How To Make An Easy Surge Protection Device Using Metal Oxide Varistor

What is a Surge Protection Device

A Surge protection device (aka surge suppressor) is a protection device usually used with electrical installations in order to protect them against high voltage surges, spikes, and transients. It is an important part of electrical protection systems and is generally used to protect equipment in power generation, transmission, and distribution. Surge protectors are also used for protecting data and telephone line, in case an AC line accidentally connects with them or a lightning bolt hits them. They are simple to design & maintain, and have a massive return on investment. So, in today’s tutorial, we are going to go over a step by step procedure on How To Make An Easy Surge Protection Device Using a Metal Oxide Varistor (MOV).

Metal Oxide Varistor (MOV)

Metal Oxide Varistor (MOV) is a voltage dependent, nonlinear device that offers excellent transient voltage suppression. A MOV is designed to protect various types of electronic devices and from switching and induced lightning surges, by simply clamping the voltage to a safe level. In basic terms, A MOV soaks up the destructive electrical energy and ejects it as heat. MOVs usually contain a ceramic mass of zinc oxide grains, in a matrix of other metal oxides (such as small amounts of bismuth, cobalt, manganese) sandwiched between two metal plates. A metal oxide varistor MUST always be connected in parallel to the electrical/electronic circuit in order to protect it against high voltage transients.

Buy On Amazon

Key Features & Specifications

AC voltage range: 130 to 1000V
High peak surge current rating up to 10kA
DC Voltage range: 175 to 1200V
Insulation resistance: 1000Mohm
Operating temperature: -55 to +85 °C
Fast response time of less than 25ns, instantly clamping of transient over-voltage
Capable to handle high surge current
High energy protection capability
Low capacitance values, ideal for digital switching circuit protection
High insulation resistance, preventing electric arcing to adjacent components or circuits

Hardware Component

You will need the following parts to build this project

S.No	Component	Value	Qty
1)	Metal Oxide Varistor	300V	1
2)	MKP Capacitor	0.47uF/275V	1
3)	LED	5mm, 3.5V	1
4)	Fuse Box	Fast blow, 10A	1
5)	Terminal Block Connectors	–	2
6)	Resistors	100K	1
7)	Soldering Iron	45W – 65W	1
8)	Soldering Wire with flux	–	1
9)	AC Bulb with Base	220V	1
10)	AC Wall outlet	220V	1
11)	Veroboard
12)	Jumper Wires

MKP Capacitor

Electronic Fuse

Useful Steps

1) Solder the input and output block connectors on the veroboard.

2) After that, solder the fuse box with the +ve pin of the input block connectors.

3) After that, solder the 300V MOV in parallel with the input terminal block connectors.

4) After that, solder the 0.47uF/275V capacitor in parrallel with the 300V MOV.

5) After that, solder the +ve pin of the LED with the 100K resistor and the -ve pin with the -ve pin of the output block connector.

6) After that, connect a 220V AC bulb with the output block connector. Also, connect the 220V AC supply with the Input of the circuit.

7) Power up and test the circuit.

Working Explanation

The working of this circuit is actually pretty simple. Under normal operation, when the input supply voltage is well under the clamping voltage of the MOV, it behaves like an insulator with very high resistance. Hence, all the current flows through the circuit and no current flows through MOV.

But in an abnormal condition, when a high voltage transient passes through the circuit, it appears directly across the MOV since it is connected in parallel with the input supply. The resistance value of the varistor will drop rapidly causing a large current to flow through the fast blow fuse box, triggering it to blow and disconnect the circuit from the input supply. In case of small irregular voltage spikes, the MOV will still disconnect the circuit momentarily by shorting and damaging itself and the fusebox, but neither of them will be completely blown. Here, we have also used a 0.47uF MKP capacitor, in order to dump irregular high voltage AC spikes to the GND of the circuit.