By continuing to use this site, you agree to our use of cookies. Find out more
Forum sponsored by:
Forum sponsored by Forum House Ad Zone

VFD Drives

All Topics | Latest Posts

Search for:  in Thread Title in  
1 2 3 Next > Last >>
macmarch17/03/2011 18:57:28
147 forum posts
1 photos
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

KWIL17/03/2011 19:30:32
3681 forum posts
70 photos
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 stephens17/03/2011 19:41:01
1049 forum posts
1 photos
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

macmarch17/03/2011 19:43:12
147 forum posts
1 photos
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 117/03/2011 20:51:11
2292 forum posts
159 photos
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.
 
 
Les.
John Coates17/03/2011 21:16:33
avatar
558 forum posts
28 photos
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 Wilson17/03/2011 21:22:35
avatar
1655 forum posts
617 photos
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
KWIL17/03/2011 21:59:48
3681 forum posts
70 photos
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 Colwill17/03/2011 22:18:02
782 forum posts
40 photos
If you choose to Earth the screen it is usual to earth only 1 end, normally the end nearest the incoming mains.
macmarch18/03/2011 09:14:02
147 forum posts
1 photos
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

Terryd18/03/2011 10:15:13
avatar
1946 forum posts
179 photos
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 Wilson18/03/2011 10:43:38
avatar
1655 forum posts
617 photos
Oh dear Terry - Freudian slip, Typo or just plain bloody old age,
 
I'm sure you knew what I meant though
 
Regards - Ramon
 
 
Terryd18/03/2011 13:23:57
avatar
1946 forum posts
179 photos
Of course Ramon, These aged fingers of mine are often guilty of typos
 
Best Regards
 
Terry
Jon17/04/2011 15:11:50
1001 forum posts
49 photos
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 Hartland17/04/2011 16:01:03
avatar
2929 forum posts
41 photos
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 117/04/2011 17:20:11
2292 forum posts
159 photos
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 Garnett17/04/2011 17:34:40
837 forum posts
27 photos
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.
Andrew Johnston17/04/2011 18:47:30
avatar
7061 forum posts
719 photos
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 Garnett17/04/2011 19:34:04
837 forum posts
27 photos
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.
Andrew Johnston17/04/2011 22:51:08
avatar
7061 forum posts
719 photos
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
1 2 3 Next > Last >>

All Topics | Latest Posts

Please login to post a reply.

Magazine Locator

Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!

Find Model Engineer & Model Engineers' Workshop

Sign up to our Newsletter

Sign up to our newsletter and get a free digital issue.

You can unsubscribe at anytime. View our privacy policy at www.mortons.co.uk/privacy

Latest Forum Posts
Support Our Partners
cowells
Sarik
MERIDIENNE EXHIBITIONS LTD
Shopping Partners
Subscription Offer

Latest "For Sale" Ads
Latest "Wanted" Ads
Get In Touch!

Do you want to contact the Model Engineer and Model Engineers' Workshop team?

You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.

Click THIS LINK for full contact details.

For subscription issues please see THIS LINK.

Digital Back Issues

Social Media online

'Like' us on Facebook
Follow us on Facebook

Follow us on Twitter
 Twitter Logo

Pin us on Pinterest

 

Donate

donate