Inductor and Transformer Testing Methods and Experience

Inductor and Transformer Testing Methods and Experience

1.Detection of the color

code inductor Put the multimeter in the R×1 gear, and connect the red and black test leads to any lead end of the color code inductor. At this time, the pointer should swing to the right. According to the measured resistance value, it can be divided into the following three situations for identification: A.The resistance value of the measured color code inductor is zero, and there is a short-circuit fault inside. B. The DC resistance value of the measured color code inductor is directly related to the diameter of the enameled wire used to wind the inductor coil and the number of turns. As long as the resistance value can be measured, the measured color code inductor can be considered normal

2. Detection of mid-circle transformer

A. Set the multimeter to the R×1 gear, and check the on-off condition of each winding one by one according to the arrangement rule of each winding pin of the mid-circle transformer, and then judge whether it is normal. 

B. Test the insulation performance. Place the multimeter in the R×10k block and do the following state tests: (1) The resistance between the primary winding and the secondary winding; (2) The resistance between the primary winding and the case; (3) ) The resistance value between the secondary winding and the housing. The above test results are divided into three situations: (1) The resistance value is infinite: normal; (2) The resistance value is zero: there is a short-circuit fault; (3) the resistance value is less than infinity but greater than zero: there is a leakage fault.

3. Detection of power transformer

A. Check the appearance of the transformer to see if there is any obvious abnormality. Such as whether the coil lead is broken, de-soldering, whether the insulating material has burnt marks, whether the iron core fastening screw is loose, whether the silicon steel sheet is rusted, whether the winding coil is exposed, etc.  

B. insulation test. Use the multimeter R×10k block to measure the resistance between the core and the primary, the primary and the secondary, the core and the secondary, the electrostatic shielding layer and the sub-second, and the secondary windings. The pointer of the multimeter should point to the infinity position. move. Otherwise, the insulation performance of the transformer is poor. 

C. coil on-off detection. Put the multimeter in the R×1 gear. During the test, if the resistance value of a certain winding is infinite, it means that the winding has an open-circuit fault. 

D. distinguish primary and secondary coils. The primary and secondary pins of the power transformer are generally drawn from both sides, and the primary windings are mostly marked with 220V, and the secondary windings are marked with rated voltage values, such as 15V, 24V, 35V, etc. Then identify based on these marks. 

E. detection of no-load current. (a) Direct measurement method. Open all secondary windings, and place the multimeter in the AC current block (500mA, serially connected to the primary winding. When the plug of the primary winding is plugged into 220V AC mains, the multimeter indicates the no-load current value. This value should not be It is greater than 10% to 20% of the full load current of the transformer. Generally, the normal no-load current of the power transformer of common electronic equipment should be about 100mA. If it exceeds too much, the transformer has a short-circuit fault. (b) Indirect measurement method. In the transformer A 10/5W resistor is connected in series in the primary winding, and the secondary is still no-load. Set the multimeter to the AC voltage block. After powering up, use two-meter pens to measure the voltage drop U at both ends of the resistor R, and then use Ohm's law to calculate the no-load Current I empty, that is, I empty = U/R. 

F. No-load voltage detection. Connect the primary of the power transformer to 220V mains, and use a multimeter to measure the no-load voltage of each winding (U21, U22, U23). , U24) should meet the required value, and the allowable error range is generally: high-voltage winding ≤±10%, low-voltage winding ≤±5%, and the voltage difference between the two sets of symmetrical windings with a center tap should be ≤±2%. 

G.general low-power power supply The allowable temperature rise of the transformer is 40℃～50℃. If the insulating material used is of good quality, the allowable temperature rise can be increased. H detection distinguishes the end of each winding with the same name. When using a power transformer, sometimes in order to obtain the required secondary voltage, Two or more secondary windings can be used in series. When using the power transformer in series, the same-named ends of the windings that participate in the series must be connected correctly and cannot be mistaken. Otherwise, the transformer will not work normally. I. Power transformer Comprehensive detection and identification of short-circuit faults. The main symptoms of a short-circuit fault in a power transformer are severe heating and abnormal output voltage of the secondary winding. Generally, the more short-circuit points inside the coil, the greater the short-circuit current, and the transformer heats up more serious. The simple way to detect whether the power transformer has a short-circuit fault is to measure the no-load current (the test method has been introduced above). The no-load current value of the transformer with a short-circuit fault will be much greater than 10% of the full-load current. When short-circuited In severe cases, the transformer will quickly heat up within tens of seconds after the no-load power is applied, and it will feel hot to touch the iron core with your hands. At this time, it can be concluded that the transformer has a short-circuit point without measuring the no-load current.