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Battery, Starter & Charging System Diagnosis

After 4 or 5 years (regardless of mileage) most batteries are getting weak and need to be replaced. If you are lucky, your battery might go 5 or 6 years, but average battery life is still only about four years. In hot climates like Arizona and New Mexico, three years is about all the heat most batteries can take. Absorbant Glass Mat (AGM) gel-cell type batteries typically last up to a year or two longer than conventional wet cell lead-acid batteries, so you might consider buying one of these when you replace the battery. Replacement cost for a new battery depending on the type and brand purchased.

When temperatures drop, no-start problems only get worse. Cold weather increases the strain on the battery, starting and charging system and tends to bring out any weaknesses in these components. Cold weather thickens the oil and makes the engine harder to crank. Normal cranking loads can require 125 to 200 amps or more from the battery depending on engine displacement, compression and temperature. At 0 degrees F, that number can increase 200 to 250 percent depending on the viscosity of the oil in the crankcase.

At the same time, freezing temperatures also sap the battery's ability to supply amps. At 0 degrees F, most batteries can deliver only about 65 percent of their normal cranking amps. At -20 degrees F, battery power is cut in half!

A battery cannot deliver maximum cranking power if it is not maintained at or near full charge - especially when outside temperatures drop and reduce the battery's amp output. So reliable starting also requires a good charging system that can keep the battery fully charged and also supply enough amps to meet all of the other electrical needs.

The battery is low or getting old, the starter is weak or there is too much resistance in the starting circuit, the combination of increased cranking load and reduced battery capacity may prove to be too much when temperatures drop. The engine may not crank fast enough to start, or it may not crank at all.



Source: tubecad.com

The first thing you should always check when diagnosing a no-start problem is the condition of the battery and state-of-charge. The battery may be run down, but a good battery will accept and hold a charge, and deliver the rated number of amps on demand. A bad battery won't accept a charge and cannot supply its normal supply of amps because the cells are damaged or worn out.

Use a voltmeter to check battery charge, even if it has a built-in charge indicator. Built-in charge indicators only read one cell, not all six cells. If another cell is bad, you cannot tell by looking at the charge indicator. A fully charged battery should read 12.6 volts. A reading of 12.4 volts equals about a 75 percent charge and is good enough for further testing. But anything less means the battery is low and needs to be recharged. Battery Voltage and State of Charge:

12.68v . . . . . . . . . . 100%

12.45v . . . . . . . . . . 75%

12.24v . . . . . . . . . . 50%

12.06v . . . . . . . . . . 25%

11.89v . . . . . . . . . . 0%


Always check the performance of the charging system when replacing or recharging a battery. A charging system that is working properly should produce a charging voltage of somewhere around 14 volts at idle with the lights and accessories off (always refer to the vehicle manufacturer specifications). When the engine is first started, the charging voltage should rise quickly to about two volts above base battery voltage, then taper off, leveling out at the specified voltage.

Source: sundevilauto.com

The exact charging voltage will vary according to the battery's state of charge, the load on the electrical system and temperature. The lower the temperature the higher the charging voltage, and the higher the temperature the lower the charging voltage. The normal charging voltage on a typical application might be 13.9 to 15.1 volts at 77 degrees F. But at -20 degrees F, the charging voltage might be 14.9 to 15.8 volts. For a hot engine on a hot day, the normal charging voltage might drop to 13.5 to 14.3 volts.

Charging output can also be checked with an adjustable carbon pile voltmeter and ammeter. The carbon pile is attached to the battery and adjusted to obtain maximum output while the engine is running at 2,000 rpm. Charging amperage is another number that can reveal the condition of the alternator. With the engine idling and no load on the charging system (lights and all accessories off, and battery fully charged), the amperage output should be relatively low (typically less than 10 amps). With the headlights and heater blower fan on and the engine running at 2,000 rpm, the output should jump to a higher reading, typically 25 to 30 amps or more.

NOTE: If a vehicle has a history of repeat alternator failures, it might mean the battery is not building up normal resistance as it accepts a charge. This, in turn, makes the alternator keep charging the battery at a higher than normal rate. The result is that the alternator runs hot, overheats and eventually fails from being over worked. The battery charging current should gradually decrease after the engine starts, and taper off to less than 10 amps at idle (with no lights or accessories on) after five minutes of running. If a fully-charged battery is still pulling 20 or more amps after five minutes of idling, the battery is defective and needs to be replaced,

Warning: Never disconnect a battery cable while the engine is running to test the alternator. Doing so can cause high voltage spikes that can damage the alternator as well as other electronics. Another way to check alternator output is with an oscilloscope. Observing the ripple voltage pattern will tell you at a glance whether or not all the alternator windings are functioning. A good pattern should look like the top of a picket fence. If any of the humps are missing, it means one or more of the windings is grounded or open, or there is a bad diode. Most battery/charging system testers also have a test function that can detect bad diodes.


Starter problems can be caused by worn brushes (carbon pads inside the motor that supply current to the rotating armature), by shorts or opens in the armature or field coils, or by worn bushings that increase drag or allow the armature shaft to rub against the pole shoes. Sometimes the starter motor works fine but the drive gear fails to engage the ring gear on the flywheel. If the drive gear mechanism can be replaced separately, there is no need to replace the entire starter. A bad solenoid can also cause starter problems. The solenoid acts like a relay to route power directly to the starter from the battery. It may be mounted on the starter or located elsewhere in the engine compartment, and is usually connected to the positive battery cable. Corrosion, poor ground at the solenoid mount or poor battery cable connections will prevent the solenoid from doing its job. If the starter tests okay but fails to crank, another possible cause may be a bad ignition switch, neutral safety switch or clutch safety switch. A low battery and/or loose or corroded battery cables can also prevent the starter from cranking the engine.


Starters and alternators often have a high warranty return rate. Often there is nothing wrong with the part because the real problem was not diagnosed correctly. To reduce the risk of misdiagnosis, have your auto parts store bench test the old starter or alternator to confirm your diagnosis. Also have them test the new or reman unit before you accept it. Replacement alternators should always have the same, or higher, amp rating as the original. The battery should also be fully charged before installing an alternator. If you are replacing a permanent magnet starter, handle it with care because the magnets can easily be damaged if the starter is dropped. An auto parts store that requires an exchange starter may not give you credit for your old starter if it is damaged. And you certainly don't want to damage the new unit before it is installed.

For Read More Visit: http://www.aa1car.com/library/2004/ic120434.htm

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Today's car repair blog: nzymkl - 2018-01-20 21:32:54