Transient Voltage MOV Selection

Submitted by Banksy on Wed, 06/17/2020 - 12:55

Hi Everyone :D

I'm fitting a new Access Control Panel With a MagLock, keyboard Etc. The manufacturers tell me that the main panel will supply power to my MagLock but that I need to put a Metal Oxide Varistor across the power rails and I'm really struggling with the maths (As a Newbie who's also rubish at theory and math !)

The MagLock draws 420mA @ 12V, the power supply provides 14.3 V at 500mA and the panel Supplies 12V @ 500mA for the MagLock. PLEASE can any one suggest a suitable MOV value? Hopefullly with a part Number/Supplier?

Any help is very much appreciated.

Thanks everyone :D




A varistor is an electronic component with an electrical resistance that varies with the applied voltage.Also known as a voltage-dependent resistor (VDR), it has a nonlinear, non-ohmic current–voltage characteristic that is similar to that of a diode. In contrast to a diode however, it has the same characteristic for both directions of traversing current. Traditionally, varistors were indeed constructed by connecting two rectifiers, such as the copper-oxide or germanium-oxide rectifier in antiparallel configuration. At low voltage the varistor has a high electrical resistance which decreases as the voltage is raised. Modern varistors are primarily based on sintered ceramic metal-oxide materials which exhibit directional behavior only on a microscopic scale. This type is commonly known as the metal-oxide varistor (MOV).

Varistors are used as control or compensation elements in circuits either to provide optimal operating conditions or to protect against excessive transient voltages. When used as protection devices, they shunt the current created by the excessive voltage away from sensitive components when triggered.

The name varistor is a portmanteau of varying resistor. The term is only used for non-ohmic varying resistors. Variable resistors, such as the potentiometer and the rheostat, have ohmic characteristics.

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