Has anybody experimented using Optocoupler on 240V AC circuit? Something like VTL5C3? Basically LED & LDR pair.
Would it be possible to substitute POT with these and build pwm controlled resistor? I only find them used in audio stuff.
An optocoupler is generally a LED + phototransistor. A Vactrol (resistive isolator) is a LED + LDR. Optocouplers are more common these days. Any particular reason why you'd want to use a resistive variant here? In principle it'll work - it's been done for decades. It'll still work today.
The main concern with either is to (1) limit the LED current and (2) limit the reverse voltage you expose the LED to (it may not like / survive seeing 325V for a moment every half-phase).
Not sure where you're going with this.
In principle you can put a pot across 230VAC, but I wouldn't recommend it for various reasons. So let's not go there.
A pwm-controlled resistor is a different matter; there are so-called digital pot meters, but the vast majority are rated for 6VDC max. There are a few that will withstand a couple dozen volts DC, but nothing HV-AC to the best of my knowledge.
A quicker route towards a solution would be if you explain the application/context. What are you trying to do?
Are you trying to make a light dimmer?
PWM is digital so you don't normally need a variable resistor.
Regular PWM doesn't (usually) work with dimmers because dimmers are normally built with TRIACs and a TRIAC latches-on until the current drops to zero (at the next AC zero-crossing). Regular PWM isn't synchronized with the AC cycle and it's too fast.
Manual/analog light dimmers do use a pot.
A regular AC light dimmeruses something like PWM but synchronized with the AC line frequency, and it "chops" the waveform so it's only on for part of the cycle.
With a digitally controlled Typically, there are two opto-isolators... One to detect the zero-crossing for synchronizing, and one special TRIAC driver opto-isolator to control the TRIAC that switches the voltage.
I know triacs, and I have those digitally controlled with zero crossing.
But I was interested of substituting a pot in 240V ac circuit.
I was asking about Vactrol (technically optocoupler), not DAC(because of voltage), to substitute a pot in existing 240V AC circuit. It would give me optoisolation and photoresistor would smooth pwm nicely. Data sheets give me insulation up to kV range, but I wanted to know if there are other factors to consider.
Can you post a schematic of the present situation with the 240V pot (or how you imagine it if you were to use a pot)?
Please also include the specifications on the pot that's currently in the circuit.
And describe what's connected to the wiper of this pot; i.e. what do you need it's variable output for - what kind of load?
Thank's.
No I don't have it on my hands now, until next summer. Anyway I opened it last summer, it's a simple "universal motor controller" diac-triac circuit with small 250kohm pot. It would be difficult to replace the whole circuit, but the pot was wired and I was playing in my mind how could one digitalize only that pot. Of course I could do it with servo, but I got curious about LDR option. That leaded me to some Vactrol datasheet and I didn't see anything telling me "not possible". I'm not asking help to make a circuit, only experience or opinion about Vactrol at 240VAC.
That option came to mind, yes.
Based on your description, I'd be inclined to dig one layer deeper and see if there's a way to 'digitalize' the circuit that sidesteps the complication of a pot-like 'thing' at 230VAC.
No, me neither, other than that the output will evidently be quite different from a pot and it's still not quite clear how you intend to replace the pot with the Vactrol. I mean, one is a pot with a wiper in the center that supposedly serves to create a reference (AC) voltage.
The other is a component that you can use to alter the resistance of its secondary, isolated side. Maybe if you used two in series and drove them in opposite directions? Maybe this complication is unnecessary and you can get away with making the Vactrol part of a 3-way voltage divider. It depends on the range it needs to cover.
Yep.
Anyway, if I remember well, that pot was wired as a resistor.
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As a variable resistor you mean, wiper tied to one of the other legs? OK, that would make the replacement even more straightforward.
Interesting idea; please post back if you happen to proceed with it.
Thank you.
Of course it would need lot of mapping and calibration, but triac output needs it anyway.
I was looking for opinion/experience for doability.
Thank's to your feedback, I don't exclude it from my "experiments to do suitcase".
If I manage to try next summer, i'll update...
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