So I have a circuit diagram to phase cut and then controlling speed of AC Induction Motor. With the code from arduino, I am able to know the zero cross and then cut the phase.

It was working well when I dont cut the phase too much, and then after that I try to cut it bigger. And something blew up, when I checked it, from the bottom(the other side of pcb) of 30K resistor there's something black mark in there, so I think it was from the resistor, but the resistors itself are fine, no black mark or some hint that the resistor is blew up. Then I checked it again, I cleaned up the black mark then I see the resistor's pin/feet's solder was not in the shape I was soldered(Its like the lead is blew up).

So was it because I'm soldering it bad? or is it there's a jumping electricity from Phase to Neutral on the pcb?

and this is the code from arduino, I think there's nothing wrong in here but who knows..

int AC_LOAD = 3;    // Output to Opto Triac pin
int dimming = 128;  // Dimming level (0-128)  0 = ON, 128 = OFF

void setup()
  pinMode(AC_LOAD, OUTPUT);// Set AC Load pin as output
  attachInterrupt(0, zero_crosss_int, RISING);  // Choose the zero cross interrupt # from the table above

//the interrupt function must take no parameters and return nothing
void zero_crosss_int()  //function to be fired at the zero crossing to dim the light
  // Firing angle calculation : 1 full 50Hz wave =1/50=20ms 
  // Every zerocrossing thus: (50Hz)-> 10ms (1/2 Cycle) 
  // For 60Hz => 8.33ms (10.000/120)
  // 10ms=10000us
  // (10000us - 10us) / 128 = 75 (Approx) For 60Hz =>65

  int dimtime = (75*dimming);    // For 60Hz =>65    
  delayMicroseconds(dimtime);    // Wait till firing the TRIAC
  digitalWrite(AC_LOAD, HIGH);   // Fire the TRIAC
  delayMicroseconds(10);         // triac On propogation delay (for 60Hz use 8.33)
  digitalWrite(AC_LOAD, LOW);    // No longer trigger the TRIAC (the next zero crossing will swith it off) TRIAC

void loop()  {
  i = 90; 

For the specification, R1, R2, R5, R6, R7 are 1W, R3 and R4 are 1/4 W, all capacitor are 630V, and BR1 is 1A.


simulate this circuit – Schematic created using CircuitLab

  • 2
    \$\begingroup\$ (Unless we've got crossed terminology here...) You can't use AC phase control on an AC induction motor to alter the speed. Phase control starts a triac conducting later in the AC half-cycle then lets it switch itself off as the triac current crosses zero. An slow-responding load device, such as a filament light bulb, will produce heat and light corresponding to the average power received. AC induction motor requires continuous AC waveform. You vary speed its by varying its supply frequency, often by high-frequency PWM and six big FETs (AC->DC->PushPullPerWinding) to make home-made winding ACs. \$\endgroup\$ – TonyM Jun 10 '17 at 13:08
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    \$\begingroup\$ What's your line voltage? (240)^2/(30k+30k) = 1 Watt in each resistor... \$\endgroup\$ – sstobbe Jun 10 '17 at 14:03
  • \$\begingroup\$ @TonyM well, yeah, I know it is not a good way to use phasecut, I already try to search an VFD for single phase to vary its frequency but there's nothing like that in my country.. And for the push pull winding, I haven't know it yet but I will try. \$\endgroup\$ – Naufal B Jun 10 '17 at 14:24
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    \$\begingroup\$ Search the internet for 'AC induction motor speed control', it's decades-old principles though far easier to do with cheap modern IC technology. Phase control here is not so much a bad idea as pointless i.e. it does nothing to the speed. A senior manager once demanded we try it and in the end it was quicker to do so and discredit it than argue. That controller went bang, I seem to remember... Anyway, good luck with the reading-up. \$\endgroup\$ – TonyM Jun 10 '17 at 14:54
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    \$\begingroup\$ @TonyM My respect for senior managers just took one extra notch down the ladder. \$\endgroup\$ – winny Jun 26 '17 at 14:51

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