Heater circuit question

[ec911]

Hi,

I've drawn a heating element circuit from a hot air station and I'm trying to learn from it to get better at understanding electronics.

It is a heating element driven by a BTA12-600B triac which is controlled by microcontroller via a MOC3021 optoisolator.

Here's the schematic (sorry if it's badly drawn  )



Could somebody explain me what the green path with the capacitor C6 and R14 is for?

[Paul Moir]

I think it's an RC snubber, which is designed to protect the triac by shunting the inductive kick that occurs when you turn off an inductive load.  It's the same idea as using a reverse biased diode on a relay to protect the transistor that turns it on and off in a DC circuit, but the RC snubber works with AC.

The thing is a heater usually has very little inductance, so I don't think it's very necessary?

[ec911]

Thanks for the reply! I was to post the answer I just found while searching on google, it is indeed a RC snubber.

I don't know about the necessity.. ??

This is from an Aoyue 852a++ hot air station.

[ec911]

Also, what would be the purpose of the big ceramic resistance R10? Is it some kind of choke for the heating element?

[Tomorokoshi]

Are there any other parts like fuses or thermal switches in the circuit? Anything thermally connected to that 1/2 ohm resistor?

[ec911]

No, I've double checked and it's in serie with the M1 terminal and the heating element.



This is the big 5w resistor

[HackedFridgeMagnet]

Also, what would be the purpose of the big ceramic resistance R10? Is it some kind of choke for the heating element?

Maybe to limit the current before the heating element is hot.

[SeanB]

Resistor limits current to the heater when it is cold, and also is supposed to be a fusible resistor if the heater goes short circuit, though there with that white ceramic resistor it is not likely to do so. The snubber across the triac limits the rate of change of voltage across the device, so that spikes on the incoming mains do not trigger it by accident.

[ec911]

Ok got it, thanks for the clarification!