VFD – which is best please ?

[Former MemberParticipant @formermember12892]

[This posting has been removed]

[Anonymous]

Part 2:

As mentioned smaller, and possibly cheaper, VFDs often use V/f control. Below base speed the applied voltage needs to be reduced in proportion to the frequency to keep phase currents constant. Open loop control V/f works reasonably well, except at low frequencies. Here the voltage drop across the rotor resistance becomes significant, meaning that the applied voltage is too low, also reducing phase currents and torque.

As MikeP mentioned these issues can be solved with vector control. There are many variants. but essentially they all transform a complex rotating vector into a quasi-stationary 2D vector via the Park-Clarke transforms. This 2D vector has two components, d (direct) which is the flux linkage component of the phase current and q (quadrature) which is the torque component of the phase current. These can then be controlled with simple PI loops. Naturally this takes some computing power, but with the availablitily of cheap DSPs is no longer difficult. These algorithms do not directly measure the position of the rotor. Sensorless vector control can estimate rotor position, provided the rotor is turning. Control can typically be maintained to a lower frequency than a V/f controller, down to about 1Hz. These algorithms can maintain constant phase current, and torque, down to low frequencies. So in that sense they are better than V/f. What they cannot do is magically increase torque at low speed. Of course they can provide a short term increase in torque, but that is not sustainable long term due to motor thermal issues.

For full torque at zero speed vector control generally needs an external measure of rotor position. Full torque at zero speed may not be applicable to machine tools, but it is important in some applications, such as electric vehicles where it is the equivalent of slipping the clutch during a hill start.

Andrew

[Former MemberParticipant @formermember12892]

[This posting has been removed]

[Gary WoodingParticipant @garywooding25363]

I've got 4 Mitsubishis – 2 on my mill and one each on my lathe and drill-press. I've fitted 2 more on a friend's mill and another friend has one on his lathe. No problems so far after 15 years use.

[Ex contributorParticipant @mgnbuk]

Why is a VFD screwed to the wall in the correct environment unsafe. ?

Beacuse a). the housings of most VFDs are not designed to an adequate IP rating to be used without a suitable enclosure.

b). the manufacturers of the VFDs (for all makes I have installed so far) state in the manuals that the equipment is to be mounted in a suitable protective enclosure. In the same way they also state whether the motor cable screen is to be grounded at one or both ends – when all else fails, RTFM

As the Start and Stop buttons are not used to Set Up parameters why are they fitted. ?

For set-up and testing – set-up of an installation being more than just entering parameters & it can be advantageous to be able to operate the VFD locally during setup rather than using remote control gear.

IIRC you have expressed these (erroneous IMO) opinions in previous discussions on this topic ? While I accept that you are quite at liberty to do as you wish in the privacy of your own environment, surely following the equipment manufacturers guidelines in the first instance should be the default position when giving advice to others ?

Nigel B.

[norm nortonParticipant @normnorton75434]

Putting a VFD in an enclosure is understood for electrical and mechanical safety. But they have cooling fans and if they are going to run cool the enclosure (case) has to be massive or adequately ventilated itself. If it is ventilated it will pull all the same amount of dust in to gradually coat its circuit boards.

So which is more important, try to let them run cool and extend their lives, or keep them clean in a sealed box?

Edited By norm norton on 31/12/2021 12:33:44

[derek hall 1Participant @derekhall1]

I am considering a Newton Tesla package as a late xmas/new year pressie for myself.

Yes it is cheaper to buy the components, but I dont want the hassle of filters, programming, building an enclosure, sourcing screened cable etc…

Someone commented on this forum recently that they don't want to waste time making tools, they would sooner be building models, nothing wrong with that, I like building models and tools, but I dont want to waste time faffing around with sourcing all the kit to convert my lathe from single phase to inverter control.

Yes the NT package is expensive but the inverter is housed in a decent looking enclosure and does "look the part"…..and yes the inverter ideally should be in an enclosure….

Kind regards

Del

[Robert Atkinson 2Participant @robertatkinson2]

I was trying to avoid this thread but I have to respond.

Emgee. A VFD mounted without an englosure is unsafe / unacceptable for a number of reasons. Firstly as Ian McV says the IP rating is not suitable for a workshop environment. Secondly the cable connections generally do not have adequate protection from contact or adequate strain relief. Thirdly the installation manual will (on better drives at least) tell you it has to enclosed. The safety and approval of the drive depends on following the instalation requirements. Note that these drives are components not equipment. They have to be correctly incorporated with other item to make a finished system. The supply of them assumes that the equipment they are incoprorated into is designed and constructed by competent persons. Note that this does not include the average electrician. In theory the completed equipment should be inspected and tested for compliance with the machinery, electriacl and EMC safety directives. Few people do this even for commercial kits.

Steviegtr. I've said this before. The installation in the video you linked to is a safety horror show. Exposed VFD, multiple adaptors and extension leads including an obviously illegal 2 pin adaptor. This i the grey one in the red extension lead. All this exposed to swarf and coolant. And to make things worse you have to reach across the lathe to reach the controls. I see no E-Stop on the operator side of the lathe either.
do whatever you want in your own workshop as long as no one else uses it but please don't put it forward as a good example. It is not. A bit of Dunning-Kruger effect maybe?

As Andrew J says there is no correct answer to the original question. ANY VFD choce will be a compromise. I'm sure Andrew was going to say this in his next installment but the VFD should adjust it's output voltage with frequency to maintain the rated current and torque. Not setting this correctly is one cause of poor low speed performance. Of course even if you maintain the current and torque halving the speed halves the power.

I do not like the cheap far eastern drives sold on ebay and the like They are generally poor quality. Most of the ones I've looked at are clearly not UKCA (CE) compliant just by looking at photographs and reading manuals. Saying that they are "made by omron" or what ever is just nonsense. It's been discussed for mechanical items that thes low cost manufacturers will build to the cost / quality the customer wants. The same applies to electronics. The cheap ones leave out parts not essential to basic operation. This includes interference (EMC) limiting components and over current / voltage protection parts. Even the basic electronic components from reputable OEMs are variable cost / performance. Capacitors are a classic case. You my have a basic requirement of 100uF 350V but do you want 85 deg C or 105 deg C temperature rating? 1000 hour life or 10,000 hour? Al else being equal a 105 deg 10,000 h capacitor will last much longer. And this is without basic improvments like de-rating for voltage and current.
Also be wary of sellers who recommend using over-sized "cheap" drives. Ask yourself why the "XkW" drive isn't considered good for XkW. The rating of a drive should be for continuous commercial service at the top of it's rated temperature for years. Such a drive should last much longer in hobby service.

If you have to ask the question of what drive to buy you probably should be buying a preconfigured kit or paying a competent person to do the work for you.

This will not be a popular answer but it is factually correct.

Robert G8RPI.

PS must type faster several other comments came in while I was typing.

Edited By Robert Atkinson 2 on 31/12/2021 12:48:19

[Ex contributorParticipant @mgnbuk]

So which is more important, try to let them run cool and extend their lives, or keep them clean in a sealed box?

Modern VFDs don't seem to generate that much heat in industrial environments & I doubt that many MEs will push their equipment hard enough for this to be an issue if a sensibly sized cabinet is chosen that meets the maker's stated operating clearances.

The manuals usually give an indication of the heat generated by the device to be considered & surface dissipation through a steel enclosure surface area can be calculated – only if the area is inadequate is ventilation required & fan inlets / air outlets are usually fitted with replaceable filter elements. I prefer heat exchangers for the environment I have to operate in (graphite machining) – heat exchange without air exchange & subsequent risk of conductive dust ingress. Korean & Japanese machine usually have heat exchangers fitted anyway as a matter of course due to being sold into hot / humid regions where air exchange is not desirable.

For the most part, when a machine arrives at work that has through flow fans fitted the first thing I do is remove them & seal off all the openings in the enclosure. The cabinet temperature is then monitored & only in one or two instances have I had to fit heat exchangers due to excessive temperature rise – in all these cases this has been on cabinets that I considered to be undersize for the amount of equipment contained by them for (usually) "aesthetic" reasons. In a couple of cases I have set the fans to circulate the air within the cabinet to forec contact with the walls & this has reduced the temperature enough such that heat exchangers were not required.

Nigel B.

[EmgeeParticipant @emgee]

Posted by Robert Atkinson 2 on 31/12/2021 12:45:59:

I was trying to avoid this thread but I have to respond.

Emgee. A VFD mounted without an englosure is unsafe / unacceptable for a number of reasons. Firstly as Ian McV says the IP rating is not suitable for a workshop environment. Secondly the cable connections generally do not have adequate protection from contact or adequate strain relief. Thirdly the installation manual will (on better drives at least) tell you it has to enclosed. The safety and approval of the drive depends on following the instalation requirements. Note that these drives are components not equipment. They have to be correctly incorporated with other item to make a finished system.

Robert G8RPI.

Robert

You are assuming the environment in the workshop is not suitable for an IP20 rated piece of electrical equipment, I did say suitable environment in my post, suitable being liquid and dust free.

There are several ways in which glanding of cables can be achieved if there is not a suitable surface area on the VFD.

I fail to see why you call a VFD a component when it is a fully functioning motor controller when connected to a motor without the addition of any further components, as a device it is no more or less than a DOL starter with other functions, perhaps you also refer to that as a component.

Many of the so called cheap units already have a filter fitted, some also have removable keypads that can be remotely mounted to provide local control, if required an emergency stop can be connected.

I believe any electrician with factory installation and maintaining motor and control devices experience would be classed as a competent person.

You again seem to make assumptions regarding the quality of the electronic components used in the VFD, have you examined any or all of the lower cost units ?

Emgee

[EmgeeParticipant @emgee]

Posted by derek hall 1 on 31/12/2021 12:39:14:

I am considering a Newton Tesla package as a late xmas/new year pressie for myself.

Kind regards

Del

Del

Check the type of motor included in the package as some packages pictured show ventilated motors, for safety you really need a totally enclosed motor with fan cooling when fitted to machinery, especially woodworking machines where the motor is fitted below the saw or planer working surface.

Emgee

[EmgeeParticipant @emgee]

Posted by mgnbuk on 31/12/2021 12:14:52:

Why is a VFD screwed to the wall in the correct environment unsafe. ?

Beacuse a). the housings of most VFDs are not designed to an adequate IP rating to be used without a suitable enclosure.

I did state suitable environment, that is free dust and water.

b). the manufacturers of the VFDs (for all makes I have installed so far) state in the manuals that the equipment is to be mounted in a suitable protective enclosure. In the same way they also state whether the motor cable screen is to be grounded at one or both ends – when all else fails, RTFM

As the Start and Stop buttons are not used to Set Up parameters why are they fitted. ?

For set-up and testing – set-up of an installation being more than just entering parameters & it can be advantageous to be able to operate the VFD locally during setup rather than using remote control gear.

If you are enclosing the VFD in a cabinet you could have the remote station to hand

IIRC you have expressed these (erroneous IMO) opinions in previous discussions on this topic ? While I accept that you are quite at liberty to do as you wish in the privacy of your own environment, surely following the equipment manufacturers guidelines in the first instance should be the default position when giving advice to others ?

I have not given any advice, my post asked the question.
Yes, I have given my opinion on this topic in previous posts but IIRC I have not offered advice on the subject. From experience if I had to give advice I would state something more with regard to an IP20 rated unit.

Emgee in answer to Nigel B

Nigel B.

[David JuppParticipant @davidjupp51506]

For information – a few lines taken from 'Application as directed' section of the safety instructions in the commissioning manual for Lenze i510 series VFD. There are other lines which I didn't copy, these ones seemed particularly relevant to some of the discussion points in this thread.

• The product serves as a component for the control of three-phase AC motors and servo motors.
• The product is not a household appliance, but is only designed as electrical equipment for commercial or professional use in terms of EN 61000−3−2.
• The product is exclusively suitable for installation in control cabinets or similarly closed operating areas.
• As the product may cause EMC interferences in residential areas, the operator is responsible for taking interference suppression measures.

For most brands of VFD the full documentation (including conformity declarations) are available on line, for those who wish to look further.

Edited By David Jupp on 31/12/2021 14:43:27

Edited By David Jupp on 31/12/2021 14:43:48

[Trevor Drabble 1Participant @trevordrabble1]

+1 for Newton Tesla . My decision was based on the fact that l knew nothing about VFD when l was fortunate enough some considerable time ago to meet a chap at a model exhibition in Lancashire who was selling both individual and packaged units. He was very patient and explained in depth the salient points to look out for , whether l bought his or someone else's . These included a good after sales service .

It turned out this chap was Mr NT . I subsequently purchased my equipment from NT and it has performed faultlessly ever since , so no complaints at all . One point of note , broadly in line with AJ comments , they recommend the motor not be run for extended periods below 800 rpm , hence the need to retain mechanical speed reduction options for maximum flexibility.

[Mike PooleParticipant @mikepoole82104]

Posted by Emgee on 31/12/2021 10:18:23:

Mike

Why is a VFD screwed to the wall in the correct environment unsafe. ?

As the Start and Stop buttons are not used to Set Up parameters why are they fitted. ?

A few months ago a complete package of VFD, Motor and remote control station were purchased by the OP for his lathe.
The motor included in the package was not a Totally Enclosed with fan cooling but an open ended type to allow cooling inlet and exhaust, that in my book is not the best choice and must come into your category of unsafe.

Emgee

Machine safety is not just about protecting people, protecting equipment is also a consideration. The correct environment for the installation of a VFD is going to be dust and liquid free and free from any accidental penetration from thin metallic objects. The wall of a workshop is unlikely to qualify. Many drives incorporate a cooling fan for the power stage electronics and heat sink which will deposit any passing airborne rubbish just where you don’t want it. To my mind the simple way of providing the correct environment for a VFD is a steel enclosure with dust and liquid proof door seals and suitable glands for wiring. I would not initially fit fans and air filters unless temperature rise was a problem and with the low duty cycle of hobby machines I doubt excessive temperature rise will be a problem.

The controls fitted to the inverter front panel are as I said really intended for service and commissioning use, the typical membrane buttons have poor durability and are likely to fail eventually if used as the main control devices.

I feel it is important to tell people how things should be done properly and having been informed and understanding why there is a correct way they choose to not implement it then it is their problem if they hurt themselves, someone else or damage the equipment. Doing the wrong thing through ignorance is rather different from making an informed choice to bodge it.

Mike

[Robert Atkinson 2Participant @robertatkinson2]

David J and Mike P. Thank you for the posts. Saved me saying it.
I hate it when people make unsupportable or unsafe statements and then respond to being "called" on it by applying impractical conditions.
I don't really care what people do in their own homes. I do care when they give unsafe advice to others or worse, challenge the safe advice given to others.

There is another side to all this. At some point there will be an accident and the "ambulance chasers" or an insurance company will come after either the supplier of substandard kit or someone who gave poor advice. We all have moral and legal responsibility for athe advice we give. Additionally I have professional responsibility.
Far fetched? Maybe, but lawers and insurance companies are always looking for new ways to make or save money.

Robert G8RPI.

[Former MemberParticipant @formermember12892]

[This posting has been removed]

[SteviegtrParticipant @steviegtr]

Posted by Robert Atkinson 2 on 31/12/2021 12:45:59:

I was trying to avoid this thread but I have to respond.
Steviegtr. I've said this before. The installation in the video you linked to is a safety horror show. Exposed VFD, multiple adaptors and extension leads including an obviously illegal 2 pin adaptor. This i the grey one in the red extension lead. All this exposed to swarf and coolant. And to make things worse you have to reach across the lathe to reach the controls. I see no E-Stop on the operator side of the lathe either.
do whatever you want in your own workshop as long as no one else uses it but please don't put it forward as a good example. It is not. A bit of Dunning-Kruger effect maybe?

This will not be a popular answer but it is factually correct.

Robert G8RPI.

Oh dear.

Clearly you did not watch all the video. Maybe the horror was too great for which i apologise for frightening you. Did you not see the swarfe guard. Page 6 of the Omron instructions says. If required you may install the inverter in a enclosure , ensuring there is a 100mm air gap all around the Inverter. We always used to fit them in an enclosure. But this was in Industrial premises. I chose not to. See picture below. I do not have to squeeze over my spinning work to switch it off. It is on the right hand side.

Next time i go past a Boots i will go & tell them the adaptor they sold me some years ago is dangerous, so thanks for that. You may have a point of plugging 2 ext leads into a ring main. But i only have a problem when i plug in 3 electric heaters. But all i do is switch them off for a while once the cables begin to smoke. All in all many thanks for your usual kind words.

Steve.

[Roger Williams 2Participant @rogerwilliams2]

Bit lost with some of the answers , but in my case , I bought a seconhand Jaguar Cub off ebay many years ago, 2.2kw for my DSG, screwed it to the wall with an emergency stop on the headstock . Perhaps Ive done it wrong, but looks safe to me anyway.

[Robert Atkinson 2Participant @robertatkinson2]

Steviegtr.
I watched the whole video. The bit of old shelf or whaterver it is acting as a "swarf guard" does not protect the VFD. Indeed it appears to be putting additional loads on the VFD wiring.

As I've said before, you can chose to do whater you wish in your workshop but please don't recommend unsafe practices to others who may not have enough understanding of the risks involved. If, as you imply, you have done this sort of work as part of your employment you should know better.

Robert G8RPI.

[SteviegtrParticipant @steviegtr]

Posted by Robert Atkinson 2 on 31/12/2021 22:11:53:

Steviegtr.
I watched the whole video. The bit of old shelf or whaterver it is acting as a "swarf guard" does not protect the VFD. Indeed it appears to be putting additional loads on the VFD wiring.

As I've said before, you can chose to do whater you wish in your workshop but please don't recommend unsafe practices to others who may not have enough understanding of the risks involved. If, as you imply, you have done this sort of work as part of your employment you should know better.

Robert G8RPI.

I do know better, that is why i never tell anyone how to do it. Just what i have done. More strain on what cable. The cable is fitted & screwed to the wall with a P clip. If you watch some of my vids of which I am sure you have. I use what i have & recycle where i can. Yes the Hardboard is functional but tatty. One of the jobs to get around to i guess. Keep watching & subscribe so you can see more of things I am sure you will dislike. By the way i did my own risk assessment on the inverter & came to the answer that it does not require to be in a enclosure. Do as you will Sir, I take it from the few pictures in your Library you have a ML2. Plus you are a crop duster. We will be doing a video eventually of renovating a Pratt & Whitney engine from a Air tractor AT-301

Happy new year to you & your family.

Steve.

[OldironParticipant @oldiron]

I have a couple of VFD's in my workshop. Neither is in an enclosure and are not required to be according to the manufactures instructions. The instructions say to leave at least 75mm clearance all round and an enclosure is optional.. I do use remote controls on both. Both out of reach of swarf and coolant. As far as I can see Steve's installation is about average for most home workshops and probably better than some.

Robert you should visit a farm workshop then you would really see the horrors of bodged installation and really dodgy wiring and dangerous practices. Can we get a link to a video of your pristine workshop so we can see how it should be done ?

regards

[SteviegtrParticipant @steviegtr]

Posted by Oldiron on 31/12/2021 22:59:13:

I have a couple of VFD's in my workshop. Neither is in an enclosure and are not required to be according to the manufactures instructions. The instructions say to leave at least 75mm clearance all round and an enclosure is optional.. I do use remote controls on both. Both out of reach of swarf and coolant. As far as I can see Steve's installation is about average for most home workshops and probably better than some.

Robert you should visit a farm workshop then you would really see the horrors of bodged installation and really dodgy wiring and dangerous practices. Can we get a link to a video of your pristine workshop so we can see how it should be done ?

regards

Here Here. +1.

Steve.

[Roger Davies 4Participant @rogerdavies4]

I’ve just spent a few days installing a Teco L510s on my Super 7B. A challenge for me, and one I would have failed were it not for the kind support and advice from this forum. Setting the parameters was much harder than it should be, and appeared to me to be in parts illogical. I certainly underestimated the complexity.

[EmgeeParticipant @emgee]

David

Thank you for the information re. the Lenze VFD range.

I believe the reason for calling the VFD a component is because the units can be supplied without a keypad, this is common for commercial and industrial users, so cannot function without another part or means of control.
As they say in another of your comments for use in Commercial and Industrial locations, where no doubt it will be connected with ethernet or similar, and controlled by the remote computer that is running the process line.

If not computer controlled initial setting of parameters can be programmed by using a hand held programmer plugged into the comms port so the VFD can function by the use of a remote hard wired control station.

If the unit is likely to cause EMC interference in residential areas it will surely do the same in an Industrial installation, I am surprised that Lenze appear to have opted out of any responsibility.

Robert

I note you have not replied to my question below.

You again seem to make assumptions regarding the quality of the electronic components used in the VFD, have you examined any or all of the lower cost units ?

As BR has made a decision to go for an already wired and connected system I hope it works out well for him.

Emgee

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