Inverter interference

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Inverter interference

This topic has 27 replies, 13 voices, and was last updated 24 February 2022 at 09:36 by Vic.

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21 February 2022 at 22:43 #586678
Vic
Participant
@vic
A friend of mine is having some difficulty with the inverter on a lathe causing occasional signal drop out between a video camera and projector. It’s assumed this is through the mains wiring. Is there some kind of filtering device that could be placed between the mains socket and the camera to prevent this? TIA.
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21 February 2022 at 22:43 #36764
Vic
Participant
@vic
21 February 2022 at 22:58 #586681
Tony Pratt 1
Participant
@tonypratt1
Look at Clough42 on YouTube 3 years ago on this very subject

Tony
21 February 2022 at 22:59 #586682
Pete Rimmer
Participant
@peterimmer30576
Yep, VFD input filter commonly available and not even that expensive. It's wired between the supply and the inverter drive.
22 February 2022 at 07:55 #586690
David Jupp
Participant
@davidjupp51506
Quality of the VFD/motor installation may be a factor.

To work well, input filter should be mounted on same metal backplane that the inverter is mounted on.

A filter may not fix things if there are other issues with the installation.
22 February 2022 at 08:12 #586691
Anonymous
I'm not sure why it is assumed that the problem is due to conducted emissions down the mains? It's possibly more likely that the issue is due to radiated emissions. Is the cable from the VFD to the motor shielded? If so, is the shield grounded at one end or both ends?

Does the problem occur when the VFD is on, but in standby, or only when the motor is being powered?

How often does the comms dropout occur and how long is each dropout?

As stated above mains filters are readily available, and are a good thing to fit, even though they may not solve the current problem.

Andrew
22 February 2022 at 09:31 #586699
PETER ROACH
Participant
@peterroach92938
Simple solution is turn the inverter off. Engineered solution is to put inverter in a grounded box with correct front end filter for it. Incorrect filter could further tune noise, rather than attenuate. Mount as close to motor as possible and screen cables, grounding at one end only so as not to create loops, back to initial star ground point. If you have a pendant, screen the wire to than also. Check any LED lights for emissions also with a radio.
22 February 2022 at 09:33 #586700
Neil Lickfold
Participant
@neillickfold44316
I tested tonight 2 different VFD's to see if they interfere with the TV and they did not. Mine do have a built in filter to the mains supply. Also all my shop and house wiring is going through the new breakers with the earth leakage things.. Either called ELCB (older models) or an RCD (the newer one.&nbsp The RCD maybe doing some filtering as well, I just don't know. Back when I had an outside shed, when the old fuse was changed to the new RCD breakers in both the shed mini power box, and the supply fuse changed to an RCD, the interference that we had in the house from some machines, was eliminated. Maybe look into an RCD in the house fuse box for that circuit.

Neil
22 February 2022 at 11:35 #586731
Vic
Participant
@vic
Posted by Tony Pratt 1 on 21/02/2022 22:58:37:

Look at Clough42 on YouTube 3 years ago on this very subject

Tony

That’s very helpful Tony, thank you. I will pass on the link.

Apparently the lathe and camera remain in fairly close proximity. The problem is somewhat reduced but not eliminated if the two items are physically plugged as far away as possible from each other.
22 February 2022 at 12:51 #586745
David Jupp
Participant
@davidjupp51506
Regarding connection of cable screens to ground, and on grounding of all items – I suggest you follow recommendations of the VFD manufacturer. Whether to ground one or both ends of the cable screen will get you at least 3 different opinions…
22 February 2022 at 12:56 #586746
Martin Johnson 1
Participant
@martinjohnson1
I recently upgraded to a cheap ebay inverter package on my lathe and while I was on the job I installed a small power supply for my Arc Euro digi bar readout. Inverter works fine, digi bar works fine until the lathe is switched on. It seems interference wipes the settings on the digi bar readout. If I use a battery supply to the digi bar all is fine, so I infer the problem is mains borne.

Have operated for some months on batteries to the digi bar now. Must get that round tewit.

Martin
22 February 2022 at 15:31 #586757
old mart
Participant
@oldmart
When I bought a Scneider VFD for the museum's Tom Senior light vertical, I had the advantage of being able to print out the quickstart guide from The Inverter Supermarket. Following this was easy and I paid strict attention to the screening of all the wiring, including remote controls and having a fully earthed metal box to house the inverter. This was in a different enviroment from a home installation and the strict adherance to the rules was necessary. So far it has caused no interference to mobile phones, radios or wifi, including 433Mhz remote controls.
22 February 2022 at 19:10 #586797
Vic
Participant
@vic
I’ve just seen this in the lathe manual.

“If a filter is required to reduce EMI install it as close as possible to the AC drive. EMI can also be reduced by lowering the carrier frequency. When using a GFC (Ground Fault Circuit Interrupter), select a current sensor with sensitivity of 200 mA, and not less than 0.1 second detection time to avoid nuisance tripping.”

This seems to be saying: “We know our inverter causes EMI but we’ve decided not to deal with the issue”.
22 February 2022 at 19:46 #586800
Robert Atkinson 2
Participant
@robertatkinson2
If it is aood quality drive by a well known manufacturer, follow their installation recommnedtions.
If some unknown far eastern item with minimal or pooly translated manual you are left with guessing.
Basically you will likely need to:

Install the inverter in a metallic enclosure
Fit a high performance EMC filter at the mains input to to the drive.

Keep th cable to the motor as short as possible and ideally use some kind of shielded cable SY flexible armued cable is a goodd compromise e.g. https://www.tlc-direct.co.uk/Products/MF2dot5slash4.html

Lacing advice from drive manufacturer dround the shield/armour at the "wall" of the metallic box enclosing the drive. Metallic cable glands designed for this are available. keep it insulated at he motor end (use a plastic strain relief) and ground the motor housing with the fourth core in the cable.

Use screened cabble for ny control pendant or similar.

That's mid-level good practice.

Robert G8RPI.
22 February 2022 at 19:59 #586803
Vic
Participant
@vic
The lathe and associated inverter are as supplied by the retailer. The inverter is already in a metal box mounted at the back of the lathe.

The inverter is possibly a Delta S1 (shown in the manual) but I’ve not actually seen it.
22 February 2022 at 20:06 #586804
Robert Atkinson 2
Participant
@robertatkinson2
Go back to the vendor of the lathe and ask them to fix it or provide details of the EMC qualification.

Robert G8RPI.
22 February 2022 at 20:20 #586806
Vic
Participant
@vic
Posted by Robert Atkinson 2 on 22/02/2022 20:06:15:

Go back to the vendor of the lathe and ask them to fix it or provide details of the EMC qualification.

Robert G8RPI.

The lathe is over ten years old and the issue has only surfaced since the video camera was replaced.
22 February 2022 at 20:34 #586808
Anonymous
Posted by Vic on 22/02/2022 19:10:48:

“We know our inverter causes EMI but we’ve decided not to deal with the issue”

Industrially the VFD is considered to be a component, which is used within a larger installation. The need for EMI filters will be considered taking into account the whole installation. That may mean a VFD has it's own filter, or a filter is shared, or one isn't needed. Consequently most VFDs do not have a built-in filter.

EMI might be lowered by reducing carrier frequency, but it's not usually clear cut. The carrier frequency determines how far apart the harmonics are spaced. How far the harmonics extend, at a significant amplitude, is determined by the speed of the waveform edges, which probably won't change much with changes in carrier frequency.

Andrew
22 February 2022 at 21:02 #586814
old mart
Participant
@oldmart
I was worried about the leakage current from the filter causing the rcd's to trip, they are lower than domestic ones, but so far there has been no problem.
23 February 2022 at 06:23 #586836
Howard Lewis
Participant
@howardlewis46836
It is possible to buy power sockets with built in suppression. My VFD is fed from a double 13A suppressed socket, and no problems with interference to domestic TV or internet have been noticed.

Howard
23 February 2022 at 08:24 #586848
PETER ROACH
Participant
@peterroach92938
Howard,

13A suppressed sockets are designed to suppress incoming spikes to IT equipment, not to reduce outgoing noise. They are typically based around a device that shorts to ground if a high voltage spike is seen. Even if they were, at the socket is not the ideal location since the cable from socket to VFD would still radiate any conducted from the VFD. If you need any additional filtering it needs to be as close to the source as possible, entry to the enclosure and chosen so that it attenuated the noise and not as a resonant with any existing front end filters in the VFD.

Peter
23 February 2022 at 10:53 #586875
Vic
Participant
@vic
Posted by Andrew Johnston on 22/02/2022 20:34:41:

Posted by Vic on 22/02/2022 19:10:48:

“We know our inverter causes EMI but we’ve decided not to deal with the issue”

Industrially the VFD is considered to be a component, which is used within a larger installation. The need for EMI filters will be considered taking into account the whole installation. That may mean a VFD has it's own filter, or a filter is shared, or one isn't needed. Consequently most VFDs do not have a built-in filter.

Andrew

it’s not industrial equipment, it’s a small wood turning lathe offered to home users.

Thanks to everyone else for your comments. There seem to be several possible solutions but at least one may require the services of someone more experienced with electrics. Possibly the simplest solution would be to use this with the camera?

**LINK**

or maybe this.

**LINK**

Any thoughts on them?
23 February 2022 at 13:00 #586892
Martin Johnson 1
Participant
@martinjohnson1
We all seem to have assumed the inverter is emitting unacceptable levels of EMC. It is quite possible you have a camera (and maybe my digi readout transformer as well) that has substandard protection from mains borne EMC.

Martin
23 February 2022 at 19:04 #586953
Anonymous
Posted by Vic on 23/02/2022 10:53:07:

it’s not industrial equipment, it’s a small wood turning lathe offered to home users.

Totally missed the point. I was trying to explain why VFDs do not generally have built-in filters. The manufacturers don't give two hoots about home users, but design for the requirements of industrial installations.

I apologise for mentioning engineering on a modelling forum.

Andrew
23 February 2022 at 19:07 #586955
Clive Hartland
Participant
@clivehartland94829
I had to earth both ends of the screened cable before the interference stopped on my set up.
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