I need advice concerning microprocessor control of a Triac.
My goal is to control a 1-phase motor (24V AC/50 Hz). The motor is used to control a mechanical 3-way shunt in an heating system.
Water temperature for radiators are regulated by closing or opening the shunt. The motor is now controlled by an analog circuit not built by me. The motor is controlled by two Triacs (TIC206D). According to datasheet they need 5 mA to turn on.
I have already built a MCU-controlled system including a number of termistors that control ON/OFF for a circulation-pump and display temperatures on LCD.
I am pretty experienced in programming MCU:s but have no experience around Triacs.
I have tried to get information on the web about Triacs, but still feel uncertain.
So far I have written software that detect zero-crossing and trigger an external interrupt on falling edge. This interrupt start a timer that will interrupt and restart every 0.2 ms. A full wave is 20 ms since my mains is 50 Hz. So the timer do 99 cycles and then a new external interrupt restart program flow. On every timer interrupt I can control the state of the pin that trigger the Triac. I have looked at the signal on my scope and it is very well syncronised with the AC-wave.So far so good.... 8)
The motor is supposed to run at full speed for one second and then halt for 20-30 seconds. The direction of the motor is controlled by a termistor that measure water-temperature. MCU compute if temperature need to be higher or lower.
Finally arrived to my questions…. :P
Where in the AC-wave should the Triac be triggered.?
Where in the AC-wave should triggering stop?
Should there be one or several trigger pulses during the AC-wave?
Since my Triac only need 5 mA to turn on, can it be connected directly to the MCU-trigger pin with only a current-limiting resistor in between?
Any other important things to consider?
I only have one motor, specially made to fit with the mechanical shunt. It is rather expensive so I’d rather not destroy it by missing some basic rules when designing
AC motor-control with Triacs.
Grateful for any advice….