BTA16-600BW not turning off

[Andre1]

Hi

I have been testing the following circuit (which apparently works). I am finding that the TRIAC (BTA16-600BW) does not turn off with an inductive load (induction motor at 240V, 3A. 50Hz) yet with a simple house lamp the circuit works switching the lamp on and off.

I have modified R9 to 360ohm (340V/1A = 340ohm) chose 360

R10 has also been modified to 360ohm

R39 was added at 510ohm

I have removed L3, C11 and C13 from the circuit.(they are for EMI)

I have swapped MT1 and MT2 so that active is now on TRIAC pin 2 and TRIAC pin 1 feeds the load.

Though this is a snubberless part I added a snubber, 560ohm 0.1uF

none of these changes make a difference.

I turn the relay on which provides power.

I turn the OPTO on which turns the TRIAC on, but when I turn the OPTO off again the motor slows a little but does not stop.

OPTO is MOC3021

Either the OPTO or TRIAC is latching on and remaining on at the zero crossing. A snubber is supposed to improve this. Maybe my values are way off.

Any suggestions?

Thanks

Andre

[FCokl.1]

Hi Andre

You are not able to turn off Triac becuse of the phase difference between Voltage and Current while driving inductive load. They never become zero at the same time to turn off the Triac if phase difference available. Try to compansate the phase difference or don't use Triac. I hope this helps you.

Regards,

Futuh

[Andrew Lohmann]

Hi Andre,

I can not see your circuit but the Triac will turn off when there is no gate current and the main current has dropped below the holding current, 50mA (probably 10 or 20mA). As Futuh indicates the current will drop to zero at a different time from when the voltage drops to zero. If you are using the Triac as a switch that should work if you are trying to phase control the motor could be burnt out unless you take care to ensure that the current is symmetrical on both the negative and positive cycles of the AC supply.

I don't know what the relay you mention is for?

The link to my website shows some old technology including a General Electric data book on some applications for thyristors and triacs. There are many applications for inverters which for example drive inductive loads and work with AC or DC supplies. The most sigificant thing is you almost can destroy a triac or thyristor they blow a fuse or something else up.

https://engineering.andrew-lohmann.me.uk/electronics/electronics---noise-cancellation