I'm using the circuit in the picture with a BTB12 600BW snuberless triac to control an universal motor (picked from a old washing machine, 220 VAC, 50 Hz) controlled by an arduino nano in customized PCB I made. At the moment only in "open loop" control.
As zero crossing I'm using the circuit below, with the output on the emittor side and a 10KOhm pull-down resistor.
https://images.app.goo.gl/VrPu1aej51YPKi3s8
The problem started when I connected the motor and ran the program, as you can see (fixed voltage, 45 VAC): https://youtu.be/5Q3df7z6ZT0
Setting a fixed or variable (ramp) voltage from arduino, the motor sometime, at a random time, "jump" at a higher velocity then return back to the imposed velocity. It seems that sometimes the triac remains close for some AC cycle before to come back to the normal behaviour, and so on.
The simple code I'm using is here: https://drive.google.com/open?id=1d2r3AmiUaU0wRjiOclEF8eqn1y7RIoIr
Note that the main loop has been purified from Serial and delay() functions to not affect the correct interrupt execution, but the problem is still present.
I passed the code to a friend of mine that have a very similar circuit (he only differ for mounting an R-C snubber on a classic not snuberless triac) and no problem of "jumping" appear to him.
At this point I'm thinking of a problem on the motor's collector. Unfortunately I don't have an oscilloscope. When the jump happen, I'm able to see a little increment in the output voltage (only the transient tail the multimeter is capable to capture).
What do you think about?
To Marko:
Yes, infact I was thinking that the R+C in my case should be used to snubber the optocoupler and not the triac (as suggested in many MOC30XX AN). For now I tried to insert a classic snubber R=100 Ohm and C=100nF on the main TRIAC side and it seems to work well. I solved temporarely but I didn't understand why a "snuberless TRIAC" requires in my case a snubber! Another test i can do is to eliminate the TRIAC snubber and insert an optocoupler snubber to see if the problem is solved the same. Maybe the current R+C I added helps in some way the turn off of the internal MOC triac, not the main triac. As last help, what size do you think I should consider in the R+C OPTO and R+C TRIAC. Currently I used 4W for the 100Ohm resistor (39Ohm in the AN) and 630V for the 100nF capacitor.
