How to Test 24V Transformer With Multimeter? Guide Of 2024

In our daily lives, transformers quietly power countless devices and electrical systems. Electricity flows efficiently from one circuit to another through these devices, often at different voltage levels, from doorbell chimes to industrial machinery. Transformers must be tested regularly to ensure seamless operation. You should know the basics of transformers before knowing how to test 24v transformer with multimeter.

What is a Transformer and its Basic Function?

Transformers play an essential role in power distribution and voltage transformation. The primary purpose of an electrical transformer is to transfer electrical energy between circuits by altering voltage levels and maintaining electrical isolation at the same time. A 24V transformer transforms an input voltage into a 24 volt output voltage, making it a valuable component in various electrical systems.

3 Major Types of Transformers

  • Power Transformer
  • Step Up Transformer
  • Step Down Transformer

1-Power Transformer

Electrical energy is efficiently transferred between circuits by the power transformer. Alternating current (AC) voltage is changed to transmit electricity with minimal loss over long distances. The power transformer steps up the voltage for long-distance transmission and then drops it again for local distribution. Transformers transport electricity generated at power plants to homes, businesses, and industries.

2-Step Up Transformer:

Step-up transformers are used to increase the voltage of AC power supplies. The secondary winding has more turns than the primary winding. It is essential to minimize energy losses during long-distance power transmission by using higher voltages. A step-up transformer boosts voltage before electricity enters transmission lines at power plants. Voltage increases allow efficient and economical power distribution throughout extensive networks, improving the grid’s reliability and stability.

3-Step Down Transformer:

Power distribution also requires a step-down transformer. Basically, it lowers the voltage of an AC power supply so it can be distributed locally. There are fewer turns in the secondary winding of this transformer. A step-down transformer converts high-voltage electricity from transmission lines to levels suitable for homes, businesses, and industries. As a result, electrical devices receive the appropriate voltage for safe and efficient operation.

Where 24V Transformers are Commonly Used?

Knowing where 24V transformers are commonly deployed will help you understand their practical significance. Transformers of this type are widely used in residential, commercial, and industrial settings. As examples, they power doorbell systems, control relays in HVAC systems, and facilitate lighting in landscapes and architectural designs. Numerous applications make them a valuable asset.

How to test 24v transformer with multimeter? Complete Guide

Now the time comes to learn how to test 24v transformer with multimeter effectively. Here are the step by step guide:

How to Test 24V Transformer With Multimeter

Step 1: Safety Precautions

Ensure your safety before testing a 24V transformer with a multimeter. If working with AC voltage, turn off the power source and be cautious of electric shocks. Make sure you are wearing the appropriate safety gear, such as insulated gloves and goggles.

Step 2: Identify the Transformer Windings

Transformers usually have two sets of windings: a primary winding (input) and a secondary winding (output). A primary winding applies voltage, while a secondary winding measures output voltage.

Step 3: Set Your Multimeter

Set your multimeter to AC voltage mode. A 50V or 100V range should be able to accommodate at least 24V.

Step 4: Primary Winding Connection

Connect one probe of your multimeter to the high voltage primary winding terminal, and the other probe to the low voltage primary winding terminal (usually marked “L” for low voltage).

Step 5: Testing the Primary Winding

In the case of an off power source, you will have to turn it on. You should now be able to see the voltage applied to the primary winding on your multimeter. It should be close to 24 volts, within the expected range.

Step 6: Secondary Winding Connection

Disconnect the probes from the primary winding terminals. The first probe should be connected to one of the secondary winding terminals, and the second probe should be connected to the remaining secondary winding terminal. Terminals are often labeled differently, such as “COM” for common and “V” for voltage.

Step 7: Testing the Secondary Winding

Your multimeter should now display the secondary winding’s output voltage while the power source is still on. The voltage should also be close to 24 volts.

Step 8: Measuring resistance

Disconnect the transformer from the power source first. Select the resistance (ohms) setting on your multimeter. Connect one probe to one of the input terminals and the other probe to the corresponding terminal for the primary winding. Keep a record of the resistance value displayed on multimeter. 

How to Test 24V Transformer With Multimeter

In the secondary winding, connect one probe to one output terminal and the other probe to the corresponding terminal. Record the resistance reading. There should be consistent resistance values on both windings of a healthy transformer, and any significant deviation could indicate a problem

Symptoms of a bad 24V transformer

The 24V transformer is a crucial component of many electrical systems, including HVAC systems and control circuits. It can cause a variety of problems when it malfunctions. Below are some signs of a bad 24V transformer:

1. Voltage Fluctuations:

There is a clear indication of a malfunction when there is a noticeable drop or surge in the output voltage from the 24V transformer. Inconsistent performance of connected devices can be caused by fluctuations in transformer wiring or coils.

2. Overheating:

An excessive amount of heat emanating from the transformer indicates a problem. Transformers can overheat due to overloading, loose connections, or short circuits. Transformers and surrounding components can be damaged by prolonged overheating.

3. Unusual Noise:

An uncharacteristic buzzing, humming, or clanking sound is usually a sign of trouble with the transformer. Noises such as these may indicate loose windings, faulty cores, or worn insulation. Further damage can be prevented by addressing these issues promptly.

4. Burnt or Discolored Wires:

Wires connected to the transformer should be inspected. A burnt or discolored insulation on the wires indicates excessive heat or arcing. To prevent further damage, it’s important to resolve the underlying problem, which could be overloading or a short circuit.

5. Frequent Fuse Blowing:

Overcurrent or short-circuit issues can be detected by frequently blowing fuses in the circuit connected to the 24V transformer. In addition to pointing to a problem with the transformer, this also poses a risk to the entire system as a whole.

6. Inconsistent Output:

Inconsistent 24V output voltage can cause erratic behavior in connected equipment. It may be caused by irregular windings, corrosion, or damaged terminals. Stability of a system depends on testing the voltage and rectifying any variations.

7. Overloaded Transformer:

Transformers operated near or above their rated capacity can overheat, drop voltage, and have shorter lifespans. Transformers must be appropriately sized for the load they are handling in order to prevent these problems.

How to replace a 24V transformer?

The replacement of a 24v transformer is essential if you notice any sign that your current transformer is faulty.

How to Test 24V Transformer With Multimeter

Step 1. Safety Precautions:

Safety should always be the first priority when working with electricity. Power should be turned off at the source, and personal protective equipment (gloves, safety glasses) should be worn.

Step 2. Gather Tools and Materials:

You will need a replacement transformer for 24V, a screwdriver, wire strippers, wire nuts, and a voltage tester.

Step 3. Locate the Existing Transformer:

Locate your current 24V transformer. It is usually located within an electrical control panel, near the thermostat, or in the HVAC system. Consult your equipment’s manual or seek professional assistance if you’re unsure.

Step 4. Turn Off Power:

At the breaker panel, identify the circuit that powers the transformer and shut it off. Verify that the transformer does not have live electricity by using a voltage tester.

Step 5. Disconnect Wiring:

Disconnect the wiring using a screwdriver from the old transformer carefully. Label or draw a diagram of the wires to remember their connections. There are normally low-voltage wires (often labeled “C” for common, “R” for power, and “W” for heat) and high-voltage wires (120V or 240V).

Step 6. Remove the Old Transformer:

It is necessary to disassemble the old 24V transformer and remove it from its mounting location by unscrewing it. These can be heavy and may be connected to conduit and other electrical components. Make a note or mark on the old transformer component, this will help you mount the new one.

Step 7. Mount the New Transformer:

Replace the transformer in the same location as the old one. Maintain proper operation by securing it securely and leveling it.

Step 8. Connect the Wiring:

Connect the low-voltage and high-voltage wires to the new transformer. Verify that the connections match your labels or diagram to avoid any errors.

Step 9. Test the System:

Ensure your HVAC or electrical system is working properly by turning on the power at the breaker panel. Make sure there are no unusual noises or malfunctions.

Step 10. Troubleshooting:

Consult the manufacturer’s instructions for troubleshooting tips if you encounter any issues. You should always consult a professional electrician or HVAC technician if you’re unsure about any aspect of the replacement process.

Final Wrap-Up

Knowing how to test 24V transformer with multimeter is not as challenging as you might think before you read this post. If you notice a faulty sign, it is recommended that you replace it. When replacing new 24V transformers, most people make mistakes. There are several mistakes that can be made, including not marking when removing the old transformer, not purchasing the same old transformer, and not securing the components tightly. When adjusting a new 24V transformer, make sure all components are tight.

Engr. Amna has been working with on multimeterworld from 2019 and have worked on multiple projects as team leader. He is currently working in JDW Sugar mills and love to write electrical testing guides. His aim is to help 1 million people each year.