Element Switching Relays

[clearwaterbrewer]

yes, physical relays are fine if you do not want 'multiplexing'.

But if you want to have two elements on at once and never draw more than 30A, and also be able to have a normal PID function work, the logic gates at the signal level work much better...

Case example... if you have the contactor/relay off, but the PID is still active, the "I" of the PID, Integral, winds up to its max value and when you put that contactor back on, the element is under full power, and may only be a degree or two away, so you overshoot badly.... Now on the other hand, if you are doing time-splicing with the PWM, maybe it misses half of the .5 second wide pulse, but the PID reacts by making wider pulses, and as one heating elements pulses are lowering in duty cycle, the other heating element is allowed to increase it's pulse width. obviously, if the priority element is full on, the other element can starve, but not only are there few times one element is full on, if the priority is set to something like the RIMS tube heater, it never is on all the way with a high power element..