Lathe/VFD/DRO issue

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

Oh, dear,

Obviously a few souls with bruised sensitivities. Rodger is trying to solve a problem outside his skills - but this forum doesn't seem to be providing a lot of help. I and others have made some suggestions, so lets give the guy a chance to work through it - no doubt he will come back to the forum if he has other questions, but rude non-productive comments don't help, do they?

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

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.

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

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

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

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?

Explained here:-

Reason for Symmetrical cable use

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

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

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

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

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

1.5mm2 is fine for 2.2kW 3 phase.

Thanks Robert,

And an input filter? Type, size, supplier?