Table of Contents
Can an alternator read good and still be bad?
The only way to know if an alternator is good or bad is to bench test it on an alternator test stand. A good alternator should produce about 13.5 to 14.5 volts with the engine idling. If the voltage reading is low (12.5 volts or less), it indicates a charging problem but does not tell you what’s causing it.
Can an alternator cause a draw?
Something is causing a “parasitic draw.” Even while your car is off, your battery provides power to things like the clock, the radio, and the alarm system. But when the engine is off, the alternator can’t recharge the battery, allowing little electrical mishaps to drain your battery entirely.
Can an alternator cause a parasitic draw?
A malfunctioning diode in the alternator can create a parasitic drain on a car’s battery. Diodes should allow current to pass in only one direction, but a bad diode will keep the charging circuit open even when the engine in not running, allowing the battery to go dead. This often happens overnight.
How long does it take for a bad alternator to drain a battery?
In this situation, the battery could last as little as 30 minutes. If you are lucky and could get up to two hours. Note: In case you have to start the car without an alternator, don’t turn off the engine once you’re going. Starting the car flattens the battery down quickly.
What can mimic a bad alternator?
Testing at the Battery Start by checking your battery terminals. Loose or heavily corroded terminals can mimic the effects of a bad alternator.
How do I test to see if my alternator is bad?
An illuminated dashboard light can indicate a problem with an automobile charging system. However, a very simple way to check if the alternator is working is to run the car and disconnect the positive terminal of the battery. If the vehicle stops running, then you probably have a bad alternator.
Would a bad alternator drain the battery?
A corroded or defective alternator diode will faultily continue charging the circuit even when the car off. This, in turn, will drain your car battery and cause the car not to start.
How do you know if your alternator is draining your battery?
If the engine starts but dies immediately, your alternator probably isn’t keeping your battery charged. If a jump starts and keeps your car running, but the car can’t start again off of its own power, a dead battery is likely your answer.
Can an alternator still charge with a bad diode?
Bad diodes are a common cause of alternator failure. If only one or two diodes have failed, the alternator may still produce enough current to meet the vehicle’s electrical needs, but it may not be enough to keep up with higher loads or keep the battery fully charged.
How much current draw is acceptable?
In fact, we suggest a 25-milliamp draw is acceptable and anything that exceeds 100-milliamps indicates an electrical issue that needs to be addressed.
Can a weak alternator cause poor engine performance?
Can bad alternator affect engine performance? Drops in electrical output from a failing alternator can cause these systems to malfunction, leading to a poorly running engine. Symptoms will be rough idle, misfires, poor acceleration, hesitation and stalling.
Can you jump start a car with a bad alternator?
You actually can jumpstart a car with a bad alternator, and the car will keep running for some time, no matter how bad the alternator is, well, considering you have a good battery. This is because if the alternator is bad and not producing the voltage required, the car will be running purely off the battery.
Does low voltage mean bad alternator?
If the charging voltage is low, or the alternator isn’t putting out enough current to keep up with the electrical loads that are placed upon it, don’t automatically assume the alternator is bad and needs to be replaced (unless you’re bench testing the unit out of the vehicle).
What sound does a bad alternator make?
Alternator Whining Noise A common sound made by failing alternators is a very high pitched whining noise that you’ll hear when the engine is running. When the RMPs increase, such as when you accelerate, you’ll hear the noise get higher in pitch as the pulley spins faster.
What are the symptoms of a bad voltage regulator?
Bad Voltage Regulator Symptoms Too High Voltage in the Battery. There are two ways a voltage regulator can fail. Dead Battery. Battery Light or Check Engine Light. Inconsistent Operation of Electrical Components. Vehicle Dies While Running. Dimming/Pulsing Lights.
Why do alternator diodes fail?
Because of the substantial load handled by the alternator, the rectifier diodes fail because of overheating, overloading or because of poor connection between the alternator output and the battery positive terminal. Leaky or shorted alternator diodes can cause rapid changes in the output voltage of the charging system.
How do I test my alternator with a multimeter?
More videos on YouTube Get a multimeter. Set your multimeter to DCV (DC Volts) above 15. Make sure your alternator’s positive and negative terminals are clean. Put the multimeter’s black cable to the negative terminal and the red cable to the positive terminal. Look for an ideal alternator reading of around 12.6.
How do I check for a battery draw?
Pull the negative off the battery. Put the test light between the post and the ground wire. If the light illuminates, you have a draw. Use the fuse pull method to find the draw; when the light goes out, you found the draw.
What is a good parasitic draw?
Parasitic Battery Draw A normal amount of parasitic draw for newer cars is between 50-milliamp to 85-milliamp current draw. A normal amount of parasitic draw for older cars is a reading less than 50-milliamp. Anything past these amounts indicates an electrical issue and should be addressed by a mechanic.
