3 Phase, monitor phase rotation? Optocoupler maybe.

Forums › Home Workshop DIY › 3 Phase, monitor phase rotation? Optocoupler maybe.

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Uber Geek

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#3024342 19-Jan-2023 21:13

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.

Resistance voltage dropping was not my first choice and I was assuming there must be something better.

Yes. You wire the relay input to the supply (potentially via fuses). It doesn't care whether you have loads connected or not; it just moves a contact to tell you what the status is, and your controls can decide to start up a motor or select a direction based on that.

Capacitive droppers can be an option but introduce a phase shift (this shouldn't matter as the shift on all three phases should be identical), and still need some series resistance to provide inrush limiting.

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.

Have you priced out the cost difference between VFDs and soft starters? For small motors like this, something like a WEG CFW300 or ABB ACS55 can be pretty cost-effective.

MrJohn

77 posts

Master Geek

#3024349 19-Jan-2023 21:39

SomeoneSomewhere:

Yes. You wire the relay input to the supply (potentially via fuses). It doesn't care whether you have loads connected or not; it just moves a contact to tell you what the status is, and your controls can decide to start up a motor or select a direction based on that.

So that is this E.g. the ABB CM-MPN.52 relay?

Capacitive droppers can be an option but introduce a phase shift (this shouldn't matter as the shift on all three phases should be identical), and still need some series resistance to provide inrush limiting.

Have you priced out the cost difference between VFDs and soft starters? For small motors like this, something like a WEG CFW300 or ABB ACS55 can be pretty cost-effective.

Capacitive dropping, thanks.

Everyone tells me I need VFDs but I do not see the advantage over the soft start solid state contactors. This is the layout I have in mind..

The problem we have is that the two motors are connected to the one supply cable which is controlled from a remote panel. The gantry gets askew and has no incentive to go back to the centred position and just scrubs the wheel flanges against the side of the rails.

The scheme is to monitor the position of one wheel and when detected off centre on the rail pause the motor on the leading side. I do not see the need for VFDs and I am unsure how they would behave with stopping and phase reversals from the remote panel. I am hoping the solid state contactors act like mechanical contactors and will oblivious to supply interruptions and phase reversals (maybe I am wrong).

Rust

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Master Geek

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#3024516 20-Jan-2023 06:27

MrJohn:

...

Everyone tells me I need VFDs but I do not see the advantage over the soft start solid state contactors....

Everyone has mentioned VFD's because they solve a lot of other problems, but its only now, after many posts, you have finally explained the actual application.

Gantries are commonplace in industry and, with the exception of very large or specialist installations, typically do not require electronic control systems to remain in alignment. Mostly this comes down to the fact that identical drive motors on each side are always rotating at exactly the same speed, and good track design takes care of the rest.

Whilst you don't indicate the actual application for the gantry, if I assume a typical crane gantry style installation then I suggest ascertaining what is causing the gantry to miss-align in the first place. Depending on the issue that may be a better problem to solve.

MrJohn

77 posts

Master Geek

#3024518 20-Jan-2023 07:00

Rust:

Gantries are commonplace in industry and, with the exception of very large or specialist installations, typically do not require electronic control systems to stay on track. Mostly this comes down to the fact that identical drive motors on each side are always rotating at exactly the same speed, and good track design takes care of the rest.

Whilst you don't indicate the actual application for the gantry, if I assume a standard crane gantry then may I suggest ascertaining what is causing the gantry to miss-align in the first place? Depending on the issue that may be a better problem to solve.

You may be puzzled at why I have not revealed the actual application and you may have noticed that although I opened with what I thought was a simple enough question the initial responses were not exactly helpful.

This is not the first forum I have sought assistance and experience has taught me that revealing the application usually only gives scope for side issues and thoroughly uninformed comments.

However, perhaps this forum is different so I can tell you that this application is related to dairy farm backing gates in a rectangular yard.

Rust

99 posts

Master Geek

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#3024528 20-Jan-2023 08:08

Ah right, I see where the miss-alignment is coming from now.

Unfortunately I am a mechanical, rather than electrical, engineering guy, so probably will not be of much help. But if you find you still need to 'sense' the phase rotation direction, I wonder if an inductive pick-up such as a hall effects sensor would be better than using something that would require tapping into the 400v lines?

mkissin

388 posts

Ultimate Geek

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#3024540 20-Jan-2023 08:42

A VFD would help solve your problem because suddenly both motors are totally agnostic to the phase settings at the remote board, and are locally controllable through a simple comms interface on your gantry. They internally create a DC bus and then generate their own output sinusoids.

Stopping one and reversing it slightly would be almost zero effort.

Sorry you think we're being unhelpful, but the lack of input info often results in giving someone just enough rope to hang themselves.

MrJohn

77 posts

Master Geek

#3024542 20-Jan-2023 08:50

I will be using** hall effect sensors to sense when the wheel flange is up against the rail.

Sensing the 400v is so that when the remote operator energises the line I know the direction before closing the contactors so I can start the forward or reverse logic. I think SomeoneSomewhere has given me a black box solution which I need to check out.

**actually, I am not doing this job myself, I just want to have something I can give the farmer to take to his electrician and I will do the logic box.

Thanks

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MrJohn

77 posts

Master Geek

#3024554 20-Jan-2023 08:55

mkissin:

A VFD would help solve your problem because suddenly both motors are totally agnostic to the phase settings at the remote board, and are locally controllable through a simple comms interface on your gantry. They internally create a DC bus and then generate their own output sinusoids.

Stopping one and reversing it slightly would be almost zero effort.

Sorry you think we're being unhelpful, but the lack of input info often results in giving someone just enough rope to hang themselves.

Ah yes, but if the VFD is agnostic how does anything on the gantry get to know what the remote operator is wanting if not by sensing the phase rotation?

MrJohn

77 posts

Master Geek

#3024630 20-Jan-2023 09:56

Hmmm.. I took at look at the ABB CM-MPN.52 relay and yes it does detect phase rotation and when that feature is enabled and a phase reversal is detected it raises an alarm and does not connect. Not exactly what I need but maybe it can be instructed to connect after alarming due to phase reversal.

Sorry you think we're being unhelpful, but the lack of input info often results in giving someone just enough rope to hang themselves.

Ah yes, "This car is not for you sir if you have to ask the price."

Rust

99 posts

Master Geek

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#3024709 20-Jan-2023 10:40

Just to elaborate briefly on my previous post, if you had to fall back on the Arduino idea, I was imagining sensors such as this installed around 2 phases. I believe this could detect which is leading the other without worrying about wiring up optocouplers?

MrJohn

77 posts

Master Geek

#3024713 20-Jan-2023 10:48

Rust:

Just to elaborate briefly on my previous post, if you had to fall back on the Arduino idea, I was imagining sensors such as this installed around 2 phases. I believe this could detect which is leading the other without worrying about wiring up optocouplers?

Excellent, those are certainly worthy of investigation.

Thank you.

mkissin

388 posts

Ultimate Geek

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#3024747 20-Jan-2023 12:16

A CT probably won't work because current would need to be flowing, implying the motor is running already. You need to sense the voltage directly, unfortunately.

Edit: unless you can sense one of the lower current lines into another piece of equipment on the same line. Getting a bit rube-goldberg for my taste, but might work for you.

mkissin

388 posts

Ultimate Geek

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#3024748 20-Jan-2023 12:18

MrJohn:

mkissin:

A VFD would help solve your problem because suddenly both motors are totally agnostic to the phase settings at the remote board, and are locally controllable through a simple comms interface on your gantry. They internally create a DC bus and then generate their own output sinusoids.

Stopping one and reversing it slightly would be almost zero effort.

Sorry you think we're being unhelpful, but the lack of input info often results in giving someone just enough rope to hang themselves.

Ah yes, but if the VFD is agnostic how does anything on the gantry get to know what the remote operator is wanting if not by sensing the phase rotation?

In this case you might need a new switch telling the drive directly.

MrJohn

77 posts

Master Geek

#3024756 20-Jan-2023 12:34

mkissin:

A CT probably won't work because current would need to be flowing, implying the motor is running already. You need to sense the voltage directly, unfortunately.

Edit: unless you can sense one of the lower current lines into another piece of equipment on the same line. Getting a bit rube-goldberg for my taste, but might work for you.

Hmmm, that does put a bit of a pause on things.

MrJohn

77 posts

Master Geek

#3024944 20-Jan-2023 20:09

I got word this evening that the gantry at one of the farms became de-railed today so the farmer wants to get right on to this project.

Concept for guided backing gate. 20 Jan 2023

The backing gate gantry can become mis-aligned and jam or even de-rail. This scheme is intended to detect and correct the mis-alignment by automatic means.

The design uses existing equipment with the addition of a few cheap components.

The key to the system is the tracking sensors which can be simple hall effect, capacitive or induction sensors, other sensor types might be used. The sensor detects when either wheel flange is close to the side of the rail. A flange close to the rail indicates mis-alignment.

The system corrects mis-alignment by pausing the motor on the leading end of the gantry.

The connection between the existing electrical box and each motor is broken and a 3 phase contactor inserted. The systems pauses the motor as required by way of a signal from the Logic Box.

The system will work equally well whichever way the gantry is moving and to do that the Logic Box must 'know' which direction the gantry is moving. To do this the Logic Box reads from the Phase Rotation Sensor.

The Phase Rotation Sensor comprises two current sense transformers which will be read by the Logic Box to determine the present phase sequence and hence motor and gantry direction.

The Logic Box will contain an Arduino single-board microcontroller plus relays or whatever is necessary to interface to the 3 phase contactors.

The low voltage power supply will provide current for the Logic Box and sensors etc. It will also provide voltage isolation between the 400V 3 phase circuits and the Arduino and logic circuits.
The current sense transforms will also isolate the logic circuits from the high voltage 3 phase circuits.

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