Member postings for Robert Atkinson 2

If you use a "normal" permanent magnet brushed DC motor this is very easy to do. The torque of the motor is directly proportional to the current so all you have to do is use a constant current supply. As long as the maximum current is less than the maximum continuous current rating of the motor it will sit stalled producing the set torque and automatically take up any slack. You would probably want a geared motor and a ballscrew would be better than a plain nut. Speed is directly proportional to voltage so this can easily be a separate control.

The biggest issue I can see is safety. This is essentially a horizontal press so would need a guard and possibly a two hand operating control. Neither of these are much use for a vice. As the law currently stands you have to be compliant with CE regulations, certainly if using for business or supplying (Inc. giving away) to another party. This means Machinery directive, EMC directive and possibly Low Voltage directive. Note CNC vices operate behind guards.

While your friend may be happy to take the risk, if there was an accident his insurance company may not take the same liberal view and come after you and your house or other assets.

Robert G8RPI.

Sandisk from Tesco is a good price quality compromise. Ebay and the like is just too much chance of gettng a fake.

Robert G8RPI.

Why silver contacts? Silver is not suited to precision low current switching. It tarnishes for s start. It's not suited to any kind of reliable low level (below 100mA 10V) switching. Commercial index switches are available such as the the Omron D5A but they are not cheap.

I'm not an armchair or shade tree engineer, I'm a chartered engineer who has designed and built motion control systems with 1 micron resolution and 10 micron repeatability. This was confirmed using laser interferometry with nanometer scale resolution.

Robert G8RPI.

Edited By Robert Atkinson 2 on 31/12/2018 11:39:32

Neither slotted optical or inductive sensors are much use for a index or refernce sensor without extreme care in the target and electronics, Both the raw signal generated by the sensor and the trigger level of the electronics vary with voltage, temperture etc. Ambient light is an issue for optos unless modulated signal are used.
A directly operated, goldplated contact with some overtravel capability is the best option. Contacts taken from a unused small signal relay or microswitch are a good choice. Normally closed (break) contacts are normally more reliable.
Some of the most accurate sensors used on CMMs have 3 sets of parallel round bar contacts spaced at 120 degrees. The contacts are wired in series and each pair of bars is shorted by a ball. The 3 balls are on a spider held down by a spring and with the input shaft at the center opposite the spring. Pressure on the input shaft in any direction will break the circuit.

Robert G8RPI.

The control signal is marked TRX which is non-standard e. It's impossible to guess what the signal format is. Can you see what the markings on the 8 pin IC (chip) identified as U5? This might give more of a clue as to what it is.

Robert G8RPI.

The motor is clearly rated at 220-240V DC 5A. The control PCB looks a bit rough, ou need to be careful as 240V DC is deadly, arguably more so than AC. The simplest way to drive this would be a Variac and bridge rectifier. A high voltage PWM drive would give better control though, possibly with speed feedback.

More photos of the PCB please.

Edited By Robert Atkinson 2 on 29/12/2018 21:24:28

I was envisoning something similar with the small really useful boxes. Ha have a set of the Bisly "A4" drawers and they are great for small tool , and measuing instruments but not really fo parts storage.

Well I actually have a nuclear fuel pellet . The problem is you still need a critical mass which limits the minimum size to something like a TRIGA at around 100kW and hardly model scale. The units used in pacemakers, satelites etc use decay heat which is uncontrolled.

The thing that people tend to skip over when talking about wind, solar and storage is the cost of producing the equipment (fiscal and environmental) and it's lifespan. The cost of bulding enough offshore wind to equal the new Sizewell nuclear proposal is about the same as the nuclear plant. However the life of the offshore wind is only half that of the Nuclear. If we bulit next generation fast reactors that can "burn" depeleted uranium and reprocessed fuel there would not even haave to be any more mining. Unfortunatly there are irrational fears over nuclear. More people die every year from illnesses caused by burning coal than have ever died from nuclear effects of power generation including accidents.

https://www.youtube.com/watch?v=0NUe-pUVEm8&feature=share&fbclid=IwAR3b-F1SuyJRwsp4W5jXgvGwcwwJSCVL5yqk9wT4CaXFnNTsQQjh5qSZfP0

The con of Drax II being "zero emission" because it burns "renewable" fuel is terrible. They are cutting down forrests in the USA etc, drying the wood and shipping the pellets to the UK in ships burning heavy bunker oil.
Trees take 3-5 years to regrow so you need to be planting 3 to 5 times what you cut down each year to be sustainable (assuming adequate water and nutrients). I see no evidence of that happening or even tht we are replanting what is cut down. Burning biomass waste from other production such as sugar cane is better but a limited source.

Not sure what any of this ha to do with model engineering. Unfortunatly I can't build a working scale model of a nuclear plant

Well it depends what you mean by heater. Typically electrically this means a resistive device which is what Phil mentioned explicitly. The youtube clip you linked to shows no resistor, just the glowing gas discharge heating the curved bimetallic strip. Ionised gas is of course an efficent heater ask anyone who has used a plasma cutter

Robert G8RPI.

Edited By Robert Atkinson 2 on 26/12/2018 12:33:28

Phils description is not quite correct. There is no heater in the starter bulb. There are a pair of contacts with one or bothh made from bimetallic strip. The contacts are open when de-energised. The enevelope of the starter contains a gas mixture, normally a neon xenon mix and freguently a small amount of radioactive material. The circuit is supply live, ballast inductor (choke), fillament at one end of tube, starter, fillament at other end of tube to supply neutral. Note that the gas inside the tube is effectively in parallel with the starter. At switch on the gas in the tube is not ionised so is non- conducting. The full mains voltge appears across the starter contacts and the gas ionises and becomes a low resistance. The current is limited to the power rating of the full tube e.g. 80W this flows through the filaments and the starter, heating all three. The bimetalic strip get hot and the contacts close. This causes more current to flow through the filament but the starter gas cools and the contacts open. This causes a sudden drop in current and th induced "back EMF" from the ballast inductor appears across the (pre-warmed by filaments) gas in the tube. The gas ionises conducts and glows emitting UV and short-circuiting the starter which now does nothing.
To the original question there are two "wear-out" failure modes, the contacts errode due to either normal use or more likely allowing it to do multiple re-starts of a faulty tube. A capacitor failure open circuit will cause faster contact wear, The other wear -out is poisioning of the gas fill due to out-gassing of the starter components. There are of course true failure modes like leaks or failed capacitors but these are random. There is a odd old stock wear-out for some of the starters with radioactive gas. The activity decay with a half life dependent on the isotope used but for some sitting on the shelf for years will cause failure due to the isotope decay.
It's good pracicw to replace the starter when the tube is changed.
While the LED replacement tubes hav become popular there are concerns over their safety see:

https://www.electricalsafetyfirst.org.uk/professional-resources/product-safety-unit/led-replacement-bulbs/

and

https://www.electricalsafetyfirst.org.uk/media/1206/best-practice-guide-9.pdf

for best practice guide.

Rert G8RPI.

This is not a fault. The meter movements in Meggers do not have a return spring and the pointer "floats" when the handle is not turned. The movment has two coils, a voltage coil that drives the pointer towards infinity and a current coil that drives it towards zero. It's a ratiometric instrument so the voltage does not have to be spot-on or zeroed like you do on an AVO.

Robert G8RPI.

I'm a big fan of Really Useful Boxes. They are available in a wide range of sizes. They stack neatly so shelves with 2 or 3 stacked on each and the occasional full depth vertical "divider" to the floor or extra shelf support on the bottom shelf to stop sagging if you have heavy contents.

http://www.reallyusefulproducts.co.uk/uk/html/onlineshop/fullrange_rub.php

They are tough (you can stand on small one or corner of a large one) and while not sealled (a good thing in my mind) they keep dust and dirt out. Not completely clear but easy to identify most contents.

Robert G8RPI.

Score with a laminate cutter
https://www.stanleytools.com/products/hand-tools/knives-blades/multi-tool/534-in-laminate-scoring-knife/stht10192
or
https://www.amazon.co.uk/Rawlplug-89-040-Laminate-Cutter/dp/B0001P0MKW
snap over a edge and then square off with a sharp block plane.

Given the difference in colour between the two case halves I'd say the front cover was damaged and it was replaced with one from higher voltage version of the same model. A quick check with a voltmeter will show if the volage is correct.

Robert G8RPI.

Edited By Robert Atkinson 2 on 20/12/2018 09:56:47

Great post Dave.

Generally any filter is better than none. Make sure it is rated at a high enough current. Physically larger or higher current is generally better. Only fit to the input of the VFD. Do NOT fit a filter between the VFD and motor unless it is specifically designed for that drive and motor. Keep leads between the filter and VFD as hort and direct as possible. Ideally mount drive and filter in a grounded metal box or at least mount both filter and VFD directly on a metal (light alloy) plate. Keep leads between VFD and motor short too.

A Corcom 10EMC1 is a good example of a dual stage filter that will help a lot with noise from VFDs and is reasonably priced.

https://uk.farnell.com/corcom-te-connectivity/10emc1/filter-10a-1-phase/dp/9586474?st=power%20filter
I'd suggest this is the minimum for a small (<1hp) VFD.

Similar and probably slightly better performing is the Schurter 5500.2603.01

https://uk.farnell.com/schurter/5500-2603-01/ac-filter-1-phase-10a-250v/dp/2134492?st=power%20filter

Hopefully it's obvious that the filter needs to be in a box or otherwise protected from contact with persons or swarf.

Robert G8RPI.

Edited By Robert Atkinson 2 on 18/12/2018 21:51:59

Hi Neil,

I'll try to find a reference but most are for manufacturers and importers. The obligation for conformity happens when a item is put on the market or is first put into use. The VFD's despite having CE marks are components and only comply with the directives if the manufacturers instructions are followed. Generally this means filters, enclosures and safety devices. Having tested many items using VFDs and electrically similar servo drives, I can say that they won't pass without significant work. There is no dispensation in the EMC directive for one-offs or personal use. The only dispensations are for electronic development kits for professional use in R&D facilities and for radio amateurs. Note that you have to be compliant, you don't HAVE to test. I feel a reasonable hobby approach is to use filters and enclosures (for electrical safety under the low voltage directive) as recommended by the manufacturer. While machinery and LCD "failures" only put you and others in your workshop at risk (maybe neighbours if it catches fire), EMC can affect many services even some distance away. These include "safety of life" systems such as emergency services radios and aircraft navigation systems.
If there is an issue, you should at least be able to show some diligence.

Robert G8RPI CEng MRAeS

Hi,
As long as the VFD has not failed it will continue to be powered by the DC "Bridge" capacitor and if the e-stop control input is active at the same time as the mains input disconnected the drive will go into dynamic breaking to stop as soon as possible. The energy in the rotating parts is actually dumped into the capacitor keeping it carged until it stops. Drives with very high inertia loads that have to stop quickly in normal operation have to have a brake resistor to dissipate the energy so the capacitor does not over charge.

I thought the green wire was a screen but it's not mentioned and not in the circuit diagram.

The current version of the EMC Directive may be dated 2014 but the original was 1989 and the law requiring comliance in the UK came into force in 1996.

Robert G8RPI.

Edited By Robert Atkinson 2 on 17/12/2018 19:41:30

Reading the original conversion article, despite the abundance of safety warnings the system does not comply with basic electrical safety, machine safety or emissions requirements.

Most importantly the "E" stop should break the input supply to the drive. This could be direct or via a no-volt release contactor wired to the LV stop. The latter is best as if there is no drive failure the drive will bring the machine to a stop faster than just cutting the power. You have to cut the power as well to cover for a drive control failure. A E stop on just a control input is not good enough.

To comply with low voltage regulations (and common sense safety) this type of drive must be fitted inside a protective enclosure. The control panel wiring should use screened cable.

To comply with emissions regulations the particular drive shown needs an external input filter. (the CUB inverters with an "E" suffix to the part number have a filter built in and come with an earthing plate) A good filter can cost as much as the drive. Technically you then have to get it tested for emissions before using it (yes even as a personal item). Testing may be a bit much, but a decent filter is essential.

Not trying to stop people doing "DIY" but we should at least try to do things correctly.

Robert G8RPI.

+1 to Mark R, Power Factor is important. Some VFDs have PF correction but most don't . An off-load motor consumes little power (I2R losses plus bearing and air drag) but it will have a poor PF. Most domestic meters read apparent power, not real power so even a low power load with poor powerfactor will cause it to over-read. This is a particular issue if you leave the motoer running but disengaged when not running.
A correctly sized 3ph motoer combined with a VFD that has PF correction an approriate mechanical speed reduction is the best solution. Any 3PH motor and VFD will be better than the same size 2ph motor.

On condenser driers the unvented heatpump types are the most efficent overall. They are fast and have low electrical consumption. They are also gentler on the clothes. The vented types extract heat from the house and dump it outside. When the house is being heated (or aircondtioned) this is a big energy loss. This energy loss is not included in the drier efficency calculations. The Input energy from a heatpump condenser is mostly dumped down the drain as liquid water. I'm biased, I have a heatpump dryer. Most buyers nad a lot of retaillers don't know the difference.

Robert G8RPI.