Re: step up/down transformer
 

People have done that here, and Mike has stepped up as one of them. You slap your +120 in the 240V live, and your -120 in the UK neutral, and everything works... electrically it's actually OK.

The risks and ramifications are somewhat more complicated, my concerns rests on energizing a neutral cable.

If you want to read more, here's a good start:

https://en.wikipedia.org/wiki/High-leg_delta

It's a north american thing.

Re: step up/down transformer
 

In term of the appliance and (also to a point the house wiring to the junction box), the neutral is normally carrying current
The difference is its potential in relation to earth


But... In a UK system we'd only have a breaker on the live phase for 240v
a North American set up for 250v would have a dual breaker on both phases (or mine did)

Re: step up/down transformer
 

As I see it, the greatest danger in using UK-sourced appliances on a jerry-rigged 240v North American supply is when the appliance has its own switch. That switch will isolate power from all the circuitry when supplied with UK-style 240v, but if the appliance is plugged in in North America, turning "off" the same switch will leave 120v feeding all the circuitry "backwards", through the neutral wire! :scaredhair:

Re: step up/down transformer
 

That a rather obscure way of looking at it
As you can and do get 250v sockets three pin -'- in NA ,.. normally in workshops for higher power tools where the 120v just can't give the push so its doesn't need to be jerry rigged

Yes one side of the circuit would still be live, but still off with no current flow
It would prove interesting if your 'domestic' appliance circuitry allowed a live feed to interact with the earth
Then it might be much more fun .... as current would still flow and it might be 'half' on :ohmy:


I look at its in a simple transformer view (as thats what your getting)
UK earth's one side of the 240v transformer and ignores the centre tap
US earth's at the centre tap/point and uses either side or both lives


In either case you don't 'dick' around inside with it plugged in but switched off ... unless you know what you're doing
Otherwise were moving from Electricity 101 to Darwin


Disclaimer However If this isn't clear and obvious then using UK appliances on anything other than a transformer shouldn't be an option for you !!!

Re: step up/down transformer
 

So, if North American 2-pin plugs have 1 live and one neutral and they appear to not care which orientation they are plugged in, this situation of live going through the neutral must happen half the time anyway on North American devices?

Re: step up/down transformer
 

Which is why many new sockets and all new appliances have two different size 'pins' to force you to set it up the 'right' way
The old same size 2 pins are being phased out


the switch controlled the current, it didn't make the unit 'safe' :(

Re: step up/down transformer
 

Yes. Ideally you'd have a double pole breaker for the 240V split-phase supply. Otherwise you're recreating the old fused neutral system the UK had pre-war, if you were unlucky the neutral fuse would trip leaving the circuit live for whoever came to fix it...

Technically the switch is there to control the appliance and you should unplug anything before going inside, but since you can switch off the live feed at the switch bad habits do emerge- pull the same stunt on a split-phase 240V and you have a higher risk of some ouch.

Most appliances that care about polarity actually have one fatter pin, which is the neutral, if they are two pin configuration with no earth. Laptop supplies etc that just convert to DC don't care so they have two slimmer prongs.

Re: step up/down transformer
 

Quote by Mike: I look at its in a simple transformer view (as thats what your getting)
UK earth's one side of the 240v transformer and ignores the centre tap
US earth's at the centre tap/point and uses either side or both lives. Unqoute.

I totally agree with your explanation.

The US 240VAC 3 wire system taps from both live wires, and doesn't connect to the centre tap. The phase-difference between the two 120VAC legs becomes the neutral. The third wire acts as ground.

What I find difficult to understand is how can UK Black and Decker drill still rotate when directly plugged to this source. I would have thought the neutral wire, internally connected to the return end of the stator windings within the motor, would be energised incorrectly.

Re: step up/down transformer
 

If you look on a US pole mounted transformer you can see the three taps, outer two taps your 120v phases, centre tap (neutral) 0v usually earthed right there on the pole ?

If you plot two anti phase 120V sine waves against each other, its give a 240V sine wave
All the motor sees is a voltage potential
Most if not all wired domestic power tools are a two wire double insulated set up ?


I'm not sure you do understand my explanation

Re: step up/down transformer
 

Single phase motors from the uk use a capacitor to phase shift the input and allow the motor to start spinning which then is kept going upto speed using the normal single phase supply.

Re: step up/down transformer
 

That's exactly what I think Mangaboy...but members here say they've managed to use a UK drill on the USA 240VAC system and I cannot follow how that's done....but I'm willing to learn.

Re: step up/down transformer
 

Thats why i edited my post to tweek the answer after reading back through the thread, plenty of experience with uk electrical systems but i really need to learn the US systems once i move over this year before starting work again

Re: step up/down transformer
 

Thanks Mike...I did say I understood your explanation to the split-transformer analogy and I'm familiar with the pole-mounted transformer although, in my street in the Vancouver suburbs, they've put all that stuff in a box and wires are now underground.

However, I understand that although you achieve 240VAC the difference in the phase-angles of the sine waves on L1 and N1 will be 180deg out. This is OK on N.A. 240V motors as the windings can be assimilated but it's not the same on UK 240V wound-motors.
How can a UK wound motor work if the designed continuous winding Line to Neutral wire, creating the magnetic stator field, use sine waves opposing at 60hertz?

Re: step up/down transformer
 

I think it's RivingtonPike that may have a number of workshop tools from the Ulk- if not he's been active in the debate.

Re: step up/down transformer
 

I do indeed have a bunch of tools that I brought from the UK. I've got 220v in my garage already, but I also have a 3000w transformer which is heavy, but in the garage, who cares. I still use 2 drills, a leaf blower, hot air paint stripper, jig saw, dyson, B&D electric screwdriver. No idea if they run faster or not, but they all work fine. As things have worn out, of course we've bought Canadian versions, but I couldn't see the point of selling my stuff in the UK for peanuts and having to replace everything. Plus I seem to remember having rather bigger issues on my mind that selling a few power tools.

Re: step up/down transformer
 

Thanks for that info Rivington but, just to clarify, do you use those inductive UK tools directly from the BC Hydro 240VAC supply or through your 3KW transformer?

Re: step up/down transformer
 

Mainly from the BC Hydro 220v. The Dyson we use around the place from time to time so use the transformer

Re: step up/down transformer
 

Thank you Rivington.
Then I'm clearly wrong in my theoretical thinking....and it is perfectly OK to plug a 240Vac UK motor into the N.A. 240Vac system with impunity...and it will go faster due to the increase in hertz.

Re: step up/down transformer
 

From the engineers at my former work place when utilizing equipment from 50hz to 60hz
the motor spins faster and its cooling fan spins faster ~ usually not an issue as excess cooling offsets the speed


60hz to 50hz slower motor slower cooling ~ risk of overheat, on this one I'm resurrecting a Compressor with 1.7KW draw shortly I'll let you know how reliable it is ??? or If I need to replace the motor


as for the voltage consider only the potential difference across the motors poles and ignore any neutral/earth reference points

Re: step up/down transformer
 

We all know that it isn't voltage that turns an electric motor..it's magnetism.

The UK 240VAC produces a single sine wave and a UK motor 'usually' has a single winding. The magnetic polarity changes with the frequency of the sine wave and the motor, once started, runs. A capacitor is the simple way to kick-start but I'm aware that there are other methods using more windings.

As the US 240VAC system uses 2 sine waves 180deg apart (that's why it doesn't need a neutral wire) I couldn't see how that can make a UK wound motor turn.....as the polarity will reverse every cycle.
However, I'm only thinking theoretically...so I bow to those who have practical information and have made the UK motors work directly from the N.A. 240VAC source without modification.

I just cannot comprehend how that works.

Re: step up/down transformer
 

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Its the voltage that creates the potential to drive it, and produces the current that creates the magnetic fields
We only care about the potential across the motor, not any arbitrary reference voltages (neutral/earth)
so if we plot a single sine wave x 240v against to two sine waves x 120v 180deg apart
we get an identical voltage profile


consider as one leg is going positive the other is as equal but negative, so one rises to +10v the other heads to -10v and this goes on up to the top of the sine with one at +120v and the other ’phase’ at -120v so at max we have a total potential of 240v this will follow the sine wave right through again until our next maximum is at -240v or -120v and +120v on the opposing phases

Re: step up/down transformer
 

Mike...you need to stop lecturing me on voltage...I've never disputed that in N.A. we have 240VAC and how it's achieved. There were sockets in both my houses (Vancouver and Arizona) providing 240VAC to the stoves and the clothes dryers. I understood the fan in the oven and the drum motor in the dryer used 120VAC. Only the heating elements used 240VAC....which are resistors.

My question is how can a single coil on a UK wound motor create a magnetic field if a N.A. 240VAC is applied using two sine waves 180deg oppositely phased.
An induction rotor turns because of the frequency of the supply, causing a sine-wave rise and fall in potential and creating an alternating North and South magnetic field.
A UK 240VAC system produces one sine wave but a N.A. 240VAC system produces two sine waves....180deg apart.
Theoretically, those opposing sine waves will cancel any magnetic field in the single winding.

Re: step up/down transformer
 

But clearly you're not getting the voltage thing :unsure:

try reading up on how Bridged Amplifiers work one side pushing and another pulling to double power, its the same principle and works for motors as well as speakers, coils in magnetic fields

Re: step up/down transformer
 

The debate here is how a UK 240VAC drill works from a N.A. 240VAC system. There aren't any bridged amplifiers in a UK Black and Decker drill.

The UK drill only has one wire that is wound around two stators to produce an alternating N and S polarity which turns the rotor.
Your point about the voltage is only relevant to how much load can be driven i.e. the amount of power available to do a particular job.
The principle is the AC sine wave creates the magnetic field.
This frequency shift creates an inductive magnetic field by alternating between sine + & - to create a N & S magnetic field.
A 12 VDC motor uses a commutator to alternate between + & - to do the same.

It's explained here.....
Electric motors and generators

Re: step up/down transformer
 

No idea what you guys are on about, but all I can say is that when I plug my uk bought drill into the wall which has a 220v socket - it works fine. With a drill in the Chuck, should I choose to, I can make holes in stuff.

Re: step up/down transformer
 

sorted, works for me also :thumbsup:

Re: step up/down transformer
 

Thanks Rivington and not2old for your practical information...I'm still trying to get my head around how that is done.

Do either of you guys mind saying if you simply re-placed the UK plug on your UK drills with a N.A. 3 pin plug and plugged into a 3-pin N.A. 240VAC wall socket.....or did you modify to fit a 4-pin N.A. 240VAC wall socket.

Both sockets are commonly used with N.A. appliances (cooking stoves, clothes dryers) so the 'heating' elements of those two appliances get the increased wattage from the 240VAC split-phase. 120VAC single-phase simply cannot provide that 'heating' power.

A N.A. drill is normally wired for 120VAC single-phase, as are most other inductive tools (circular saw, grinder, compressors) used by the DIYer.

Re: step up/down transformer
 

This is the best way of explaining it.

Re: step up/down transformer
 

What I did: I have a BIG 3 pin socket on the wall in the garage like you have for a washer, oven etc. I bought a plug that fitted that (was about $30) and put it on a UK 4 way plug adapter bar thingy. I could then just plug everything into that. Only needed to use one thing at time though. No need to change over all the UK plugs then.

Re: step up/down transformer
 

Pizza..you are agreeing with Mike on his explanation of how to get 240VAC from the split-transformed 120VAC N.A. supply...I also agree and have repeatedly said so.

Where the contention is...how does this 'turn' an inductive motor like a drill?

I'm sure we all understand that a motor 'mechanically turns' due to a magnetic field. This isn't created by volts....it's created by the sine wave (frequency) of that EMF (electromotive force) 'making and breaking' a magnetic field. It's the reverse of a generator which mechanically 'makes and breaks' a magnetic field to produce an EMF.
It's possible to plug the wires of a single-phase UK 240VAC drill into the single-phase 120VAC N.A. socket and it will turn...but wont do much work as the voltage is insufficient...maybe become an expensive and cumbersome screwdriver.

What I still cannot comprehend, and haven't had a satisfactory explanation, is how the 240VAC supply in N.A., which provides a split-phase of 180 degrees apart, produces a magnetic field. My opinion is the opposite sine-phases would cancel each others N/S magnetic field.

However, Rivington has said he does it and I'm not back to B.C. till next summer....so cannot test his practical and my theory.
I do know, when putting the + lead of a multi-meter into a single-phase 240VAC live supply socket it reads 240V and when reversing it reads zero.
I'm wondering if the same from Rivington's 240VAC outlets in his garage?

Re: step up/down transformer
 

I always hated physics at school

:scarper:

Re: step up/down transformer
 

Thanks to students of physics we can drive cars, fly on aircraft, sail on cruise ships, cross bridges and have surgery when sick....without physics there probably wouldn't be life as we know it.:nod:

Re: step up/down transformer
 

That's true but it was my least favourite of the sciences - one could have surgery without physics- anyhow...I don't want to derail the thread so will say no more. Apart from the fact that I brought all my power tools from the UK I tried to get the electricians to sort out the appropriate sockets, just needing adapters in the garage but they were bloody useless.:thumbdown:

Re: step up/down transformer
 

hahaha...nor me but, co-incidentally, in a few hours I'm having my belly cut to have an open Incisional Ventral Hernia repaired... so your comment about basic surgery, without equipment created with the knowledge of physics, hasn't inspired nor given me much confidence...fortunately I'll be asleep...:thumbsup:

Re: step up/down transformer
 

Good luck :thumbup:

Re: step up/down transformer
 

Best wishes with your surgery and hope you have a quick recovery.

Re: step up/down transformer
 

Doesn't a center tap split phase system invert one leg, though? (it's effectively wired "backwards" so is 180 degrees out of phase with the other leg). I suspect, Davita, you're overcomplicating the issue in your own mind. The motor, with its single winding, "sees" just a straightforward 240V sine wave, in a single phase, between its two wires. Here's a picture:

http://www.diychatroom.com/attachmen...-chart.emf.jpg

The blue and red lines are the two legs of the split-phase 120V power. The pea-green line is the potential difference between these two - a 240V single-phase power supply, which quite happily makes the drill motor go round and round.
:)

Re: step up/down transformer
 

Very well explained Mr O.

Unfortunately, for making the dark wizardry that is electrical engineering look understandable, I am going to have to kill you. I'll do my best to get to the next pissup ;p