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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: I once built a go cart
06/04/2020 11:25:41

Had one with Pram wheels
Have driven a proper one on a go-cart race track
Have drag raced a milk float.

Robert G8RPI.

Thread: Todays news -- well done
06/04/2020 10:39:25

While walking the dog and getting my exercise yesterday I noticed what appeared to be a young man in he childrens play area. wandering over (no closer than about 15ft) I discovered a man, toddler and obviously pregnant woman on the paly equipment. I pointed out the area as closed and the signs. The Man was totally dismissive, "I'll be alright" clearly no understanding of transmission or care about anyone else. They commented on my being out and I said walking, the dog, exercising, keeping my distance and not touching anything.

I think essential checks on club facilities, if alone and subsituted or combined with that days exercise, is reasonable. Needs to be only ONE member doing it though. If every member checked or there was a rota that is a classic cross contaminaion case.

Robert G8RPI.

Thread: How can I remove this mould from painted surface?
05/04/2020 16:03:08

An effective, safe fungicide is benzalkonium chloride. This is used for everything from eye drops to patio cleaner. Dettol dishwasher cleaner is a good low volume source. It works well on sensitive surfaces. Bleach (Sodium Hypochlorate solution) most certainly DOES kill fungal growth and inactivates spores. It also bleaches any colour deposits. The disadvantage is that it causes corrosion.
Killling and removing the fungus may not restore the surface finish. Chemicals secreted by the fungus can etch or corrode the surface causing damage that has to be repaired by re-finishing or polishing. Fungus won't grow on aluminium but it will grow on contamination on surface, even finger prints. Th secretions can still etch the aluminum giving the impression that the fungus "eat" it.

Robert G8RPI.

Thread: BBC Micro Boxford TCL125
05/04/2020 13:52:01

I would approch this as if you were looking at concverting a manual mill and had already mounted the stepper motors. Look at the mill and get motor part numbers and see were the limits switches are located. With that informtion look at the guides for a CNC conversion. As others have said, it's not worth reverse engineering the old electronics. New stepper drivers will work fine with older motors, at most you might have to adjust the suppply voltage or current settings.

Robert G8RPI

Thread: How can I use this motor economically?
04/04/2020 21:55:35

The only resonable option to run the motor would be a cheap brushless DC motor driver if the motor has suitable hall sensors. It's a lot of messing about though. It can be hard enough when you have the drive and motor data and the are supposed to be compatible

My suggestion is list it on ebay as working motor and faulty amplifier. do a search for completed listing (do it on ebay.com to include USA) to get an idea what they have old for. You may get enough to buy a 3 phase motor and VFD.

Robert G8RPI.

Thread: Wow, what a battery
04/04/2020 20:13:12

The fact that the listings say they are super high capacity and they can't print the actual capacity because they would not be allowed on aircraft is a bit of a giveaway. Some sellers also list an actual capacity in the "small print". Fake battery and cell capacities are a well known problem on ebay, amazon bangood and similar market places.
Deliberately under-representing lithium ion battery capacities causes a serious risk to air transport. The rules on sending batteries by air are there for good reason and there have been a number of incidents with fires caused by them. Even sending a package within the UK can result it being loaded on an aircraft.

Robert G8RPI.

04/04/2020 18:20:34

This is not a mistake, it's deliberate deception. It is the same as a recent thread on 2TB USB sticks.

If it's too goo to be true it's probably a scam

Read the sellers feedback especially negative.

Robert G8RPI.

Thread: New design of mains plug?
02/04/2020 16:03:59

While the instruction cards should be removed, leaving one in place is not a significant hazard as the don't touch the conductive part of the live or neutral pin and the thicknes is not likely to significantly affect the contact engagement.
That said, the card in the first picture posted by Neil (black printing) is significantly better thn the second as you have to take the card off to get at the screws. You would have to be very odd to put it bak on when you had finished wiring the plug. Does make you wonder what the designer of the second one (orange print) w thinkingg when he added the three holes for the screws. It probably even added cost.

Robert G8RPI.

01/04/2020 10:57:34
Posted by SillyOldDuffer on 01/04/2020 09:33:06:

I came across this exciting circuit for testing fuses in one of my old books:

fusetester.jpg

With the switch closed so current bypasses the fuse, rheostat R is adjusted until the ammeter reads 100 Amps. Then the fuse is tested by opening the switch.

As 500V × 100A = 50kW, the test fuse is likely to explode and arc. The purpose of this extreme test is to confirm fuse designs can deal a gross overload without the fuse itself causing a fire.

Don't try this at home folks!

Dave

What was the book? That is not a practical test. The 50kW is dissipated in the variable resistor, not the fuse. All the fuse sees is 100A and 500V, either of which could be applied indendently. The critical test for fuse explosions is maximum breaking current which can be thousands of amps even in domestic situations. Typically applied by a capacitor bank, fixed resistance and a large spark gap (or possibly a solid state switch given capability of modern devices). The diagram looks like something thought up by somone with no practical experience, or a gross simplification. You would not use a DC supply unless specfically testing DC fuses. If it does arc you can't stop it easily. With AC in a test like this, any arcing stops at the zero crossing. With a capacitor bank (DC by definition you have a controlled energy limit.
50kW variable resistors do exist, I've used one for testng aircraft ground power units years ago (it was old even then). It was a trailer filled with what looked like slates, but were carbon plates, ther were 6 rows (3 phase, two rows per phase) 6 leaf springs, and a big acme thread pressing on the centre of the springs. you adjusted the resistance by varing he pressure, an effect unique to carbon afik.

Robert G8RPI.

01/04/2020 08:27:22

Interestingly the report linked to by Roger B used a load current of 20A on leads clearly marked as 13A maximum load. This is an abuse load and seems to have been carefully chosen to be as high as possible without causing a 13A fuse to fail quickly. While a 20A load could clearly be applied to these leads, its a very specifc case. What is clear is that you should not allow plugs to be covered by anything flammable like paper or cloth.
It;s also clear that the hard thermoset plastic bodied plugs are safer. They also end to give off a distinctive smell if they are overloaded.

Robert G8RPI.

31/03/2020 19:54:32
Posted by Maurice Taylor on 31/03/2020 16:16:52:

Can anybody remember why we changed from red and black wires to brown and blue for live and neutral ? I think this was approx 50 years ago for flex but only 15 years ago for twin and earth.

Twas long before the EU or even EEC. The reason was because red-geen colour blindness id fairly common and swapping over the red and green on a item with exposed metal meant the metal was live. A lot of peopl were electrocuted as a result.

Roert G8RPI,

31/03/2020 19:50:31
Posted by herbert punter on 31/03/2020 13:54:38:

It is allowed to supply an EU plug with a UK adapter if the adapter cannot be removed or cannot be removed without the use of a tool.

Bert

Theres always an exception.....
Those "adaptors" are fused, only usable on double inculated appliances and approved and are more of a plug that that need a 2 pin 4mm plug fitted first.

Robert G8RPI.

31/03/2020 12:56:02

Coming late bu a few comments

1/ SOD - excellent expalnation.

2/ Electrical wiring parts ad mains plugs are not CE marked nor should they be (componens no articles)

3/ In UK plugs must be approved to BS1363. use of non-eu plugs with adaptors in not acceptable.

4/ It is the IMPORTERS responsibility to ensure compliance. If you buy something from China and then complain about compliance you are complaining about yourself.

5/ The OP's unit must be switchmode to met the ratings in the size.

6/ Testing to "20M" is not an indication unless you are using a 1000V insulation tester.

7/ Personally I won't buy ANY mains powered item that is shipped from the far east or where an ebay seller has a far eastern address even if they ship from the UK.

It probably won't happen, but if you buy a mains powered item on banggood or the like and it burns the house down your insurance company could have grounds to reject a claim .

Robert G8RPI>

Thread: Inverter failure guidance
29/03/2020 18:15:52

I take it the "FAULT" LED is off?

Are you sure you are in local mode and have commande the motor on?

Is the "REMOTE LED on or OFF?

What is the "DIRECTION" LED showing?

One thing to try is to reset it to factory defaults (see page 34 of the manual https://www.sentridge.com/wp-content/uploads/ACS200USERMANUAL.pdf ) then set the drive up "from new" following the manual.

Robert G8RPI.

Thread: Minilathe/Mill motors
28/03/2020 18:49:14

SOD, this is an SCR controlled bridge. These are old technology now. The switching rate is limited to 2 x the line frequency (100 or 120Hz often causing audible noise) and as (most) SCRs can't be turned off they stay on until the next zero crossing of the mains supply. They have been made obsolete in most applications by the development of high voltage and current power transistors.

Robert G8RPI.

Edit as crossed with other post.

Edited By Robert Atkinson 2 on 28/03/2020 18:57:53

28/03/2020 13:25:12

I need to type faster..... and SWMBO gave me a chore in the middle of typing.

Robert G8RPI.

28/03/2020 13:23:54

I don't have information on the motors fitted to thee machines but there is no reaon why the same motor could not be used on both.
The motor controller uses pulse width modulation (PWM) to control the power supplied to the motor. Basically the mins is rectified to DC of around 340 or 170V (you are correct in your maths, I used 240V) this is then switched by the transistor (the IRFP450 is a MOSFET not an IGBT) to acheive the correct power. This switching is at high speed, tens of thousands of times per second, and the ratio between the on an off times (pulse width) control the power delivered. For example for 120V mains and a 170 volt motor, transistor off all the time (0%) is 0V and no power, on all the time (100%) is 170V and full power. So if it is on half the time (50%) the average power is 50% or 85V. If we leave it at 50% and change the input to 240V AC we get 340/2 =170V or full power using the same motor. Note that the peak voltage is double that of the 120V input case but the avrge current is less. The pulses are fast compared to the inductance of the motor windings so the motor responds ot the avergage value, any where between 0 and 100%
The control circuit has feedback and can be used to control voltage (speed), current (torque) or more likely in our case speed feedback with voltage and current limits.

So as long s the circuit is designed for the worst case voltage and current for the voltage range it oes not require any changes to work with both 120 and 240V. Note however that while average power is the same, in the 240V case peak voltage and current iss higher so components and motor insulation are more stressed . This may result in less reliable operation if components are marginal. Also with thi simple aproach the feedback, if digital is less precise on 240V than 110V. This is because it is only using half of the control range, 0 to 50% for 0 0 100% power.

Better designs use a switchable voltage doubling rectifier and storage capacitor arrangement that produces around 340V with either 115V (doubled) or 240 (full wave) rectification this can be link or switch selected or even automatic. This design can usually be identified by the presence of two identical large electrolytic capacitors in the rectifier circuit. These are in series for 120V and parallel for 240V operation.

The ideal set-up is a 300 Volt rated motor with a voltage doubler when used on 120V. The lower rated motor gives some overhead in the control for losses and lower than nominal mains voltage.

Robert G8RPI.

Thread: Electrical conducting paint
27/03/2020 13:59:04

Assuming the element is on the surface, rather than embedded in laminated glass, the best repair is t use silver loaded conductive epoxy. Not cheap though
https://uk.farnell.com/multicomp/mc002966/epoxy-adhesive-syringe-6ml-silver/dp/2917615?st=ilver%20epoxy

Make sure it says it is ELECTRICALLY conductive, some are designed for thermal conducttivity and may not be good electrically.

Robert G8RPI.

Thread: 7 pin connector 240v?
27/03/2020 13:26:01

The GX-16 "aviation" connectors sold on ebay are not made to ny aiviation specifiction I'm aware of. They are not normally found on aircraft, certainly not commercial ones. The most common use for them is microphone connectors on two way radios but even there they are being displaced because they are large compared to modern radios.
Thet are not suitable for mains power.

Robert G8RPI.

26/03/2020 20:52:57

For 3 Valves you only need 5 pins, 3 switched lives (or neutrals), 1 neutral (or live) and earth. I'd suggest a HAN A 4+PE

https://uk.rs-online.com/web/c/?sra=oss&r=t&searchTerm=HAN+A

You need a female on the power source obviously. You can get screw or crimp terninals and plastc or metal shells.

Robert G8RPI.

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