How to Use a Multimeter

Multimeters are essential for DIY electrical troubleshooting around the home. It can be used to test batteries, identify faulty wiring and check electrical sockets. Ryan Davis, my electrical engineer brother in law, showed me recently how to use it. This is a summary of what I've learned. You might find it useful.

What does a multimeter measure?

The multimeter measures the three electrical properties.

Measure voltage to check battery charge or verify power in outlets. Current (Amps), the flow of electricity through a conductor that indicates how much electricity moves through a circuit, is measured to verify battery charge. Measure current to verify that circuits or devices are drawing the correct amount of electricity.Resistance (Ohms): How much a material opposes electrical flow. A higher resistance indicates less electricity flow. To check for component continuity and to verify that a fuse or wire is not broken, measure resistance.

Basic Multimeter Components

Analog and digital multimeters are available. Digital multimeters are auto-ranging, which means that the multimeter will automatically select the right measurement range for whatever quantity you are testing -- voltage or current -- and you won't need to manually set a range. Digital multimeters are easier to use for beginners because they automatically select the correct measurement range.

Multimeters (digital or analog) are primarily composed of:

Ports: COM port (black), two red ports (one for milliamp/mA, voltage, resistance and milliamp/mA measurement, and another for high current up to 10A). Ports are separated for milliamp/mA and voltage/resistance measurements on most professional multimeters. You will use a specific port to measure voltage and resistance. Do not plug in the 10A jack except when you are measuring high currents. Probes: Connect black (negative) and a red (positive), wire to test points.

Real-World Applications

Test Batteries Voltage

Use a multimeter in order to check if the batteries are still charged. How to test your batteries:

Connect the red probe to the milliamp/mA connector and the black probe to the "COM" port.

Set the dial to DC voltage.

The red probe should be placed on the positive terminal of the battery, and black on its negative.

When charging, AA/AAA batteries should read around 1.5V and 9V around 9.V. Car batteries should be 12.6V.

Test for Parasitic Drawing (Current).

My car would not start in the mornings a few years back. After I jumped the car's battery, everything was fine. The battery was fine. The car would not start again a few days after that. I checked to make sure that I hadn't left dome lights or anything on.

I took it to a mechanic who used a multimeter and discovered a parasitic pull from a wireless adapter that was plugged into the lighter. How I could have diagnosed this myself with my multimeter:

1. Install your meter