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Member postings for Robert Atkinson 2

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: VFD Cable Supplier Recommendations
21/06/2022 20:56:21

Twisted pairs are not suitable for reducing interference on 3 pahse circuits like VFD to motor. For twisted cable to be effective the signal on the conductors should be balanced. For two core thai is easy to understand the fields from the conductor carrying current out are cancelled by the fields caused by the current coming back. You can see this with a compass, a few feet of wire and a AA cell. lay the wire in a big loop with the compass 1/4 way along the wire. Connect the cell for a second (yes a short circuit) and the compass will deflect. Now bring the last 1/4 of the wire and lay it close to the fist part without moving the first wire or compass. Connect the battery for a second and the compass deflection will be much less. Twist the two wires together as they pass the compass and there will be no deflection.
For 3 phase you need 3 wires twisted together. If you use
In practical terms adding a 4th wire carrying little current (the ground conductor) to the twist it has little effect, However using two twisted pairs.causes an imbalance because 2 have balanced surrents and one does not.

As others have mentioned a length of 2.5 mm 4 core SY cable (i also use TLC for short lengths ) Is perfectly adequate for your application.

Robert G8RPI.

Thread: Replacing a 24V AC machine lamp
18/06/2022 19:44:30

No problem getting G6.35 24V AC LED lamps

Random amazon example

No idea if it is a good seller just an example of a lamp.

Robert G8RPI.

Thread: Thoriated tungsten electrodes
18/06/2022 14:14:34

As a private individual you now need a Explosives Precursors & Poisons (EPP) licence to possses Mercury. This applies even if you already had it. There are exaemptions for when it is part of something else e.g. fluorescent lamps.

Mercury is of course both a EP and a P.

Robert G8RPI.

Thread: A TOPICAL point, FANS.
17/06/2022 16:38:29

WD 40 is flammable. Don't spray it on the brushes when the motor is running!

Thread: Battery fire in electric cars after a collision
12/06/2022 07:29:36

One big difference with batteries compared to petrol, diesel, LPG CNG or even hydrogen it is hard to remove the energy source after accident damage. The fluid fuels can be drained, vented or even deliberatly bunt off. If the casing is damaged in a crash they tend to be self emptying. All thesw leave a safe wreck for disposal.
Current EV battery technology is based on thousands of small cells. Failure of one or two of these cess can start a chain reaction throughout the battery. This can hapen some time after the inital damage b=due to isulatio craping under pressure or movment due to thermal cycling (day/night). The protections used in small batteries like laptops and power tools are not really applicable due to the number of cells and currents involved.
The only way to "empty" a damaged battery is to fill the housing with conductive liquid or immerse the whole car in conductive liquid (water with a source of ions eg. salt). This is of course destructive.

The battery packs do have an isolator that is used for servicing / rescue and will also protect against shorts external to the battery pack. On my Plug In Hybrid (Outlander) this is a plug on the top of the underfloor battery pack and is accessed through the rear passenger footwell. It does however need tools to operate it. I carry the required tool in my glove box so in the event of any incident I can isolate it myself.

Robert G8RPI.

Thread: Thoriated tungsten electrodes
06/06/2022 19:59:33

A couple of facts:
Old gas and paraffin lamp mantles contain significantly more Thorium than welding rods and once lit the ash is much easier to breathe in. There have been few issues with that.
Magnesium-Thorium alloy with up to 4% Thorium is specfically considered to NOT be radioactive material under UK radiation legislation. Thus it does not need any special handling or disposal. There is an odd exception, if it is being used for it's radioactive properties (e.g. as a test source) then you have to comply with the regulations.
Generally Thorum is not considered a significant hazard. Certainly no worse than Cadmium (plating, rechargable batteries) or many other engineering materials.

Robert G8RPI

Thread: Grinding and cutoff discs for angle grinders
05/06/2022 21:18:56

+1 for Nicholas Wheelers comment

Cheap off-brand grinders tend to be heavy, noisey and poorly balanced (both handling and vibration). For anything other than very occasional, rough work the investment in a branded tool will be repaid with easier use, better performance and less noise.
Personally I like Bosch and DeWalt (I have a battery DeWalt, not something to keep in the car unless you want a conviction for "going equipped" frown).

Thread: Failed Miller Transportation
04/06/2022 12:40:30

Lucky it didn't fall through the soft side of the lorry and hit another vehicle.

Thread: Vickers Bl 8 inch Howitzer cannon of 1917
28/05/2022 10:11:04

Not directly related but the pictures of obturators reminded me of this accident report:

In short a sad story of firing the main gun without the obturator fitted excerbated by poor storage discipline.
Apart from the safety lessons there are interesting details of a modern breech system.

Robert G8RPI

Thread: Nostalgic moment
26/05/2022 12:47:42
Posted by Jon Lawes on 26/05/2022 07:22:13:
Posted by Robert Atkinson 2 on 25/05/2022 20:49:16:
.... Turned out they were showing a clip about Thrust SSC (Which I helped build and run) and I was in the background.

Robert G8RPI.

I have a funny feeling I remember that coming to Boscombe Down for testing? Or did I make that up?

Yes it did a couple of times. We spalled the concrete in one of the ground running bays with the re-heat . Though the bay was rated for the Phantom which used the same engines (RR Spey 202) the car was closer to the ground.
I also visited Boscome down to rob parts from ne of their phantoms for the car. We needed the alternators and control unit but as we had to take the enges out to get to the alternators we had the engines too

Yes The HA was 1983.

Robert G8RPI.

25/05/2022 20:49:16
Posted by Nicholas Farr on 24/05/2022 23:20:53:

Hi Nigel B, Opps! blush bit more like a Bedford HA van, but it did have a very good turning

Regards Nick.

My first "car" was a Bedford HA van. Bought in 1883 for £50 and did most of my learing in it. As bought it had a habit of going into reverse instead of first. A mate and I dropped the gearbox and found the thin wall tube suporting the gear selector was bent at one end. I forget the exact deatils but a replacement was turned up from a bit of aerospace ggrade structural steel tube at a local company as a favour. Aftter it was all back together the Haynes manual arrived and apparently we should have taken the engine out rather than just unding the mounts and pushing it forward. We didn't hve a engine crane or similar. I drove it from Bristol to Northern Ireland fand back on holiday. Unfortunatly the person I sold too crashed it while under the infuence.
For such a common van at the time they are rare now and fetch relatively high prices. Most rusted away.
SWMBO was watching "antiques road trip" the other week and called out "you are on the TV". Turned out they were shg8owing a clip about Thrust SSC (Which I helped build and run) and I was in the background.

Robert G8RPI.

25/05/2022 20:20:03
Posted by noel shelley on 18/02/2022 12:57:08:

Gentlemen, thanks to those who have contributed so far ! The intention was to use plastic floats and on reflection ali rod would make good arms ! Some damping would help to stabilise readings ! Is there any theoretical way to calibrate the instrument or is it down to a still day and mount it on the roof rack,of the car, Knowing the speedo is 2MPH fast. As for hares there's more than a few round here, that's why there's a long barreled full choke 12 bore in the cupboard. When it was given to me I was warned not to shoot at anything I wanted to eat at less than 35yards. The local gun club stopped laughing when one day I used this weapon to stop clay pigeons just before they hit the ground, some considerable distance away ! Noel.

Edited By noel shelley on 18/02/2022 13:01:14

Yes this, but do at least two runs in opposite directions to average out the effect of wind. Don't try to calibrate to any unit at this point just measure the "raw" frequency from the sensor with a frequency counter, digital tachometer readout or similar. Ideally do a range of speeds and plot the results in a graph to see how linear it is. Ideally the graph should be a straight line.

Robert G8RPI

Thread: Barograph 'stiction'
12/05/2022 21:57:58

Swarf's comment on a buzzer is spot on. Many aircraft altimeters (basically aneroid barometers) have internal buzzers to overcome stiction. Altimeters have very good bearings but stiction is still an issue.

Robert G8RPI.

04/05/2022 13:06:11

The medium specified in the IP5x test is talcum powder. This is non conductive. To test with anything else would not be compliant with the standard.

I have looked at several cheap VFD and their claims for compliance generally were dubious.

Robert G8RPI.

P.S. Part of my day job is witnessing compliance testing and reviewing other peoples tests. I also sit on a committee that defines a environmental test that includes dustproofness.

Edited By Robert Atkinson 2 on 04/05/2022 13:08:33

03/05/2022 16:25:46

The IP 5x test uses nonconductive dust (talcum powder) so is not adequte to protect electrical equipmnt against conductive dust.

Yes you can get fully protected VFDs, at a cost. Most model engineers on here seem to use the cheap far eastern VFDs. On many of those wven the basic IP20 is dubious

Robert G8RPI.

03/05/2022 12:45:16

Just a note, IP54 only provides protection against limited amounts of dust. It is not generally adequate for electronics in a machine shop.
The fundamental issue is that almost all VFDs are components and need to be installed in accordance with the instructions. The instructions are intended for qualified competent persons. Virtually all VFDs need to be enclosed with proper protection, earthing cable strain relief etc etc.



02/05/2022 11:51:38

Any VFD should be in an enclosure.
Metalllic or carbon dust will cause failures if it gets into a VFD and could even cause a fire.
Check the requirements for your VFD the smaller ones taht we tend to use may not need forced air cooling of the enclosure if the enclosure is big enough.
If you do decide on forced ventillation of the enclosure , go for low velocity as this is less likely to pick up dust, A larger low volume fan is better than a small screamer. Have the fan blowing out of the case and have a filtered inlet area greater than the fan area. They sell filters to go on fans like this
These can be on the case away from the fan.

Would need data on VFD to be specific on size.

Robert G8RPI.

Thread: Domestic Chemistry
13/04/2022 19:00:44

Mixing vinegar and bicarbonate of soda while visually impressive does not make a good cleaner. Try them on their own next time. Mixing them basically makes water and CO2 with possibly a tiny amount of sodium nitrate (lye) but it's insignificant.
At least one commercial oven cleaner is mainly bicarbonate of soda paste. It works well

Robert G8RPI.

Thread: Determining/measuring sub-micron displacement
01/04/2022 12:43:04

How about a sine bar on a surface plate and slip gauges or a micrometer head? Effectively a leaver of known length. The probe on top surface just past the center of the low end roller and gages under the other end. Possibly put the low roller in a V block to stop it moving.

otherwise stick a mirror on it and set up a laser interferometer. Not as hard as it sounds. Needs a helium neon laser, couple of mirror a beam splitter (microscope slide cover slip) bit of ground glass and a magnifier to see and count the fringes.

Robert G8RPI.

Thread: Liquid Plus Gas
30/03/2022 12:41:04

A 50:50 mix of acetone and automatic transmission fluid has a good reputation.

Robert G8RPI

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