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Heat treating oven, 240VAC 20A 4800W
One 30A double pole breaker will be used as an ON switch for the oven (shown here as twin SPST switches) energizing both SSR’s, the PID temperature controller as well as a PWR ON indicator light. The PID (represented here by a 12v source on a relay to simulate the 12v command signal about a 70% duty heating cycle, it’s switch being the RUN command) operates two 25A SSR via a 12v PID command signal. A momentary switch on the door interrupts the PID output signal to isolate the coils when the door is open. A second set of SPST switches represents a DPDT ON-ON switch used for a COIL OFF setting, cutting the PID command line while energizing the COIL OFF lamp. Energized elements are indicated by a light for heating cycle observation. All lamps will be 240v rated LED, displayed here as standard lamps for simplicity. I designed this for a 6”x4.5”x40” internal chamber with twin 36” series run elements per wall, run in parallel. Coils are ideally 12 ohms each, these are set to my actual measurements. Segmented elements for easier replacement.
Flip the 30A “breaker”on the left to energize the oven. Flip the switch on the “PID” to simulate setting it to RUN and it will begin heating. A door open condition is simulated by flipping the switch on the right, cutting the relay signal. Flip the double switches for the COIL OFF override switch near the center. The whole thing is powered by a 7.2kV supplied transformer providing twin 120v lines for 240v to simulate my residential supply.
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