Member postings for Robert Atkinson 2

To answer the original question.

Yes Bob would be liable to prosecution under the explosives precursors and poisons (EPP) regulations. Max penalty is 2 years in prison.
You now need a licence to possess many previously common chemicals. If the Hg was sealed in a valve, lamp or instrument it is exempt, but a bottle of it needs a licence. Also applies to battery acid, many plating chemicals etc. Note that it does not apply to professionals or businesses.

See:

https://www.gov.uk/government/publications/licensing-for-home-users-of-explosives-precursors/licensing-for-home-users-of-poisons-and-explosive-precursors

Robert G8RPI.

I'm not a lawyer but this one is pretty straightforward. Get professional legal advice if you need it , but I doubt there is much case law on this one yet, don't be the first.

Robert.

Edited By Robert Atkinson 2 on 04/06/2019 07:19:44

Can you provide details of the controller model?
The more advanced conntrollers actually use a 0-5V (or similar) control voltage which is generated by a potentiometer a 5V supply. If thi is the case you could use a single pot with 3 connections (common, 5V and variable) to one controller and two (common and variable) to the other. If they are cheap ones using a RC circuit then you will need a dual potentiometer. Make sure that it is linear NOT log or "audio" taper. The matching between sections would normally be better than 5%.

https://uk.rs-online.com/web/p/potentiometers/1638384/

Rober G8RPI

Another well documented issue is the inclusion of terminating resistors in Chinese "ELM327" OBDII car diagnostic interfaces. These are used to read fault codes etc on cars by interfacing to the CAN bus. This bus is terminated on each end by a 120 ohm resistor. As a resistor appears on the data sheet application typical circuit the Chinese include it. This results on 3 resistors connected to the bus and depending on other factors like cable length and number of bus nodes this can stop the bus working properly. Remving the resistor from tye interface fixes the problem. It's been known about for years but they keep fitting them.

Robert G8RPI.

While microstepping improves torque ripple and position overshoot, it does not necessarily provide improved positional accuracy. This is particuarly true ff the load (torque) is variable. Performance depends on the motor, controller and load. It's easy to get caught up in the numbers but the whole system must be considered or you may be wasting effort for no real improvement.

Robert G8RPI.

A proper three phase supply would be a positive advantage if you are at all likely to buy an electric or plug-in hybrid car in the future. It would allow the installation of a fast charger.
Additionally what is the rating and load on your existing single phase supply? Many only have a 60A feed which is 14kVA. This seems a lot but if you have electric heating / cooking / shower you might be running int the limits at peak demand.

Alternatively take a tap off a couple of neighbours of street lights for the other two phases
(just for clarity that;s a joke I don't advocate stealing electricity or making dangerous taps into wiring.)

Robert G8RPI.

To add to Andrews excellent response, this means that best use of a VFD is to run the motor faster than the "50Hz" spee but at reduced power and current for small parts and keep the belt ratio high so you maintain power at low speed for larger workpieces. Obviously you need to make sure you do not overspeed the bearings or rotor particuarly if its an older motor.

Robert G8RPI.

Well it’s clear that the Americans who won’t vaccinate their children have caused a lot of trouble. I’m of the view that a bit of exposure promotes the immune system. That’s how vaccines work after all.

Robert G8RPI.

Hi,

If using in the same room as electronics beware of getting swarf into it. Little bits can fly quite far. As long as top ventillation holes are under a shelf or similar it should be fairly safe though.

Robert G8RPI.

Andrew has explained this perfectly. I do note that SoD's calculations look bit suspect. For starters it's normal to use peak to peak rather than peak. More importantly, the root two factor only applies to pure sinewaves.
The 13 amp fuse will not be stressed at all by 18A at a couple of milliseconds. The main effect is thermal and this will be averaged by the mass of the wire and the sand packed around it. In fact a 13A BS1362 fuse will not blow when passing 20A (RMS or DC) for long periods of time (hours). It will take 100A for 10ms without blowing.

So a 13A plug fuse will not blow under this load and a 5A one would probably be a better choice as it will actually blow under sustained load. You might get failures if you try to start the motor under load though. An MCB needs to be higher current rating or/and B orC type as they operate on magnetic attraction so are much more sensitive to pulse currents.

Edit: found a good explanation of 13A fuse rating https://www.pat-testing-training.net/articles/fuse-operation-characteristics.php

Robert G8RPI.

Edited By Robert Atkinson 2 on 20/05/2019 21:31:45

Edited By Robert Atkinson 2 on 20/05/2019 21:32:58

I went to the Dunstable Downs amateur radio boot sale. The only thing I was looking out for was a UHF signal generator. Typically I didn’t find a signal generator but did come away with an arbor press (BNL No.1 MP1), a Sorba HV5 5” rotary table and a 12” APE microball micrometer height gauge. The press seems better made with a round rack rather than the square common on cheaper modern ones. I’d not come across the microball height gauge before. It seems quite nice and the size suits my small surface plate. These were all items on my shopping list for the workshop so at £60 I’m pleased even though I didn’t get a sig gen (I did get some other electronics )

Robert G8RPI.

Virtually all non water based adhesives will last longer if stored in a fridge or freezer. Locktite and PVA should not be frozen. datasheets available online often give advice or at least a minimum temperature. Aero space sealents that are normally two part are also supplied pre-mixed and frozen. Annealed 2017 and 2024 alloy rivets stay soft longer if stored in a fridge too.

Hi,

The new switch is not suitable as it does not have a no volt release coil. This is a safety feature and it is likely that the emergency stop will not operate without it.

Robert G8RPI.

Edited By Robert Atkinson 2 on 17/05/2019 21:05:24

Where are you located? maybe there is someone nearby with electrical / control knowledge who could help.

Robert G8RPI.

That brings back memories. 40 years ago I was a fairly newly licenced radio ham and a member of RAYNET covering the races providing communications for the Red Cross and St Johns Ambulance. I was at the last first aid post on Quarry Hill when Tom Herron crashed. 1979 was a bad year, three riders died. I left NI a couple of years later.

Robert G8RPI.

Mid Wales is a bit too far I'm afraid.
Any imbalance or residual magnetism will cause it to rotate. Not much torque though.

Robert G8RPI.

Where are you located? I could come over - seriously.

I like a challenge. One motor problem I had was a machine with a geared squirrel cage induction motor, The gearbox output was running backwards after somene "fixed" it. After spending time studying the gear box I finally reallised they had flipped the coil and stator over (not the whole motor, think about it) wich caused the shaded pole to be on the other side and the motor to run in reverse

Robert G8RPI.

One option to get around keeping a credit card account is to use one of the pre-paid cards that are available from places like supermarkets, normally on display with gift cards. You do a pay a premium and may be left with a unusable balance that can expire but you don't give out your bank details. Most you can loose to fraud is the balance on the card. Also useful for recurring subscriptions that are hard to cancel like gym membership.

Robert G8RPI.

Some info from contemporary literature

Images in my Album.

Robert G8RPI.

Edited By Robert Atkinson 2 on 12/05/2019 12:21:23

Reversing either the field OR the armature (brush) connections will reverse a "universal" motor which is what a Dynamo in motor mode is. Are you sure you actually reversed only the field? Does the dynamo produce plenty of torque when motoring? you might have only reversed on section of the field winding or wound / connected one or more section in the wrong direction. "Flashing the Field" produces a residual field of fixed polarity that makes the dynamo self starting in the correct polarity. If for instance there are two field coils and you would one in the wrong direction or connected one backwards the two electic fields would cancel out but the dynamo would still draw a large current and possibly turn on the residual permanent magnetic field. The torque would be much lower though. If a field s open circuit the ame would apply but current would be lower.

Direction of rotation does make a difference in two ways:
1/ Field distortion. The rotating and fixed fields interact changing the neutral position of the brushes and causing sparking at the commutator. Often the brushes are offset to compensate. Reversing the direction of rotation increases the offset and makes sparking worse. Compensating windings, or on old desigins moving brush holders, are also used on big machines to acheive the same effect over a range of loads.
2/ Cooling fan will run the wrong way reducing efficency.
These may not apply to a small Austin 7 dynamo of course.

Dynamos are still used as starter-generators on small turboprop and turboshaft engines on aircraft.

Robert G8RPI.

Light, particuarly the shorter wavelengths, will speed the decomposition of hydrogen peroxide so it should ideally be stored in opaque or light filtering containers. The online sellers are being cheap. If kept in a dark place it makes no difference.

Robert G8RPI.