I asked before about triac not working with induction fan.
After few experiments i found out that triac stops functioning properly after everytime there is a power cut and the fan supply switches from mains to inverter.
Can anyone suggest why is this happening and what can i do to prevent this.
What's happening to triac is that it probably starts leaking some current.
In off condition the fan continues to spin very slowly and make loud humming noise.
But when i start controlling its speed with moc3021 and microcontroller it works perfectly.

Any suggestion is appreciated.
Thankyou.

 

The output of a good inverter is indistinguishable from the mains. Sounds like you don’t have a good inverter.

 

Your invertor may not be sine wave. It's output may be Distorted Square wave.

You can try a solution putting a 2.2 K resistor between the Gate and MT2 (the lower terminal) to prevent dv/dt triggering of the triac.

 

The opto triac is much more susceptible to dV/dt triggering than the main triac. Try the circuit in section 2.4 of ST’s application note AN5114, that should remove the high dV/dt if the inverter is one of the so-called “modified” sine wave types,

 

R16 seems to have a much too high value. 180 to 470 ohms is what I would expect.

 

I will try the the circuit suggest by Ian0, hopefully it will work.

And R16 works perfectly even with such high value i decided to use it just to be safe.

Thanks

 

The opto triac is much more susceptible to dV/dt triggering than the main triac. Try the circuit in section 2.4 of ST’s application note AN5114, that should remove the high dV/dt if the inverter is one of the so-called “modified” sine wave types,

Values for this circuit are shown in section 3.2

 

I will try the the circuit suggest by Ian0, hopefully it will work.

And R16 works perfectly even with such high value i decided to use it just to be safe.

Thanks

A triac with to little trigger current is much more likely to fail than one with plenty, due to slow turn on,
100k gives 3.25mA at mains peak, less at every other trigger angle. The BT136 is only guaranteed to trigger at 5mA,
I use 100Ω, not 100k, designed to give as much trigger current as the opto device can withstand.

 

The opto triac is much more susceptible to dV/dt triggering than the main triac. Try the circuit in section 2.4 of ST’s application note AN5114, that should remove the high dV/dt if the inverter is one of the so-called “modified” sine wave types,

The circuit didn't work well for me.
The fan just started rotating at full speed.
I will try replacing the R16 with 100Ω resistor.

Thanks for your suggestions.

 

The circuit didn't work well for me.
The fan just started rotating at full speed.
I will try replacing the R16 with 100Ω resistor.

Thanks for your suggestions.

If that is the case, your opto-triac is dead