conductor subjected to a variable magnetic field, the polarity of which depends on the direction of the field and the value of the current flow through it.

An alternator is an alternating current generator that works by constantly changing the polarity of the field (through an external source of mechanical energy, generally a combustion engine) so that there is movement and generates energy, finally this is converted into direct current by means of a rectifier bridge (diode holder 'or diode).


Method 1 of 2: Recondition the Alternator

Step 1. Disassemble and clean the components

Use a degreasing agent (industrial degreaser, gasoline, NEVER USE THINNER or another solvent of similar strength, this can damage the insulating enamel of the rotor and stator windings).

Step 2. Check the condition of the components for obvious damage (bumps, cracks, etc.)


Step 3. Check rotor tracks and ground for continuity (there should be continuity

between tracks but NOT between tracks and ground), check rotor for field leakage

Step 1. Desolder the diode holder of the stator, verify the operation of the rectifier bridge (Each diode must allow the passage of current in only one direction)

Step 2. Check the stator coil for continuity and insulation

There must be continuity between the coil terminals and these must be isolated from ground.

Step 3. Check the condition of the bearings and replace if necessary

Step 4. Check the condition and length of the coals and replace if necessary

Step 5. Paint the housings and fan if necessary

Step 6. Assemble the alternator and perform a bench check


Once an alternator has been reconditioned, it is necessary to carry out a bench check to evaluate its operation and determine if it is correct. An alternators check bench consists of a table equipped with a motor (generally electric) to move the alternator by means of a belt, the connection cables, a voltmeter, an ammeter and two switches, the first to start the engine and the second to power by means of a battery the rotor.


Alternator monetized on a test bench

Method 2 of 2: Additional Information

Parts of an Alternator

Step 1. Front cover

Step 2. Stator and diode holder assembly:

In the stator, the alternating current is induced by the rotor, being rectified in the diode holder to deliver direct current to the output of the alternator.

Step 3. Rotor:

It consists of a shaft and a coil with a soft iron core that make up an electromagnet which produces the magnetic field to induce alternating current in the stator, it is fed by two terminals (tracks) where the coals make contact.

Step 4. Back cover

Step 5. Fan and Pulley Assembly

It is the transmitting element of the mechanical energy from the internal combustion engine to the alternator in addition to cooling it.

Step 6. Front bearing

Centers and stabilizes the rotor shaft in front of the alternator

Step 7. Coals

Its function is to feed the rotor so that it becomes magnetized and produces the magnetic field

Step 8. Carbon holder

Step 9. Rear bearing retainer

Step 10. Rear bearing

Centers and stabilizes the rotor shaft at the rear of the alternator


Alternators are reliable and effective machines, however, like all machines, they require certain maintenance, which consists of verifying the condition of the coals (their length), the tracks where they slide, the bearings, the diode holder and certain specific checks of the rotor and stator. An alternator rotates at several thousand revolutions per minute, together with working conditions such as vibrations and dirt, they can generate wear on the rotor (especially on the tracks and carbons), connection terminals as well as on the rotor if the shaft of the rotor suffers some eccentricity. (produced by a strong blow or faulty bearings); Another frequent failure in alternators occurs in the rectifier bridge, since the diodes are semiconductor elements built with silicon crystals, they are sensitive to vibration, the diodes used in alternators are robustly built to withstand use in these conditions however After a long time of service, they can break, thus opening the electrical circuit of the alternator and causing it to “stop commanding”. For this reason, during a reconditioning the state of the bearings must be checked and replaced if necessary.. Another factor that can cause an opening of the alternator circuit is a failure in the internal insulation of the rotor or stator coils, this failure is not usually common but can occur due to overheating or chemical attack to the insulating coating of the coils during a poorly executed cleaning procedure. All reconditioning must be carried out according to the alternator manufacturer's instructions, however the procedures are very similar, so a general procedure will be described below in an illustrative way:

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