In household appliances, a power supply is often used, in the event of failure of which it is important to know how to check the transformer with a multimeter. This will significantly reduce equipment repair costs. It will be enough to order a new or repair an old transformer. If you do it yourself, saving on diagnostics will be significant.
Methods
It is advisable to familiarize yourself in advance with the question of how to check the transformer with a multimeter. This is the easiest way to fix the problem and save on repairs. Coils can be diagnosed by measuring resistance in ohmmeter mode. In the process of measurements, the goal is to determine the state of the windings by the quantitative characteristics of resistance, current, voltage.
You can figure out how to check the transformer with a multimeter, if you consider the simplest electrical circuit. In the connections use: load resistance, supply circuit, transformer windings. Measurements are carried out in the mode of an ammeter, voltmeter. Compare the obtained values with the passport values.
External inspection of damaged windings helps to simplify the diagnostic task and quickly figure out how to check the transformer with a multimeter. First of all, measurements are taken at terminals having damaged insulation or charred areas. Resistance is often underestimated in such cases or a short circuit is observed at all.
Resistance
Much more often, the ohmmeter mode is used when deciding how to check the health of a transformer with a multimeter. In the process of the so-called "continuity", the conclusions of the windings are determined if there is no marking. The input winding often has a high resistance of up to hundreds of ohms - this is a step-down transformer.
The smaller the dimensions of the transformer, the higher the resistance values of the primary winding will show the measurement with a multimeter. A cliff will be immediately visible on the screen, as a short circuit will show an infinity sign. Each terminal of the winding is called on the transformer housing to eliminate leakage currents. The latter lead to low voltage and deviation of the device from the nominal modes.
Voltage
Transformer windings can be checked by measuring the input and output voltages. The dt 832 multimeter will help in this, which is first determined with the leads of the windings in ohmmeter mode. A voltage is applied to the primary (it has high resistance for step-down devices), a voltmeter is connected to the secondary (lower resistance).
In the dt 832 voltmeter mode, the deviation of the received voltage from the passport data is measured. If the error exceeds 20%, then we can conclude that the transformer is faulty. In this case, there is an interturn circuit. Carefully inspect the windings for carbonization of the insulation.
When you turn on the network after a while, you can smell the burning, this continues to melt the insulation. Such a transformer is no longer recommended to load, it has already failed. Another clear evidence of the inter-turn circuit is the increased heating of the winding with a slight load or in idle mode.
Nuances
Some transformer windings cannot be ringing. It is recommended to pay attention to the presence of a microassembly soldered into the transformer case. This can be a rectification circuit on the output winding or an interference filter.
The winding may not ring at high resistance, the absence of readings in this case does not indicate a malfunction. Also do not forget to check the short circuit to the case, if the resistance of the windings is in order. Each terminal of the device is tested.
Unstable operation of the transformer may be associated with voltage fluctuations in the supply network. Moreover, the value of idling, when only the first winding is connected, will be within acceptable limits. Under load, however, the power will significantly “sag”.
Typical malfunctions
When diagnosing the technical condition of the transformer, the following types of malfunctions are identified:
- Open winding - resistance infinity.
- Inter-turn short circuit - resistance below the table values.
- Deviations of voltage and current.
- Short to the case - the winding melts, the power fuse blows.
Externally, you can determine the type of transformer, the purpose is determined according to the electrical circuit. The lowering wire is thicker at the output, the raising wire is thicker at the input. Accordingly, the primary winding of the step-down has a high resistance, and the step-up value is higher at the output.
The windings of a powerful device cannot be checked with a multimeter . In this case, special devices and additional electrical networks are used for diagnostics. In ohmmeter mode, you can check almost all household transformers: in chargers, televisions and other devices.