PDA

View Full Version : Teaching nippers electrickery - especially in the US

Loose rivets
8th May 2012, 05:54
I'd kind of given up on teaching my g-son about electrickery. He works so hard at school and hits straight A's in an advanced school, but there never seemes time to ramble on about another subject after long, long days.

(Barmy box-ticking world of funding based on marks.)

The boy's a bookworm, so no Rivetes' genes there, but tonight we sat at my hobby bench and looked at meters, resisters etc. He asked intelligent questions, but despite having started 'Robotics' at school, his knowledge of the fundamentals was limited.

It's possible he may now have time for a bit of study, but I hit a problem: The direction of current flow - Do we use conventional, or electron flow?

I'd just happened to notice the Americans seemed to teach negative to positive way back when my son did A level electronics in an English Grammar School. He was still using the conventional + to -

Also, when I learned about tellies and ohms law, we used e for volts, and I for current. What's the deal now, V's and a's ?

cwatters
8th May 2012, 07:24
Conventional +ve to -ve current flow.

Only really need to know about electron flow when it comes to understanding the inner workings of transistors and the like. Not needed to design basic circuits that use transistors.

Voltage : symbol V : units Volts
Current : symbol I : units Amps

Examples:

Vout = 5V or 5 Volts
Iin = 1A or 1 Amp

Ohms Law..

V=IR

In Europe (at least) the unit replace the decimal point now. So 1.5 Volts is frequently written 1V5

cwatters
8th May 2012, 07:39
Perhaps see..

SI units..
SI Units (http://www.qsl.net/g4cnn/units/units.htm)

B Fraser
8th May 2012, 07:58
In Europe (at least) the unit replace the decimal point now. So 1.5 Volts is frequently written 1V5

They can stick that in the same place as the hectopascal :suspect:

James Clerk Maxwell must be spinning in his grave at such a rate that hooking him up to a dynamo could light half of Edinburgh.*

*using that Geordie invention, the light bulb.

UniFoxOs
8th May 2012, 08:05
They can stick that in the same place as the hectopascal

I find 4K7 a lot more convenient to write or type than 4.7K, it's one movement (25%) less.

UFO

Fareastdriver
8th May 2012, 08:15
4K7 a lot more convenient to write or type than 4.7K

When I am LOOKING at a label I find that 4.7K is a lot easier to understand than 4K7.

8th May 2012, 08:24
I think I prefer 4k7. What does throw me at times is 1,5 instead of 1.5
Capacitor markings are strange, too these days.

I would never go for conventional current flow, always electron flow. For those of us brought up on valves (American 'tubes'), it's the only thing that makes sense. Although you have to watch it with Fleming's rules.

For transistors, it's complicated when holes come into it.......30 years as a semiconductor applications engineer and I never did like the concept of holes!

8th May 2012, 08:27
I thought the Cousins taught about electrickery using the Shock and Awwww method! :p

B Fraser
8th May 2012, 08:40
I find 4K7 a lot more convenient to write or type than 4.7K, it's one movement (25%) less

You don't have a valid point.;)

pulse1
8th May 2012, 08:56
Having sold complex 3 phase equipment to the US for some years, I always thought of them as a third world country when it comes to electrickery.

8th May 2012, 09:03
Yes - having been brought up (in UK) on 13 amp fused plugs - which are never allowed in bathrooms - it always seems strange to see US plugs about as basic as they can get, and sockets (and normal light switches) all over bathrooms.*

* by which I mean rooms where one washes and/or bathes - not a euphemistic lavatory.

UniFoxOs
8th May 2012, 09:27
You don't have a valid point.

That's right - another point in favour of the "new" notation - decimal points being small and easy to miss as you get older and eyesight fails, and take a bit of effort to write clearly so you won't miss 'em when you read what you wrote.

Cheers
UFO

vee-tail-1
8th May 2012, 09:33
Hmnn ... I have an 1880 110 volt DC waterwheel powered electrical system in my mill. Finding 110 volt DC equipment in the UK is difficult, and 110 volt immersion heaters impossible. So I tried to order a couple of 110 volt immersion heaters from the US. The reaction from some American electrical suppliers was comical ... they seemed genuinely astonished to get an order from outside America and informed the DHS. Fortunately an airline colleague bought the items for me on a stateside trip and delivered them to Wales. I have now made a quite neat adapter to allow the American units to fit into our European immersion heater sockets.
However I await the extradition summons to answer a possible charge of ordering bomb making equipment from the US ... :hmm:

lasernigel
8th May 2012, 09:53
Working with electrics/electronics and a US company feel that the standards in the US domestic area are pretty dire. The plugs are not childproof and yes they allow AC mains in bathrooms. That is a big NO in the UK unless through an isolation transformer for a shaver socket.
I still think our standard of having each plug individually fused is safer than most other countries. I am against earth leakage trips. I have experienced first hand the panic of an elderly person in sheltered accomodation, that when a bulb blows the trip normally goes as well, plunging the whole house into darkness. Not good if you are infirm.
I seem to remeber the reason behind the US going for 110v as opposed to 220/240v was that in the late 19th century, the gas company in New York took the electric company to court saying 220v was more dangerous than 110v because it was bigger. The judge ruled in favour of the gas company! But now we know it's amps that kill.
I'm old school don't believe in hole flow and prefer electron flow, e.g. -ve to +ve.
Also don't like the new notation of components.

Not forgetting that µ = gm x ra :ok:

pulse1
8th May 2012, 10:07
It's not only the domestic area where they are poor. For three phase power, in some States they allow the earth to be used as the neutral. This is illegal in the UK.

Fox3WheresMyBanana
8th May 2012, 10:07
cwatters is correct.
At least, this is what I teach at a Canadian University, and it's what they teach at MIT. Use conventional current flow unless you are modelling or designing at the atomic level physics.

only point to add is that the algebraic symbols are e, V and I, so
electromotive force = 4 volts is: e = 4V
current = 1 amp is: I = 1A

e is generally used for the ideal voltage, V for the terminal voltage

and for completeness:
Some physicists use E for ideal voltage (lazy), but this conflicts with E for the Electric Field Strength, and the Young modulus for engineers
i,v (lower case) are usually used for variable quantities,

MagnusP
8th May 2012, 10:51
I have experienced first hand the panic of an elderly person in sheltered accomodation, that when a bulb blows the trip normally goes as well

Getting to know that one well. Get 'phone calls from mother-in-law around the corner when the failure of one of 8 halogen spots in her kitchen plunges kitchen, dining room and hall into darkness. Coat, torch, door, 250m, reset breaker, note which lamp to replace later, 250m, coat off, pour another glass, mutter for a while.

Dan Gerous
8th May 2012, 10:59
In my last job, we bought electric heaters from an American company and had to faff about adapting them to meet UK/Euro standards. The quality of workmanship was very poor, and they looked like something that might have been Hi Tech in the early 50's.

Way back in 77/78 when the Spams came to Lossie for a bombing comp, they asked us what voltage our Ground Equipment Generators put out. We always used the terminology 200V 400 HZ, to describe it, even although it was a standard Nato socket. They said theirs worked on 110V, and we told them it would be ok as we measured Phase to Phase voltage and they were using Phase to Neutral. They were wary of this information, and we had to go and get an Avo and physically show them the two different voltage readings from the same socket.

Blacksheep
8th May 2012, 11:11
The direction of current flow - Do we use conventional, or electron flow?In our day particle physics was still highbrow PFM so they were loath to emphasise electron flow and stuck with the old ideas.

Teach him electron flow. Quantum Mechanics are school science fare these days, so its best to go straight in with the particles.

Semiconductors? Holes going backwards always baffled me. Its really all about the electrons.

arcniz
8th May 2012, 12:05
...put this in the same place as the hectopascal

Perhaps those in the know would be kind enough to share knowledge of where, exactly, they prefer to put THEIR hectopascals for use and/or safe-keeping.

Teaching young folks is partly a matter of passing on the formalities of names, symbols, and such other clatures as may seem necessary, but that is the baggage, not the contents.

Important and not unoften forgotten in the process of professing about things is teaching the essential gut concepts in ways that intuition and innate accumulated knowledge already in the pupil's noggin can grapple and embrace for stronger essential grasp of how stuff works.

In the case of electrizzery and kin, that would be the concepts of pressure, flow, volume and force demonstrated by the hydraulics of familiar old plumbing, Roman-style tech from the early 0000's.

B Fraser
8th May 2012, 12:25
Re: circuit breakers. One has long memories of fiddling with fuse wire in the dark.

8th May 2012, 12:32
Back in 1971, I was doing the 'first fitting' of a new 100 watt marine SSB transceiver on a trawler in Hull - yes, Hull had trawlers then. This transceiver ran off 24 volts, and by some mistake, they provided a 5 amp supply rather than a 25 amp supply. Thus the fuse blew as soon as I pressed the transmit switch. While they were fixing it, the shipyard foreman electrician was talking to me.

'These 'ere new ships', he said,'they've got this 'ere new fangled AC on them. Tha's got two wires like wot thee has wi DC, but they keep turnin' rahnd!'

Fareastdriver
8th May 2012, 13:06
the failure of one of 8 halogen spots in her kitchen

Could well be illegal if they are 240 volt GU10s. Your are better off getting transformers and 12V halogens. It is not that expensive, is safer and because they don't blow the circuit breaker when one goes it saves you a lot of walking.

MagnusP
8th May 2012, 13:19
Thanks, Fareastdriver, but I've started replacing them with 4W surface mount LED GU10s, so the problem will eventually go away.

lasernigel
8th May 2012, 14:23
One has long memories of fiddling with fuse wire in the dark.

Remember about 18yrs ago, went to Istanbul where they were moving a dye laser across to another part of the hospital. Eventually after it had been man handled up 6 flights of stairs and connected up, it kept blowing the floors fuses. This was 415v 3 phase at 35A a phase. He opened up the junction box where they had twisted the wires together and used insulating tape, and promptly changed the fuses for nails..I joke not!. System did then turn on but after all the bashing about took 3 days to re-align.

charliegolf
8th May 2012, 15:03
In Europe (at least) the unit replace the decimal point now. So 1.5 Volts is frequently written 1V5

I finished an OU degree made up almost entirely of Physics courses in 2010: not once was this mentioned, shown or suggested. Perhaps it's more the case that there was no problem that EVER came out as simply 1V5- rather in tortuous scientific notation.

CG

chuks
8th May 2012, 16:32
I know of an operation that needed a photocopier in Escravos, Nigeria. One was shipped at great trouble and expense from Miami, Florida. The local electrician hacked the American plug off the power cable, put one of those old-fashioned British ones on, plugged it in to the mains and turned it on. Sorted! Well, sort of... I think there was a 'pop' sound, a wisp of smoke and... that was all. I was told the story after I noticed this large, new-looking Xerox machine shoved off in a corner unused.

Another time, I watched a Nigerian electrician wiring up a three-phase supply for an air-conditioner. Job finished, he fetched a bowl of water from the kitchen, kicked off his flip-flops ('Nigerian safety shoes'), wet a patch on the cement floor, stood on the wet patch, and flicked his fingers over the wires to see that they had 'powah.' No lie, I watched this happen, albeit with a certain degree of skepticism about what I was seeing.

Loose rivets
8th May 2012, 16:42
Smashing thread. Thanks for the input.

arcniz's comment:

Important and not unoften forgotten in the process of professing about things is teaching the essential gut concepts in ways that intuition and innate accumulated knowledge already in the pupil's noggin can grapple and embrace for stronger essential grasp of how stuff works.

I so wish some of the people that taught me had thought like that.

It seems I can go with conventional current, but make him aware of the physics and the possibility of having to think the other way round. I know I found it hard working through an American nephew's school electronics, when it was minus to plus. This was c 1980. Kept holding the book upside down.

Mullard issued a wonderful colour book of transistor physics when they were selling the first transistors. It made great mention of holes. One transistor cost a hunk of one's pocket money then. That was c 1958, but I don't recall when the first transistor radios came on sale.

It seems 'I' is standard for current, but he must be aware of e and V being (to some extent) interchangeable, though I was unaware of the protocol of which to use - until now :ok:

I think the Ground fault interrupter/RCD is the best invention since rocks were tied to sticks, but yes, there is supposed to be a circuit that allows one lighted egress.:ooh:

I put a Crabtree Starbreaker system in my house in Essex and 6a breakers on the lighting circuits. Cheap bulbs would trip them when they popped, but never the RCCD - which guarded about 10 of the 15 circuits. (appx) However, I did that funny thing old-timers do, and one night put my hand on the soldering iron to see if it was warming up. The house was plunged into darkness. The very expensive RCCD had tripped. (didn't feel a thing)

I had not wanted a single unprotected wire in the main part of the house - so, I staggered about with a torch. The sting in the tail was the RCCD, almost new, would not reset, and I had to hammer a piece of heavy wire flat at both ends, and make a link. Crabtree treated this very seriously, sending a rep down the next day. They did know about the problem.

Yes, my favorite iron was faulty.

Krystal n chips
8th May 2012, 16:47
Have a browse through this excellent series.....you might find some worthwhile advice and a means of making it interesting for the recipient to understand.

BBC Four - Shock and Awe: The Story of Electricity (http://www.bbc.co.uk/programmes/p00kjq6d)

UniFoxOs
8th May 2012, 17:20
That was c 1958, but I don't recall when the first transistor radios came on sale.

I remember I couldn't afford a ready made one as an apprentice in 1962 and I built a pocket-sized one from a kit. Used to do a bit of work at a builders and put the little tranny inside a 4" clay soil pipe to improve the sound.

Could just about get Luxembourg in the evenings with it.

UFO

balsa model
8th May 2012, 17:44
It seems I can go with conventional current, but make him aware of the physics and the possibility of having to think the other way round.
Excellent choices, me thinks.

The story of how the "conventional" direction came to be, and, much later, how they discovered the electron and found out that the other way around it would have been easier to visualize, is interesting in itself. Just the kind of stuff that kids like to listen to and that helps them retain stuff.

Other than the cathode ray tubes and all their tube relatives, I can't think of any device where we use the concept of "electric current" and where the knowledge of particle flow matters. (There is a flow because the hot cathode ejects electrons - not because the hot cathode attract some positive charge holes.) You can still write (approximate) equations for the tubes using conventional current.

And finally, think about measuring the DC current with ammeter (probably modern DVM). It will show + for conventional direction of flow from battery (+) to (-). If you teach against convention, you'll be setting the kid up for a lifetime of mental contortions trying to remember when to visualize - sign when he sees the +. :{

Fareastdriver
8th May 2012, 18:34
I had the main RCCB go in my apartment in China. I went around switching off and eventually unplugging everything but it still kept tripping. My Landlord came with an electrician who did the same as I did then picked up his bag and walked out. I asked the landlord what was the problem.
“Too difficult.” he replied.

It was now up to me. Having some experience with house wiring I unscrewed a few 15 amp round pin sockets. The wiring was horrendous! It was a kind of ring main with the wires joined up with insulation tape. It was installed in steel conduit and the colour coding seemed to depend on what drum of wire was handy at the time. One socket was still live; it must have been wired into next door.

Eventually I found the problem. When they installed the shaver socket in the shower room they hadn’t chased the wall out sufficiently. The socket was loose in its box so a wire had chafed to earth.

Modern Chinese wiring uses Australian type sockets but they are 180 degrees out from Australia and you never know whether the live is on the left or the right.

Milo Minderbinder
8th May 2012, 18:45
I don't understand what the fuss is about
Forty years ago my physics teacher simply put it thus (more or less)
"Electricity is electron flow. Electrons move from negative to positive. The reason they move from negative to positive is because the discoverers of electricity had to make a decision on standardisation - and they chose the wrong one"

Fareastdriver
8th May 2012, 18:54
I the late fifties/early sixties motor cars started to be wired 'Positive Earthed' It was a fad which lasted about ten years before everything went back to normal.

Loose rivets
8th May 2012, 19:16
And finally, think about measuring the DC current with ammeter (probably modern DVM). It will show + for conventional direction of flow from battery (+) to (-).

An obvious point . . . but one I'd missed entirely! :\

I can never resist (no puns please) showing this. It's in the Bucket, so . . .

Why do kids have to grow up? His kid is as big as me now.

EDIT: On that circuit, it shows a pair of transistors. The one showing the emitter at the bottom, looks totally natural, but 'tother way up it interferes with one's brain in an un-efficacious manner.

http://img.photobucket.com/albums/v703/walnaze/Family/Scottdoingelectronics-1.jpg

MagnusP
8th May 2012, 19:20
Chuks re your Nigerian sparkie, I helped a family member when he was extending his house in Shetland. After years of building, boat-building, sailing, digging peat and other manual stuff, he had skin on his fingers that was tougher and thicker than the skin on my heels. When it came to wiring in the external lights, he had to wet his fingers before he could tell whether a cable was live. :eek: AVO? What AVO?

Loose rivets
8th May 2012, 19:32
I'm sure I've mentioned this before, but I wrote this for a UK radio restoration forum to go with that picture.

Such a mind-boggling piece of good luck to have one's car break down when someone is stealing it.

That little steel cased multi-meter saved my bacon one morning. Off to an exam in London c 1969 and Mk 10 Jag wouldn't go. It enabled me to find the broken braid feeding the points in the distributor. Someone had tried to steal the car that night in Edgeware, and failed, because it wouldn't start! He was five hours old when that happened.

Krystal. Thanks for the link, but I have to get it through iPlayer it seems. I tried, but just got the same message. Will ask son, he knows how to do it. I'll be asksing the grandchildren how to do things soon. Oh, my.

Loose rivets
9th May 2012, 05:47
Yep, done it. Nice to watch a Beeb program again. :ok:

But what was that about very high frequency AC? Were they saying he could conduct it because of the frequency?

9th May 2012, 08:59
I always used V for Volts (capital letters where the unit is derived from someone's name), E for EMF, e for instantaneous voltage, i for instantaneous current, I for current (so there's the rule broken! which is measured in A).

The fun comes with ms and mS: milliseconds and milliSiemens. I much preferred mhos.

This from Radio Laboratory Handbook by M. G. Scroggie, where he quotes B.S. 1991: Part 1 1967, Letter Symbols, Signs and abbreviations.

Phalconphixer
9th May 2012, 22:43
Could well be illegal if they are 240 volt GU10

Que?

In my house in Spain I have a string of eight of these things (50w) in my kitchen and another string of six (50w) in the bathroom. Hell of a lot of power consumption for such a p*ss poor lighting system...

Serious question... illegal? Why then do they sell ready to install boxes of four fittings? Certainly its a P.I.T.A. when one blows because it does take out everything... Thinking of replacing them with the new fangled low energy fluorescents...

pp

lasernigel
10th May 2012, 14:19
I much preferred mhos

So did I, ohms for resistance, reverse it mhos for conductivity.:ok:

Reminds me of all those "forgotten" things we used to learn...Kirchoffs law, Flemings left and right hand laws, Faradays law and then Tesla who at first had my mind spinning. J notation (square root of -1), I was told not to try to understand it but just get on with it. I did but those who questioned it soon found that it became hard to do.