I am planning on using a WATLOW DC2T-24C0-0000 power controller for a three phase electric kiln.
It is a zero-cross 3 phase, 2 leg controlled contactor capable of driving 46 amps with its huge heat sink. Its principle of operation is basically the same as a contactor (as far as I understand), except of course that it can switch much faster since it's zero cross and on a 60 Hz system there will be 120 zeros per second for each AC wave.
Mine is just activated with a 4.5-32 VDC signal, though WATLOW offers other DIN-A-MITE power controllers which utilize analog input signals (4-20mA or 0-10VDC) to automatically adjust power as shown in the manual:
"With variable time base control, the power controller automatically adjusts the time base and output power with respect to process input. Accelerated life testing verified that variable time base control significantly reduces expansion and contraction of the heater element. This extends heater and SCR life while improving process temperature control. You save money on heaters, downtime and maintenance."
Since the model I bought is basically just a really fast contactor that lasts a lot, I was planning on using a 1 second switching period and have an algorithm that determines how much % of time it needs to be ON and the rest is OFF. Clearly this isn't as precise as the variable time base models, so what I want to know is:
- For a big kiln with >300 kg of ceramics inside, will the thermal response justify getting a fancy power controller or is my plan more than adequate?
- Is variable time base possible to program for the contactor models? I am already using a microcontroller (ESP32) to control the kiln with a PID algorithm.
On the last note, today I tried using a Arduino NANO to test the switching capabilities of the SSR with different codes. I used a filament lamp and an oscilloscope in order to see how the controller switched. I can conclude that a) given that the maximum switching frequency is 120 Hz, I couldn't see much of an effect on the oscilloscope and b) the switching is nowhere near as smooth as that of a modern dimmer.