Checking transformers and inductors. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Measuring technology

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When repairing electronic equipment, it may be necessary to quickly check the discrete components of the device. When all possible versions of the malfunction have been worked out and turned out to be ineffective, it remains to pay close attention to transformers and inductors.

Inductors, chokes, transformers are checked visually or for an open circuit using an ohmmeter. A simple method for checking winding inductors and transformers for continuity is with an ohmmeter in resistance measurement mode. To detect short-circuited turns inside the coil, the circuit shown in Fig. 1 is recommended.

Ris.1

At the output of the generator of sinusoidal oscillations, a frequency of 1 kHz is set and a signal with an amplitude of 5 V is applied through the resistor R1 to the tested winding L1. The resistance of the limiting resistor depends on the amplitude of the generator signal, which is selected depending on the parameters of the tested coil L1. When the amplitude of the output pulses of the generator is 5 V, the resistance of the resistor is chosen within 1 kOhm. The voltage on the winding L1 at point A is controlled using an oscilloscope. The appearance of differentiated pulses at point A indicates the presence of a short-circuited turn in the coil winding. This method has proven to be effective and affordable in a conventional home laboratory.

In practice, transformer failures often occur, and due to the short circuit of the secondary windings, there is a risk of electric shock. Of course, it is also possible to check the transformer windings for suitability visually, for example, if smoke comes out of the transformer when it is turned on and there is a specific smell of burning, and it does not matter how many good windings it has and what the nature of the fault is, because such a transformer is not practical to use in the future. However, if there are no visual signs of a malfunction, there is an alternative method. The second test method proposed below allows you to detect short-circuited windings in a power transformer.

An alternating voltage from 2 to 1 V is applied to the primary winding T1 from the autotransformer T15 through an EL25 incandescent lamp, the power of which is 0 ... 170 W (it should approximately correspond to half the power of the tested power transformers).

When first powered up, the output voltage of the autotransformer must be set to "0". After that, in the device assembled according to the scheme of Fig. 2, the output voltage of the autotransformer is smoothly brought to the maximum value (150 ... 170 V). An industrial LATR 220/170-50-20 or another similar one is used as an autotransformer.

Ris.2

At this stage of the test, with the tested transformer T2 in good condition, the indicator lamp EL1 should not light. If the EL1 lamp still lights up, then there are short-circuited turns in the secondary (secondary) winding. This will be confirmed by the absence of a change or a slight change in the filament of the EL1 lamp.

For power transformers with several windings, each secondary winding is checked.

Author: A.P. Kashkarov

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