Everything You Need to Know About Controlling Your Kiln

Guide for understanding the difference between different types of kiln relays
Picture of Scott Shannon

Scott Shannon

All About Kiln Relays

No matter what type of kiln or heat treat oven you have, choosing the right kiln relay is super important! Kiln relays play a fundamental role in regulating the temperature of the kiln, as well as ensuring kiln safety. Over the course of this article we’ll be explaining what a kiln relay is, how they work, as well as what type of kiln relay is right for your kiln or oven build.

We’ll also be exploring how TAP Controllers and safety limit controllers like TAP Monitor can help protect you from the consequences of kiln relay failure, so let’s get started!

What Is a Kiln Relay?

Kiln relays are a mechanism that receive signals from the kiln controller and then regulate the amount of electricity sent to the elements of the kiln. Kiln relays rapidly cycle on and off – or “close” and “open.”

When kiln relays cycle on, the circuit closes, and the elements receive electrical current. The kiln element’s electric resistance converts that current into heat, and the kiln gets hotter. When the kiln’s relays cycle off, or opens, it interrupts the current to the elements. This causes the kiln to naturally lose heat.

Kiln relays can open and close extremely fast – ranging from 50 milliseconds for mechanical relays to 20 nanoseconds for solid states relays. This speed, when combined when precise inputs from the kiln controller allows the kiln to execute kiln firing schedules with extreme precision.

Types of Kiln Relays

Not all kiln relays are created equal. They differ by the mechanism they use to open and close the circuit. This mechanism affects their performance, precision, and durability. Kiln relays also differ by their environmental friendliness. For instance, mercury relays are banned in several states and aren’t commonly used for modern kilns, since mercury is highly toxic. Below are explanations of the different types of relays.

Mechanical Relays

Mechanical relays use a physical switch to open and close the relay. That’s why you can hear them click! Mechanical relays are affordable. But since the switch is physical, mechanical relays are more prone to failure. If mechanical relays fail in the open position, your kiln will no longer heat up, which can be a major inconvenience. However, it’s when they fail in the closed position that you have major issues. This causes your kiln to heat up indefinitely – threatening your project and your kiln.

Additionally, since mechanical relays rely on a physical mechanism, they are significantly less precise than other options. And since they have a shorter lifespan, they have a higher environmental cost.

Mercury Relays

Mercury relays use gravity and displacement to open and close the relay. Mercury relays consist of a metal weight in a tube of mercury. Gravity causes the metal weight to fall, displacing the mercury until it closes the circuit. A coil at the top of the tube electromagnetically lifts the weight when it receives current, causing the mercury to recess and open the circuit.

Since mercury relays only use a single moving part, they are extremely reliable – significantly more so than mechanical relays. However, there are some issues with this mechanism. Firstly, it takes time for the displace and recede – so mercury relays have the same level of precision as mechanical relays. Secondly, mercury is highly toxic and exposure to mercury has significant health and environmental risks. These two factors have made mercury relays largely obsolete.

Solid State Relays (SSRs

Solid state relays use semiconductors, electronic parts, and LED or infrared sensors to turn the circuit on and off based on signals from the controller. They do not rely on contact switches or any other moving parts to open or close the circuit. This mechanism has several advantages over other types of kiln relays. First, the lack of moving parts means there is no contact erosion – so solid state relays are extremely reliable and will last pretty much forever, when appropriately rated for the application.

Additionally, the fact that solid state relays rely on electric signals, light, and sensors makes them extremely fast, offering a greater level of precision than any other type of kiln relay. Since solid state relays almost never have to be replaced or thrown away, they are far less taxing on the environment.

What Type of Relay Should You Choose for Your Kiln?

If the summaries above don’t make it obvious, we strongly recommend investing in a solid state relay for your kiln. While they are more expensive than mechanical relays, you’ll end up saving money in the long run by never having to worry about replacement costs. That’s not to mention the potential costs of relay failure, which you exponentially reduce the risk of facing by using an SSR.

Most new kilns have the option for solid-state relays – and your TAP Kiln Controller will be compatible with all three types of relays! If you’ve got an older kiln with mechanical or mercury relays, consider swapping them out for solid-state the next time they need replacement.

How the TAP Ecosystem Helps Protect You from Relay Failure

When we designed TAP, we included all of the quality of life features that we ourselves would want as artists. That included allowing the controller to track usage on kiln components and sending out preventative maintenance alerts, so that artists would be able to replace kiln elements, kiln relays, and thermocouples before they reach the end of their estimated lifespan. All you have to do is enter the life expectancy for your relay(s), elements, and thermocouples provided by your kiln manufacturer or the component’s product sheet!

The TAP Kiln Controller tracks kiln relay usage to provide preventative maintenance alerts to help users replace relays before kiln relay failure occurs.
The TAP Kiln Controller tracks kiln relay usage to provide preventative maintenance alerts to help users replace relays before kiln relay failure occurs.

Additionally, later this year, we’ll be releasing TAP Monitor – the most advanced digital pyrometer and limit controller ever created. TAP Monitor adds the convenience and peace of mind of precise, remote temperature monitoring to your smartphone or tablet. When purchased as a set of configurable components, TAP Monitor can also be wired to a redundant safety relay to act as a safety limit controller, making sure your kiln shuts off safely in case of relay failure.

Explore Kiln Control Solutions by SDS Industries

The TAP Ecosystem includes a host of solutions to enhance kiln safety and help you prevent (or safely respond to) kiln relay failure. In addition to being the most advanced, precise, and easy-to-use programmable digital kiln controllers on the market today, the TAP and TAP II Controllers by SDS Industries provide advanced diagnostics, preventative maintenance alerts, and remote real-time kiln monitoring and error alerts via TAP Kiln Control Mobile app. These features help you prevent and proactively address any potential failures in your kiln or oven build.

Additionally, our soon-to-be released TAP Monitor Digital Pyrometer & Limit Controller can be added to any kiln or oven build, regardless of your current kiln control method, to provide safety redundancy and real-time remote kiln monitoring.

We invite you to explore our selection of programmable kiln controllers, pyrometers, standalones, and conversion kits on our online store. You can also purchase TAP Digital Controllers or TAP Controlled Kilns and Heat Treat Ovens through one of the following distributors:

Shop the most advanced programmable digital kiln controllers for sale.


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