Here is a list of all the postings Robert Atkinson 2 has made in our forums. Click on a thread name to jump to the thread.
|Thread: 3 phase supply (again)|
It's unusual but I have to disagree with you a bit Andrew,
Starting a smaller motor first has also been mentioned on this thread and even running an un-loaded motor permanently connected is suggested by some sources. Not very efficient.
I don't need to ring them. The simple fact that they do not publish a datasheet, never mind an instruction manual on their website means I would not even bother.
VFDs are popular because they allow control of the speed, torque, ramp speed (accel and decel) etc but cost litttle more than a phase converter
I would not use chipboard, old or new. It can have a lot of abrasive material in it. Kitchen worktop routers etc use carbide cutters for good reason.
|Thread: LP gas tank construction|
Another consideraton is low temperature. The liquid gas will cool was it evaporates. Many materials, including many steels become brittle at low temperatures.
|Thread: Three phase reversing|
DO NOT reverse the the motor switch with the spindle moving.
|Thread: Highway Code|
Another rule often overlooked or not known about is the speed limit for vans, pick-ups and minibuses on a dual carriageway in the UK.
Anyone who thinks it is 70MPH needs a refresher. The speed limit for commercial vehicles on a dual carriageway is 60MPH. That's not just vehicles over 7500kg. There are exceptions. The main one is for "Car derived vans" but it has to say this as he body type on the registration document of the vehicle. There are also exemptions for Dual-purpose vehicles. Dual-purpose vehicles include 4WD and "crew-cab" types with two rows of seats. However the max GVW is 2005kg. Again it depends on what it says on the registration document. This makes pick-up trucks difficut to judge. A 2WD 2 or 3 seater is limited to 60 MPH otheres may not be. The curent boom in pick-up trucks is mainly due to their low taxation as a company vehicle.
Sorry, can't agree on the cycle lanes. Around here (Cambridgeshire) they have laid new ones with flush LED lighting the lot and some cyclists still insist on riding on the road. One in particular is on a unlit country road and they won't use the LED lit cycle path. Then there are the bus drives who won't use the bus lanes. I've had one pull out of recessed bus stop, come across the bus lane and cut me up in the traffic lane. He then proceeded to do about 20 in a 30 zone. And n there weren't any ikes in the bus lane. There is another one where there is a traffic light cotrolled junction where buses go straight on. They have bus lane with it's own light that changes in their favour automatically. This stops the straight on main traffic so they can join. They use it when it's busy, but if its quiet and the main light is green they pull out at the lst minute into the main lane. Thay have already tripped the bus lane sensor so the main traffic lights recycle for no reason. If you are waiting to yurn right you have to wait a full cycle of the lights. that can be 2 minutes or more. I've been held at the line for three cycles due to two used doing this.
|Thread: Paranoid about Android|
Much as they would like you, and ask you repeatedly in several ways, you do NOT have to share or Sync your contacts with your Google account. You also don't have to log into your Google account to access the Play store. Just continue without agreeing. I just did all this with a new device I got for Christmas.
|Thread: VFD - which is best please ?|
My concern was an installation where not even the filters required for industrial levels were fitted. Not a compliant factory installation.
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?
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.
Happy new year and stay safe,
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.
David J and Mike P. Thank you for the posts. Saved me saying it.
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.
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.
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.
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.
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
|Thread: Suitable Metal for Electro-magnet Levers|
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.
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.
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. "
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.
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.
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