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Triac switching circuit is frying resistors

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raldred

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Having trouble with my triac switching circuit.
My circuit is based on the solid state relay circuit (using triacs) electronics-lab

I have tried 0.6W resistors and 2W
the 0.6 680 Ohm is fried instantly.
the 2W 680 Ohm smokes

It works with the 2W, it does switch on an off.
but its obviously drawing too much current across the resistors i cant figure out why.

There is sequencing circuit using flipflops using the the AC side could that be affecting it?

Or are my resistors just not limiting the current enough, a few people iv spoken to reckon i should have more like a 2.5K to replace the 680 Ohm

Here's my circuit as it stands. I hope to have 4 of these identical circuits running in parrallel from the same fused 240Vac source
46_1275654007.gif
 

The resistors shouldn't get too hot.

The opto-couipler manufacturer suggests 360Ω where you have 180Ω and 470Ω where you have 680Ω but the values are not super critical.

Two things come to mind - are you sure you don't have the two main terminals of the Triac reversed?

and

What load are you using? Some loads kick back substantial amounts of energy which cause misfiring of the Triac. If this is the case, try connecting another capacitor (same as the first one) with 100Ω in series with it, directly across the Triac. It will slow down the rise and fall of spike interference. Triacs also trigger when the voltage across them changes abruptly such as when spikes appear on load or supply.

Brian.
 

Yeh im surpirse I have found many circuits like this which all claim to do exactly what I want.

I don't think I have the triac reversed... I will have to double check that but I think leg 1 is connected to GND, leg 2 connected to the (-) on the bulb and leg 3 is the gate connected directly to the opto pin 4.

Where abouts do you suggest the second capacitor? in the same arrangement as the current one?

Thanks
--Rob

I'm using a standard 60Watt bulb.
 

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