The control of power

More than ever, engineers are designing electrical process heating systems with SCR (thyristor) power controls. Using an SCR has many advantages; more precise control of the heating process, longer heater life, improved product quality at faster production speeds and lower maintenance costs.

An SCR is a solid-state switching device that can provide fast, stepless, and proportional control of electrical power. Unlike a mechanical relay or contactor, an SCR power controller has no mechanical parts that can wear out. The SCR will not flicker or be affected by dirty contacts. A mechanical relay must be replaced after a certain number of cycles. Due to the slow cycle time inherent in mechanical relays, control can be poor, which can damage the heated process and shorten the life of the heating element due to thermal shock.

Mercury displacement relays can switch faster than mechanical relays. However, the mercury relay will explode if it overheats due to overclocking or overloading.

This creates problems with hazardous materials, and due to stricter government regulations, mercury relays are also becoming increasingly difficult to ship and dispose of.

Solid state relays (SSRs) are a popular alternative to contactors, but they don't usually come with connectors that make a solid connection for higher power levels. Additionally, they are not always sold with heat sinks, voltage protection, or the necessary fuses to protect and operate the relay safely.

Importance of the rating values

Other issues could also arise from the ratings of the SSR. Almost all solid state relays are rated at 25℃. Under actual operating conditions, where internal electrical enclosure temperatures reach over 40°C, the SSR may fail when operated at full power. Most manufacturers have a derating chart to compensate for this discrepancy. Unfortunately, many users rely only on the maximum rating when choosing a solid state relay, resulting in the wrong choice for their application. Most SCR power controllers are designed for an ambient temperature of 45°C at full rated power.

It should be noted that in real-world situations, using a CD Automation thyristor stack or an SSR can help eliminate downtime by up to 95% and lower your total cost of ownership on the product life up to 90% compared to using a traditional mechanical contactor. This is a huge cost saving that cannot be ignored if you are serious about an efficient process.