Introduction to common types of power plugs measured by multimeter
One Transformer type
This power supply method is generally used in electrical appliances such as radios, recorders, speakers, black and white televisions, and early remote-controlled televisions.
The power plug is directly connected to the power transformer or standby transformer, and some may add a power switch in the middle.
When measuring, turn on the power switch and use a multimeter to measure the two pins of the power plug. At this time, the primary coil of the transformer inside the machine is measured, and the resistance value is generally between a few hundred and two thousand ohms.
II Switching power supply type
This type of electrical appliance is now the most common. Various mobile phone chargers, power adapters, and most LED lighting fixtures belong to this type
When measuring, the Rx 1K or R × 10K range of the pointer multimeter can be selected. At the beginning, the resistance will show a small value and gradually increase. It is similar to the scenario of measuring small capacity electrolytic capacitors.
But this measurement is only limited to pointer meters. Due to the low output voltage of most digital meters, it is difficult to break through the cutoff area of the rectifier bridge, so it is possible that the resistance value cannot be measured.
III Simple electric heating appliances
Electric heating appliances mainly include electric heaters, electric kettles, and rice cookers. They usually use mechanical temperature control switches to control the heating wire for heating. Since we usually measure at room temperature, when the temperature control switch is turned on, the measured resistance is the resistance of the heating wire.
The resistance of this type of electric heating wire is usually below 100 Ω. The term 'simple' in the subheading mainly refers to electric rice cookers. Because the control circuit of some multifunctional rice cookers needs to be powered on to work, using a multimeter directly to measure the resistance may not be able to measure it.
4 Resistance capacitance voltage reduction type
Resistive capacitive voltage reduction type is generally used in low-end low-power appliances, such as LED bulb lights, small flashlights, or chargers inside razors.
Due to the small capacity of capacitors, it is difficult to measure with a multimeter. But there will be a discharge resistance of several hundred K to 1M Ω on the capacitor, so the measured resistance will be the series resistance between this resistance and the load. Its value will be slightly greater than the discharge resistance.
For the measurement of the above four situations, pointer or digital meter can be used for the first and third, while pointer meter must be used for the second and fourth.
Due to the diverse design of power supplies nowadays, it is difficult to accurately determine the quality of electrical appliances solely by measuring the power plug. But in most cases, the measurement results can serve as the basis for whether the tested electrical appliance can be powered on for trial operation, which can minimize accidents caused by sudden power on.
