Member postings for Robert Atkinson 2

Steviegtr said:
" As for the home hobbyist needing to buy filters for the input i would say no. Not required. As an example I have a Dab radio sat on a shelf directly above my inverter, which i always have switched on. Never bats an eyelid "

Why did you say this? Are you just trolling?

EMC is not just about you. It's mostly about affecting others. How do you know that you are not interfering with aircraft navigation? Emergency communications? For example can you be sure that if an ambulance parked outside your VFD would not stop their datalink system or upset their ECG machine or other equipment?
You CAN'T.
As a minimum for your installation you might have done a quick sweep with a spectrum analyser but I doubt it. VFDs are typically used in an industrial environment and any internal filtering or external filtering recomendations are based on the allowable emissions for industrial. Hobby lathes are used in domestic environments. The allowable emissions for this are typically 1/10 of industrial (10dB lower. Exact levels depend on standard used, frequency etc). So to acheive the legally mandated emissions for home use methods such as additional screening and filters wil be required above those stated in the manual.

Suggesting even the minimum filtering is not needed is just irresponsible.

Robert G8RPI.

I will not be posting pictures of my workshop as it is far from pristine and I would not want people to think what I do in my personal workshop is an examples of good practice. I have enough training and experience to assess the risk to me and put appropriate mitigation in place. My acceptable risk to myself is higher than I would expose others to either directly or by giving advice.
I will post pictures of my ML2 and it's new drive system when i get round to doing some more work on it. I've never been a "crop duster" but have designed and built systems, including motorised flight controls, for a British turboprop agricultural aircraft.

Happy new year and stay safe,

Robert G8RPI.

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.

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.

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

Use steel. If there is not a lot of force to pull it off put a thin nonmagetic (plastic aluminium etc) shim on the electromagnet to maintain a small gap. I'd expect maxium force in the contact positionfor you application so shim should not bee required.

Robert G8RPI.

Do your "solenoids" have magnetic cores? I read the original post as they had. If they have fixed magnetic cores technically this makes them electromagnets, not a solenoids. A solenoid has no fixed magnetic core and the moving part is normally Iron. This works because there is nothing ferromagnetic for the core to stick to if it retains magnetism. The moving part attracted to an electromagnet, the armature, is normally made from a material thati s harder to magnetise. This is typicall steel.
I think this subtle distinction between soleniods and electromagnets has caused some confusion as to a suitable material for the armatures.

Robert G8RPI

Some supporting data from Eclipse

" The armature plate may also be known as a keeper plate. An electromagnet or electro-permanent magnet always needs a ferromagnetic surface to clamp onto – the ferromagnetic surface required is generally a mild steel or ferromagnetic stainless steel. "

https://www.eclipsemagnetics.com/products/magnetic-tools-and-standard-magnets/armature-plates-for-electromagnets/

Robert G8RPI.

Note that iron is more easily magetised than steel. It is also more easily de-magetised which is why it is used for transformers. As the holding electromagnets are DC they will not demagetise the armature (moving part). This will eventually result it it sticking even with the electromaget de-energised.

The armature should be STEEL not iron.

Robert G8RPI.

Steel. Mild is OK but when doing this sort of application in the day job we used gauge plate. We had it electroplated but the environment was fairly agressive. Don't go too thin, the force will be reduced.
Iron will get magnetised.

Robert G8RPI.

A X-Y table and Z gantry takes at least 50% more X width. All else being equal the Z mounting will be less rigid. However as there is no change in load point it is easier to predict any flex and it will be consistent regardlesss of XY position.
As usual it is a compromise between volume, accuracy, speed, weight, cost etc.
The application matters. Machining, printing, laser? How heavy is the table and work holding? If the table and mounted workpiece are heavy keep them fixed. Have a gantry traveling in X allong the table, Y on gantry cross beam and Z on Y.

Robert G8RPI.

Hi
The drive you linked to has no facility to use a potentiometer with a switch. The potentiometer with switch will work if you just ignore the switch wiring. However you will loose bit of mechanical and electrical travel and thus control at the low speed end of the range. The potentiometer without switch would be a better choice.

Robert G8RPI.

Those almost certainly use a "universal" burushed motor. much simpler to control. Not as smooth torque as a 3 phase. Brushed motors are sometimes used on small lathes but a 3ph and VFD is much better.

Robert G8RPI.

If it is a reasonably flat surface and the leak is slow try this approach.
Cut a thin metal patch about 30-40mm in diameter. clean and degrease the area around the hole. Put a bead of 5 minute epoxy around the perimiter of the patch. Do a final degrease of the pan working inward. use acetone or similar fast drying solvent. Press the patch up to the pan and hold or tape in place while the epoxy sets.

Robert G8RPI.

Whatever way fitted a pair of plain nuts provide only minimal locking against vibration. There are much better technical solutions. The only justification to use two nuts is historical accuracy. That being so, fit them as they were on the original design. If you need locking use a tab washer, split pin or modern solution.

Robert G8RPI.

If it is recycled it ia almost certainly thermoplastic and may melt. Nothing wrong with using normal metal cutting coolant or minimum concentation soluble coolant. No more risk to mill than cutting metal. Fast feed rates help too.

If you have lot to do it might be worth making a jig with stops for a circular saw. A custom "table saw" with 3 ganged cutters on a spindle might be worth considering as you have a lot to do.

Robert G8RPI

I bought one of ARC Eurotrade's lower cost ones and am very pleased with it.

Robert G8RPI.

Any 2 part paint is unlikely to keep for very long once mixed. Putting in the fridge will help. Some 2 part materials can be frozen once mixed to stop them curing. This is used for some ircraft sealants.

The Phoenix website says 3 hour pot life. Closing the lid will make no difference to this.

https://www.phoenix-paints.co.uk/products/60pq31

Robert G8RPI.

There are other examples of "inside out" induction motors. However most of these have the inner part with electrically connected windings stationary and the outer rotating. This means they need no brushes. A well known type is by PAPST (now EBM-PAPST). These are shaded pole types and connonly used for fans
https://www.hermannpapst.de/the-engineer/the-most-successful-developments/the-most-successful-developments/

Robert G8RPI.

OK, A picture is worth a thousand words.
It appears to be a switch (centrifugal) start induction motor. The oddity is that it is "inside-out". The induction part is the stator and the powered winding is the rotor.
The most likely reason for this was to get around a patent. It does simplify the centrifugal switch arrangement thoough.
AC power would just be connected to the brushes as shown in the picture.

Robert.