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Isolated zero cross detection w/ AC mains

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wraper:

--- Quote from: coppice on October 08, 2019, 01:35:09 pm ---Even 1206 resistors are only rated for 200V. Two of those gives you a 400V rating. The peak of a 264V sine wave (upper bound of 240V mains) is 373V, so they are marginal best, with no allowance for harmonic peaks or surges.

--- End quote ---
They usually have 1.5-2 times of that as surge rating. http://www.royalohm.com/pdf/product2017/GeneralPurpose.pdf

coppice:

--- Quote from: wraper on October 08, 2019, 01:51:05 pm ---
--- Quote from: coppice on October 08, 2019, 01:35:09 pm ---Even 1206 resistors are only rated for 200V. Two of those gives you a 400V rating. The peak of a 264V sine wave (upper bound of 240V mains) is 373V, so they are marginal best, with no allowance for harmonic peaks or surges.

--- End quote ---
They have 1.5-2 times of that as surge rating.

--- End quote ---
Yes, but when you try something like the standard fast pulse transient tests they can arc very badly.

wraper:

--- Quote from: coppice on October 08, 2019, 01:53:29 pm ---
--- Quote from: wraper on October 08, 2019, 01:51:05 pm ---
--- Quote from: coppice on October 08, 2019, 01:35:09 pm ---Even 1206 resistors are only rated for 200V. Two of those gives you a 400V rating. The peak of a 264V sine wave (upper bound of 240V mains) is 373V, so they are marginal best, with no allowance for harmonic peaks or surges.

--- End quote ---
They have 1.5-2 times of that as surge rating.

--- End quote ---
Yes, but when you try something like the standard fast pulse transient tests they can arc very badly.

--- End quote ---
If you don't use MOV, you can say the same about say PCB connector for mains input.

beduino:

--- Quote from: wraper on October 07, 2019, 11:39:13 pm ---Optocoupler reacting only to peak voltage is not very helpful for accurately detecting zero cross. There is not always ideal sine waveform in mains to allow you to accurately calculate zero cross from that. Ideally you want it to turn off only as close as possible to zero voltage. Also one need to consider that if it works now, does not mean it will work over time. Optocoupler CTR tend to degrade and one should consider that when designing things.

--- End quote ---
I've connected my "prozerocross" detector shown a few posts above to logic analyzer (Saleae) and as I said it looks like we do have two digital waveforms for positive and negative mains 230VAC sinewave, so now it should be easy in software calculate zero crossing time prediction what ever logic 0 or logic 1 we take based on its width, so it doesn't matter if optocoupler degrade over time as well as we can see that optocoupler is not reacting only to peak voltage  8)


However, there is something which is strange and didn't expected or maybe logic analyzer inverts logic level, since EL817 are connected in zero cross circuit as shown below (Vcc is Li-ion ~3.7V), so I have no idea for the moment what the hell is going there, while I'd rather expeced to see high logic levels shorter than logic low in given 50Hz time periods ~20.02ms, but it looks like optocouplers turn on its outputs for longer time?  :o
I've used EL817 with cut off frequency around 80kHz shown in its datasheet  ???


I've attached also Matlab 1s 1MHz sampled those two digital outputs pulled down via 100k resistors.
NOTE: Nope, it is not possible attach .mat or .mat.gz files ...

What is going there?   :-//

Anyway, I'm working now on MPU software to predict zero crossing based on those two (positive and negative mains sinewave) optocoupler responses and output in real time to see on logic analyser channel0 for analysis if we do hit somewhere (in the middle I hope) between rise/fall since there must be zero cross I guess.

Maybe I missed something?

schmitt trigger:
If you are using emitter resistors, then don’t use collector resistors. Or viceversa.

100k is way too large an optocoupler load resistor, go for 10k or 5k.

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