Understanding Kiln Relays

A kiln relay is an essential component of electric kilns. They act as a switch, turning power to the heating elements on and off when directed by the kiln controller. There are three types of kiln relays, mechanical, solid state, and mercury displacement. The most commonly used are mechanical and solid state relays. Below, we’ll discuss how a relay works and the differences between the types. 

What do kiln relays do?

Put simply, kiln relays switch the electric current running through the elements on and off with information from the kiln controller. They do this by opening and closing the electric circuit within the kiln. When the electrical circuit is closed the electric current is “on” and power flows to the elements. When the circuit is open, the electric current is “off.” Relays are an important part of the kiln and help to ensure your pieces are fired consistently at the right temperature. 

Mechanical Relay

A mechanical kiln relay uses moving parts to create a physical connection inside the relay. The coil receives an electric current from the controller when the temperature needs to be adjusted, based on the firing schedule you input. This generates a magnetic field, pulling the armature towards the coil which then moves the contacts into either the on or off position. 

One downside is that mechanical relays are more prone to wear and tear because of the physical parts within them. Rate of decline depends on how hot you fire, how often you fire, how long you're firing, and how full the chamber is. It is recommended to check mechanical relays periodically for signs of wear and replace them according to the kiln manufacturer’s recommendation.

Solid State Relay

Solid state relays use semiconductors and electronic parts to turn the circuit on and off based on signals it receives from the controller. This makes them faster and more precise than mechanical or mercury relays. They generally have a much longer life because there are no mechanical contacts that wear out, which is great if you fire your kiln often.

Solid state relays are the most expensive relay option, but because their lifespan is long and they are highly precise, they are a worthwhile investment.

Mercury Relay

Mercury relays use gravity and mercury displacement to open and close the electrical circuit. Gravity pulls the metal weight down which displaces the mercury and closes the electrical circuit. When the controller indicates the temperature needs to be reduced, the coil at the top of the tube receives an electric current and electromagnetically lifts the weight from the bottom of the tube to the top. This moves the mercury back down and opens the circuit, cycling the heat off. This allows frequent switching with less mechanical contact wear.

Because mercury is highly toxic and exposure to it has many risks, mercury displacement relays are not very common in newer kilns and at this time their use is prohibited in 10 US states.