Hello everyone, welcome to the ZimZim DIY channel. Today, I will explain the working principle of an electronic device called a varistor. This device is a type of semiconductor device with a main structure made of zinc oxide. Its advantage is that it can change its resistance value according to the voltage level. If we look at a general resistor, it will have a single resistance value, right? Whichever value it is, that's it. Or a variable resistor, it has to be manually rotated by hand to change the resistance value. But with a varistor, its resistance value depends on the voltage. When V is higher than normal, it will change the value of R to decrease. Its real name is (metal oxide varistor). So, the foreigners took the first letters of each syllable and combined them to call it MOV. Many of you may have heard that a varistor is a device that can protect electrical appliances from lightning strikes. In fact, it can really protect. But it's sad because it will sacrifice itself so that other electronic devices can survive safely. Therefore, electricity will flow through it as one of the first devices. If you look at the UPS board, you will see that it is placed as the input of the circuit here. It will be covered with a rubber tube. It may prevent the fragments from flying far when it explodes. How do you know that this device is a varistor? 1. Look at it. It will be screen printed with letters. Most of them will start with these letters: MOV, ZOV, TMOV, ZOV, CNR, CVR, TVR, ZNR, DNR, KVR, VDR, or varistor, also called VDR Voltage Dependent Resistor. We will also see the names VDR, CNR, CVR, TVR, ZNR, DNR, KVR used as well. 2. Look at the circuit board. It will be screen printed according to the letters I just mentioned, or it will be a varistor symbol, it will look something like this. As for connecting and using. Mostly, I see there are 2 types. The first type is a two-wire circuit pattern, L and N. They will connect a varistor across both of these patterns. The second type is a 3-wire circuit pattern, with both L, N and G. They will place the varistor L against the ground, N against the ground, and L against the N. There are three of them. If you look at the standard lightning protection power plugs, some models, such as the one I took apart, you will see that the company will also connect varistors across every power path. Normally, 220V home voltage should have some varistor voltage. It is not true that 220V home voltage will have exactly 220V varistors. Because sometimes the home voltage may exceed 230V - 240V. I have seen it before. Therefore, he will reserve more volts and may also add % of malfunction and RMS. Therefore, the varistor used with household electricity that we see will be around 275V. In my understanding, I would like to divide it into 4 operating periods as follows: Period 1 Normal use, let's say we use a 275V varistor connected across L and N. Nothing will happen if the voltage does not exceed the specified value because the varistor has a very high resistance value that is infinite and cannot be measured. Period 2 When the voltage is slightly higher than the specified value, it will work similar to a zener diode, which is that it will try to maintain the voltage as before. Excess voltage or excess current will try to absorb some of it and pull some of it down to the neutron. Now we can still maintain the voltage level in a normal condition. Period 3 When the voltage is even higher than before, the varistor will act to divide the electric current to itself more and more. And now the varistor's resistance value starts to decrease a lot. When the resistance decreases a lot, more current can flow through it. The breaker sees an abnormality, causing a leak. It will cut off the work. But the Varistor is actually often used with a fuse, such as placing a 15 A fuse in series at the Line. If the power is too high, it is like we are touching two wires and shorting them. The fuse filament will overheat until it breaks. After that, we find a new fuse to put in. The circuit board will be able to work normally again. And the fourth phase, lightning strikes. There will be a huge voltage along the wire. The electricity flowing through the wire meets the varistor. The varistor will not hesitate and explode immediately. The varistor is shorted, causing the fuse to blow. If we just change the fuse, it will still blow because the varistor is shorted. If we put in a new fuse, it will short again. Therefore, we must replace the new varistor first and then put in the new fuse. Then the machine will work normally again. In conclusion, the varistor is used to protect various devices from being damaged when the electric current or voltage in the circuit changes to a high level. We are familiar with the varistor as blue like this. If we look at it superficially, it is similar to a capacitor. In any case, friends must check carefully first. The commonly used ones have a diameter of 5 mm - 32 mm.