Transient Suppression MOV Selection?

[Karl Banks]

Hi Everyone

I'm fitting an Access Control Panel with a MagLock, Keyboard entry etc. The manufacturers advise me that The panel can/will supply power to the Maglock without the need for an addition power supply but I'l nee to fit aMetal Oxide Varistor across the power rails in the MagLock to suppress transient Voltages. The MagLock Draws 420mA 2 12 Volts, The panels power supply provides 500mA @ 14.3 V 

I'm struggling with the math ( PLEASE can someone suggest a suitable MOV and a part number/supplier?

Any help would be much appreciated

Banksy.

 

[HarryA1]

I have not used varistors but not letting ignorance slow me down. The V20E14AUTO  is a 16 volt MOV.

Voltage Rating DC: 16vdc
Varistor Voltage:  22 volts this is where the varistor starts to conduct at 1 ma. Varistors draw some small current always
Clamping Voltage:  43 volts the voltage any spike is truncated to.
Peak Surge Current: 20 amperes.
Surge Energy Rating: 28 joules.  28 watts-1 second, 56 watts-500 ms, etc

Unlike Zener diodes that fail as an open circuit varistors fail as a short circuit so in some cases a fuse
is used with them. Most likely on the larger ones..
see:

https://www.mouser.com/ProductDetail/Littelfuse/V20E14AUTO?qs=%2Fha2pyFadugE%2FoOLoA7J9TCvi67Mtc%2F%2FOVMAqZDk45RR%2F7GD1QKNkA%3D%3D

or:

https://www.digikey.com/products/en?mpart=V20E14AUTO&v=18

That is my best guess; perhaps someone else has experience with varistors?

"The MagLock Draws 420mA 2 12 Volts, The panels power supply provides 500mA @ 14.3 V "

Do you need to reduce the 14.3 volts to 12 volts?