How to Test Alternator with Multimeter?

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A multimeter is a sort of electrical instrument that is commonly used by electronic workers and engineers. It is a multi-measurement electronic measuring instrument, also known as a VOM (volt-ohm-milliampere).

Electrical faults in motors, power sources, appliances, circuits, and wiring systems are diagnosed using them by electricians. DIYers can also learn how to use multimeters to take simple measurements around the house.

The three basic electrical characteristics of voltage, current, and resistance are all measured with it. It can also be used to assess whether two points in a circuit are interconnected electrically.

They can be used for everything from simple testing like battery voltage measurement to complex diagnostics and fault detection and they come in both digital and analogue configurations.

Types of Multimeter

  • Analog Multimeter: A moving coil meter and a pointer that indicates the scale reading make up the analogue multimeter, also known as a VOM (Volt-Ohm-Milliammeter). A coil wound around a drum and placed between two permanent magnets makes up a moving coil meter. It has the advantages of being inexpensive, not requiring a battery, and being able to measure fluctuations in readings.
  • Digital Multimeter: The Digital Multimeter’s internal circuitry includes signal conditioning and an analogue to digital converter, as well as an LCD and a knob for selecting different variations of the three electrical characteristics. Its benefits include a direct display of the measured value, high accuracy, and the ability to read both positive and negative values.
  • Fluke Multimeter: The Fluke digital multimeter can be customized to include a variety of collaboration features. It usually has a large display and is used to measure voltage and electrical resistance. It is primarily used to calibrate currents, volts, and other electrical units.
  • Clamp Multimeter: Electricity flow is measured using a clamp digital multimeter. When the probes measure volts, this multimeter’s clamp feature measures amps. While measuring, the appropriate feature is used.
  • Autoranging Multimeter: The auto-ranging multimeter is the easiest to use of all the digital multimeters, but it is also the most expensive. It has fewer positions and a knob in the center. This instrument can be used for simple projects, and it is highly recommended for beginners as well as home electricians.

Benefits of Multimeter

  • The electrical output can be used to send and receive data with other devices.
  • There is no effect from loading due to the high input impedance.
  • A clear reading can be obtained at greater viewing distances.
  • The display of the output can be done automatically.
  • It can auto-polarize.
  • These are less expensive because of the integrated technology.

Limitations of Multimeter

  • The LCD is primarily powered by an external source, such as a battery because the LCD becomes dim and difficult to read when the battery is depleted.
  • The meter must be used following the manufacturer’s specifications and the category rating; otherwise, the meter will be damaged, resulting in the loss of equipment.
  • The multimeter’s limit is 1V, so if it’s exceeded, it’ll be damaged.
  • Power supply and isolation requirements

Multimeter Applications

  • Testing for continuity and resistance
  • Determining the frequency
  • Testing the switch
  • Testing the batteries
  • An outlet can be tested.
  • It’s used for environmental and temperature control.
  • Diode testing       
  • AC/DC measurement
  • Voltage measurement (AC/DC)
  • Old incandescent light bulbs can be tested.
  • Measurement of time and frequency

Before you test your alternator, consider the following symptoms that it may be faulty:

  • The dashboard’s battery light is on.
  • Your engine is either cranking slowly or not cranking at all.
  • The batteries, headlights, and/or interior lighting appear to be in poor condition.
  • Rumbling or squeaking sounds are coming from the alternator.
  • You’ve attempted and failed to jump-start your vehicle.

How to Test Alternator with Multimeter?


Ascertain that your battery is completely charged. To keep your battery in good condition, use a contemporary trickle charger.


Connect a multimeter to the battery connections while turning off the engine. Connect the red to the red and the black to the black.


Check that all of your vehicle’s accessories are turned off. Everything is included, including the radio, lighting, and air conditioner.


Examine the power supply. It should be between 12.6 and 12.6 volts. Restart the engine and check the voltage once more. The voltage should range between 14.2 and 14.7 volts.


Turn on all of your vehicle’s electrical gadgets, including the radio and lights. Examine the voltage once more. It must be at least 13 volts. If it does, it means the alternator isn’t charging the battery sufficiently.


Turn off your accessories first, followed by the engine. The voltage should be approximately 13 volts when you check it. This shows that the alternator has been charged.


How to Test Alternator with Multimeter?

Your car’s alternator is a critical component. Without it, your battery will discharge and your vehicle will not start. To learn how to test an alternator with a multimeter, follow the procedures outlined above.


What is the root cause of alternator failure?

The most typical reason for failure is old age. A typical alternator will last between 5 and 8 years before showing indications of deterioration.
A faulty battery might also hasten the demise of your alternator. Batteries in need of replacement will require additional charging current from the alternator. It isn’t built for this, and the excess heat produced can cause the alternator to fail.

What does a faulty alternator sound like?

If there is a rumbling, grinding noise, it is a solid sign that the bearings have failed. If, on the other hand, you hear a whining noise, the regulator may have.

How do you use a test light to check the alternator?

Examining your internal lights is a simple technique to detect potential alternator problems. When an alternator begins to fail, you may notice that your interior lighting or dashboard lights begin to flicker.
This is a clear indicator of a defect in the electrical charging circuit and should be investigated.

Read: How to Use a Multimeter in 6 Steps?

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