|Electrical Components - Maintenance|
It could be any one of the three. It could also be an undetected current drain caused by a trunk light, underhood light, or glovebox light that does not go out when the lid is closed or even a chaffed wire making contact with a metal body part.
Check the battery first
The first thing that should be checked is the battery state of charge. If it has a built-in hydrometer (charge indicator), a green dot means the battery is 65% to 75% charged and okay for use or further testing.
If the charge indicator is dark, the battery is less than 65% charged and needs to be recharged and load tested.
On 1985 and later model Chrysler vehicles, the charge indicator on some batteries also contains a red dot which shows if the battery is less than 50% charged.
(With green dot)
(No green dot)
If the charge indicator is clear or yellow, the level of electrolyte inside the battery has dropped too far to give a reading. It also means the battery will need to be replaced soon. Once water level drops below the top of cell plates, they dry out and lose their ability to hold a charge.
Never attempt to jump start or charge a battery with a low electrolyte level. It may explode.
The state of charge of a sealed top battery without a built-in charge indicator can be determined by measuring its open circuit (no load) voltage:
A low charge level does not mean anything is wrong with the battery or charging system, it simply means the battery is low and needs to be recharged.
A conventional load test is performed with a carbon pile battery tester. The load created by the carbon pile is adjusted according to the battery's cold cranking amp (or amp/hour) rating. The carbon pile is usually set to one half the battery's CCA rating (or three times its amp/hour rating).
Temperature compensation is also important because a cold battery puts out fewer amps than a warm one. The load is then applied to the battery for 15 seconds while voltage output is observed. If voltage remains above 9.6 volts, the battery is good. If it drops below 9.6 volts, the battery can be recharged and retested, or given a three-minute charge test.
Slow charge the battery at 40 amps for six minutes, then check voltage across the terminals with the charger on. If the voltage is above 15.5 volts, the battery is not accepting a charge. Slow charging for 20 hours can sometimes reverse the sulfated condition, otherwise the battery is junk.
When the engine is first started, charging voltage should rise quickly to about two volts above base battery voltage, then taper off and level out at the specified voltage.
Exact charging voltage will vary according to battery state of charge, load on vehicle electrical system, and temperature. The lower the temperature, the higher the charging voltage. The higher the temperature, the lower the charging voltage.
On a GM application, for example, accepted voltage charging range is 13.9 to 14.4 volts at 80 degrees F. At 20 degrees F below zero, charging range is 14.9 to 15.8 volts. At 140 degrees F, the charging voltage is 13.0 to 13.6 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 voltage output while the engine is running at 2,000 rpm.
The exact procedure for full fielding an alternator varies from vehicle to vehicle depending on how the alternator is wired. Basically, the regulator is bypassed by connecting a jumper wire between the field (FLD or "F" terminal) and battery positive (BAT) terminal on the alternator.
On older GM applications with Delco integral regulator alternators, inserting the tip of a screwdriver through the D-shaped hole in the back of the alternator full fields the unit.
Either voltage or current output can be compared against manufacturer specs to determine if the alternator is functioning at full capacity. Generally speaking, alternator output should fall within 10 amps or 10% of its rated capacity at 2,000 rpm.
For several reasons, it is important to follow full fielding test procedures exactly. If only one diode or stator winding is bad, for example, the alternator may still make enough electricity at high rpm to keep the battery charged, but not at idle or low speed. The alternator and/or regulator can also be damaged if the wrong test procedure is used.
On Chrysler externally regulated alternators, for example, you do not apply voltage to the "F" terminal. This system is full fielded by grounding the green wire at the regulator connector. On externally regulated Ford alternators, the alternator is full fielded by disconnecting the four-wire connector from the regulator and jumping across the "A" and "F" terminals.
A slipping fan belt is one of the most common causes of under charging. A fan belt that holds at idle or low rpm may slip when the alternator is under load. Glazed or burned streaks on the belt are an indication of slipping.
If the battery and charging system are okay and the battery keeps running down, check for a current drain somewhere in the electrical system. To isolate the cause, remove one of the battery cables and connect an amp meter between it and the battery.
A current drain will cause a reading on the meter. Disconnect fuses one by one until the circuit is found that causes the reading to disappear.
On-board electronics such as the computer, an electronic clock, etc., will draw a few milliamps all the time, but should not be enough to run the battery down unless the vehicle is not driven for long periods of time.
CCA rating is an indication of a battery's ability to deliver a sustained amp output at a specified temperature. Specifically, it is how many amps a new, fully-charged battery can deliver at 0° F for 30 seconds and still maintain a minimum voltage of 1.2 volts per cell.
A rule of thumb says a vehicle's battery should have a CCA rating equal to or greater than engine displacement in cubic inches. A battery with a 280 CCA rating would be more than adequate for a 135 cubic inch four-cylinder engine, but not big enough for a 350 cubic inch V-8.
Even though battery manufacturers might say bigger is better, we still contend that for most cases 1 CCA / cubic inch of engine displacement is adequate. You should only consider exceeding 1 CCA / CI for exceptional conditions, such as heavy industrial use or very harsh climates
Notes: If you upgrade to a greater capacity battery, make sure:
The filament in a halogen bulb is thinner and burns hotter. They are called halogen bulbs because of the gas mixture used to fill the glass; halogen plus krypton, argon and/or nitrogen. The gas mixture conducts heat away from the filament to prevent it from burning out. Halogen helps redeposit microscopic particles of tungsten that boil off the filament back onto the filament. This extends filament life and prevents bulb darkening with age.
Too many people have tried to take advantage of the system. Instead of using proper diagnostic procedures, some people (mostly do-it-yourselfers, but also some so-called professionals) resort to trial-and-error parts swapping when they don't know how else to fix an electrical problem. When parts they have installed do not fix their problem, they want to return them and try something else.
Electrical/electronic parts are easily damaged by improper installation or testing. Because electronics are very sensitive to voltage overloads, it does not take much of a voltage spike to ruin a component.
Unplugging a wiring connector while the key is still on can create a momentary voltage surge of hundreds of volts. Crossing up the wrong wires or using the wrong test procedures can also damage sensitive electronics. You have no way of knowing whether or not the part has been used or damaged.
Because of such risks, many jobbers refuse to allow returns on any electronic components. This may seem unfair to some customers, but it protects the next customer who might get a bad part that had been returned.
Most jobbers will allow returns or exchanges on rebuilt starters and alternators if there is a problem with the unit.