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Inverter interference

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Vic21/02/2022 22:43:34
3089 forum posts
16 photos

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.

Tony Pratt 121/02/2022 22:58:37
2023 forum posts
12 photos

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


Pete Rimmer21/02/2022 22:59:46
1256 forum posts
69 photos

Yep, VFD input filter commonly available and not even that expensive. It's wired between the supply and the inverter drive.

David Jupp22/02/2022 07:55:26
838 forum posts
17 photos

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.

Andrew Johnston22/02/2022 08:12:46
6668 forum posts
701 photos

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.


PETER ROACH22/02/2022 09:31:59
50 forum posts
25 photos

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.

Neil Lickfold22/02/2022 09:33:11
890 forum posts
195 photos

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.  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.


Vic22/02/2022 11:35:50
3089 forum posts
16 photos
Posted by Tony Pratt 1 on 21/02/2022 22:58:37:

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


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.

David Jupp22/02/2022 12:51:56
838 forum posts
17 photos

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...

Martin Johnson 122/02/2022 12:56:10
154 forum posts
1 photos

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.


old mart22/02/2022 15:31:22
3892 forum posts
268 photos

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.

Vic22/02/2022 19:10:48
3089 forum posts
16 photos

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”. laugh

Robert Atkinson 222/02/2022 19:46:38
1240 forum posts
20 photos

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.

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.

Vic22/02/2022 19:59:06
3089 forum posts
16 photos

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.

Robert Atkinson 222/02/2022 20:06:15
1240 forum posts
20 photos

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

Robert G8RPI.

Vic22/02/2022 20:20:39
3089 forum posts
16 photos
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.

Andrew Johnston22/02/2022 20:34:41
6668 forum posts
701 photos
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.


old mart22/02/2022 21:02:43
3892 forum posts
268 photos

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.

Howard Lewis23/02/2022 06:23:50
6305 forum posts
15 photos

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.


PETER ROACH23/02/2022 08:24:56
50 forum posts
25 photos


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.


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