VFD Drives

[macmarchParticipant @macmarch]

[macmarchParticipant @macmarch]

Not sure which forum to put this on.

I am enjoying my newly fitted FVD drive. The thing is that I have the dreaded RFI problem. Searching t’internet has resulted in so much conflicting information that I now turn to those who have been there/done it.

From what I can glean, it seems that the cable from vfd to motor is the main culprit. Shielding this should reduce the problem. Can anyone advise :-

 

Metal Conduit.

Earth one end or both.

Link that earth back to the common Inverter earth or direct to supply earth.

Metal cover over inverter,  (with provision for air to enable the fan to cool correctly), again earthed to supply.

Fit new earth from lathe to supply.

 

I need to sort something out the intreference is MW, FM and DAB to at least 20 feet from the workshop.

 

ray

 

 

Edited By macmarch on 17/03/2011 18:58:31

[KWILParticipant @kwil]

Ray,

 

1 Has the VFD got a built in or added on mains filter? The manufacturer will specify.

 

2 Do what the circuits say, shield the control wires in one screen and the motor wires in its own, earth ONLY one end of the screen on the motor leads. Have a good strong earth to the lathe, the incoming mains supply earth is OK to the main common earth but make it of a good wire gauge.

 

3. You can run inside conduit AS WELL, I did on my M300 but only for convenience

 

I have 4 inverters, all clean without problems, All as it happens, are inside a metal cabinet for safety reasons, but as I did not take any precautions where the screened cables pass through the metal wall, the cabinets are not really providing any real screening.

 

All my cables are SY screened flexibles, screens earthed one end only.

 

All my kit is in the garage and additional workshop, which are under the house (I live on a hill).

 

Hope this helps.

 

K

[chris stephensParticipant @chrisstephens63393]

Hi Ray,

Is the interference on a battery or a mains radio? If mains it could be interference going down the ring main. This can (?) be fixed with a line filter like the one Arc Euro sell . If battery radio then you will probably have to shield the VFD and motor feed.

I admit to not being an expert on the subject, so no complicated questions please.

chriStephens

 

This was being written while Kwil posted his reply, but it still holds true.

Edited By chris stephens on 17/03/2011 19:44:19

[macmarchParticipant @macmarch]

Thank you Kwil,

 

I’ll run the motor leads in conduit. I’l have to leave the last 2 inches and cover this with a floating bit of tube and connect by use of clamps and heavy earth wire . The control cable has NO screen at all, but as its only low voltage and is 4 switches and 1 pot it shouldn’t be a problem.

As the inverter has the mains and motor earths I’ll ;ink the conduit to the lathe and on to the supply earth.

You didn’t mention the inverter. I’ll assume that a cover in the form of a vertical channel would be better than nought.

 

cheers for the info,

 

ray

[Les Jones 1Participant @lesjones1]

Hi Ray,

I noticed the other day that Arc Euro Trade are selling screened power cable and mains filters to go with their high speed spindles. (Which use an inverter.) Chris’s idea about using a battery operated radio to identify whether the interference is coming from the leads from the inverter to the motor or from the mains lead to the inverter is a good one. This will help you to decide whether to try screened cable first or a mains filter. From the schematic of the filter it should not cause problems with tripping an RCD.

Here is the link to the relevant section of the Arc Euro website.

 

Arc Euro high speed drives.

 

Les.

[John CoatesParticipant @johncoates48577]

Must admit I have had no problems after converting my lathe and mill to VFD with an inverter per machine. All I did was buy some shielded cable and each one has this connected between motor and inverter with the shielding fixed to the ground point of the inverter. Have a DAB radio within three feet of the lathe motor and about 6″ of the shielded cable to that motor and it has no interference whatsoever.

 

Have you used shielded cable in your setup?

 

regards

 

John

[Ramon WilsonParticipant @ramonwilson3]

Hi Ray,

I too have just fitted VFD drive to lathe and mill – see elsewhere – but to date have not experienced any RF noise at all.

 

‘As the crow flies’ the (mains) radio is about twelve feet away from the inverter though it is mounted behind a wooden interior wall. The radio, a Sony, and from the very bottom of the range has no aerial other than the supplied twisted wire variety

 

The cables from motor to inverter are as supplied ie not run through conduit and likewise those of the control stations. I did ensure that these were not run side by side however and have them about 100m apart for most of their run though by neccessity they all come together as they aproach the inverter.

 

The inverter is mounted directly into a Contiboard shelf unit and though shrouded on four sides is totally open at the front.

 

I am getting the whine so well described by Peter Gain on the Indian made lathe motor and at the top end am finding it mildly irritating whilst the lathe spindle is not engaged but I guess I will get used to it eventually. Having read elsewhere on here that this can be improved by resetting the frequency I have checked this out with the supplier of the VFD but it is already set to the best limit for this problem.

 

As an aside I set this up initially as one inverter with two outlets – one for lathe the other for mill via plugs and socket. I am so pleased with the system but so fed up with the constant changing of plugs that today I’ve ordered another inverter.

 

Hope you solve your problem, as an avid R3 listener I can certainly sympahise – I would be far more irritated if my unit had affected that

 

Regards – Ramon

[KWILParticipant @kwil]

Ray,

 

I did say all Inverters were inside metal cabinets, but that the passing of the cables through the metal wall, without any precautions on the screening would probably negate the screening by the cabinet.

 

Looking at the “Standard Wiring” diagram of just one of my inverters, a Yaskawa, they clearly show the control wiring within screened cables. It is not the low voltage that matters, they could be acting as an antenna to radiate RF interference. This I have done with all 4 I have in use.

[David ColwillParticipant @davidcolwill19261]

If you choose to Earth the screen it is usual to earth only 1 end, normally the end nearest the incoming mains.

[macmarchParticipant @macmarch]

Thanks for all the replies. I have now conducted tests and found the problem not so bad as first experienced.

 

Medium wave. A definite no no even 50ft away. ( I like Gold)

VHF. I moved the radio away, took off the wire extra aerial wire. At 8 ft from the lathe there is only a hint of noise.

DAB. Oofficially, according to the BBC, here in the fens we should not be able to receive at all. I get a very strong signal by attaching the earial wire to the screen of the satellite cable. My DAB indoors is fine but in the workshop no way.

Oddly enough using my mobile standing at the lathe has no effect whatsoever!!!!

I’ll put the mains and motor cables through separate flexible metal conduit and a box tunnel over the inverter and see what happens.

 

I’ll report back in a few days.

 

cheers all

 

Ray

Edited By macmarch on 18/03/2011 09:16:21

[TerrydParticipant @terryd72465]

Posted by Ramon Wilson on 17/03/2011 21:22:35:

Hi Ray,

I too have just fitted VFD drive to lathe and mill – see elsewhere – but to date have not experienced any RF noise at all.

………………….

The cables from motor to inverter are as supplied ie not run through conduit and likewise those of the control stations. I did ensure that these were not run side by side however and have them about 100m apart for most of their run though by neccessity they all come together as they aproach the inverter.

 

Regards – Ramon

 

 

Hi Ramon,

 

Cables 100m apart, your workshop is bigger than I thought!

Best regards

 

Terry

[Ramon WilsonParticipant @ramonwilson3]

Oh dear Terry – Freudian slip, Typo or just plain bloody old age,

 

I’m sure you knew what I meant though

 

Regards – Ramon

 

 

[TerrydParticipant @terryd72465]

Of course Ramon, These aged fingers of mine are often guilty of typos

 

Best Regards

 

Terry

[JonParticipant @jon]

Ray and Ramon, what is your electric bill like now?

Of course this would have to be on a like for like basis.

 

The reason i ask and to be honest cannot believe myself my findings, the power consumption of these digital inverters drawing way more than double a rotary of same size.

 

3HP lathe motor with the Teco MA7200 uses 61p/hr, Transwave rotary 31p/hr + vat of course, both under no load.

[Clive HartlandParticipant @clivehartland94829]

I have had a VFD unit fitted to my bench drill for some 20 years odd. I did at first have an interferance which I chased back through the screened cable to the clamp inside the VFD unit which had come loose.

Since then no problem.

I hooked up with a screened five core cable which is easy to get and it is earthed at the machine end.

 

Clive

[Les Jones 1Participant @lesjones1]

Hi Jon,

How are you measuring the running cost of your inverter ? I suspect that the units being sold to monitor your power consumption may not give accurate results with the current waveform drawn by the inverter. I think the best method is to count revolutions of the wheel in your electricity meter and calculate the cost from that. If the results are correct then there must be a lot of heat generated somewhere as the power is not doing any mechanical work.

Les.

[Steve GarnettParticipant @stevegarnett62550]

Les is quite correct – all the figures I’ve ever seen, and my own measurements indicate that for small VFD power units (which is all we are talking about) the efficiency is around the 82.5% level at a bare minimum when run at rated speed. As far as I’m aware a rotary converter is nowhere near this efficient – 70% at best. And that’s for a proper rotary converter, not one of the static phase converters, which are very inefficient as an overall system, because you have to derate the motor by about 50%. If you try to get more out of it, it just gets hot – making the efficiency even worse.

 

Even if you don’t use converters at all, and run 3 phase motors from a 3 phase supply, you could get a significant saving by using VFDs, assuming that the machinery is all you have 3-phase for. Simply because by running it from a single phase, the electricity supply company isn’t charging you more for the extra metering. Dunno how much that works out to these days, but it’s probably significant.

[Anonymous]

Posted by Steve Garnett on 17/04/2011 17:34:40:

 

Even if you don’t use converters at all, and run 3 phase motors from a 3 phase supply, you could get a significant saving by using VFDs, assuming that the machinery is all you have 3-phase for. Simply because by running it from a single phase, the electricity supply company isn’t charging you more for the extra metering. Dunno how much that works out to these days, but it’s probably significant.

 

Not sure I understand the above comment? As far as I’m aware I don’t pay any more for my three phase supply than I would for a single phase one. I also pay a normal domestic tariff for the units used. Units seem to go up and up, but that’s another story! My electric bill doesn’t mention anything about three phase; just the number of units used and the rate per kWh.

 

Regards,

 

Andrew

[Steve GarnettParticipant @stevegarnett62550]

I’ve been told repeatedly that in our Industrial unit we get charged extra, apparently, because of the number of electricity meters used – it’s a source of complaint by the management. Whether this pans out everywhere else still I’m not sure – but it certainly used to. Of course it could also be that I’ve been fed a crock of sh*t about it… I will investigate further.

[Anonymous]

Hi Steve,

 

Ah, that may be true, I’ve only got the one electricity meter, in a domestic environment, it just happens to be a three phase meter. I don’t know what you might get charged if you have more than one meter. The single phase supply for the house is split off after the meter, but before the three phase distribution box.

 

Before I had three phase installed I asked the supplier three questions:

 

1) Would I pay extra for a three phase supply/meter? – No

 

2) Would I pay the same domestic rate per kWh? – Yes

 

3) Would the meter cope with an unbalanced input? – Yes

 

Regards,

 

Andrew

[Steve GarnettParticipant @stevegarnett62550]

The only thing I’ve discovered is that whilst there appears to be a universal agreement about how electricity is supplied to your billing company, there isn’t quite such universal agreement about how they should charge for it. Some places it all comes out equal, and in other places there are tariff differences, even domestically, if you have a three-phase supply. So it might be a bit of a postcode lottery – or at least worth shopping around if you are one of the disadvantaged ones.

 

I would have thought though, what with all this competition and all that, that perhaps they would be competitive over this – maybe that’s why the old differences have gone away?

[Ramon WilsonParticipant @ramonwilson3]

 

Posted by Jon on 17/04/2011 15:11:50:

Ray and Ramon, what is your electric bill like now?

Of course this would have to be on a like for like basis.

 

 

Hi Jon,

I’m afraid I can’t answer your question specifically and apart from ‘counting the wheel’ as suggested would have no idea at all. We have had no bills in yet to compare either. Last year, when I did the heads for the BR2 the mill was contantly start/stopping for near four weeks – this was with single phase 3/4 hp. This certainly did show up on the bill – as was pointed out to me!!.

 

What is noticeable however is that the lights in the house no longer dim as lathe or mill start up – whether there is a running cost over and above the running of the motor with VFD remains to be seen – I’m sure that it will be pointed out too.

 

The thing I do notice though is that the quieter, smother running of lathe, despite the slight whine, is such that I forget to turn it off something that was always done with the old set up.

 

Regards – Ramon

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, Well to be honest I’m not sure how I’m chargred for my electricity, except that I get cheap rate between midnight and 7.30 AM GMT, and I pay my bills on a monthly plan by DD. In the old days you used to get a standing charge for supplying electricity, which I presume ment a charge for every meter you had, and then a usage charge for each and every meter. I assume its still much the same.

 

Regards Nick.

 

Edited By Nicholas Farr on 18/04/2011 00:15:17

[John OlsenParticipant @johnolsen79199]

You may well find that if your setup needs more than one meter that they charge more for it. I suppose such a charge would be to cover the depreciation and interest costs of the extra meter, plus I guess a healthy profit margin. Or they may just pick a number out of a hat, who knows.

 

As far as the actual devices go, the efficiency of an inverter is high enough that you should only be paying for the actual power used, the power dissipated in the device is negligible. If it was not, the inverter would get rather hot. It is possible that the power meter might not cope well with the harmonics that the rectifier in the inverter can produce, but modern units are designed to keep the harmonics low anyway.

 

With the phase converter gismos the same sort of thing should apply, the inductors and capacitors in them should be fairly low loss or they will make themselves evident pretty quickly. Where there is an idle motor, that is going to consume a certain amount of power to overcome its own friction, so that will cost something. One aspect of things is that such convertors are likely to have a poor power factor…there may be some attempt at correcting this, but it won’t be right for all loads. I have heard of cases where a poor power factor affected the meter reading…it was an inductive load and it actually reduced the measured power consumption for the month. This should not happen in theory, since if the meter should be measuring true power. So adding the somewhat inductive arc welder across the normal domestic load for the month should have resulted in an increased consumption, but it actually reduced it. Not guaranteed to work with all power meters!

 

Anyway, typical workshop consumption is likely to be a lot less than you would use if you used electricity for heating.

 

regards

John

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