How To Test Safety Capacitor | Hacker Noon

The capacity of a fixed safety capacitor below 10pF is too small, so if you use a multimeter to measure, you can only qualitatively check whether it has

. When measuring, you can use a multimeter R×10k block. Use two test leads to connect the two pins of the capacitor. Resistance should be unlimited. If the measured resistance value (the pointer swings to the right) is zero, it indicates that the capacitor is leaking damage or internal breakdown.

Test whether the 10PF~01μF fixed safety capacitor has charging phenomenon, and then judge whether it is good.

The multimeter uses R×1k gears. The β value of both transistors is greater than 100, and the penetration current is very small. silicon

For example, 3DG6 can be used to form composite pipes. The red and black test leads of the multimeter are respectively connected to the emitter e and collector c of the composite tube. Due to the amplification effect of the composite triode, the charge and discharge process of the capacitor under test is amplified, and the pointer swing of the multimeter increases, which is convenient for observation.

 During testing, especially when testing small-capacity safety capacitors, it is necessary

In the test, contact with A and B to clearly see the movement of the pointer of the multimeter.

C For safety capacitors greater than 0.01μF, the R×10k range of the multimeter can be used to directly test the charging process of the capacitor and internal short circuit or leakage, and the capacity of the capacitor can be estimated based on the amplitude of the capacitor. The pointer swings to the right.

(1) Because of capacity

JEC safety capacitors are much larger than general fixed capacitors, so appropriate ranges should be used for different capacities when measuring. According to experience, the R×1k block can usually be used to measure the capacitance between 1~47μF, and the R×100k block can be used to measure the capacitor larger than 47μF.

(2) Connect the red test lead of the multimeter to the negative pole and the black test lead to the positive pole. When contacted, the pointer of the multimeter will deflect to the right by a larger deflection (for the same electronic fence, the greater the capacity, the greater the swing), and then gradually turn to the left until it stops at a certain position. The resistance at this time is the forward leakage resistance of the electrolytic capacitor, which is larger than the reverse resistance value

.

Practical experience shows that the leakage resistance of electrolytic capacitors should generally exceed several hundred kΩ. Otherwise, it will not work properly. In the test, if there is no charge in the forward and backward directions, the pointer is not moving.

This means that the capacity disappears or the internal circuit is damaged; if the measured resistance is very small or zero, it means that the capacitor has

Either

. Can no longer be used.

(3) For electrolytic capacitors with unknown signs, the above method of measuring leakage resistance can be used for judgment. That is to say, you must first measure the leakage resistance arbitrarily, remember its size, and then replace the test lead to measure the resistance value. The larger resistance value in the two measurements is the positive connection method.

More specifically, the black test lead is connected to the positive electrode, and the red test lead is connected to the negative electrode. Then, using the resistance profile of the multimeter and the positive and negative charging method of the electrolytic capacitor, the capacity of the electrolytic capacitor can be estimated according to the amplitude of the pointer swing to the right.

(1) Rotate the shaft gently by hand, it should feel very smooth, and will not feel tight or sometimes stuck. When pushing the load shaft forward, backward, upward, downward, leftward, rightward, etc., the shaft should not be loose.

(2) Rotate the shaft with one hand, and touch the outer edge of the film set with the other hand, and don't feel any looseness. The variable capacitor with poor contact between the rotating shaft and the moving blade is no longer used.

(3) Set the multimeter at the position of R×10k. Connect the two test leads to the moving and fixed parts of the instrument with one hand

, Slowly rotate the shaft several times with the other hand. The pointers of the multimeter should all be fixed at infinity.

In the process of rotating the axis, if the pointer sometimes points to zero, it means that there is a short-circuit point between the moving part and the fixed part; if an angle is encountered, the multimeter reading is not infinite, but a certain resistance value. Indicates that the variable capacitor is moving. There is a leak between the sheet and the fixed sheet.

4. What tests have been made on the safety capacitor before leaving the factory? What is the difference with ordinary capacitors?

(1) Safety capacitors need to do a lot of testing and inspection certification. The main difference is

. use

, The flame retardant effect may be better. From a material point of view, they are no different.

(2)

 It is different from safety capacitors in some aspects.

(3) Safety capacitors are mainly used to suppress interference and are divided into X-type and Y-type.

Used to suppress differential mode interference. Generally, it is connected to L and N in four levels. The withstand voltage of each grade is different. Will not cause harm to human body when it fails.

In order to suppress common mode interference,

There are usually four levels between L and G. Leakage current is very common. The circuit choice is generally to use cheaper ceramic capacitors, the disadvantage is that the leakage current is large.

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