Electronics > Beginners

trouble with a triac

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kripton2035:
the optocoupler must be between A2 and G of the triac for the triac to operate "normally"


soldar:

--- Quote from: Zero999 on April 17, 2019, 01:50:21 pm ---
--- Quote from: 1makermold on April 17, 2019, 01:15:02 pm ---when I would fire the triac across the 24 vac, I would measure it and it would read 12 vac, I think it was triggering on both half cycles,

--- End quote ---
What's the opto-coupler's part number? Does it have zero crossing?

If so, then I suspect that could be the problem, rather than the TRIAC. Opto-couplers with zero crossing won't fire, until the voltage is above around 30V, which is close to the peak voltage of 24VAC and would explain why you're measuring half that. Replace it with an opto-coupler which doesn't have a zero-crossing detector and if you need zero-crossing, do it separately.

--- End quote ---

Good thinking! I had not thought of that. But a quick look suggests the diac is indeed zero crossing. Maybe someone con confirm. A 'scope would confirm it easily.

Zero999:

--- Quote from: 1makermold on April 17, 2019, 02:03:16 pm ---The optpcoupler is a moc3023, the voltage that I am looking for is 22-23 vac, I do relize that there will be a voltage drop going through the triac

--- End quote ---
The Q4006l has a built-in DIAC so would be no good either, as it won't trigger until around 30V.

The BAT16 and  MOC3023 should be good though.

How are you triggering the opto-coupler? Is the circuit isolated from the 24VAC supply?

A good alternative to an opto-coupler is a pulse transformer, but it's more difficult to use.

1makermold:
I am triggering the circuit from an isolated source

soldar:

--- Quote from: Zero999 on April 17, 2019, 02:32:54 pm --- A good alternative to an opto-coupler is a pulse transformer, but it's more difficult to use.
--- End quote ---


I cannot see any reason to not use an opto-isolator but if there was a strong reason then a plain old relay would work. A reed relay can be tiny and do the job.

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