How do you choose varistor voltage?
How do you choose varistor voltage?
Choose a varistor with an energy absorption rating that equals or slightly exceeds the energy values associated with the event the circuit may experience. If, however, the transient voltage is due to an external event, the magnitude of the source energy is unknown.
What is the clamping voltage of a varistor?
This rated or clamping voltage is the voltage across the varistor measured with the specified DC current of 1mA. That is, the DC voltage level applied across its terminals that allows a current of 1mA to flow through the varistors resistive body which itself is dependant upon the materials used in its construction.
How do I choose a varistor?
Select a model to provide the required voltage-clamping characteristic A final consideration is to choose the appropriate package style to suit the application. Consider the maximum continuous voltage that will be applied to the varistor including any high line conditions (i.e., 110% or more of nominal voltage).
What do the numbers on a varistor mean?
The energy rating for the varistor is often defined using standardised transients. The transient is expressed in the format x/y where x is the time for the transient rise and y is the time to reach its half peak value. Typical formats are 8/20 and 10/1000.
What will happen if the power rating of a resistor is exceeded?
Resistors which exceed their maximum power rating tend to go up in smoke, usually quite quickly, and damage the circuit they are connected to. If a resistor is to be used near to its maximum power rating then some form of heatsink or cooling is required.
What happens when a varistor fails?
Varistors need to absorb the energy deposited by temporary overvoltage, switching surges, or lightning impulses. The energy absorption capability can be divided into thermal energy absorption capability and impulse energy absorption capability. …
What does the power rating of a resistor indicate?
The power rating of a resistor indicates how much power a resistor can handle before it becomes too hot and burns up. Power is measured in units called watts. The more watts a resistor can handle, the larger and more expensive the resistor is.
Is it OK to use a higher wattage resistor?
Re: Using higher wattage resistors Yes you can use 1 watt resistors in most cases. The resistor in power supply feed is a low value to prevent a fire or damage to the radio. that’s the only place to use original wattage.
Why would a varistor burn out?
When the varistor leakage current is too large, and the temperature rises to a certain extent, the low melting point metal is melted, thereby varistor from The cutting in the circuit can effectively prevent the varistor from burning.
Are varistors polarity sensitive?
Does a varistor have polarity? In the case of metal oxide varistor, a zinc-oxide layer is basically sandwiched between two metal electrodes. As a result, there is no polarity.
Is power rating related to resistance value?
The Resistor Power Rating is sometimes called the Resistors Wattage Rating and is defined as the amount of heat that a resistive element can dissipate for an indefinite period of time without degrading its performance….The Resistor Power Triangle.
| Type | Power Rating | Stability |
|---|---|---|
| Wirewound | High up to 500 Watts | High 1% |
What happens if you use the wrong resistor?
The equipment will cease to function in short order either by the resistor itself burning up, or by the heat it generates burning up an adjacent component or possibly the circuit board its mounted on or even foil pattern on the circuit board, or maybe all three.
What is the movselection rating of a varistor?
MOVselection 1. Continuous Voltage Rating,RMS or DC, should be >110% of the maximum expected voltage. 2. Device sizedepends on the transient energyor currentexpected or on the required clamping voltage. 3. Energyand Peak Currentratings are a measure of capability.
How to determine the voltage of a varistor?
Determine the necessary steady-state voltage rating (working voltage) 2. Establish the transient energy absorbed by the varistor 3. Calculate the peak transient current through the varistor 4. Determine power dissipation requirements 5. Select a model to provide the required voltage-clamping characteristic
When does a varistor need to be replaced?
Energy Peak Current Capacitance (typical) VAC VDC Joules Amps Vpeak Amps pF 130 170 100 10000 185 min225 max340 100 1900 Clamp Voltage 8×20µS Voltage Rating, Continuous Varistor Voltage at 1mA VDC After only 1 hit of these two max limits, the MOV will need to be replaced.
What do you call a voltage dependent resistor?
Sometimes they are referred to as a VDR, or Voltage Dependant Resistor, by some manufacturers. An MOV is a voltage dependent device which has an electrical behavior similar to back to back zener diodes.