Solid State Relay (SSR)
Evenheat's Quiet Drive Solid State Relay System does away with the mechanical relays traditionally used in kilns and replaces them with solid state relays.
Traditional, mechanical relays wear out and fail at some point. They have to and they always will. Not so with the solid state. Solid state means there are no moving parts, nothing to wear out and nothing to replace.
Solid state also means superior heating element operation resulting in tighter temperature control, longer element life and enhanced performance.
Evenheat's Quiet Drive Solid State Relay System is available as an option on all Evenheat models except for the Studio Pro STP.
First of all....... what's a relay anyway?
A relay is basically a switch. In the case of a kiln, it's the switch that turns the heating elements on and off to control chamber temperature.
Traditionally, kilns have used mechanical relays for temperature control. Mechanical relays, in their most basic form, contain a set of metal contacts that physically open and close and a magnetic coil that makes that happen. These parts move and electrically arc during the operation of the relay.
Solid State Relays (SSR), in their most basic form, contain a semiconductor which is a solid block of material. There are no moving parts or electrical arcing in a solid state relay.
While each style of relay essentially does the same thing; solid state offers some great advantages over the mechanical design.
Solid State Relay Advantage 1 - Long Life
Mechanical relays physically move and electrically arc as they operate. If you're familiar with a traditional kiln or oven, the "clicking" sound you hear is the mechanical relay(s) operating.
It's not unheard of to have a mechanical relay turn on and off a thousand times during a firing. This constant On/Off causes wear, especially with electrical arcing seen at the switch contacts. At some point the mechanical relay simply wears out and fails.
SSR's have no moving parts and run silent, hence our term "Quiet Drive". Mechanical wear or arcing does not exist with a solid state relay.
Evenheat fully expects our SSR's to last the life of the kiln or oven.
Solid State Relay Advantage 2 - Tight Temperature Control
There is a limit to how frequently a mechanical relay can or should be operated. For the kiln manufacturer this is a balancing act between good control and relay life but is generally limited to no more than one cycle every 10 seconds and usually 14 seconds. While these times do allow for good control, very tight temperature control can only be achieved if we drastically shorten this time.
A solid state relay operates at 120 times per second, as needed. This control resolution, if we can call it that, is measured in milli-seconds rather than multiple-seconds and presents a great opportunity for the control to make very quick heating decisions resulting in very tight temperature control.
All of our controls, except for the Set-Pro, are designed to take advantage of the SSR's fast operating capability.
Solid State Relay Advantage 3 - Longer Heating Element Life
Heating elements are powered from the AC power line. AC is alternating and therefore the voltage becomes 0V 120 times every second (North America). Heating elements love to be turned on and off at 0V and they show this love by lasting longer.
So what does this have to do with the relay?
Mechanical relays have no clue what the line voltage is, ever. They turn on and off without any timing or feedback from the line voltage. What this means is that the mechanical relay does nothing to help extend heating element life. They would if they could, but they can't, so they don't.
Solid state relays on the other hand, can be selected to turn on and off only when the line voltage is at 0V. This is called "Zero Crossing". The solid state relays we have selected are designed this way. Heating element life is extended with this Zero Crossing feature.
Better by Design - 30 Amp Rated
We've chosen solid state relays that are rated for 30 amps, while limiting the actual current we run through them to 15 amps. We're basically running our SSR's at half of their full capacity. Why? Headroom!
Our goal is to provide a solid state system that works well and continues to work well into the future. Our 30 amp SSR's run very cool with a 15 amp load; well below the derating curve for proper operation. We do expect our SSR's to last the life of the unit.
Better by Design - SSR Heatsinks Externally Mounted
Solid state relays get warm as they operate and require airflow for proper cooling. We mount our SSR heatsinks externally to provide unrestricted airflow and prevent heat build-up. We don't place our heatsinks within the control enclosure which would limit their cooling and lead to the SSR failure. Mounting the SSR heatsinks internally also introduces unnecessary heat to other kiln control components which shortens their life.
We mount our SSR heatsinks on standoffs that provide an air gap between the control enclosure and SSR. This gap provides added air flow while also severely limiting heat transfer between the control enclosure and the SSR.
We believe we have created the ultimate SSR operating environment and 6 years of zero failures confirms that. Better by Design in all we do.