Every car has a battery to crank the engine, and power the fuel pump and ignition at startup, but then the alternator starts spinning and providing the power. Because of this, you can often jump start a car with a failing battery, then drive it to the auto parts store to get a new one. With the motor running, and the alternator putting out power, the battery doesn’t have much to do. There are only a few ways an alternator can go bad, but they tend to happen suddenly without a lot of warning.

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Here are the common symptoms:. Undercharging - This is the most common problem, and can often be caught in the early stages. If you notice your headlights get dim with the engine at idle and get bright when you rev it, chances are your alternator is not putting out enough power. Overcharging - This isn’t a problem with the alternator itself, but rather a problem with the voltage regulator (often built into it).

An overcharging alternator can kill a battery and boil the fluid out of it. No Charge at All - This can appear just like an undercharge condition, but revving the motor does nothing. Get home or to a service station quick, as a modern car will only run a short time before the battery is dead.

Mechanical Issues - This category of failure often just involves the bearings wearing out and squealing, or in extreme cases, seizing up. Besides not charging the battery, this can also throw the serpentine drive belt, causing overheating. Like all rotating machines, the bearings in an alternator have a finite life and will eventually go bad. You can minimize the chances of this happening prematurely by keeping the drive belt and tensioner in good shape.

Nothing will kill the bearings quicker than a too tight belt, but a belt that is too loose isn’t good either. If your car has a spring-loaded tensioner, you should at least inspect it at 50,000 miles when you change the belt. If you have an older car with a manual tensioner, be sure to tighten it to the specification found in your Haynes Manual. If you notice an acidic smell or your battery is leaking fluid, it may be because the alternator is overcharging. You can easily check by measuring the voltage at the battery with the car running, which should not go above 15 volts even with the engine revving.

First, check that all the wires to the alternator and regulator are connected properly and not broken. If your car uses a voltage regulator, either separate or built into the alternator, it is inexpensive and easy to change.

If you have a car where the voltage is regulated by the ECU, you may need to talk to an expert technician. An alternator that won’t put out at least 13.8 volts is in need of replacement or at least a rebuild. But, if the low output is combined with squealing noises, it may just be a case of a slipping serpentine belt. If the belt is good, low output can be caused by the insulation breaking down on the internal alternator windings, or it may just be worn brushes; either way, the unit needs to come off and come apart. Finally, if there is no charge at all, there are several possibilities. It is possible that the drive belt has broken or come off the pulley, or the tensioner went bad completely.

Alternators put out alternating current, and the battery needs direct current to charge, so there is a voltage rectifier that converts it, and it can suddenly go bad, too. A faulty voltage regulator can also stop an alternator from charging at all.

Otherwise, a no charge condition can mean an internal break in the windings, bad brushes, or burned out slip rings. If all the external wiring seems good, it is likely an issue inside the alternator. The single best thing you can do to keep your alternator working well is to keep it clean and dry. Dust and dirt can get into the alternator, and over time cause shorts or wear on the brushes. The wire windings of the alternator only have a thin insulation on them and won’t produce a magnetic field if it fails, so avoid getting solvent on them, like carb cleaner or gasoline. Heat and oil can also shorten the life of an alternator, so fix under hood leaks as soon as possible.

Volvo 850 S70 V70 C70 service & repair manual ALTERNATOR & REGULATOR 1995 Volvo 850 1995-96 STARTING & CHARGING SYSTEMS Volvo Alternators & Regulators 850 NOTE: Some Volvos are equipped with a Nippondenso generator. Testing information on these generators is not available from the manufacturer. DESCRIPTION Bosch generators are a conventional 3-phase, self-rectifying type. Bosch 55-amp through 75-amp generators have 3 positive and 3 negative diodes connected to stator windings to rectify current. Bosch 80-amp through 120 amp generators have 14 diodes.

All generators use 3 exciter diodes connected to stator windings. These diodes turn off the generator indicator light and supply power to voltage regulator while engine is running. Voltage regulator is transistorized. ADJUSTMENTS No adjustments or maintenance is required on generator or voltage regulator. TROUBLE SHOOTING NOTE: See TROUBLE SHOOTING – BASIC PROCEDURES article in GENERAL INFORMATION.

ON-VEHICLE TESTING WIRING CONTINUITY TEST 1) Connect a voltmeter between generator B+ terminal and ground. Voltmeter should indicate battery voltage.

If battery voltage is not indicated, check wiring between generator and battery. 2) Turn ignition on and ensure generator indicator light comes on. If light does not come on, check wiring between generator and warning light. VOLTAGE DROP TEST – POSITIVE SIDE 1) Connect a voltmeter between positive battery terminal and generator B+ terminal. Start engine and run at 2000 RPM. Turn on headlights, rear window defogger and heater blower. 2) If voltage drop is more than.2 volt, check circuit between generator B+ terminal and starter for corroded or loose connections.

Also, check circuit between starter and battery positive terminal. VOLTAGE DROP TEST – GROUND SIDE 1) Connect a voltmeter between negative battery terminal and generator housing. Start engine, and run it at 2000 RPM.

Turn on headlights, rear window defogger and heater blower. 2) If voltage drop is more than.2 volt, check battery terminals, chassis grounds and engine grounds for corroded or loose connections.

OUTPUT TEST 1) Ensure connections at battery, generator, and starter are clean and tight. Ensure generator, engine and body are properly grounded. Ensure generator drive belt is tight and in good condition. 2) Connect ammeter following manufacturer’s instructions. Connect voltmeter leads to battery terminals. Run engine to 2000 RPM. Adjust carbon pile on tester until voltmeter reads 12 volts.

Generator output should be 49-55 amps. (55-amp generator), 63-70 amps (70-amp generator), 31-80 amps (80-amp generator), 81-90 amps (90-amp generator). If generator output is low, replace generator. OVERHAUL NOTE: Use illustration for exploded view of Bosch generator.

Illustration of Nippondenso generator is not available from manufacturer. 1: Exploded View Of Bosch Generator (Typical) Courtesy of Volvo Cars of North America. GENERATOR SPECIFICATIONS GENERATOR SPECIFICATIONS (BOSCH) Part No. Amps 0 120 213 007. 100 0 120 411 577.

80 0 120 465 006. 120 0 120 465 012. 100 0 120 465 018. 100 0 120 468 010. 100 0 120 468 016. 100 0 120 469 787. 80 0 120 469 789.

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80 0 120 469 793. 80 0 120 469 935. 80 0 120 469 993. 80 0 120 469 995. 80 0 120 469 997. 80 0 120 488 131.

55 0 120 488 230. 65 0 120 488 231.

65 0 120 488 260. 55 0 120 488 262. 65 0 120 510 348.

120 0 120 510 423. 100 0 120 545 002.

100 0 123 213 006. 100 0 123 310 017. 80 0 123 310 030. 80 0 123 500 004. 100 0 123 545 001.

100 0 123 545 003. 120 GENERATOR SPECIFICATIONS (NIPPONDENSO) Part No. Amps 100 211-8370 80 100 211-8620. 100 100 211-8630. 100 100 211-8960 80 WIRING DIAGRAMS Fig. 2: Charging System Wiring Diagram (1995-96).