I would like to detect only the positive going zero cross of the phases. In single phase,this would be a simple Live to resistor then resistor to anode of diode then cathode of diode to anode of optocoupler led and cathode of this led to neutral, then on the other side of Arduino I detect a rising edge.Which is the same thing I want to do with 3 phase, problem is there is no neutral. How do I create a virtual neutral so that I have 3 optocouplers each for each phase to detect only the positive zero cross going and detect a rising edge with Arduino on the other side? I even don't know if this virtual neutral can be able to load the leds in the optocouplers.
Do you have access to ground? As in the muddy stuff outside. Neutral is neutral because it's connected to ground, so for voltage sensing purposes ground should do the job. Do not use ground for any load. Do not do this if you don't understand the safety implications.
I don't know the maths off hand but you should be able to compute what you want from monitoring the voltages between the 3 phases.
Thank you for your immediate reply,but what is your suggestion on this Perry Bebbington and yes sometime the neutral may be there for other single phase loads.
If you have the neutral for single phase loads then you have the neutral. I don't understand why it would be a problem.
The purpose for this is to detect the phase squence, You say if I locate the neutral from the "muddy stuff somewhere " haha I just liked that phrase, this will work?
That you monitor the voltage between each phase and earth. If you do this there are safety implications you will need to address. I'm not going to advise you more because this is something you need to address with local expertise, not from advice given to you by a stranger on an internet forum.
At least in the UK neutral is neutral because it is connected to ground, as in the muddy stuff. I can't speak for other countries but I imagine they are the same.
If by 'work' you mean give you a reference for measuring the individual phase voltages with respect to neutral, then yes, it should work.
A 3 phase induction motor will do this, just check which way it rotates. To do electronically you don't need neutral, you just need to monitor phase 2 with respect to phase 1, phase 3 with respect to phase 2 and phase 1 with respect to phase 3. See what order the peaks or zero crossings are in and you'll get your answer.
Some of the questions you have asked worry me because they make me concerned that you don't know enough to know what is dangerous. If this is the case please get help from someone who knows.
Ok brother thank you so much.My plan was to use 3 optocouplers connected in single phase format half wave connection for each phase with one diode and resistor of course with neutral and then detect the individual positive going zero cross.
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If i remember my three-phase power, there is NO neutral if you have a "delta" connection. There is a neutral if you have a "Y" connection. Which three-phase system do you have?
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Interesting question, which I shall ask someone who might know. As far as I know local distribution in the UK is always connected star, so has a neutral. Whether the neutral is connected to a particular load is a different question, there wouldn't be any need for a 3 phase motor for example. All the transmission network is delta, which is obvious from looking at the cables: they are in threes.
No need for a neutral. Just connect your optocouplers across the 3 phases.
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Please Mr Jim-p, explain more on this, how can I do it.As you may have seen, I need to detect only positive going zero crosses.
Star and "Y" are different names for the same configuration. In the US the standard three-phase is "Y" because any one phase to common/ground is 120 volts, the standard voltage for powering almost everything. The difference between any two phase is 177 volts which is the standard for industrial lighting.
If you following the transmission network, 22KV, the wires do a permutation of the positioning of the wires every few miles. Sometimes I see the distribution line go for 20 miles or so with no drops. This is in the Eastern Oregon desert.
Remember, LEDs are diodes and will light for one connection direction based on your AC. So if you are not getting positive going crosses, reverse the opto connection.
Yes Mr Paul_KD7HB, but I need to know the physical connection between the 3 optocouplers hot side and the 3 phases
If that is the case, you failed your licensed electrician test!
What are the line-to-line voltages of this three phase system?
Why Mr Paul_KD7HB, i think that is why we are here for, to ask what we don't know and get advise what to do and what not to do in order to achieve what we want.But not insult.
Nice people, I don't see any problem someone asking how they hold a knife.If I see it as a funny question I will simply not answer it and someone else willing will answer it however simple it looks.
It was not an insult is was an observation that you have not been to the classes in electrical distribution systems and do not seem to be aware of the electrical power available to kill you when dealing with three-phase electrical systems.
You have not told us the voltage and current available from your 3-phase power source for some reason, so we can only relate to what we have worked on. If your three-phase system is less than 5 volts AC, we can continue.