The most effective way to minimize heater element temperature cycling, and the most expensive solution, is to use solid state relays (SSRs) and SCR power controllers coupled to PID temperature controllers. This combination provides the best performance for both your thermal system as well as for the heater itself. Solid state switching devices cycle power to the heater very rapidly (from one second with a SSR, down to milliseconds with phase-angle fired SCRs). This fast-power cycling dramatically reduces heater element wire temperature excursions and substantially extends heater life.

Tip 6: Prevent excessive heater cycling wrote:Excessive temperature cycling is very detrimental to the life of a heater. The most detrimental is the cycle rate that allows full expansion and contraction of the heater resistance wire at a high rate (30 to 60 seconds' power ON and power OFF). This causes severe stress and oxidation of the resistance wires inside a heater. A bad temperature cycle is typically found when thermostats are used. Thermostats respond slowly to temperature changes and have large switch ON/OFF temperature differentials. An improvement, but a somewhat more expensive solution, is to use ON/OFF or PID controllers with mechanical relays. It is crucial to not switch the frequency or cycle time too rapidly (somewhere between 3 to 10 seconds), because the relay contacts can wear out quickly.

Kristi wrote:Yeah, and it seems to stress that a long 30-60sec heating on time or off time is bad because it allows big changes in the element, whereas the little changes due to a PID are probably negligible.

Thanks.

AndyS wrote:A watlow guy once told me that a one second cycle time was almost as good as pure analog control when it came to extending heater life.