How to check if your alternator is bad?
Alternator is a component on your car were produce an electricity when the engine is running. The alternator has two major function, the first is to recharge your car battery and the second is to provide an electric energy which is use as a battery subtitute.
Yes, when the engine runs, the alternator is taken the battery function as an electic power source. A bad alternator will drain your battery faster and stops your car as the battery drains out.
In previous post, we have discuss on how to test an alternator without multimeter. However, the methode was unsafe and very risky to do mainly on the alternator voltage and current test when removing the positive battery terminal while the engine runs.
So, how to test the alternator in a better way so we can decided if the alternator is bad or not? There are two ways to test if your alternator is bad or no. The first test is using a voltmeter and the second test is using an amperemeter.
Voltmeter is used to know how much the alternator voltage output were produced to charge the battery, while the amperemeter is use to know how much the alternator output amperage were produced to used in all electrical car components. So here they are on how to test if your alternator is bad or no.
To test an alternator voltage, we can use a general multimeter, but for better measurement result, it is recommend to use a Digital Volt Ohm Meter (DVOM). So,here's how we do it:
Result :
If the alternator voltage output is less than 13.50 Volt while the engine rpm is at 750-800 rpm, then it is the sign that your alternator is going bad, this condition is called as "Undercharge". And if the alternator output voltage is more than 14.70 Volt, then this condition is also called as "Overcharge". Overcharge means that the alternator is going bad.
As a recap, see the table below for an alternator voltage testing
Read also:
After we test the alternator output voltage and to make sure that the alternator is bad or no, we have to conduct an alternator amperage output test. In several cases, the alternator can produce good voltage but it less amperage.
The amperage is the power for every electrical components on your car. It's powered the headlamps, the radio tape, or even the engine control unit. If your alternator produces less amperage, then it's reduce the electric power for the car, the effect is your charging system will fails and it will drain your battery soon.
A good alternator amperage output if the measurement value is more than 70% of maximum amperage. For example, if your car using a 100 Amp alternator, then the good alternator will produce 70 Amp. If it less then 50% then its a sign that your alternator is going bad.
To conduct an alternator amperage test, we need an amperemeter which has bigger value than your alternator amperage size. It is very recomended to use an ammeter plier (clamp type) than the regular amperemeter because of easy of use. So, here an alternator amperage output test.
Result :
Your alternator is going bad or need attention to change or repair if :
Yes, when the engine runs, the alternator is taken the battery function as an electic power source. A bad alternator will drain your battery faster and stops your car as the battery drains out.
In previous post, we have discuss on how to test an alternator without multimeter. However, the methode was unsafe and very risky to do mainly on the alternator voltage and current test when removing the positive battery terminal while the engine runs.
So, how to test the alternator in a better way so we can decided if the alternator is bad or not? There are two ways to test if your alternator is bad or no. The first test is using a voltmeter and the second test is using an amperemeter.
Voltmeter is used to know how much the alternator voltage output were produced to charge the battery, while the amperemeter is use to know how much the alternator output amperage were produced to used in all electrical car components. So here they are on how to test if your alternator is bad or no.
I. Using a voltmeter
To test an alternator voltage, we can use a general multimeter, but for better measurement result, it is recommend to use a Digital Volt Ohm Meter (DVOM). So,here's how we do it:
- Pick up your digital multimeter and set the knob to the DC volt measurement
- Put the red lead of DVOM to the positive terminal battery and the black lead to the negative terminal battery.
- In this step, we can see the measurement result of the battery voltage value on the DVOM screen. Good battery voltage is between 12.15 volt -12.60 volt.
- Turn the igniton key to ON position. Turn off if any electrical component's live such as radio tape, air conditioner, or headlamp. Make sure the electrical components are off.
- Start your engine until it reach an idling rpm (750-800 rpm)
- See the DVOM screen, the voltage should arise between 13.50 volt to 14.00 volt as the engine runs.
- Raise the engine rpm by pushing the acceleration pedal until it reach 2000rpm, the voltage should arise 0.50 volt - 0.70 volt. For example, on idling rpm, the voltage was 13.50 volt, and when it reach 2000rpm, the voltage should reach 14.00 voltage or 14.20 voltage.
Result :
If the alternator voltage output is less than 13.50 Volt while the engine rpm is at 750-800 rpm, then it is the sign that your alternator is going bad, this condition is called as "Undercharge". And if the alternator output voltage is more than 14.70 Volt, then this condition is also called as "Overcharge". Overcharge means that the alternator is going bad.
As a recap, see the table below for an alternator voltage testing
| ENGINE RPM | VOLTAGE | CHARGING STATE | ALTERNATOR CONDITION |
|---|---|---|---|
| 750 - 800 rpm | 13.50V - 14.00V | NORMAL | GOOD |
| 1500 -2000 rpm | 14.00V - 14.20V | ||
| 750 - 800 rpm | Less than 13.50V | UNDERCHARGE | BAD |
| 1500 -2000 rpm | |||
| 750 - 800 rpm | More than 14.70V | OVERCHARGE | BAD |
| 1500 -2000 rpm |
Read also:
II. Using an amperemeter
After we test the alternator output voltage and to make sure that the alternator is bad or no, we have to conduct an alternator amperage output test. In several cases, the alternator can produce good voltage but it less amperage.
The amperage is the power for every electrical components on your car. It's powered the headlamps, the radio tape, or even the engine control unit. If your alternator produces less amperage, then it's reduce the electric power for the car, the effect is your charging system will fails and it will drain your battery soon.
A good alternator amperage output if the measurement value is more than 70% of maximum amperage. For example, if your car using a 100 Amp alternator, then the good alternator will produce 70 Amp. If it less then 50% then its a sign that your alternator is going bad.
To conduct an alternator amperage test, we need an amperemeter which has bigger value than your alternator amperage size. It is very recomended to use an ammeter plier (clamp type) than the regular amperemeter because of easy of use. So, here an alternator amperage output test.
- Start your engine and let it reach an idling rpm
- Shut off all electric components such as radio tape, air conditioner, headlamps, etc.
- Put on the ammeter clamp type to the alternator output harness that connected to the battery. Pay attention for the arrow direction when put the ammeter. See the picture below
- Raise the engine rpm to 2000rpm and see the measurement value
- The alternator is going bad if the measurement value is less than 50%. For example, your car alternator use a 60 Amp alternator; if the measurement value less than 30 A, its a sign that your alternator is going bad.
Result :
Your alternator is going bad or need attention to change or repair if :
- The value of the alternator output voltage when the engine is in an idling rpm is less than 13.50 volt or not more than 14.70 voltage.
- The alternator output amperage is less than 50% of alternator maximum amperage.