Electromagnetic Wave Interference

I have just converted my Lathe with a Newton Tesla 3 Phase 1 hp motor kit which includes a Mitsubishi D700-SC Inverter. The problem that I now have is that the Inverter is transmitting a lot of EMC noise, so much so that the DRO Console [M-DRO] counters are counting crazily.

Newton Tesla instructions suggest fitting a Mitsubishi FR-BSF01 Line Noise Filter, but these are near on impossible to find and purchase.

My question is, is there anyone out there with the same problem? I do not know much about electronics, so I’m hoping that some one can help me, there must be another type of popular line filter that I could use instead of the FR-BSF01

Howard

Not your problem.

Contact Newton Tesla about sending it back as not fit for purpose / defective.

Whole point of buying a full motor and inverter kit is that its properly engineered and just works.

At the very least I'd expect Newton Tesla to say "Ooops, shouldn't happen. Try the enclosed filter. If it works please pay £ ---.". As the instructions admit to a potential problem they should, subject to supply chain issues, have the filters in stock.

Obviously at consumer prices the ultimate in EMC protection cannot be provided but getting a workmanlike and legal system goes with the territory. I would have expected Newton Tesla to have performed basic EMC tests on the assembly as a matter of course with some documentation indicating what to expect if installed as advised without messing around with the wiring.

That level of EMC noise is just plain wrong and I suspect the inverter is defective in some way. Mitsubishi have a well deserved reputation for decent engineering. Certainly the two older ones I have show no EMC issues despite very basic installation.

Clive

If all else fails, feed the inverter via suppressed power socket . Hopefully, this will prevent the replacement from sending any nasty spikes back up the mains.

Don't know what my inverter does in the way of EMI, since it has always been fed from such a socket, and there have been no problems seen or reported..

Howard.

Look at the earthing and screening of the DRO. Also routing of wires, where its mains is plugged in. Then same for speed control. You can use an old Long wave radio to get a feel for the range and power of the emissions.

Contact Newton Tesla about sending it back as not fit for purpose / defective.

Mmm, not sure abt that...It all depends...Most reputable VFD suppliers manuals give reasonable guidelines towards appropriate installation. Generally this includes size and max lengths of wiring, routing guidelines for the wiring from VFD to motor, etc. Are such guidelines in the NT VFD manuals and have they been reasonably adhered to?

Almost all cases of excessive LOCAL EMI from VFD's stems from the wiring from VFD to motor - not from VFD to mains supply. The level of EMI in the wiring tween VFD and Mains plug is orders of magnitude less that in the wires to the motor.

The motor wiring carries 400volt peak, PWM switched voltage, with very fast rise times and high peak currents - these currents can be 2 to 10 time the RMS current flowing in the motor winding circuit. It is precisely those PWM volts/currents that are the culprit in most cases. The mains side is supplying said current peaks as well, but the mains is converted to DC inside the VFD and feeds large electrolytic and Mylar or Polypro capacitors. These do a not to shabby job of filtering out most of the serious peaks, leaving the mains lead EMI 'tolerable' for home workshop applications.

If you route the motor wiring circuit at all near the DRO circuits, you will have trouble. It you have long wire lengths you increase the radiated EMI field greatly. The wiring is the antenna and the bigger the antenna, the further the filed can reach.- 1 meter of wire between VFD and motor should be an easily achievable limit ( try for less), grouped tightly together, away from all DRO or other machine electronics, and if still a problem, enclose the motor wiring in a shield - the outer braid from some heavy coax cable, copper or aluminium tape wound around the wire, and ground the VFD end to the VFD ground.

Mitsubishi's EMC advice here, which looks comprehensive. The Line Noise Filter is discussed in Section 7. Available in the US, but not Europe by the look of it, which is odd. The pictures look like a simple Ferrite Ring through which the mains cable is looped several times. They don't say what the ferrite is, I guess it's a high permeability type. Something from the RS range might do.

The other advice is pertinent too. Separating the DRO and Inverter wiring would help if they are routed together. Coils of wire jumbled together round the back is asking for trouble. Some of their advice about screening and earthing is easy to apply.

Clive is keen to send the Inverter back, but be aware off-the-shelf EMC protection is expensive and you may not consider the real thing to be affordable.

And the M-DRO is at fault too: it shouldn't react to EMC! If a roof leaks, should you blame the rain or fix the roof? Probably necessary to put toroids on the Inverter and the DRO. I'd start with the DRO because it's sensitive.

EMC isn't an easy fix because so much depends on the transmitter, receiver, and their environment. Have a read of Mitsubishi's document and apply any of it that's not too difficult: a few simple counter-measures might be good enough. If not, look to the Toroids.

Dave

PS. When playing Radio, I hate Model Engineers with their inadequately protected pulse mode power supplies and howling electric motors. The level of interference you lot pump into the ether is appalling. When playing lathes, I hypocritically buy affordable equipment, even if does wipe out air traffic control and the ambulance service...

Joseph

Good points with which I entirely agree with for a VFD box bought as a stand alone unit for customer installation.

However Newton Tesla supply the motor, inverter and pendant as a complete kit with all wiring save for the power input to the VFD. As such the EMC issues should have been dealt with as bought and no problems ought to occur so long as the VFD to motor wiring isn't modified or, if not already pre-wired, not installed as per the instructions.

If the controls are on a separate pendant it would seem to take some seriously misguided creativity to get the VFD and its output wiring close enough a reasonably made DRO box for it to be affected by radiated EMC.

Obviously given the price / performance limitations of anything sold on the consumer market there will be edge cases where ambient sensitivity to EMC may be such that a normally acceptably low level of emissions may still be too high making extra filtration and installation precautions needful.

Lathe plus DRO is pretty much standard these days for anyone whose pockets are deep enough to buy an off the shelf motor and VFD kit. So it should just work.

Newton Tesla have earned a decent reputation for supplying workmanlike equipment so it sounds as if something is seriously wrong.

SOD

Having had some experience with sorting EMC issues back in the days when it first became a thing it really isn't something where individual experimentation beyond simple cook book add ons is likely to be rewarding. Bottom line is that the rules for decently well behaved equipment design are now well established as are those for proper installation.

A kit of decent quality equipment from a reputable supplier should  "just work" unless there is something seriously odd going on or if you want to use it for duties its not made for. This is a bread and butter product for Newton Tesla and the expectation is that any EMC issues will be minor and associated with something unduly sensitive. Modern DROs should cope with any emissions from a reasonably positioned VFD just fine.

Clive

Edited By Clive Foster on 17/04/2022 16:36:20

Before we leap to conclusions it would be nice to have some more information.

• What does the OP mean by "kit"? Is it just the motor + inverter + pendant, or one of their "packages" where everything is built into a box that fits on the front of the lathe and includes a filter and has EMC approvals?
• If the former then it's quite clear from their website that a filter is not included and of course even with a filter the EMC performance will depend on correct wiring.

There have been previous threads on this subject here and I'm sure that either finding those threads or just looking on Inverter Drive Supermarket will find something suitable.

https://inverterdrive.com/Catalogue.aspx?search=filter

**LINK**

For what it's worth I have an NT package on my S7 and it "just worked" and I certainly haven't noticed any interference to the CNC electronics driving the lathe.

As far as I recall the EM noise emissions allowed for industrial installed equipment is far more that that allowed for Laboratory/Domestic installation. So Newton-Tesla may say their kit is designed for industrial installation. To meet domestic requirements they may say you need to buy a filter. An extremely crude filter can be made by simply winding the mains lead around a lump of steel rod and this may be sufficient to prove that conducted EM noise is causing the issue with the DRO.

CS

Taking up Joseph's point the cable from the inverter to the motor should have an earthed screen bonding the motor casing to the inverter and to the machine to prevent radiated EM noise .

CS

OMG! Thanks guys for all your help, but I did not think that the problem would be so difficult to solve. It looks like I'm about to spend many hours investigating and trying out some of your solutions. But I agree with Clive it is not acceptable that such a problem comes from a firm such as NT. I sent an e-mail to their support team about a week ago about the problem but at the time of writing have had no reply. Once again Thanks guys

Howard

I think that dialogue with NT should be the way forward and Howard has already emailed them with the details of the problem, perhaps after the Easter break a phone call would help provide the resolution. Dave W

REO UK Ltd Filters are a good point to start with (if you have to)

/www.reo.co.uk › emc-filters1

Another data point. I have an MDRO system on my mill with a VFD, no filter, no screened cable, no problem. Don't assume the VFD is the problem, check all the dro connectors and earthing.

I've recently installed the same setup and had no problems with interference. Did find NT very helpful (and quick) in sorting a couple of other minor issues.

I agree with some of the replies in that you should first check the earthing of everything, cable routing etc to eliminate the obvious. If all Ok, what about lashing up a temporary 'faraday' metal screen box for the inverter to see if that improves things and if it does you can build / get a proper one later?

regards Mike

I’ve no idea what a “kit” might include. I have had no known problems with the six VFDs I have used.

Questions:

Is the VFD housed in a suitable enclosure?

Are the VFD to motor conductors (properly) screened?

Is the DRO suitably protected?

.

The items shown on this page would appear to fit the description “kit”

**LINK**

https://www.newton-tesla.co.uk/product-category/lathe-speed-controls/inverter-motor-packages/

“ … for you to build into your own system.”

MichaelG.

By te way when earthing everything make sure you avoid 'earth loops'. They are often the source of the coupling from one system to another. The bane of the old HiFi music equipment. .

Indeed, and a dialogue with Newton Tesla, who I've found to be most helpful, would seem more appropriate than sending it back as not fit for purpose.
This is particularly so, as they also advertise a fully pre-wired kit, which they state is "EMC / CE Compliant. Designed and manufactured here in the UK."
I have one of these on my Warco 720 (Myford S7 clone) and it works well; I've not noticed any interference on other kit or the radio.
https://www.newton-tesla.co.uk/product/av750-1-0hp-package-for-myford-super-7-raglan-mk5-boxford-aud-cud/

Bill

There we go, a fully pre wired plug and play kit intended for the unskilled masses against a cheaper kit, but not supplied with a power lead, which means you are supposed to be a competent person to officially install it.

We previously had a DRO (last year I think) display issue when the motor was run caused by bad earths. Worth trying to run the lathe via an extension lead from the house and see if it still does it. It wouldn't be the first time a wall socket had a poor earth.