How to test a transformer with a multimeter? Instruction

2024 Author: Henry Conors | [email protected]. Last modified: 2024-02-12 02:42

It is often necessary to familiarize yourself in advance with the question of how to test a transformer. After all, if it fails or becomes unstable, it will be difficult to look for the cause of equipment failure. This simple electrical device can be diagnosed with a conventional multimeter. Let's see how to do it.

What is the equipment?

How to check a transformer if we don't know its design? Consider the principle of operation and varieties of simple equipment. Coils of copper wire of a certain section are applied to the magnetic core so that there are leads for the supply winding and the secondary.

Energy is transferred to the secondary winding in a non-contact way. Here it becomes almost clear how to check the transformer. Similarly, the usual inductance is called with an ohmmeter. The turns form a resistance that can be measured. However, this method is applicable when the target value is known. After all, the resistance can change up or down as a result of heating. This is called inter-turn shorting.

Such a device will no longer provide reference voltage and current. The ohmmeter will only show an open circuit or a complete short circuit. For additional diagnostics, a short circuit test to the case is used with the same ohmmeter. How to test a transformer without knowing the terminals of the windings?

This is determined by the thickness of the outgoing wires. If the transformer is step-down, then the lead wires will be thicker than the lead wires. And, accordingly, on the contrary: the booster wires are thicker. If two windings are output, then the thickness may be the same, this should be remembered. The surest way to look at labels and find equipment specifications.

Views

Transformers are divided into the following groups:

• Breaking and raising.
• Power often serve to reduce the supply voltage.
• Current transformers for supplying the consumer with a constant current value and holding it in a given range.
• Single and multi-phase.
• Welding purpose.
• Pulse.

Depending on the purpose of the equipment, the principle of approach to the question of how to check the transformer windings also changes. A multimeter can only ring small devices. Power machines already require a different approach to troubleshooting.

Dial method

The ohmmeter diagnostic method will help with the question of how to check the power transformer. The resistance between the terminals of one winding begins to ring. This establishes the integrity of the conductor. Before this, the body is inspected for the absencedeposits, sagging as a result of heating equipment.

Next, measure the current values in Ohms and compare them with the passport. If there are none, then additional diagnostics under voltage will be required. It is recommended to ring each output relative to the metal case of the device, where the ground is connected.

Before taking measurements, disconnect all ends of the transformer. It is also recommended to disconnect them from the circuit for your own safety. They also check for the presence of an electronic circuit, which is often present in modern power models. It should also be desoldered before testing.

Infinite resistance speaks of a whole isolation. Values of several kilo-ohms already raise suspicions about a breakdown on the case. It can also be due to accumulated dirt, dust or moisture in the air gaps of the device.

Energized

Energized testing is done when the question is how to test a transformer for an interturn short circuit. If we know the value of the supply voltage of the device for which the transformer is intended, then measure the idle value with a voltmeter. That is, the output wires are in the air.

If the voltage value differs from the nominal value, then conclusions are drawn about the interturn short circuit in the windings. If crackling, sparking is heard during operation of the device, then it is better to turn off such a transformer immediately. He is defective. There are tolerances formeasurements:

• Voltage values may vary by 20%.
• For resistance, the norm is a spread of values of 50% of the passport.

Ammeter measurement

Let's figure out how to check the current transformer. It is included in the chain: regular or actually made. It is important that the current value is not less than the nominal value. Measurements with an ammeter are carried out in the primary circuit and in the secondary.

The current in the primary circuit is compared with the secondary readings. More precisely, the first values are divided by those measured in the secondary winding. The transformation ratio should be taken from the reference book and compared with the calculations obtained. The results should be the same.

The current transformer must not be measured at no load. In this case, too high voltage may form on the secondary winding, which can damage the insulation. You should also observe the polarity of the connection, which will affect the operation of the entire connected circuit.

Typical malfunctions

Before you check the microwave transformer, we will give frequent types of breakdowns that can be fixed without a multimeter. Often, power supplies fail due to a short circuit. It is established by inspecting circuit boards, connectors, connections. Mechanical damage to the transformer case and its core occurs less frequently.

Mechanical wear of transformer lead connections occurs on moving machines. Large Feederswindings require constant cooling. In its absence, overheating and melting of the insulation is possible.

TDKS

Let's figure out how to check the pulse transformer. An ohmmeter can only establish the integrity of the windings. The operability of the device is established when connected to a circuit where a capacitor, a load and a sound generator are involved.

A pulse signal is sent to the primary winding in the range from 20 to 100 kHz. On the secondary winding, measurements are made with an oscilloscope. Establish the presence of pulse distortion. If they are absent, they draw conclusions about a working device.

Distortion of the oscillogram indicates damaged windings. It is not recommended to repair such devices yourself. They are set up in the laboratory. There are other schemes for checking pulse transformers, where they investigate the presence of resonance on the windings. Its absence indicates a faulty device.

You can also compare the shape of the pulses applied to the primary winding and output from the secondary. A shape deviation also indicates a transformer failure.

Multiple windings

For resistance measurements, the ends are freed from electrical connections. Choose any output and measure all resistances relative to the rest. It is recommended to write down the values and mark the checked ends.

So we can determine the type of winding connection: with mediumoutputs, without them, with a common connection point. More often found with a separate connection of the windings. Measurement can be done with only one of all the wires.

If there is a common point, then we will measure the resistance between all available conductors. Two windings with a middle terminal will only make sense between the three wires. Multiple terminals are found in transformers designed for operation in several networks with a nominal value of 110 or 220 Volts.

Diagnosis nuances

The rumble during transformer operation is normal if it is a specific device. Only sparking and crackling indicate a malfunction. Often the heating of the windings is the normal operation of the transformer. This is most often seen with step-down devices.

Resonance can be created when the transformer case vibrates. Then you just need to fix it with insulating material. The operation of the windings changes significantly with loose or dirty contacts. Most of the problems are solved by stripping the metal to a shine and re-wrapping the leads.

When measuring voltage and current values, the ambient temperature, the magnitude and nature of the load should be taken into account. Supply voltage control is also required. Checking the frequency connection is mandatory. Asian and American appliances are rated at 60 Hz, resulting in lower output values.

Incorrect connection of the transformer may cause a malfunction of the device. Under no circumstances should direct voltage be connected to the windings. The coils will melt quickly otherwise. Accuracy in measurements anda competent connection will help not only to find the cause of the breakdown, but also, possibly, eliminate it in a painless way.