(I apologize for the quality of the photo)
Today I woke up a distinct smell of smoke and the exclamations of my wife – "get up quickly , At you there something burns in a workshop ". After a couple of seconds, I saw the source of the fire that had almost started, when a lukey 852d + was plugged into a socket, the fryer was heated to a red glow, a plastic handle was burning with a bright fire.
So, what happened? When all the consequences of ignition were removed, I opened the soldering station and was unpleasantly surprised. The fact is that the management of heated hairdryers in almost all hatchways is carried out through a triac power regulator, which in this case received an PWM signal from the Atmega's leg through an opto-triac pair.
This circuit is powered directly from the input 220 volts, from protection only snubber RC chain and everything. If the triac BTA16 fails due to a surge in voltage, the hair dryer begins to glow happily at all its 700 with copecks of Chinese watts.
What should I do?
1) Put parallel to this triac varistor with a cutoff of 275 volts – with short bursts the excess will dissipate in a spiral, and the triac will remain locked.
2) Open the circuit using a 220 volt 10 A relay, by hanging the control winding through a 1,500μf capacitor, a diode and a small transformer to the pump terminals. The logic is simple – if the pump does not work, then the power supply circuit of the heating spiral is a priori open.
Well, do not trust the Chinese, leaving unguarded Uncle Liao's technique in stand-by, even if she worked without shoals for the last 5-6 years