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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: Trembling laptop
15/07/2020 13:03:51
Posted by Bazyle on 15/07/2020 12:55:01:

My previous laptop did this for years - nothing to worry about, The newone is all plastic so doesn't do it. I tused also to be a problem with CRT TVs that were plastic so had no earth wire. If tthe aerial cable wasn't earthed then the owner might buy a metal cased VCR which became 'live ' through the scart cable but it was just an indued votage so no current to do actual harm.

The above is incorrect and misinformed to put it nicely. You cannot possibly know if there is a problem with the OP's laptop / powersupply or not. Just because you were not electrocuted does not meant that your old laptop was OK either.

Don't give safety advice when you are not competent in the area.

Robert G8RPI

15/07/2020 10:18:45

This tingle is caused by leakage current from the power adaptor. The leakage current is often caused by interference suppession components, as has been mentioned by others, in particualy a "Y" capacitor across the isolation barrier. This current should be less than 210 microamps (0.2 mA 0.0002 A). and not normally detctable.

My concern is that this is a used device so you don't know it's history and the AC adaptor may have been replace at some time, possibly by a "clone" that might not meet current safety standards. From the photo it doesn't look the 4 years old that date on the unit implies and used latopts often come with "new" power supplies. Ideally you dhould have it checked.

If you have a meter that reads AC milliamps you can do a quick check yourself. Place the laptop on an insulating surface (plastic cutting board is good), switch it on with mains power and connect the meter (set to AC milliamps) between a known earthed object (e.g head of the screw holding down the mains socket) and an exposed metallic pat of the laptop. The OUTER metallic part of a USB socket is good, but don't put the probe into the socket itself. Use proper test leads and don't touch any metal parts when doing the test. If you get a reading of more than 0.2mA stop using the charger and get professional advice.

Robert G8RPI.

Thread: Gluing metal
15/07/2020 09:54:36

4mm wide, but how long snd how thick? What is the bond area? That said a metal filled epoxy like JB weld, Araldite Steel is likely to be the best choice if you want a hidden bond as the glue line or fillet will look like steel. but from your described requirements any epoxy or super glue would work. For structural meatal bond toughned acrylic like Loctte 330 or Permabond TA435 are a good option.

Robert G8RPI

Thread: Basic Electrics
14/07/2020 14:22:10

Posted by Steve Neighbour on 13/07/2020 23:02:24:

<SNIP>

There are, I'm sure many of us who undertake 'home electrical work' and I suspect that a lot is not even close to meeting the requirements of the Institute of Electrical Engineers 17th edition Regulations.

If there are folk on here who can offer qualified and SAFE advice, then in my mind that has to be a good thing, and if the advice offered is dubious, then knowing how forums work, it will be corrected PDQ by someone who knows better !

Steve

Or even the 18th editon of BS7671cheeky(the curent one)

Also BS7671 does not cover the wiring of equipment, just the fixed installation.
Most questions would be about equipment.
Nothing wrong with putting a small machine tool on a 13A plug. It has the advantage of easy nd 100% isolation for starters.

Robert G8RPI.

Thread: Glow plug driver
12/07/2020 11:17:47

Hi,

You only need fancy drive circuitry if it's a flight engine where weight and endurance are important.

Phils radial engine circuit has issues, particuarly the 0.47uF capacitor across the gates of the MOSFETs. This stresses the mocrocontroller outputs and keeps the MOSFETs in their linear region longer increaing heating and battery consumption. Fo a simple sequential switch a couter decoder like a CD/HEF 4017 or 4022 would be easier to use.

For a flat four I'd run the plugs series / parallel. Put a link / busbar between the two plugs on each side then connect the battery (or other source), with a voltage twice the rating of each plugs, between the two links. The crankcase will be at half battery voltage but as long as the battery is isolated tthat is not an issue.

For bench running a transfomer can be used, glow plugs don't mind if power is AC or DC.

Robert G8RPI.

Edited By Robert Atkinson 2 on 12/07/2020 11:34:34

Thread: Hallite washers
11/07/2020 17:05:38

Hallite washers are fibre wahers with a wire mesh reinforcement.

Robert G8RPI.

Thread: I'm thinking of selling up, whats it worth?
11/07/2020 12:56:23

Listing at 99p start on ebay does carry some risk. The market for Myford lathes may be firm but you never know. The 99p start was common when ebay was primarily a auction site, but it is now a marketplace and the dynamics have changed. I have bought a lot on ebay comprising several bits of test equipment on ebay for 99p (no other bids) and sold ONE of the items for £1500 (Buy It Now taken, auction had £500 start) a week later.
Other people list items BIN higher than you can buy new or from a dealer but they still sell. I can only assume they think because it is more expensive it must be OK.
Ebay says you HAVE to take paypal for auctions. If collected get he buyer to sign a collecion note and take a photo of the item in their car. For high value item, even if ebay/paypal don't play ball there is always the small claims court.

Robert G8RPI. (ebay buyer and seller for 20 years)

Thread: Laser DRO sensor
09/07/2020 16:18:32

One issue with mouse sensors is that their intended use has a human in the control loop by definition. This means that even faily gross error are corrected subconsiously. In the machine application even small errors will accumulate. A good high contrast, regular pattern for the sensor to look a would help but you may still accumulate errors.

Robert G8RPI.

Edited By Robert Atkinson 2 on 09/07/2020 16:19:04

Thread: Jumpy readout DRO scales on WM16 mill
09/07/2020 14:56:53

The fact you had issues without the locking screw fitted indicates that it, or the metl it is forcing into contacr is providing the ground connection. This is not acceptable for a safety ground. The safety ground path shoud be properly engineered and not reliant on casual contact between parts. I wonder if it would have passed our test withut the screw fitted. While a DMM will identify gross errors, to properly test safety earthing a bonding test that passes significanr current, around 20A for a small machine tool, is required.

Robert G8RPI.

08/07/2020 17:22:37

Oh dear,
That is an indication that the safety earthing on these machines is not as good as it should be. A clamping screw is not an adequate ground path.

Robert G8RPI.

Thread: Butterfly Bolt or Thumb Screw
05/07/2020 19:07:03

You can get moulded cps specfically to turn cap screws into "knobs"

https://uk.rs-online.com/web/p/knobs/0771667/

Other suppliers do them too.

Robert G8RPI.

Thread: Parvalux motor
04/07/2020 13:36:26
Posted by Ian Parkin on 04/07/2020 13:25:10:

Or this style

https://www.ebay.co.uk/itm/AC-DC-DC-24V-5A-Universal-Regulated-Switching-Power-Supply-Transformer-LED-PSU/164248272740?_trkparms=aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D225113%26meid%3D5adc9fd092634b1fbd654524ac8c9b80%26pid%3D100005%26rk%3D6%26rkt%3D12%26mehot%3Dpf%26sd%3D193550898066%26itm%3D164248272740%26pmt%3D1%26noa%3D1%26pg%3D2047675%26algv%3DDefaultOrganic%26brand%3DUnbranded&_trksid=p2047675.c100005.m1851

Personally I would not touch that with a barge pole (unless it was certified as insulating )

Clearly not compliant with regulations, it does not even have a part number. I would be concerned about it' safety.

Robert G8RPI.

04/07/2020 13:26:01

Most, if not all Parvalux "DC" motors are brushed "universal" motors. This means they will run fine on AC, You just need a 24 V transformer (a dual 12V will do too).
A SMPS is overkill and may not actually work depending on the size of the motor and the design of the SMPS. Many do not like the inrush current of a DC motor with a heavy load. I'm not sure how Ian determined a 5A requirement.

Robert G8RPI

Thread: ISO Container for Workshop
01/07/2020 19:39:34

Three comments
The proper military workshop and special purpose "containers" are built from scratch with insulated wall panels. Nice but can be expensive

You can get "one trip" used containers fairly cheaply as many countries export more than they import. I know if a plasterboard plant in Nevada re-opened and are shipping mot of their output to the far east at minimal costs s otherwise the ships would be in ballast.

If you get refriderated contaner the first thing to do is add at least some fixed ventillation as they are airtight to the point you could suffocate nd fumes etc can't escape.

Robert G8RPI.

Thread: Overview of fitting variable frequency drive (VFD) to a Myford ML7
30/06/2020 20:33:47

This is just based on review of the material on the Newton-Tesla website, but their ML7 Super7 prewired kits look quite good. They appear to have the inverter in a proper enclosure which is a safety requirement and not met by just buing an inverter, Chinese or otherwise. It also comes properly set up for the motor. Unless you are reasonbly skille with electrical systems I'd strongly recommend buying a pre-made unit like their AV750.
Manny home inverter installations are at best non-compliant with regulations or just plain dangerous, Even Newton Tesla' pre wired packages are not compliant unless they are properly installed in an enclosure with strain reliefs etc. An inverter, motor and box of bits from ebay may have a lower ticket price, but even aside from safety, the time spent selecting parts and buliding it up soon adds up. Even our non-work time costs, either in time taken from other aspects of the hobby or family and friends.

Robert G8RPI.

Thread: ISO Container for Workshop
30/06/2020 07:29:30

I second Bo'sun's Comments. Plain ISO containers will literally generate their own climate including "rain" from condensation. You need to at least line it with wood and preferably insulation. A 20ft or two will be easier to handle and be moore practical, The extra end wall area means you waste less space for accesses. Fully stuffing a 40ft or 2x20ft gives the same volume, but if you have to alllow access to the contents 2x20ft work a lot better.

Robert G8RPI.

Thread: Ultrasonics and citric acid
29/06/2020 20:05:20

Ed's suggeston is good and standard practice for cleaning small items in a ultrasonic cleaner. A glass laboratory beaker works well. Use hot water in the taank and cleaner, citric acid in this case in the beaker. Ideally float the beaker with a collar of closed cell foam. A thin (cheap) pressed stainless steel cat's food bowl works well too.

For non-ferrous alloys a dilute solution of ammonia with a drop of washng up liquid works well.

Robert G8RPI.

Thread: Stroboscopic effect
29/06/2020 12:40:15
Posted by Michael Gilligan on 29/06/2020 11:06:43:
Posted by Robert Atkinson 2 on 29/06/2020 10:58:59:

When I designed LED lighting for microscopes, I Used PWM control because of the efficency, but then filtered it to produce DC through the LED. Basically a switchmode current source with optical and current feedback.

.

Good approach, Robert yes

... but I’m sure you don’t need me to tell you that.

MichaelG.

Thanks Michael,

It was part of this patent
https://patents.justia.com/patent/6878949

But we kept some information back

Robert G8RPI.

29/06/2020 10:58:59

When I designed LED lighting for microscopes, I Used PWM control because of the efficency, but then filtered it to produce DC through the LED. Basically a switchmode current source with optical and current feedback. It was for quanttive fluoresence so hd to e controlled intensity. I've also used white LEDs as strobes, thay turn off slot faster than a conventional xenon flash lamp.

Robert G8RPI

29/06/2020 06:50:20

Going back on topic, I like others, would nor recommend using a stroboscope to "freeze" the lathe or workpiece.
On inadverent strobing, It is impossible to make generic statements about LED lights as there are too many variables in the electronics that drive them. If they are driven from DC with just a series resistor or analoge constant current source they are fine, but this is now uncommon as it is not efficent. running a lower powered 12V AC/DC MR16 lamps run from a prroper 12V DC supply (NOT a LED power supply unless you are sure it's smoothed DC output), you will probably avoid stroboscopic effects but you might get one that has electronic control rather thn simple resistors.

Robert G8RPI.

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