How to Test a Step-Down Transformer Using a DMM

A digital multimeter provides an easy to read screen for testing a step-down transformer.
••• polimetro image by ANTEQUERANUS from Fotolia.com

Step-down transformers reduce an alternating current (AC) voltage source down to a lower voltage level by inducing the electricity from a primary coil of wires into a smaller secondary coil of wires. Step-down transformers are found in electric power company systems and in a multitude of appliances for household and industrial uses. Size ranges are found from in a cell phone charger up to one the size of a house at the end of a high voltage transmission line. For standard household transformer testing a digital multimeter (DMM) makes a good test.

    Set the multimeter to read AC volts at a scale equivalent to the highest voltage needed. Most digital multimeters have a dial to turn for the different functions and scales.

    Touch your DMM leads to the input to the transformer. You need to know what the input voltage is, and read within 10 percent of that reading. If you don't have an input to the transformer, you cannot test it with the DMM.

    Touch the DMM leads to the output terminals of the transformer. The meter is not working.

    Tips

    • Many digital multimeters are alike in many respects. If you don't have a user's manual for the one you own please read a generic one (see Resources).

    Warnings

    • Know and observe safety precautions when working around energized electrical equipment. Never work alone. Never attempt to work on a step-down transformer that is part of an electric power company's service. Call them if you have any questions or problems.

Related Articles

How to Read Amps on an Analog Multimeter
How to Build an EMF Detector
How to Connect Step-Up 3-Phase Transformers
How to Use Micronta 22-167
How to Use a Variac
How to Calculate CT Ratio
Analog Multimeter User Instructions
How to Increase 208V to 230V
How to Wire a Lighting Contactor
How to Size a Transformer KVA
How to Diagnose a Circuit Board With a Bad Transistor
How to Use a Cen-Tech Digital Multimeter
How to Use a Multimeter for the Beginner
How it Works: Voltage Relay
How to Test Multimeters
How to Test DC Motors
How to Check Three-Phase Voltage
How to Lower Amperage
How to Test a Toshiba DLP Ballast