Member postings for Robert Atkinson 2

Very few modern shavers use the resonant armature type mechanism Howard describes. All of the Braun shavers I have had for at least 20 years have had a brushed DC motor. Larger mains powered hair clippers still tend to use a resonant armature though.

I will say agin NO ONE ON THIS FORUM HAS ENOUGH INFORMATION (based on what has been posted so far) to make any reasonable judgement about the OP's safety when using an electric razor.

Robert G8RPI CEng FRAeS

NDIY,

This is not a helpful post. You obviousy have no training or expertise in EMI/EMC. Things are constantly changing in both the EMI/EMC and Medical device worlds. The OP should follow the guidance given by the device manufacturer and / or medical professionals.
No one on this forum has enough information to suggest anything else. We do not even know the type of medical device involved.
You seem to have the view on this and other threads that "I/we/they/ have done it for ages without any problem so don't worry about it" for safety and compliance issues. This approach is irresponsible at best.

Robrt G8RPI.

Edited By Robert Atkinson 2 on 25/03/2020 12:31:25

Mains or battery shaver does not matter, they can both cause interference.
To answer the original question, wrapping the shaver in aluminium foil is not a reliable means of reducing intterference. This is mainly because it will not provide reliable contact, even with itself. It might even form a resonator making emission worse for specific frequencies or directions. Covering the razor with self adhesive copper foil, soldering all the seams and providing a ground connection would probably help, but without making measurements you cannot be sure.
An isssue with modern implantable medical devices is that many have a "remote control" capability sometimes with an antenna remote from the device. This makes them more vunerable to interference.
This is a classic case of safety probability / impact assessment. The probability of emissions causing problem is low (probably "extremly remote,10-7 in safety terms) but the effect is catastrophic (death) so additional precautions, keep emitters away from device) are required to bring the probabilty dowm to an acceptable level (<10-9).
Note that on another threads on VFDs I have commented on the need to fit proper EM/EMC filters. Your device is one reason for this so please take care aroung machines with electronic speed controls particuarly DIY set-ups.

Note that the interference drops with the square of the distance, doubling the distance reduces interference by 4, so knowing were the device an any antenna are would allow for a better judgement to be made. If they are in the neck/head then electric shaving is a no-no, if they are in the abomen then you could make a judgment call.

As a professional engineer involved in EMI/EMC I can only recommend you follow the advice given by the device manufacturer and your medical specialists.

Robert G8RPI.

I agree with Simon Don and George.

13A is appropriate if cable is large enough. Plug fuses are only intended to protect the cable.

What switch gear, Start/Stop/Reevese is fitted? This may need checking or replacement.

Robert G8RPI.

Only really worthwhile for two reasons:

1/ Learning how to do it for self satisfaction

2/ To keep the motor for reasons of originality or rareity

Otherwise just get a replacement motor.

Robert G8RPI.

That is clearly a "component" meant to be incoroporated into a final "product" by a competent entity that ensures it's safeand compliant. Most VFDs fall in the same category it's just not so obvious from looking at them that you need to put them in a box with an isolator, fuse, filter etc.

Robert G8RPI.

Mycomment that most of the low cost drives were not compliant is based on experience and observation. It is often possible to tell from pubished information and images that a item is most likely not compliant. It appears that a lot of the far eastern suppliers (and some UK ones) are either ignorant or don't care.
As noted any VFD is potentially hazardous and even quality ones are intended or installation by trained professionals. Unfortunatly even they don't always get it right. As noted in another thread on supply of lathes, resellers based in the UK may themselves have limited knowedge.

I'm not suggesting that all hobby installations should, or need to, meet all the standards required of equipment used by industry or the average consumer. They should however have a reasonable level of safety and not affect others. Unfortunatly modern equipment is deceptively easy to use (and abuse) while having potential issues that are not immediately obvious. As mentioned before, causing interference is one of these. This can affect your machines, for example interference from the VFD on one machince causing another to start, stop or overspeed without warning, or other people and systems. Even quality VFDs can suffer from these issues if the filtering earthing, screening etc specified in the installation manual. Sometimes they do even when you do follow the instructions. I have seen this more than once and have even been involved helping a major manufactuer sort out issues on a new product line theat my employer was an early user of.

Just because you, or Fred Bloggs or SWMBOs hairdressers cousin has been "doing it" for years does not mean it won't all go horribly wrong in the next few seconds. Most serious accidents require 3 or more issues aor circumstances to align. Any two can be there, right on the edge of disaster for years without you noticing. Unfortunatly I don't have all my digits intact as a result of old surplus equipment with a hidden defect, minimal control and monitoring topped off with someone not following instructions, distraction and tiredness. However a lack of following my "safe" practice in positioning associated piece of equipment by the person who did not follow instructions was a blessing. If it had been positioned where I habitually put it, I would have been killed rather than having a couple of damaged digits as my head would have been where my hand was. Luck plays a part but we should not rely on it.

Robert G8RPI.

Edited By Robert Atkinson 2 on 22/03/2020 18:06:51

Actully you can't just "pays yer money and takes yer choice" there are legal requirements that everyone, even hobbists at home, are required to meet.

Yes I know there is virtually no enforcement and most people don't bother. I didn't want to go down that rabbit hole which is why I didn't mention specific standards. But you raised so here it is.
To be legally used the installed VFD must as a minimum meet the Low Voltage Directive, the EMC Directive and depending on the application the Machinery Directive. This provides CE compliance. You also need to meeet the wiring regulations for the mains connection. Some VFDs are CE marked which is interesting as they could be considered components which don't need marking, but even in this case it does not mean that the installation is compliant.
These is not just a legal requiements the are good reasons fr them The matter of EMC (interference) is particuarly important and this does not just affect you, it can spread beyond your property and affect others including, possibly, safety of life systems or services.
Yes, extremely improbable that it happens, but if it does you could b prosecuted. Somewhat more probable is that a poor installation causes a a fire or injury and you end up on the wrong side of an insurance dispute. Even if you have not fully complied with the law, following good practice and using qualitity parts will considerably reduce the chance of being there and give you some defence.
I'm all for people doing this stuff for themselves, but lets support them to do it properly, not give advice that safety and quality don't matter.

Robert G8RPI.

I would note that regardless of being "Commercial" or not, most of these cheap far eastern VFDs do not meet accepted safety and quality standards. Additionally tthe internal components may be sub-standard or under-rated. This is why many sources (including at least one UK reseller) recommend buying a larger unit than should be needed.
Even quallity units need to be mounted in a proper enclosure and most also require a EMI filter on the mains unless te VFD specifically states it has one internally. A good filter can cost more than the VFD.

Robert G8RPI.

Hi,

There are several refernces available but I have direct knoowedge fron tests made during development of machine sterilisation systems (I have an invention for this https://patents.justia.com/patent/7247429). A lot depends on the organism, the Polio virus is very resistant. I did a quick search and more recent research shows 80% Ethanol 5% IPA (balance water / gelling agent) is mos effective aginst viriuses.
My main point, perhaps not made well, is that using neeat alcohol is not a good idea.This is because it is not effective an is more damaging to your hands.

Robert G8RPI.

Edited By Robert Atkinson 2 on 19/03/2020 12:48:21

Note that 100% alcohol is not fully effective. Between 50 and 80% is much better.

Robert G8RPI

This is not totally correct, but having ignited bulk thermite (not easy, nomal approch is to use magnesium ribbon) I can see were you are coming from. "Thermite" sparks are actually common but not often recognised. They were identified as a cause of ignition in refinery fires when aluminium (or titanium) objects were dropped on rusty steel. Hot steel sparks thrown onto a pile of mixed aluminium and rust can and does cause ignition (not when you want it to).

There are other hazards with light alloys I once set "fire" to a 5" diameter by 8" long piece of unknown composition alloy when tappng some blind holes. I used some spray solvent to clean chips out of the blind hole and noticed smoke coming out. The solvent was trichloreythlene and reacted with the alloy. A handy bucket of water stopped it.

Robert G8RPI.

Edited By Robert Atkinson 2 on 17/03/2020 15:07:39

Another safety hazard with LPG tanks is that being a liquid in a pressure vessel if they are heated and the pressure relief is faulty or inadequate you get a Boiling Liquid Expanding Vapour Explosion (BLEVE.). This same as a steam boiler explosion where the sudden drop in pressure causes the superheated liquid to turn to gas virtually instantly with the increase in volume causing a pressure wave. With LPG the gas then ignites causing a second (or is it third, pressure vessel, BLEVE, gas) explosion. This video shows even a vent may not be enough

**LINK**

You can get a BLEVE with any constrained liquid heated above it's boiling point.

Robert G8RPI.

The oft quoted "most of the power will be used up heating the motor windings" or references to reduced back EMF or torque are at best simplistic and do not reflect the basics of VFD operation. A correctly set up VFD will reduce the appled voltage proportionall with frequency maintaining the current and thus the torque. Resistive heating is I2R so remains the same regardless of speed. Thus the reduction in power with reduced speed is purely mechanical, less speed at the same torque is less power. Reduced cooling due to lower fan speed can be a problem but normally only if running at full load for extended periods. A external fan like those used in PCs can help with this.
When setting up a VFD and motor the motor should always be running at the highest speed possible so get a 2 pols motor and ad use pulley/belt reduction to get the maximum spindle spee you want (or max rating or spindle) with the motor runng at 60 or 65Hz. Two pulley ratios can still be an advantage even with a VFD if you do both high and low speed work.

Robert G8RPI.

As well as adding solder to the joint (as suggested by Andrew) it is also very helpful to add flux. (Rosin based not Bakers fluid!). I now use the liquid flux sold for SMD rework but have in the past just dissolved rosin (for violin bows) in alcohol (IPA or ethyl are fine).

Robert G8RPI.

This event is patently spurious. As the charge in a cartridge is enough to eject shot and wad from the barrel removing the shot would not cause a wad to be let in the barrel. If they removed the propellent s well, why put the wad back and the noise would be less thn a "banger"
Maybe he used an alarm or saluting blank but they don't have wad.

I see no problen if you machine the end caps and pins and your friend assembles them to tubes and loads them.
There are no restrictions on empty case parts.

Robert G8RPI.

Regardless of any T&C's or guarantee, an item sold in the UK must be fit for purpose and suitable quality. Limiting the guarantee on elecrical components to 6 month's is unreasonable. most electronic components do not wear out and should last much longer than a year.

Robert G8RPI.

From the Amadeal website for mini lathes " Ideal for the professional engineer or model maker " So thier bench lathes should be OK for professional use.

Intrestingly thay sell "customer returns" for repair which seems to confirm their lack of technical back-up

If they do not respond properly to your email, opem a small claims court claim on line. This is easy and often brings a prompt resolution. You can do it online:
https://www.gov.uk/make-money-claim

Claim the item is not fit for purpose, they have not responded properly and you want a full refund.Make sure your claim includes them paying for the cost of returning the lathe.

Robert G8RPI.