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triac wiring

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npomeroy

New Member
I'm trying to use an optoisolated (MOC2031) triac (BT137) to drive resistive loads up to a few 100W (light bulbs for incubator heating). The output to drive the MOC input is 6v as the output of a 555 timer. This is in series with 360ohm to the MOC2031. On the power side the hot 240v line goes to pin1 of the the triac and a 360 ohm 1/4W resistor to pin 6 of the MOC. Pin 2 of the triac is connected to the other hot wire which goes to the load (currently 150W bulb).
Pin 3 of the MOC is connected direct to pin 3 of the triac. This seems to copy the circuit shown on the fairchild data sheet for the MOC, without the snubber components. But the triac does not turn on. There is about 20mA going through the input LED of the MOC.
Am I missing something obvious?
 

npomeroy

New Member
triac wiring correction

"Pin 3 of the MOC is connected direct to pin 3 of the triac. " should read "pin 4 of the MOC..."
 

duffy

Well-Known Member
I'm afraid you may have blown out the triac. That 360Ω gate current resistor on the 240V side would be more than 10 times too low for that circuit, if it's hooked up the way I think it is. Could you post a schematic? Even a pencil or PC Paint drawing would help.
 
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npomeroy

New Member
Triac wiring schematic

Attached is the same circuit but copied from elsewhere. R2 is actually 360 ohm.
Terminal A2 is pin 1 on my triac.

npomeroy
 

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npomeroy

New Member
I've attached a couple more diagrams, one showing the wiring digram from the optocoupler data sheet, and my one showing my connection. Sorry it's a clumsy word file.

OK, on the BT139 pin 1 IS T1. What I meant was that my circuit differed my posted schematic in that I had optocoupler connected to pin 1 of the triac (via the resistor). I see now perhaps it should be pin 2 not pin 1.

I can try this. Is the resistor still too low value do you think?
 

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duffy

Well-Known Member
No, that's backwards - you have T1 and T2 switched. Look at the schematic symbol, the gate is on the side with T1.

The resistor is probably fine, my mistake, I just looked at a bunch of other schematics and it's a lot lower than I remembered.
 

npomeroy

New Member
Triac wiring solved

Thanks Duffy
I switched the resistor to pin 2 and it works fine. For 150W it should be passing a bit more than 1/2 A. Do you usually need heat sinks on triacs? It didn't seem to warm up (I disconnected power before feeling!).

NPomeroy
 

duffy

Well-Known Member
Did you run it under load? Yes, triacs often need heatsinks, and even at just 1/2 amp that triac will have to dissipate around a watt, so it should be getting quite warm.
 

aesar

New Member
555 timer

what frequecny range beappliedthrough 555 timer,how the pulse should be,please send its circuit aslo(555timer),is the same pulse can be applied to run 30 Watt load
please do reply
[email protected]
 
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