Lathe/VFD/DRO issue

[Roger ClarkParticipant @rogerclark]

Posted by JasonB on 22/06/2023 14:18:00:

Roger, you said you had connected the Screen (assumed DRO screen/panel) to the other two earth wires(assume earths in VFD)

What Robert has suggested is earthing the metal sleeve around the cable from VFD to motor as you don't have a metal box for a metal gland to connect two he has suggested using a metal plate that all other earths can be connected to. If this is what you meant by screen then do similar to the DRO sleeves and also check the VFD instructions to see if they say one end or both connected to earth

He also suggested an EMF filter as your VFD may not include one. Does it?

When I said screened cable I meant the cable from the vfd to the motor which I may have mistakenly thought the wire wrapping was the scrrened part of the cable, think it was a case of me thinking one thing and you understanding another. I would never directly connect the dro panel earth into the vfd earth, that would be a no no.

Roger

[JasonBModerator @jasonb]

That is why the metal plate or a cabinet is useful so you can easily join all the earths, they all go back to the same place in the end.

[Dave HalfordParticipant @davehalford22513]

Posted by Rockingdodge on 22/06/2023 13:53:46:

Posted by John Doe 2 on 22/06/2023 12:00:00:

Posted by Rockingdodge on 22/06/2023

Putting the vfd into a metal box would mean I would not have access to the controls so what next guys?

Roger

Robert was trying to explain that to you, and has explained similar questions on other VFD threads. But you told him to "butt out".

Very rude.

Edited By John Doe 2 on 22/06/2023 12:01:28

No not rude just fed up of members talking over my head about what I should have bought and how I should reach industrial standards in a little one man hobby shop.

What I need, reall really need, is someone to walk me through in baby steps what to try in order to succeed in eliminating the interference, that's all I asked for and all I need.

Jason

I've tried Roberts suggestion as indicated in the post before your reply.

Dave Halford

Good point, I'd assumed the cable was screened as it was 4 core cable for 3 phase and that the wire wrapping was the screening, bought way back before the DRO installation.

I tried earthing the dro panel and initially seemed to work with one of the dros but not the other so I'll discount that as a coincidence.

so what do I try next? replacement cable first?

Roger

Roger,

Don't discount it, it's a positive change, look at the scale cable routing, are they the same?

If you swap the scale cables over does the fault move display port as well? If it does take the d-type plug covers off making sure you don't loose the screws and see if the earths are both terminated the same. If they are try a temp earth to the scale read head.

If it stays the same port the display is likely duff inside and you may have to shield the VFD, as in, wooden box, glue some earthed kitchen foil inside , bodge etc. Or buy decent cable and move it further away till it's out of range.

[Roger ClarkParticipant @rogerclark]

Roger,

Don't discount it, it's a positive change, look at the scale cable routing, are they the same?

If you swap the scale cables over does the fault move display port as well? If it does take the d-type plug covers off making sure you don't loose the screws and see if the earths are both terminated the same. If they are try a temp earth to the scale read head.

If it stays the same port the display is likely duff inside and you may have to shield the VFD, as in, wooden box, glue some earthed kitchen foil inside , bodge etc. Or buy decent cable and move it further away till it's out of range.

Thanks Dave,

Some positive steps to try, just watched a Clough42 utube as he had similar issues albeit affecting his cams and monitors so I think my initial steps should be to purchase some 3 core and earth cable (what size cores for 2,2kw? plus a filter for the mains input, again what one should I get?

Roger

[Mike PooleParticipant @mikepoole82104]

Roger, the situation you have found yourself in is a perfect example of what can go wrong when an installation does not properly address the control of electrical emissions. Very often a noisy VFD will not be a problem until a piece of equipment that is sensitive to noise is operated in range of the noise source. You may have unwittingly bought a noisy VFD, a sensitive DRO and a wiring installation that does not meet the requirements to control emissions. Input and output filters are often omitted from drives to keep cost down but the filters are usually available as separate components. The incoming mains filter can help to reduce the noise fed back into the wiring system but emissions radiated from the drive can be usefully screened with a metal enclosure. The braid of an SY type cable is primarily a mechanical protection and other types of cable will have copper braid screen and maybe a copper foil layer in addition, CY is a cable with better electrical screening. The reason they make all this stuff and have recommended earthing strategies is because you are not the first to run in to trouble and I doubt the last. Much research has gone into the practical methods of emission control and it is worth following the recommendations. An industrial Ethernet installation in a car body welding shop has extensive earthing requirements and checking compliance was a part of the buy off process. Mains noise brought our factory to a halt for 15 hours and cost a lot of money, although we did not prove it conclusively we strongly suspected that a large VFD was the source of our problem.

Mike

Edited By Mike Poole on 23/06/2023 10:19:18

[Roger ClarkParticipant @rogerclark]

Posted by Mike Poole on 22/06/2023 15:39:21:

Roger, the situation you have found yourself in is a perfect example of what can go wrong when an installation does not properly address the control of electrical emissions. Very often a noisy VFD will not be a problem until a piece of equipment that is sensitive to noise is operated in range of the noise source. You may have unwittingly brought a noisy VFD, a sensitive DRO and a wiring installation that does not meet the requirements to control emissions. Input and output filters are often omitted from drives to keep cost down but the filters are usually available as separate components. The incoming mains filter can help to reduce the noise fed back into the wiring system but emissions radiated from the drive can be usefully screened with a metal enclosure. The braid of an SY type cable is primarily a mechanical protection and other types of cable will have copper braid screen and maybe a copper foil layer in addition, CY is a cable with better electrical screening. The reason they make all this stuff and have recommended earthing strategies is because you are not the first to run in to trouble and I doubt the last. Much research has gone into the practical methods of emission control and it is worth following the recommendations. An industrial Ethernet installation in a car body welding shop has extensive earthing requirements and checking compliance was a part of the buy off process. Mains noise brought our factory to a halt for 15 hours and cost a lot of money, although we did not prove it conclusively we strongly suspected that a large VFD was the source of our problem.

Mike

Thanks for the explanation Mike I appreciate and understand what you are saying and also what others have said but that is not getting me any further forward, when I bought the cable from Inverter Drive it was for the vfd to motor connection, at that time I didn't know or planned to add DROs to the lathe. What I am trying very hard to get is advice on what size cable (only need 2 mtrs, and possibly from where) plus what size filter to get and from where?

Roger

[Nick HughesParticipant @nickhughes97026]

For the VFD to Motor wiring, this is the type of cable that you need and the correct gland:-

Cable

Gland

Also ask them to recommend which of there mains filters would be suitable for your VFD

[Roger ClarkParticipant @rogerclark]

Posted by Nick Hughes on 22/06/2023 16:41:39:

For the VFD to Motor wiring, this is the type of cable that you need and the correct gland:-

Cable

Gland

Also ask them to recommend which of there mains filters would be suitable for your VFD

Thanks Nick but why do I need 3 earths?

[Nick HughesParticipant @nickhughes97026]

Explained here:-

Reason for Symmetrical cable use

[Robert Atkinson 2Participant @robertatkinson2]

I've been working all day so am just catching up. Mike and Nick have covered just about everything I would have suggested.
CY cable will be better than the SY you are using. The Inverter drive supermarket cable suggested is a little unusual. It appears to suggesting the three earths are used as balanced conductors with the motor drives. This may or may not make a difference. The inverter outout is not balanced so that is no help. They will provide a conductor connected to ground that is closely coupled to to each motor feed conductor. This will provide a path for high frequency EMI to ground. Unfortunatly the capaitance of such a cable can affect the correct operation of the VFD.

Those saying gland plates will make no difference. This is plain wrong. 360 screening is well proven. Even with the same connector changing from a pigtail screen connection to flaring it out evenly over a ferrule and clamping under the cover make a huge difference, typcally at least 30dB (1000 times).

This is part my professional field of expertise. EMI/EMC is part of my day job. I am currently involved in producing the next revision of the EMI/EMC standard for civil aircraft. I have significant practical experience, including on industrial type equipment. This includes design and testing.
Im happy to help forum members with problems, and have provided parts FOC that solved a EMI issue for another member. But you cannot ignore the basic installation requirements for VFDs. This problem is exactly why you need to pay attention to EMI/EMC.

Robert.

Edited By Robert Atkinson 2 on 22/06/2023 17:36:44

[Roger ClarkParticipant @rogerclark]

Posted by Robert Atkinson 2 on 22/06/2023 17:22:31:

I've been working all day so am just catching up. Mike and Nick have covered just about everything I would have suggested.
CY cable will be better than the SY you are using. The Inverter drive supermarket cable suggested is a little unusual. It appears to suggesting the three earths are used as balanced conductors with the motor drives. This may or may not make a difference. The inverter outout is not balanced so that is no help. They will provide a conductor connected to ground that is closely coupled to to each motor feed conductor. This will provide a path for high frequency EMI to ground. Unfortunatly the capaitance of such a cable can affect the correct operation of the VFD.

Thos those saying gland plates will make no difference. This is plain wrong. 360 screening is well proven. Even with the same connector changing from a pigtail screen connection to flaring it out evenly over a ferrule and clamping under the cover make a huge difference, typcally at least 30dB (1000 times).

This is part my professional field of expertise. EMI/EMC is part of my day job. I am currently involved in producing the next revision of the EMI/EMC standard for civil aircraft. I have significant practical experience, including on industrial type equipment. This includes design and testing.
Im happy to help forum members with problems, and have provided parts FOC that solved a EMI issue for another member. But you cannot ignore the basic installation requirements for VFDs. This problem is exactly why you need to pay attention to EMI/EMC.

Robert.

I am interested in what you say even though it's like skylab passing over my head and apologise if any of my previous posts upset you, that wasn't intended but some of us have to run our hobby on state pension and these days it doesn't go far at all, especially when the missus goes clothes shopping.

I just need little cost effective steps to get to the point of having a workable solution please.

Where would the 3 earths connect to in the motor?

Roger

[Robert Atkinson 2Participant @robertatkinson2]

Hi Roger,

I'm not upset.
I can't recommend how to connect the 6 conductor cable as I've never used it. It will no doubt bring the "earth screen at one end / both ends" debate up. The variability of these things means that the only way to know for a particular design is to try the combinations and make comparative measurements. Obviously this is outside the capability of most industrial users never mind hobbists. I have the capability but am very much the exception. For a VFD with good support you should first follow the manufacturers recommendations. I'm not sure how good or valid the instructions supplied with your drive are. Those I've seen for generic drives haven ot been very good.
We have not even been to determine if this is radiated or conducted interference so it is all just trial and error.

Robert.

Edited By Robert Atkinson 2 on 22/06/2023 17:51:11

[Nick HughesParticipant @nickhughes97026]

In my case, I just crimped all three earths into one insulated ring terminal and then mounted this on to the earth point in the motors terminal box.

Edit:- Used the same method at the VFD end.

As for the shield grounding, I'm in the:- 

If trying to stop the noise "escaping" out from the cable, then ground at both ends.

If trying to stop noise getting into the cable, then only ground at one end.

Edited By Nick Hughes on 22/06/2023 18:13:26

[Roger ClarkParticipant @rogerclark]

Thanks Robert, Nick,

But surely if I tie the 3 earths and the shield together isn't that a case of 3 potentially current carrying earths in with the shield? I'm sure I've read that somewhere but am probably wrong as usual.

Will the 1.5mm2 be ok for a vfd of 2.2kw ?

Roger

[Robert Atkinson 2Participant @robertatkinson2]

1.5mm2 is fine for 2.2kW 3 phase.

[Roger ClarkParticipant @rogerclark]

Thanks Robert,

And an input filter? Type, size, supplier?

[SillyOldDufferModerator @sillyoldduffer]

Posted by Rockingdodge on 22/06/2023 18:31:50:

Thanks Robert, Nick,

But surely if I tie the 3 earths and the shield together isn't that a case of 3 potentially current carrying earths in with the shield? I'm sure I've read that somewhere but am probably wrong as usual.

Will the 1.5mm2 be ok for a vfd of 2.2kw ?

Roger

I don't know what to do with the 3 internal earths either, but it wouldn't hurt to earth them all at one end.

1.5mm2 should be fine for 2.2kW – it can take about 14A buried in a wall without overheating.

Simple answer, see Robert, Mike and others. Unfortunately, doing everything properly guarantees results, but is expensive.

There's no sure fire alternative to doing it properly. The technique is to unscientifically add layers of protection until the problem is controlled. Results are uncertain because exactly what's causing the trouble varies case-by-case, and difficult examples often end up by forcing the victim to do the job properly in several painful steps.

On the other hand with a bit of luck simple change might fix it, so worth trying a few. Things to try:

• The source is the VFD:
  • Change the cable, because it's cheap and easy, and the type already used isn't particularly good at shielding interference. (It's better than nothing, but not good enough)
  • The VFD is a component, with a only thin plastic case providing minimal physical protection, and no shielding. They're meant to be enclosed in an outer box, ideally made of earthed metal. The box protects the VFD from dirt and physical accidents, it protects the operator from shocks, and it helps contains the radiation that's zapping the DRO. It also allows the screened cable above be terminated correctly, important because simply dangling wires through a hole will leak. A box is relatively cheap, and can be home-made, but it means a pedant will have to be wired in. The pendant has a forward/off/reverse switch, an emergency stop, and a speed control, also in a box. Bit of a faff.
  • The VFD probably isn't fitted with a filter, which prevents EMC escaping into the mains, and from there getting into other equipment. Good filters are expensive, so I wouldn't rush to fit one unless putting the VFD in a shielded box doesn't fix the problem. I've thought of fitting a washing machine filter to the mains input. Far from ideal, but it might reduce the problem to 'good enough' level. If a filter is fitted, it works best inside a shielded box.
• The DRO is guilty too – it shouldn't respond to EMC.
  • Its leads should all be shielded. (I think they are)
  • It helps to keep the DRO and VFD cabling and the electronics well away from each other, certainly not running wires parallel in the same conduit.
  • All cables should be as short as possible
  • The DRO power supply should be filtered (but this is cheaper than a VFD filter).
  • Ideally the DRO should be in a shielded metal box
• The next bit should be only be followed after consulting an electrician. Mains safety earths are often complete poo when dealing with EMC. Various shortcomings, for example a safety earth wire might be routed all round the house before it connects to ground, turning the earth into an antenna blasting VFD muck with gay abandon rather than shorting it to ground. To remove EMC, the earth lead should be as short as possible, A separate earth might help, but don't install one unless certain the extra earth compatible with the electrical safety earth. Be embarrassing to get the DRO working and then burn the house down. I'm not a qualified electrician.

Might help to listen to the VFD with a battery powered portable medium wave radio. Close to, VFDs emit a harsh roar covering most of the band in a series of broad peaks and troughs. The radio can reveal if interference is on the mains cabling, or on the motor cable, or the VFD, which helps target the problem. Sorry to be a Jeremiah, but it will probably be all of them.

Good luck,

Dave

[Robert Atkinson 2Participant @robertatkinson2]

The input filter needs to be rated for at least 10A and ideally a dual stage type. There is also the issue of how it is mounted and connected. I really does need a metal plate under the VFD and filter and cable clamps or glands for the cable screen grounds.
For a new filter I'd look at something like this:
https://uk.farnell.com/schurter/5500-2603-01/ac-filter-1-phase-10a-250v/dp/2134492

I may have something suitable in my spares box. PM me your address and I'll have a look.

Robert.

Edited By Robert Atkinson 2 on 22/06/2023 21:17:27

[John HaineParticipant @johnhaine32865]

Posted by SillyOldDuffer on 22/06/2023 20:01:25:

Posted by Rockingdodge on 22/06/2023 18:31:50:

Thanks Robert, Nick,

• • ……it means a pedant will have to be wired in.

Good luck,

Dave

I love it!

[Roger ClarkParticipant @rogerclark]

Posted by John Haine on 23/06/2023 10:50:31:

Posted by SillyOldDuffer on 22/06/2023 20:01:25:

Posted by Rockingdodge on 22/06/2023 18:31:50:

Thanks Robert, Nick,

• • ……it means a pedant will have to be wired in.

Good luck,

Dave

I love it!

I'm lucky in that the pendant is removable so if I have to buy/build a box I an get a longer cable and mount it outside.

Roger

[Robert Atkinson 2Participant @robertatkinson2]

A comment was made elsewhere about the cost of the 360 degree screening cable glands and was there alternatives.
One possibility is a 15mm brass compression fitting as used in domestic plumbing. The main limitation is that they will not provide strain relief so a P clip or similar needs to be used as well. The body of the fitting needs to be fastened through the box wall or to a bracket on the metal mounting plate. One end of the compression olive needs to have the sharp edge removed by filing or similar. The nut and olive are placed on the cable and the screen conductors folded over the dull edge of the olive and tightened into the body.

Robert.

[Roger ClarkParticipant @rogerclark]

Just got the cable delivered from Inverter Drive, downside was the postage cost about the same as the cable

If I were to go down the metal wall box route how do I go about cooling the vfd without comprising the shielding?

Roger

[Roger ClarkParticipant @rogerclark]

Posted by SillyOldDuffer on 22/06/2023 20:01:25:

Might help to listen to the VFD with a battery powered portable medium wave radio. Close to, VFDs emit a harsh roar covering most of the band in a series of broad peaks and troughs. The radio can reveal if interference is on the mains cabling, or on the motor cable, or the VFD, which helps target the problem. Sorry to be a Jeremiah, but it will probably be all of them.

Good luck,

Dave

Just checked with an am radio and the source does seem to be the output cable from the vfd so we'll see if it makes a difference when I change the cable.

Roger

[noel shelleyParticipant @noelshelley55608]

One thing that would make good flexible shielding/conduit is an old chrome shower hoseand the fittings at each end are 1/2"BSP. Just check continuity between flex pipe and end fittings. Simples. Noel

[Robert Atkinson 2Participant @robertatkinson2]

Posted by noel shelley on 24/06/2023 14:19:37:

One thing that would make good flexible shielding/conduit is an old chrome shower hoseand the fittings at each end are 1/2"BSP. Just check continuity between flex pipe and end fittings. Simples. Noel

Totally useless as shielding, It's a sprial with virtually no continuity between turns.

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