A varistor, or voltage-dependent resistor, is an electronic component used to protect circuits from damage caused by overvoltage. They are commonly found in power supplies, surge protectors, and other electrical devices. If you need to test a varistor, it’s important to know how to do it properly. In this article, we will discuss the different ways to test a varistor and provide some useful tips on how to get the most accurate results. Let’s get started!
What is a Varistor?
A varistor is a semiconductor device that is used to protect electronic circuits from overvoltage and transient voltage events. Varistors are also called voltage-dependent resistors (VDRs), because their resistance changes in response to an applied voltage.
There are two types of varistors: metal oxide varistors (MOVs) and silicon carbide varistors (SICs).
MOVs are the most common type of varistor. They are made from a mixture of metal oxides, such as zinc oxide (ZnO), manganese dioxide (MnO), and lead dioxide (PbO). MOVs are typically used to protect against transient voltage events, such as lightning strikes or power surges.
Varistors in general are commonly used in consumer electronics, such as televisions, computers, and cell phones. They are also used in industrial controls, telecommunications equipment, automotive electronics, and other applications. Varistors are manufactured in a variety of shapes and sizes, depending on the field of use. [1], [2]
How do Varistors Work?
The resistance of a varistor decreases as the voltage across it increases. This makes varistors ideal for protecting electronic circuits from overvoltage and transient voltage events. Varistors are typically used in parallel with the circuit to be protected. When a transient voltage event occurs, the increased current flow through the varistor causes its resistance to decrease, which limits the amount of current that can flow through the protected circuit. This prevents damage to the electronics in the circuit.
Varistors are also used to protect against lightning strikes. In this application, a large number of varistors are connected in parallel and installed on top of or near an electronic device that is susceptible to lightning damage. When a lightning strike occurs, the high current flows through all of the varistors, which limits the current flowing through the device and prevents damage.
They can also be used to protect circuits from voltage transients caused by switching power supplies and inductive loads. In these applications, the varistor is placed in series with the circuit to be protected. When a transient voltage event occurs, the increased current flow through the varistor causes its resistance to decrease, which limits the amount of current that can flow through the protected circuit. This prevents damage to the electronics in the circuit.
The ability of a varistor to protect a circuit from transient voltage events is determined by its clamping voltage. The clamping voltage is defined as the maximum voltage that can be applied across a varistor without causing it to break down and short circuit. The clamping voltage is a function of the varistor’s material composition, geometry, and rated current. [1], [[2]
Testing a Varistor
Testing a varistor is a process that can be carried out for a number of reasons. One of the most common reasons to test a varistor is during the manufacturing process, as it can help to ensure quality and compliance with specifications. In addition, testing a varistor may be necessary if there are any concerns about its performance or reliability. Finally, periodic testing can help to catch any potential issues before they become bigger problems.
No matter what the reason for testing, it is important to understand how to properly do so. Let’s get started!
Now we shall proceed through the steps for this process.
Disconnect it from the outlet
The first step in testing a varistor is to disconnect it from the outlet. This will help to avoid any accidental shocks and will also ensure that the device is not powered on during testing.
When you open the outlet cover, you will see the varistor located somewhere on the circuit board. It is important to be aware of which side of the device is connected to the ground and which side is connected to the live wire. To avoid any potential confusion, it may be helpful to label each side of the varistor before disconnecting it from the outlet. [2], [3]
Disconnect and desolder varistor’s lead
Once you have identified which side of the device is connected to each wire, you can begin to disconnect and desolder the lead. To do this, you will need a soldering iron and some solder.
Be very careful when disconnecting and desoldering the leads, as they may be very small and delicate. If possible, use a magnifying glass to help you see what you are doing. Disconnect the lead with pliers but be careful not to damage the lead.
Once the leads have been disconnected and desoldered, set them aside for later use and remove the varistor. [2], [3]
Now that the varistor is disconnected from the outlet, we can move on to testing it.
Use a multimeter to test the varistor
A multimeter is a device used to measure electrical properties such as voltage, current, and resistance. Multimeter indicates the resistance in ohms (Ω).
When testing a varistor, it is important to set the multimeter to the correct range. The most common range for testing a varistor is chosen based on the nominal value of the resistance you plan to measure.
To test the varistor, connect one probe of the multimeter to each lead. Make sure that the probes are connected to the same side of the device (e.g. ground and live wire).
If you are not getting a reading on the multimeter, it means that the device is not functional and is not passing current. This could mean that the device is damaged or has failed.
Once you have finished testing the varistor, it is important to reattach it to the outlet cover and reclose the circuit board. Be sure to reconnect and solder the leads properly so that there is no danger of accidental shocks.
If your varistor is faulty, it’s important to replace it as soon as possible. A faulty varistor can be a safety hazard and may also cause damage to your electrical system. [2], [3], [4], [5]
Comparison of Indicators for Testing Varistors
In this table, we compare various indicators that can be used to test a varistor, including clamping voltage, surge current rating, energy rating, leakage current, breakdown voltage, and capacitance. By understanding these indicators and the corresponding test methods, you can ensure that your varistors are performing optimally and providing the necessary protection for your electronic devices.
| Indicator | Test Method | Acceptable Range | Equipment Required |
|---|---|---|---|
| Clamping Voltage | Impulse Test | Within Specified Limits | Impulse Generator |
| Surge Current Rating | Impulse Test | Within Specified Limits | Impulse Generator |
| Energy Rating | Impulse Test | Within Specified Limits | Impulse Generator |
| Leakage Current | DC Test | Below Specified Limit | DC Voltage Source, Ammeter |
| Breakdown Voltage | DC Test | Within Specified Limits | DC Voltage Source, Voltmeter |
| Capacitance | AC Test | Within Specified Limits | AC Voltage Source, Capacitance Meter |
In this table, each row represents a different indicator that can be used to test a varistor. The first column lists the name of the indicator, the second column lists the test method used to measure the indicator, the third column lists the acceptable range of values for the indicator, and the fourth column lists the equipment required to perform the test.
The indicators listed in the table include clamping voltage, surge current rating, energy rating, leakage current, breakdown voltage, and capacitance. These are all important indicators to consider when testing a varistor.
Read more guides to improve your understanding in electronics:
- How to Stop Resistors Getting Hot?
- What is a Bleeder Resistor?
- How to Charge Capacitor Without Resistor?
FAQ
How do I test a MOV varistor with a multimeter?
Testing a MOV varistor with a multimeter is relatively simple. First, set the multimeter to measure resistance (Ω). Next, connect the leads of the multimeter to the two terminals of the MOV varistor. Finally, observe the reading on the multimeter. If the meter displays a value other than zero, then the MOV varistor is functional and will offer some level of protection from electrical surges.
What happens when a varistor fails?
If a varistor fails, it will not offer any protection from electrical surges. In addition, the failed varistor may become very hot and could potentially cause a fire. For this reason, it is important to test MOV varistors regularly and replace them if they fail.
Do varistors fail open or short?
Varistors can fail open or short, but they are more likely to fail short. When a varistor fails short, it will cause an immediate power surge and could potentially damage electronic equipment. When a varistor fails open, it will not cause an immediate power surge, but the failed component may still become very hot and could pose a fire hazard. For this reason, it is important to test MOV varistors regularly and replace them if they fail.
How do you know if a varistor is working properly?
The most common test for a varistor is the resistance test. This measures the ability of the device to resist electrical current. A good varistor will show a multimeter reading of infinity or at least more than 100 Ohms. If you’re not sure, check the datasheet for the specific varistor you’re testing.
A blown resistor can measure 0 Ohms or close to it. This means you need to replace it, the sooner the better!
Are there any special precautions that need to be taken when testing a varistor?
Yes, there are a few special precautions that need to be taken when testing a varistor. First, always test the varistor with a multimeter/ohmeter set to the highest resistance range. Second, make sure that the leads of the ohmmeter are not touching each other or anything else while you are taking the measurement. Finally, do not exceed the maximum voltage rating of the varistor when testing it. Doing so could damage the varistor and potentially cause a fire.
What are the benefits of using a varistor?
There are many benefits of using a varistor. One benefit is that it can help protect your home or office from electrical surges. Another benefit is that it can help prolong the life of your electronics by absorbing excess voltage.
Varistors can also be used in a variety of industries, including telecommunications, automotive, and consumer electronics. In fact, varistors are often used in circuit boards and other sensitive electronic components to protect them from damage caused by electrical spikes.
Are there any downsides to testing a varistor?
The potential downsides to testing a varistor include damaging the varistor, incorrect testing methods, and not having the proper equipment. However, following the proper procedures and using the right tools will minimize these risks.
It is also important to note that some varistors may be designed for one-time use only and cannot be reused after being tested. Always consult the manufacturer’s instructions before testing a varistor.
Are there any downsides to testing a varistor?
The potential downsides to testing a varistor include damaging the varistor, incorrect testing methods, and not having the proper equipment. However, following the proper procedures and using the right tools will minimize these risks.
It is also important to note that some varistors may be designed for one-time use only and cannot be reused after being tested. Always consult the manufacturer’s instructions before testing a varistor.
The most noticeable negative of varistors however, is their price. Varistors can be expensive, and the price will only continue to rise as demand increases.
What are some of the most common mistakes people make when testing a varistor?
One of the most common mistakes people make when testing a varistor is not properly preparing the device for testing. This can include forgetting to remove any protective covers or not properly attaching all of the leads before beginning the test. Additionally, people often do not take into account the voltage rating of their multimeter when testing a varistor. If the voltage rating on your multimeter is too low, you could damage both the varistor and your meter.
Another mistake that people make is not allowing enough time for the varistor to settle after applying power. This can lead to inaccurate readings or even damage to the device.
Do varistors have a polarity?
No, varistors do not have a polarity. This means that they can be connected in either direction and still work properly. This is because the varistors have a symmetrical construction. Variable resistors are nonlinear devices, which means that their resistance changes with the voltage applied to them. This means you don’t have to worry about which way they are connected.
Why would a varistor burn out?
There are a few reasons why a varistor might burn out. The most common reason is if there is an electrical surge that is too strong for the varistor to handle. Other reasons can include physical damage to the component, or manufacturing defects.
If you suspect that your varistor has burned out, the first thing you should do is check for any obvious signs of physical damage. If there is no visible damage, then you will need to test the component to confirm that it is defective.
Is a varistor a capacitor?
No, a varistor is not a capacitor. A varistor is a resistor that changes resistance with voltage. A capacitor stores energy in an electric field between two conducting plates. A varistor does not store energy; rather, it dissipates energy in the form of heat when there is a sudden increase in voltage (a voltage spike).
Is varistor a resistor?
No, a varistor is not a resistor. A varistor is actually an electronic component that is used to protect against voltage spikes while a resistor is used to create a voltage drop in a circuit.
So as you can see both varistors and resistors are used to control the flow of electricity in a circuit but they serve different purposes.
Is varistor a diode?
A varistor is not a diode, it’s an electronic component made of semiconductor material that has a very high resistance to electricity. While it’s similar to a diode, it allows a bidirectional flow of current unlike a diode. Diodes also have a lower dynamic resistance than a varistor.
What is a varistor made of?
A varistor is made of a material that has a high resistance to electricity, but can conduct electricity under certain conditions. This material is usually a semiconductor or an insulator. Varistors are made of different materials depending on their application. For example, some varistors are made of silicon, while others are made of carbon. Metal oxide varistors are made of a metal oxide, such as zinc oxide, and are used in electrical circuits to protect against surges.
Varistors can also be made of other materials, such as ceramic or glass. However, these materials are not as common as semiconductors and insulators.
Useful Video: How to test varistor
Conclusions
So, now you know a little more about varistors and why they’re important. We hope this article has helped to clear up any confusion and that you feel confident in your ability to test them. So, how do you test a varistor? By using a multimeter! A multimeter is your key to measuring the resistance of your varistor. It will help you to indicate the resistance of your varistor and whether it is functioning properly or not. Be sure to take necessary measures depending on the result to prevent some major and dangerous problems!
References:
- https://www.circuitstoday.com/varistor-working
- https://www.utmel.com/blog/categories/resistor/varistor-definition-function-working-and-testing
- https://www.ehow.co.uk/how_7675090_test-varistor.html
- https://www.electronics-notes.com/articles/test-methods/meters/multimeter-resistance-measurement.php
- https://eepower.com/resistor-guide/resistor-types/varistor/