Transformers are passive electromechanical components that operate on the principle that every electrical field generates a magnetic field, and every magnetic field generates an electrical field. This allows the isolation of 2 electrical circuits by having the first electrical circuit create a non electrically conductive magnetic field. The second electrical circuit then recovers the energy from the generated magnetic field. Use these tips to learn how to test a transformer.
1Inspect the transformer visually. Overheating, which causes the internal wiring of the transformer to run at elevated temperatures, is a common cause of transformer failure. If the transformer exterior is bulged or shows what appear to be burn marks, don't test the transformer.
2Determine the wiring of the transformer. The transformer should be clearly labeled. However, it is always best to obtain a schematic of the circuit containing the transformer to determine how the transformer is connected. The schematic for the circuit will be available in the product documentation or on the website of the circuit manufacturer.
3Identify the transformer inputs and outputs. The first electrical circuit, which is generating the magnetic field, will be connected to the primary of the transformer. The voltage being supplied to the primary should be on both the transformer label and the schematic. The second circuit that is receiving power from the magnetic field will be connected to the secondary of the transformer. The voltage being generated by the secondary should be on both the transformer label and the schematic.
4Determine the output filtering. It is common to attach capacitors and diodes to the transformer secondary to shape the AC power from the output into DC power. This filtering and shaping will not be available from the transformer label. The filtering and shaping will be shown on the schematic.
5Prepare to measure circuit voltages. Remove covers and panels as necessary to gain access to the circuits that contain the transformer. Acquire a digital multimeter (DMM) to take the voltage readings. DMMs are available at electrical supply stores and hobby shops.
6Confirm proper input to the transformer. Apply power to the circuitry. Use the DMM in AC mode to measure the transformer primary. If the measurement is less than 80 percent of the expected voltage, the fault could lie in either the transformer or the circuitry providing the primary with power. In this case, the primary must be separated from the input circuit. If the input power (not the disconnected transformer primary) climbs to the expected value, then the primary of the transformer is bad. If the input power does not climb to the expected value, then the problem lies not with the transformer, but with the input circuitry.
7Measure the secondary output of the transformer. If you have determined that there is no filtering or shaping being performed by the secondary circuitry, use the AC mode of the DMM. If there is filtering and shaping in the secondary circuitry, use the DC scale of the DMM. If the expected voltage is not present on the secondary, either the transformer or a filtering or shaping component is bad. Test the filtering and shaping components separately. If the testing of the filtering and shaping components shows no problems, then the transformer is bad.
- Do not assume that the primary side and secondary side of the transformer are referenced to the same electrical ground. The transformer primary and secondary are frequently referenced to different grounds. Be aware of this split grounding while taking measurements.
- A buzzing or cracking sound is frequently an early sign that a transformer is about to develop a burn.
- While the circuits are exposed and energized for testing, accidental contact with circuit power could cause injury. Touch the circuit only with the probes of the DMM.
Things You'll Need
- Schematic of the circuit
- Digital Multimeter (DMM)
Categories: Motors Generators and Transformers
In other languages:
Thanks to all authors for creating a page that has been read 201,440 times.