3 Phase, monitor phase rotation? Optocoupler maybe.

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MrJohn

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#303134 19-Jan-2023 07:07

I want to monitor the rotation of a 3 phase supply, 400v.

So what I really want to do to have an Arduino control a couple of 750w 3 phase motors. First I must determine which direction the motor(s) are rotating and I can do that by determining the rotation direction of the supply.

Basic idea is trigger an interrupt when phase 'x' is going positive and at that time check polarity of phase 'y'. If 'y' is positive then 'y' is leading 'x' and rotation is clockwise.

What do I need to do to monitor 400v lines and couple to Arduino? i.e. how do I couple 400v to optocoupler?

Thanks

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388 posts

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#3023484 19-Jan-2023 08:41

Probably what you actually want (and which would be vastly safer for you) is a shaft encoder to read the direction and speed of the motor directly.

MrJohn

77 posts

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#3023531 19-Jan-2023 08:54

Yes, maybe a good idea but the motor is not turning yet!

mkissin

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#3023532 19-Jan-2023 08:59

When you say "control"? What do you mean? Speed and/or direction?

Whatever device you're using to achieve that will almost certainly have provision for telling you the speed and direction.

This is the sort of question that, because you're asking it, you probably shouldn't be doing things directly to the 400V mains yourself anyway. You'll probably die.

mkissin

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#3023555 19-Jan-2023 09:34

Just to add to this, the three-phase phasor relationship isn't a surprise in any way. It never changes.

Wire the motor up, if it turns the wrong way, reverse two phases. Bingo, bango, done. No arduino or control needed.

MrJohn

77 posts

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#3023917 19-Jan-2023 14:14

mkissin:

When you say "control"? What do you mean? Speed and/or direction?

Whatever device you're using to achieve that will almost certainly have provision for telling you the speed and direction.

This is the sort of question that, because you're asking it, you probably shouldn't be doing things directly to the 400V mains yourself anyway. You'll probably die.

Am I to consider myself 'told off'?

Decal

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#3023923 19-Jan-2023 14:25

Have you looked at a VSD you can communicate to via Serial or Ethernet?

MrJohn

77 posts

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#3023928 19-Jan-2023 14:32

I do not want or need a VFD...

As per my opening post "What do I need to do to monitor 400v lines and couple to Arduino? i.e. how do I couple 400v to optocoupler?"

Thank you.

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mkissin

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#3023931 19-Jan-2023 14:35

MrJohn:

mkissin:

This is the sort of question that, because you're asking it, you probably shouldn't be doing things directly to the 400V mains yourself anyway. You'll probably die.

Am I to consider myself 'told off'?

Warned, is closer to the truth.

Would an optocoupler give you the info you want? Yes.

Is it the correct solution? There's not enough detail to tell, but it seems unlikely since you apparently want to detect whether your phase rotation is positive or negative and then...do something based on that information? But that will never change, so you don't need to detect it anyway, just get it right at installation time.

Plus, an optocoupler is physically small and needs other circuitry as well to do what you want. Are you capable of turning it into an adequately safe circuit that you could then connect directly to 400V 3-phase? I'd say not.

I'm not trying to be annoying, I design high frequency 75kW+ inverters for a job, and this stuff can be really dangerous.

If you outline what you actually want to achieve, perhaps we can provide a better overall solution.

MrJohn

77 posts

Master Geek

#3023939 19-Jan-2023 14:45

mkissin:

Plus, an optocoupler is physically small and needs other circuitry as well to do what you want.

I believe that is what I asked.

If you outline what you actually want to achieve, perhaps we can provide a better overall solution.

I apologize if I did not make that clear in my opening post.. "So what I really want to do to have an Arduino control a couple of 750w 3 phase motors. First I must determine which direction the motor(s) are rotating and I can do that by determining the rotation direction of the supply."

mkissin

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#3023944 19-Jan-2023 14:48

MrJohn:

I apologize if I did not make that clear in my opening post.. "So what I really want to do to have an Arduino control a couple of 750w 3 phase motors. First I must determine which direction the motor(s) are rotating and I can do that by determining the rotation direction of the supply."

But you'll know which way they're rotating....because it'll always be the same way, unless you're in control of those 3-phase voltages, in which case you probably also know because you set it.

It sounds to me like there's almost certainly a safer way to achieve what you want.

Otherwise, you just need a resistor, properly sized to your optocoupler, whatever that is.

MrJohn

77 posts

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#3023947 19-Jan-2023 14:51

mkissin:

Otherwise, you just need a resistor, properly sized to your optocoupler, whatever that is.

Thank you.

richms

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#3024048 19-Jan-2023 16:08

There are phase rotation relays on aliexpress for very cheap that will do all the hard work of checking that it is correct and give you a dry contact output when the rotation is correct. There are ones that will do voltage as well so if its bad they will turn it off.

Were like $30 when I last looked at it.

Richard rich.ms

MrJohn

77 posts

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#3024173 19-Jan-2023 18:42

There are a few devices there to look at but I cannot claim to have identified one that would give me what I need?

SomeoneSomewhere

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#3024222 19-Jan-2023 19:00

Yeah, phase rotation/conformity relays are a common piece of electrical equipment.

Note that most only have one (changeover) relay contact, so you get "OK, CW rotation" or "something's wrong" - which could be wrong rotation, lost phase, or potentially under/over voltage.

As such, you may need either two relays or a relay module with two outputs, so that you can get 'OK CW', 'OK CCW', or 'FAULT'. Or you can just assume that a fault is going to be phase sequence and not anything else...

It looks like suitable relays are often called phase correction relays. E.g. the ABB CM-MPN.52

'Arduino' and '400VAC' generally should not be in the same project. Optocouplers are nice, but 400VAC with DOL motors nearby can be nasty - big spikes. Watt-wasting with resistors is also going to require serious consideration of heat. You're also potentially going to have fun with noisy industrial power that may well cross zero many times per cycle.

MrJohn

77 posts

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#3024333 19-Jan-2023 20:26

SomeoneSomewhere:

Yeah, phase rotation/conformity relays are a common piece of electrical equipment.

Yeabut, will they tell me phase rotation direction before switching motor on? When I start this machine I want to know which way it is going to go and the supply comes from a remote control panel which has reversing capability and I have no way of telling if they have selected forward or reverse.

'Arduino' and '400VAC' generally should not be in the same project. Optocouplers are nice, but 400VAC with DOL motors nearby can be nasty - big spikes. Watt-wasting with resistors is also going to require serious consideration of heat. You're also potentially going to have fun with noisy industrial power that may well cross zero many times per cycle.

Resistance voltage dropping was not my first choice and I was assuming there must be something better. So far I have found simple resistance drop 400V to optocoupler (2V?) and a circuit using 1N4004G, resistance and 7400N gates. I did not stumble on any 400/12v transformers in my junk box but I guess they are available.

The scheme being considered starts and stops the 750w motors via solid state contactors which advertise soft starting. I have no doubt that the multitude of pumps, vacuum pumps, compressors and irrigators in the immediate vicinity will be kicking up a fair racket electrically but I expect there will be scope for filtering the trickle of 400V being bled off to the optocouplers.

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