Overview of fitting variable frequency drive (VFD) to a Myford ML7

[Mike PooleParticipant @mikepoole82104]

Steve, I was quite surprised by your picture of the inverter installation. You have mentioned your panel building skills before so for the sake of £50 why not put the inverter in the enclosure it should have in a workshop? One stray chip from an interrupted cut on the lathe could be game over for the inverter. My Dewalt fast charger bit the dust when a tiny chip found its way in through its IP20 casing. Unfortunately although I also know how the job should be done my own workshop falls short of the standard it should be at. They always say a barber needs a haircut and I suppose the same goes for the electrical business. If I take a camera in my workshop I shall not be sharing my lash ups
To some extent I feel that as the only user of my workshop and am very aware of its shortcomings then I can take a few liberties. In industry we had to make everything idiot proof, and did they like to test it?.

Mike

[Paul KempParticipant @paulkemp46892]

Now correct me if I am wrong but I thought most members of this "happy" group were "model engineers" or amateur metal bashers (and no that is not being derogatory as there are some very talented people on here producing some fantastic stuff!). The point of my comment is we are doing this in garages and garden sheds or even back rooms, some on very limited budgets or resources and others with less limits and some pretty fancy kit but the common theme is doing this stuff for fun, personal education or amusement at HOME and not for profit.

Why then do we get this constant insistence of imposing industrial standards, insistence on compliance with every obscure British and European standard that may be front and centre or lurking in a dusty file somewhere? We are all grown ups and surely capable of making our own risk assessments, we do not have employees, I doubt many of us conduct tours for the public of our facilities, all we are doing is amusing ourselves and putting only ourselves at risk.

By all means people should feel free to comment on things they see that they perceive to be dangerous but some of the judgmental willy waving comments quoting professional qualifications and high flying positions are starting to get a little boring. I have letters after my name too and also spent years travelling internationally fixing problems, so what? If I see my neighbour doing something daft I might pass a mild comment or give freindly advice but certainly wouldn't be shouting my professional qualifications over the garden fence! If he wants to kill himself in his own back yard who am I to judge as long as I have flagged the issue?

So let's just have a little reset here, please. This is one of the most heavily moderated forums I frequent but interestingly one of the ones with the poorest attitudes when it comes to this type of issue! Let's leave the day job at the office, that's the whole purpose of a hobby!

Paul.

[Neil WyattModerator @neilwyatt]

Please can we calm down a bit?

I worry that some form members are being a tad over-zealous.

If you want people to take safety messages seriously, then don't dilute them with spurious claims.

And all sides, the politer you make your comments the more likely they are to be listened to rather than just heard.

Neil

[PeroParticipant @pero]

I hope I am being calm ( as in keeping CALM and CARRYING ON ).

I have a number of VFDs – Newton Tesla on the Myford and a variety of others, large and small, to be fitted to various machines, so I am very interested in the technical / practical discussion on the installation of same.

The following comments reflect my ( undoubtedly limited ) understanding of VFDs and points I would like to clarify so if anyone would like to respond CALMLY, I would be very grateful.

Firstly – Enclosures. VFDs are designed for air cooling. Some with internal fans and slotted case, some with just slotted case and some with an exposed heat sink. Placing these into a closed secondary enclosure would appear to severely limit the capacity for air cooling. Unless the secondary enclosure is vented in which case we are back to the beginning. It is possibly something you could get away with in a cool climate with a large enclosure but probably not in a hot climate.

Sounds like a straight forward case for not using an enclosure provided it is out of the line of fire of heavy objects and swarf and cooling fluids. However some VFDs have exposed wiring terminals, usually on the lower front of the case which, although designed to minimise the risk of accidental finger contact, do give rise to some concern. Fitting a cover to such terminals could be sufficient to address any issues here.

Secondly – EMI. Most of the documentation I have read suggests this is not an issue where cable runs ( VFD to motor ) are short. Unfortunately I have not seen anything which indicates how short is short. In the good old days we would place the multi band radio in close proximity to the item of concern, run it through the bands and if no interference was detected it was deemed good to go. These days with so many bands in use this technique may not be totally successful. My understanding of EMI filtering and the remedies is not so good. If the typical low cost filter installed on the mains lead is sufficient then there is not a real case for not using one. Total cost for the filter, a bit of additional wire and perhaps a small case being only a few dollars. If however it is a relatively high power three phase filter on the motor side of the VFD costing potentially more than the VFD and Motor combined, the you need to be fairly certain it is required before running to this level of investment.

How effective is the use of shielded cable in preventing EMI issues and could this be the reason that some VFD instructions recommend earthing at both ends of the shield?

As in most things i would seem that one size does not fit all and systems should be installed after a consideration of all relevant issues – as long as you understand them.

Tranquilly yours

Pero

[HopperParticipant @hopper]

Crikey. I think I'll stick with moving a rubber belt 'arf inch to the left to change speed. All this stuff is way above my pay grade. I only just graduated from using the wall outlet as the main (ie only) on-off switch. The concientiously safety oriented types have told me it couldn't be done. But it worked for 50 years until I was dragged kicking and screaming into the 20th century — 10 years after it ended.

And when I dismantled the open ventilated winding type motor it was packed solid with metal swarf between armature and field coils with maybe enough gap to slide a fag paper in there. 

Amazing the stuff that actually works. But i did relocate it to under the bench and away from the swarf as a nod to modernity.

Edited By Hopper on 21/07/2020 07:18:19

Edited By Hopper on 21/07/2020 07:23:04

Edited By Hopper on 21/07/2020 07:25:15

[PeroParticipant @pero]

Ahh. Thems were the good old days Hopper. When things were made to last and cope with a bit of a hard life.

Just think what todays elf and safety would do with a treadle operated lathe – RSI of the ankles for a start!

What they would make of a pole operated lathe just doesn't bear thinking about.

Nothing against elf and safety – particularly my own – I just like to have the right to make may own assessment of risk and work from there.

Not to cast any nasturtiums but I have a suspicion, in my local jurisdiction at least, that there is a certain degree of self interest in the electrical standards and regulations, which is to say: maximising the sales of electrical fittings and accessories and promoting and protecting the work of the electricians who fit them.

Running for cover now.

Pero

[HopperParticipant @hopper]

Yes Pero, I think your nasturtiums are about right. Just had the local gasfitter around today to see about installing my newly purchased stove cooktop. Oh Crikey! No we can,t just install it and connect the pipe up. The burners are too close to an overhanging ledge so shield must be installed. The igniter cant be run off the fridge power point with a three foot extension cord. New powerpoint must be installed inside the adjoining cupboard. The pressure regulator on the outdoor refillable gas bottles has been in the wrong position for the past 20 years and so new one must be installed correctly before a completion certificate can be issued for insurance etc. And by the way your hot water heater is too close to the outside of the bathroom window I really should do that….

I knew I should have just done the job myself and hooked the pipework up to the new stovetop. I think I could manage the soapy water leak test the professional used to check it.

[Mike PooleParticipant @mikepoole82104]

Mains borne interference is very hard to track down, the factory I worked in suffered £1,000,000 of losses due most likely to an inverter on the ventilation and heating system. Charging the DC link of a VFD can produce a very distorted load on the mains which can distribute noise to other equipment. Recreating 3 phases with PWM is going to leave some interesting holes in our DC link that only has a 50Hz sine wave to fill, when loads don’t match supplies you will get noise. It may not be obvious that the failure of one of our dozens of pieces of domestic electronic equipment is caused by our unfiltered VFD. We have all suffered devices that lock up and sort themselves out after a power cycle or reboot. The Skybox that stops responding or the microwave that won’t program anymore may just have had a visit from some spikey rubbish from your VFD.

Mike

[not done it yetParticipant @notdoneityet]

Posted by not done it yet on 17/07/2020 13:36:22:

… If you wish to carry on like that it's up to you.

Agreed, but poor showing to put that sort of thing on a video or pic that others, less well informed, might copy – unless, of course it is flagged up as p poor practice by the video/pic provider. Too many, out there in the real world don’t think before copying that sort of thing.

In addition, or explanation, to my post above may not be acceptable to some but we have to remember that half the population is always below average – that might (but likely would not) include brain surgeons where electrical safety is concerned (just as an example). The whole spectrum of ability can be watching (and some following) carp youtube presentations that clearly promote p poor practice.

One example which easily comes to mind is of sandwich boxes being extolled as a suitable enclosure for mains wiring (with bare terminals in the box). In addition, one such installation was to be located outdoors!

Having been brought up (and survived) the dangers of 1950s (and earlier) farm machinery, I am careful with my own safety, but would not expect everybody to as careful as me. YMMV, but poor practices should not go un-flagged, or allowed to be demonstrated on youtube videos as perfectly acceptable. We now live in a world where most of the less-careful or safety-minded are protected by the H&S legislation, so fewer look after their own safety as carefully as the older generation, perhaps.

I very occasionally chat with a retired ‘aviation safety person’. His arguments for best safe practice are incredibly strong ones. Quite rightly so when it is someone else's safety you are potentially affecting – especially particular if flying without a safety net.🙂

[SillyOldDufferModerator @sillyoldduffer]

Posted by Pero on 21/07/2020 05:16:10:

…

Firstly – Enclosures. VFDs are designed for air cooling. Some with internal fans and slotted case, some with just slotted case and some with an exposed heat sink. Placing these into a closed secondary enclosure would appear to severely limit the capacity for air cooling. Unless the secondary enclosure is vented in which case we are back to the beginning. It is possibly something you could get away with in a cool climate with a large enclosure but probably not in a hot climate.

Sounds like a straight forward case for not using an enclosure provided it is out of the line of fire of heavy objects and swarf and cooling fluids. However some VFDs have exposed wiring terminals, usually on the lower front of the case which, although designed to minimise the risk of accidental finger contact, do give rise to some concern. Fitting a cover to such terminals could be sufficient to address any issues here.

Secondly – EMI. Most of the documentation I have read suggests this is not an issue where cable runs ( VFD to motor ) are short. …

How effective is the use of shielded cable in preventing EMI issues and could this be the reason that some VFD instructions recommend earthing at both ends of the shield?

…

Pero

A couple of pictures may help with the enclosure requirement, I offer two 12Vdc switch mode power supplies.

First, a domestic in-lead power supply sold with a computer monitor:

The power supply is double insulated inside a more-or-less completely sealed box, and it came with a suitably fused lead made with a moulded plug and socket. This is very safe, and spilling a mug water on it is unlikely to be lethal. However, it's not suitable for use outdoors.

Second up, an LED power supply popular for powering rotary tables and other home motorised workshop equipment:

Although this type of power supply has lots of cooling holes, it's not intended to be air-cooled in the open. It demands a suitable enclosure. The user is meant to protect it and himself by shielding it inside another enclosure, The cooling holes leave the electrics highly vulnerable to liquids, dirt and swarf. Further, the mains and DC output connections are made via an exposed terminal strip with no provision for strain relief. Again, both problems are addressed by mounting the power supply inside something else.

Most VFDs are closer to the LED power supply than the computer monitor PSU.   Exposed terminals, flimsy box, no built-in strain relief etc.  VFD's are almost always components, meant to to be protected in the same way as switches and contactors, not user facing.

EMC is a complex issue not well understood, least of all by electricians. Many switch mode PSUs and VFDs are dirty dogs, incontinently spraying the neighbourhood with electronic crap. It can interfere with nearby equipment, and telecommunications. As electronic excrement is invisible and odourless, offenders often poop off in blissful ignorance. EMC can be harmless or serious, ranging from zapping a tired mum's Baby Alarm to disrupting an Airport.

Several ways of tackling EMC. Putting the power supply inside an earthed metal box. Careful attention to RF earthing as well as safety earths, Minimising cable lengths, and routing to avoid cross-coupling. Shielded cables, steel mesh helps, copper is much better, and heavy copper braid over copper or aluminium foil is best. EMC filters. As it's a difficult subject, the usual approach is to implement 'best practice', which often means following apparently pointless instructions. An unshielded, unfiltered VFD on the end of a long cable isn't EMC savvy.

Pero says '… systems should be installed after a consideration of all relevant issues – as long as you understand them.' Absolutely right! If you don't understand read the manual! The hard part is recognising we don't understand everything.

I regret people make mistakes and aggressively defend them! Despite the blow to my ego, I'm pleased to have the forum put my mistakes right; it's how engineers learn and improve. Pride is a deadly sin!

There's something else wrong with the way I wired the LED PSU to test it, and I didn't notice when I did it. Award yourself a Gold Star if you can see my mistake, it would be obvious if the photo was properly lit. Not the end of the world exactly, but don't imitate my bodges.

Dave

 

 

 

 

 

Edited By SillyOldDuffer on 21/07/2020 11:23:01

[JasonBModerator @jasonb]

You are probably in more danger from the lack of chuck guard and leadscrew cover on a Myford but that seldom seems to worry anyone

[Henry BrownParticipant @henrybrown95529]

Not wishing to be involved in any of the above shenanigans here is my inverter installation. I was guided by Peter at Inverter Supermarket and a friend who was the works electrician where I used to work in the choice of mounting and the enclosure.

Hope this is of interest…

The enclosure sits just above my lathe and is spaced 25mm from the wall. There are rearward facing louvers at the top and bottom with some fine mesh to stop most particles that can get that way. When I took these pictures today it obviously works as there is only the merest hint of dust in there.

[Robert Atkinson 2Participant @robertatkinson2]

SOD,
Using a plug without insulating sleeves on the live and neutral pins?

While this old style plug is considered OK if already fitted. they should not be re-used on other equipment or if the power cord is replaced.

I strongly recommend that any of this type of plug used in an electronics or engineering workshops are replaced. There is a chance of a wire off-cut or bit of swarf getting trapped beteen plug and socket, touching the un-sleeved pin and becoming live. It can then be touched as you reach to remove the plug or operate the switch on a switched socket resulting in a shock, possible injury or even death, Old plugs should be destroyed to preveent re-use.

Robert G8RPI.

[Robert Atkinson 2Participant @robertatkinson2]

Posted by Henry Brown on 21/07/2020 11:53:59:

Not wishing to be involved in any of the above shenanigans here is my inverter installation. I was guided by Peter at Inverter Supermarket and a friend who was the works electrician where I used to work in the choice of mounting and the enclosure.

Hope this is of interest…

The enclosure sits just above my lathe and is spaced 25mm from the wall. There are rearward facing louvers at the top and bottom with some fine mesh to stop most particles that can get that way. When I took these pictures today it obviously works as there is only the merest hint of dust in there.

Very nice!

[SillyOldDufferModerator @sillyoldduffer]

Posted by Robert Atkinson 2 on 21/07/2020 12:01:34:

SOD,
Using a plug without insulating sleeves on the live and neutral pins?

While this old style plug is considered OK if already fitted. they should not be re-used on other equipment or if the power cord is replaced.

I strongly recommend that any of this type of plug used in an electronics or engineering workshops are replaced. There is a chance of a wire off-cut or bit of swarf getting trapped beteen plug and socket, touching the un-sleeved pin and becoming live. It can then be touched as you reach to remove the plug or operate the switch on a switched socket resulting in a shock, possible injury or even death, Old plugs should be destroyed to preveent re-use.

Robert G8RPI.

Gold Star to Robert.

More obvious it's a wrong 'un if I brighten the image up.

So, despite knowing the plug shouldn't be used, and understanding why not, I somehow fitted one earlier this year. On the plus side, not completely negligent – I put a 3A fuse in it.

Action required: follow Roberts advice and destroy any old plugs found in my spares box.

Dave

[Mike PooleParticipant @mikepoole82104]

All the regulations, standards and good practice for electrical installations tend to be generated after things have gone wrong and would be best not repeated. Although they do make life difficult that is not the purpose of them. The wise learn from other people’s mistakes as well as their own.

Mike

[Bob Brown 1Participant @bobbrown1]

Posted by Henry Brown on 21/07/2020 11:53:59:

Not wishing to be involved in any of the above shenanigans here is my inverter installation. I was guided by Peter at Inverter Supermarket and a friend who was the works electrician where I used to work in the choice of mounting and the enclosure.

Hope this is of interest…

The enclosure sits just above my lathe and is spaced 25mm from the wall. There are rearward facing louvers at the top and bottom with some fine mesh to stop most particles that can get that way. When I took these pictures today it obviously works as there is only the merest hint of dust in there.

Not that different to my setup other than mine has shielded cables and a filter

 

Edited By Bob Brown 1 on 03/10/2020 13:19:49

[Author]

Posts