No matter what type of kiln or heat treat oven you have, choosing the right kiln relay is super important! Electric kiln relays play a fundamental role in regulating the temperature of your kiln, as well as ensuring kiln safety.
Over the course of this article we’ll be explaining what kiln relays are, 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 receives signals from the kiln controller and then regulate the amount of electricity sent to the elements of the kiln. Electric 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 open, 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-state relays. This speed, when combined with precise inputs from the kiln controller, allows the kiln to execute kiln firing schedules with extreme precision.
Types of Electric 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 performance, precision, and durability.
Kiln relays also differ by their environmental friendliness. For instance, mercury is highly toxic. Mercury relays are banned in several states and aren’t commonly used for modern kilns.
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, when relays fail in the closed position, you have major issues. This causes your kiln to heat up indefinitely – threatening your project, your kiln, and even your personal safety.
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. This mechanism has several advantages over other types of electric 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!
Additionally, for added safety, we recently released 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 II and TAP II Pro 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 recently 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:
- Evenheat
- Hot Shot Oven & Kiln
- Paragon Kilns
- Mobile Glassblowing Studios, LLC
- Jen-Ken Kilns
- Kiln Frog
- Sheffield Pottery
- Delphi Glass
Electric Kiln Relays FAQ
What happens when kiln relays fail?
Kiln relay failure can be a minor annoyance that causes your project not to fire – or it can be a catastrophic danger that poses damage to your property or health. It all depends on what position the relay fails in.
If your electric kiln relay fails in the “open” position, then no electric current gets to your kiln’s elements and your kiln fails to heat. This can be annoying but doesn’t pose any major risks.
However, if your kiln relay fails in the “closed” position, the opposite happens. Non-stop electric current flows to your kiln’s elements, causing them to heat up indefinitely. This is obviously bad. If you’re not using a safety limit controller, there is no way for your kiln to automatically shut off or reduce power to your elements.
This type of relay failure can cause your project and kiln to melt or, if left untended, can cause fires.
Proper kiln maintenance and regularly replacing mechanical relays help reduce these risks – but, better yet, we recommend upgrading to a solid-state relay and investing in a safety controller.
How do solid-state relays help me save money in the long run?
At time of purchase, mechanical relays are usually less expensive than solid-state relays (SSRs). However, over time, SSRs save you a significant amount of money.
Why is that the case?
Mechanical relays have a finite lifespan. Kiln Frog recommends replacing them every 12-24 months. Other artists recommend replacing them every 200 firings. However, if you’re running a commercial kiln, consistently firing up to Cone 10 or hotter, or firing projects on a consistent basis, you may need to replace your mechanical relays more often than that.
Solid-state relays, on the other hand, usually last the lifespan of your kiln (or longer!). That means that by the time you replace your mechanical relays one or two times, just purchasing an SSR from the start would’ve saved you money. And that’s not even accounting for the cost of potential relay failure – which can cost tens of thousands of dollars.
What factors impact relay lifespan?
Different factors can impact how long or short your relay lasts. Compared to other types of electric kiln relays, mechanical relays have the shortest lifespan. That’s because they rely on moving mechanical parts to regulate electricity.
However, factors that can reduce the lifespan of your mechanical relay include:
- Firing to higher temperatures.
- Using schedules that have aggressive ramp rates.
- Frequently firing your kiln.
- Exposing your kiln to moisture or environmental elements.
Since solid-state relays don’t rely on any moving parts, far fewer factors impact the lifespan of solid-state relays. These include:
- Exposure to high temperatures (that’s why it’s important to make sure SSRs are vented with proper airflow).
- Exposing your kiln to moisture or environmental elements.
