How to Test a Transformer with a Multimeter (4-Step Guide) 

Transformers are vital electrical components that transfer energy between two or more circuits. However, they can occasionally fail and cause a circuit failure. Hence, it’s crucial to test your transformer to keep your devices operational without the risk of fire or any hazardous events.

In general, you could test a transformer using a multimeter by following these steps: 

  • Remove electrical covers 
  • Insert the leads to the multimeter
  • Connect the leads to the primary side
  • Do the same thing to the secondary side 

There are various methods to test transformers, and the most effective one is through a digital multimeter. So, read on and learn how to test a transformer with a multimeter! This guide will lead you through it step-by-step!

Identifying Transformer Issues

transformer symbol

There are a few methods for determining if your transformer is malfunctioning and a digital multimeter is one of them. A digital multimeter is the most effective tool for detecting transformer faults, aside from its basic function to check voltage, current, etc. If all goes well, you’ll be able to discover any defects with your transformer and learn how to fix them so it can function properly once again.

So before you start to check the transformer with a multimeter, it would be best to identify the critical information about the transformers first. Hence, you should:

Visually Examine the Transformer

A typical cause of transformer failure is overheating, which causes the transformer’s internal wire to run at high temperatures. As a result, the transformer or the space around it is frequently physically deformed. Do not test the transformer if the outside bulges or has burn marks, and replace it instead.

Figure Out the Transformer’s Wiring

On the transformer, the wiring must be clearly labeled. However, the most straightforward approach to figuring out how the transformer is linked is to get a schematic of the circuit. You can find the circuit schematic in the product information or on the circuit manufacturer’s website. (1)

Know the Transformer’s Sides

primary and secondary unit of a transformer

A 24-volt transformer has a primary (high voltage) side and a secondary (low voltage) side.

  • The Primary (High Voltage) Side – is the transformer’s line voltage and the electrical connection to the feeding voltage, typically 120 VAC power.
  • The Secondary (Low Voltage) Side – is the power turned into 24 volts.

In a transformer utilized for a 24-volt application, there is no direct electrical connection between the high and low side sections.

How to Test a Transformer with a Multimeter (Steps)

technician testing transformer with a multimeter

In this guide, we’ll be testing a 24V transformer, and you’ll need the following:

  • Screwdriver
  • Multimeter

So, how do you test a power transformer with a multimeter? Follow the steps below:

Step 1: Remove Electrical Covers 

Turn off the circuit’s electricity. Remove any electrical covers that are covering the transformer using a screwdriver. I recommend checking the manufacturer’s instructions to confirm access to the transformer.

Step 2: Insert the Leads to the Multimeter

testing transformer with a multimeter

Change the multimeter’s setting to “ohms,” then insert the red and black test wires into the multimeter. The black lead goes into the typical opening, while the red lead goes into the “ohms” slot. After that, touch the two leads’ ends together. It should read zero ohms or a closed circuit.

Step 3: Connect the Leads to the Primary Side 

Connect the multimeter’s leads to the high-side or primary transformer leads. The meter should identify a resistance reading, and the type of transformer utilized in the circuit will influence this reading. If the meter reads an open circuit or infinite resistance, you need to change the high-side transformer.

Step 4: Do the Same Thing to the Secondary Side 

technician reading the result for testing transformer with multimeter

Carry out the same procedure in step 3 for the connections in the low-side or secondary. The meter should report the exact resistance measurement in ohms for the low side. Then, if the multimeter indicates an infinite or wide-open reading, the low side is broken internally, and the transformer must be changed.

 Essential Tips

  • A buzzing or cracking sound is a common warning indicating that a transformer will burn out.
  • When you touch the probes together, and only one side of the transformer is not operating, you can hear a buzzing noise. In that case, the transformer has no current flowing through it and is attempting to work against itself.
  • Don’t conclude that the transformer’s primary and secondary sides are connected to the same electrical ground. Different grounds are routinely used to reference them. Hence, while taking measurements, be cautious of the split grounding.
  • You can also have a transformer continuity test. A transformer continuity test is crucial to see if there is a path for electricity to flow between two contact points. If there is no current path, something has gone wrong inside your transformer, and it needs to be repaired.

Safety Precautions

technician putting safety precaution sign to electronic materials on the table

To check the transformer safely, you should take note of the following:

  • Remove all power from the electrical appliance or device before performing any testing. Never test a device that is connected to an external source of electricity.
  • Always do your testing in a secure, dry location away from children and pets.
  • Accidental contact with circuit power when the circuits are exposed and activated for testing could result in shock or damage. Only use the digital multimeter probes to touch the circuit.
  • Working with electricity is exceedingly dangerous. Hence, exercise caution when doing so. You should not plug in a transformer with frayed wires or visible damage since they may cause shock.
  • Only test a transformer if you are familiar with electrical equipment and have used a multimeter to check voltage, electric current, and resistance over a wide range of values.

Transformer: How Does it Work? (Bonus)

transformer

A transformer is an essential electrical device that modifies the alternating current (AC) signal’s voltage. It accomplishes it by transforming AC electricity into high or low-voltage signals. It is essential because it enables safe electricity transmission over long distances. In addition, you can use a transformer to step down or step-up the AC signal’s voltage before it enters a building.

Transformers exist in various sizes and configurations, but they all work by creating a magnetic field around two wire coils known as windings. One winding is connected directly to an alternating current source, like a power line. On the other hand, the other winding is connected to an electrical load, such as light bulbs. When current runs through one coil, it creates a magnetic field surrounding both coils. If there are no gaps between these two windings, they will always have opposite polarities, one pointing north and the other facing south. That is how the transformer generates alternating current.

Primary and Secondary

A transformer’s primary and secondary coils are the wire coils that generate alternating currents. The primary coil is linked to the power line, while the secondary coil is connected to the electrical load. You may modify the voltage output by the transformer by varying the amount of current that goes through each winding. (2)

Other multimeter learning guides below that you can also check.






References
(1) website – https://www.computerhope.com/jargon/w/website.htm
(2) power line – https://www.sciencedirect.com/topics/engineering/power-line

About Sam Orlovsky

b1d87d2ee85af3e51479df87928bdc88?s=90&d=mm&r=gI realized early on carpentry was a huge passion for me and I’ve stayed in the industry for over 20 years now. This gives me a unique ability to really be able to tell you what the best tools and recommendations are. I’m not only a carpenter but I also like machinery and anything to do with electrics. One of my career paths starting off was as an apprentice electrician so I also have a lot of experience with electrical products and anything related.