Transformers - are they safe?

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patrick j

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Dec 29, 2006, 12:53:44 PM12/29/06
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Hi

My octogenarian mother has become fearful that the small black
transformers which are supplying electricity to various things around
her flat might burst into flames.

She has a good reason for her fears, one of them some time ago became
very hot indeed to touch. She has had it fixed by an electrician she
knows and it is now always at a mildly warm temperature.

However after that experience she now has taken to unplugging these
transformers all the time which actually involves plugging and
unplugging quite a lot just to turn things on or off.

Conversely in my little house I just leave these transformers plugged
in and "on" all the time. I do turn off the things they are supplying
but I don't bother turning off at the wall very much.

Is my mother right or am I right?

Perhaps the truth lies somewhere in the middle?

--
Patrick
Brighton, UK

<http://www.patrickjames.me.uk>

tony sayer

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Dec 29, 2006, 12:59:58 PM12/29/06
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In article <0001HW.C1BB06A8...@News.Individual.Net>,
patrick j <pat...@jamesnews.orangehome.co.uk> writes

Yes over the years we've had the odd few do a nasty and catch light but
fortunately when people were around!...
--
Tony Sayer

Harry Bloomfield

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Dec 29, 2006, 1:24:58 PM12/29/06
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patrick j was thinking very hard :
> Hi

The modern ones are supposed to be fitted with a thermal fuse. If they
should over heat, the fuse melts and that is the end of the wall wart
(plug in transformer) for further use. They are designed to be plugged
in and on 24/7, but there were a few problems with the early ones in
the bad old days.

I would be more concerned as to how the overheating one was 'fixed', as
all modern ones are sealed units.

--

Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk


Sylvain VAN DER WALDE

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Dec 29, 2006, 2:36:41 PM12/29/06
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"Harry Bloomfield" <harry.m1...@tiscali.co.uk> wrote in message
news:mn.ec507d6cc...@tiscali.co.uk...

A carefully used junior hacksaw opened one for me.
In a previous thread about this, people suggested using a small cutting disc
as used in Dremel (and other) miniature electric drills.

Sylvain.

Phil Kyle

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Dec 29, 2006, 4:17:42 PM12/29/06
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Harry Bloomfield <harry.m1...@tiscali.co.uk> verbally sodomised in
news:mn.ec507d6cc...@tiscali.co.uk:

Concerning.

--
Phil Kyle™

T
h i
i s
s l
f i l
S o n o
i u e n
g r s g

Dave Plowman (News)

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Dec 29, 2006, 7:16:37 PM12/29/06
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In article <0001HW.C1BB06A8...@News.Individual.Net>,

patrick j <pat...@jamesnews.orangehome.co.uk> wrote:
> Conversely in my little house I just leave these transformers plugged
> in and "on" all the time. I do turn off the things they are supplying
> but I don't bother turning off at the wall very much.

> Is my mother right or am I right?

Pretty well every electronic device has a low voltage power supply -
whether internal or external like a wall wart. So if those need to be
unplugged for safety, so do alarm clock radios and video recorders, etc.
Most cookers etc too.

--
*Am I ambivalent? Well, yes and no.

Dave Plowman da...@davenoise.co.uk London SW
To e-mail, change noise into sound.

meow...@care2.com

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Dec 29, 2006, 9:12:54 PM12/29/06
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patrick j wrote:

Any electrical appliance is capable of catching fire, and many do each
year.


NT

Andrew

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Dec 30, 2006, 5:19:16 AM12/30/06
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Harry Bloomfield wrote:

> They are designed to be plugged
> in and on 24/7, but there were a few problems with the early ones in
> the bad old days.

The old traditional 'wall wart' (transformer, some diodes and a
capacitor) seems increasingly rare, with many devices this days being
supplied with some form of SMPS (which has a much small but
high-frequency transformer).

These always run much cooler : in practice does this make them safer?

regards,
Andrew

Dave Plowman (News)

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Dec 30, 2006, 5:32:38 AM12/30/06
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In article <1167444774.4...@73g2000cwn.googlegroups.com>,

<meow...@care2.com> wrote:
> Any electrical appliance is capable of catching fire, and many do each
> year.

Yup - the prime case of electrical fires - not wiring. Which makes part
pee a bigger joke.

--
*Why is it considered necessary to screw down the lid of a coffin?

Roger R

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Dec 30, 2006, 8:08:14 AM12/30/06
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"Dave Plowman (News)" <da...@davenoise.co.uk> wrote in message
news:4e9d121...@davenoise.co.uk...

> In article <0001HW.C1BB06A8...@News.Individual.Net>,
> patrick j <pat...@jamesnews.orangehome.co.uk> wrote:
>> Conversely in my little house I just leave these transformers plugged
>> in and "on" all the time. I do turn off the things they are supplying
>> but I don't bother turning off at the wall very much.
>
>> Is my mother right or am I right?
>
> Pretty well every electronic device has a low voltage power supply -
> whether internal or external like a wall wart. So if those need to be
> unplugged for safety, so do alarm clock radios and video recorders, etc.
> Most cookers etc too.

As the quest for minimising electricity usage is so popular perhaps there
should be some regulation preventing the use of transformers instead of
switch mode power supplies. Obviously a single wall wart is not going to
make any difference, but when the vast number of these things is considered
their total combined effect may be considerable.

The inductive load imposed by transformers has a very bad effect on the
efficiency of the supply. I seem to recall from school that if all the
loads placed on generating stations were inductive rather than resistive
then four times as many generating stations would be required.

This consideration was sufficiently important for factories with numerous
motors to install capacitor rooms where large capacitors were wired across
the supply to neutralise the inductive effect and present a resistive load.
The power factor of the factory would be an important element in calculating
the firms electricity bill.

Roger R

Dave Plowman (News)

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Dec 30, 2006, 8:52:49 AM12/30/06
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In article <116748407...@damia.uk.clara.net>,

Roger R <d-e-c-...@clara.co.uk> wrote:
> As the quest for minimising electricity usage is so popular perhaps
> there should be some regulation preventing the use of transformers
> instead of switch mode power supplies. Obviously a single wall wart is
> not going to make any difference, but when the vast number of these
> things is considered their total combined effect may be considerable.

Many of these things are not supplying any current but left plugged in.
And a decent transformer will use very little more quiescent current than
a SMPS.

> The inductive load imposed by transformers has a very bad effect on the
> efficiency of the supply. I seem to recall from school that if all the
> loads placed on generating stations were inductive rather than resistive
> then four times as many generating stations would be required.

And SMPS mess up the waveform. Try looking at mains these days on a scope.

> This consideration was sufficiently important for factories with
> numerous motors to install capacitor rooms where large capacitors were
> wired across the supply to neutralise the inductive effect and present a
> resistive load.

Most factories would use three phase motors.

> The power factor of the factory would be an important element in
> calculating the firms electricity bill.

--
*(on a baby-size shirt) "Party -- my crib -- two a.m

meow...@care2.com

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Dec 30, 2006, 10:14:35 AM12/30/06
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Roger R wrote:
> "Dave Plowman (News)" <da...@davenoise.co.uk> wrote in message
> news:4e9d121...@davenoise.co.uk...
> > In article <0001HW.C1BB06A8...@News.Individual.Net>,
> > patrick j <pat...@jamesnews.orangehome.co.uk> wrote:

> As the quest for minimising electricity usage is so popular perhaps there
> should be some regulation preventing the use of transformers instead of
> switch mode power supplies.

no

> Obviously a single wall wart is not going to
> make any difference, but when the vast number of these things is considered
> their total combined effect may be considerable.

no


> The inductive load imposed by transformers has a very bad effect on the
> efficiency of the supply.

no

> I seem to recall from school that if all the
> loads placed on generating stations were inductive rather than resistive
> then four times as many generating stations would be required.

no


> This consideration was sufficiently important for factories with numerous
> motors to install capacitor rooms where large capacitors were wired across
> the supply to neutralise the inductive effect and present a resistive load.
> The power factor of the factory would be an important element in calculating
> the firms electricity bill.

Yes. This is done with magnetic ballasted fl lights too. The load of
small transformers is so small this isnt worth doing.


NT

Roger R

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Dec 30, 2006, 10:29:00 AM12/30/06
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"Dave Plowman (News)" <da...@davenoise.co.uk> wrote in message
news:4e9d5cd...@davenoise.co.uk...

However small the current drawn by the wall warts they still present an
inductive load, even when the appliance itself is turned off. Multiply by
millions. By contrast the millions of alternative SMPS won't add up to a
large inductive load even though they may have poor effect on the waveform
in your home.

I don't think the considerations of inductive loading in factories is
changed by utilising three phase. The three phase load is still inductive
with negative effects on the power factor. The use of three phase, apart
from enabling smaller sized motors, enables the load to be applied equally
to all three phases, rather than just loading one phase for which the supply
company would have to find other users to balance out the phases or end up
with a highly undersirable large neutral return current.

Roger R


meow...@care2.com

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Dec 30, 2006, 10:46:28 AM12/30/06
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Roger R wrote:

> However small the current drawn by the wall warts they still present an
> inductive load, even when the appliance itself is turned off. Multiply by
> millions. By contrast the millions of alternative SMPS won't add up to a
> large inductive load even though they may have poor effect on the waveform
> in your home.

smps produce far worse mains current waveform than small wall warts.
You've got it backwards there. Lagging load is correctable relatively
simply, but the kind of current waveform smpses produce isnt, so the
generators have to supply for it.


NT

Jonathan Schneider

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Dec 30, 2006, 11:01:14 AM12/30/06
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"Roger R" <d-e-c-...@clara.co.uk> writes:

> with negative effects on the power factor. The use of three phase, apart
> from enabling smaller sized motors, enables the load to be applied equally
> to all three phases, rather than just loading one phase for which the supply
> company would have to find other users to balance out the phases or end up
> with a highly undersirable large neutral return current.

There's another important reason. A three phase motor delivers
constant (rather than 100Hz) torque. That makes the machine smooth
running with the benefits that brings.

Jon

kimble

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Dec 30, 2006, 9:42:57 PM12/30/06
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patrick j wrote:
> My octogenarian mother has become fearful that the small black
> transformers which are supplying electricity to various things around
> her flat might burst into flames.
>
> Is my mother right or am I right?
>
> Perhaps the truth lies somewhere in the middle?

On one hand, the non-zero probability of a wall-wart or appliance
catching fire. On the other hand, the increased risk of injury to the
octogenarian mother from having to bend over, reach behind appliances,
etc. to unplug the things.

On the gripping hand, a well-maintained set of octogenarian-suitable
(eg. ones that light up, alert a neighbour, linked to vibrating or
flashing wotsits if she has a high-frequency hearing loss, or whatever)
smoke alarms, and a decent night's kip.


Kim.

The Natural Philosopher

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Dec 31, 2006, 5:14:29 AM12/31/06
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You all realise WHY we have wall warts at all don't you?

Health and safety.

Some bright spark decreed that every piece of mains connected equipment
must pass a safety test and pass it. If it had a metal case that had to
be earthed as well. And it had to be switched and fused IIRC. This was
an expensive test too.

Manufacturers, faced with the requirements to produce tons of different
variants of mains powered devices each one equipped with an IEC sockets,
switch, fuse and power supply decided it was easier to create a range on
isolated, tested and insulated and internally fused wallwarts, and then
skip the test on the box that it powered.

The result is these nasty things have proliferated, and they do make a
mockery of energy conservation, and sometimes the internal fuses don;t
work, and they do catch fire..

Dave Plowman (News)

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Dec 31, 2006, 7:03:54 AM12/31/06
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In article <116756031...@damia.uk.clara.net>,

The Natural Philosopher <a@b.c> wrote:
> You all realise WHY we have wall warts at all don't you?

> Health and safety.

Not so. It's more to do with the device it powers being universal and only
the wall wart needing to be supplied for individual country's voltage and
plug types. As well as making the device smaller and cheaper. And wall
warts will be cheaper due to larger and longer production runs - they
don't need re-styling every few months.

> Some bright spark decreed that every piece of mains connected equipment
> must pass a safety test and pass it. If it had a metal case that had to
> be earthed as well. And it had to be switched and fused IIRC. This was
> an expensive test too.

Just how many metal cased devices do you find with a wall wart driving
them?

> Manufacturers, faced with the requirements to produce tons of different
> variants of mains powered devices each one equipped with an IEC sockets,
> switch, fuse and power supply decided it was easier to create a range on
> isolated, tested and insulated and internally fused wallwarts, and then
> skip the test on the box that it powered.

How much do you think testing costs in terms of production? Besides, the
use of a wall wart is restricted to low powered devices. And of course
makes that device smaller. Plenty of things would be unwieldy with the PS
built in - cordless phones etc.

> The result is these nasty things have proliferated, and they do make a
> mockery of energy conservation, and sometimes the internal fuses don;t
> work, and they do catch fire..

Any device can catch fire if badly made and left on.

--
*Errors have been made. Others will be blamed.

The Natural Philosopher

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Dec 31, 2006, 7:43:48 AM12/31/06
to

Mate, a friend of mine went this route with a custom piece of hardware.
He examined all the options, and the safety/RFI testing was too onerous
even for decent volumes to do anything but buy a standard wallwart.

Which is how I know.


meow...@care2.com

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Dec 31, 2006, 7:51:32 AM12/31/06
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Dave Plowman (News) wrote:
> In article <116756031...@damia.uk.clara.net>,
> The Natural Philosopher <a@b.c> wrote:

> > You all realise WHY we have wall warts at all don't you?
>
> > Health and safety.

> Not so. It's more to do with the device it powers being universal and only
> the wall wart needing to be supplied for individual country's voltage and
> plug types. As well as making the device smaller and cheaper. And wall
> warts will be cheaper due to larger and longer production runs - they
> don't need re-styling every few months.

What both of you say is true. Much as we dont love warts, they do make
the cost of goods lower.


> > Some bright spark decreed that every piece of mains connected equipment
> > must pass a safety test and pass it. If it had a metal case that had to
> > be earthed as well. And it had to be switched and fused IIRC. This was
> > an expensive test too.

> > Manufacturers, faced with the requirements to produce tons of different
> > variants of mains powered devices each one equipped with an IEC sockets,
> > switch, fuse and power supply decided it was easier to create a range on
> > isolated, tested and insulated and internally fused wallwarts, and then
> > skip the test on the box that it powered.

> How much do you think testing costs in terms of production?

Its all the stuff you have to go thru to get it to pass the test. First
there are a bunch of design requirements that dont exist if you use a
separate wart. Then theres all the mains gubbins, socket, fuse etc, and
there are implications for the whole product design. Use a wart and you
dont need to waste a minute on electrical safety matters, its not a
mains device. You dont even need a designer trained in mains voltage
design, with its many issues.


> > The result is these nasty things have proliferated, and they do make a
> > mockery of energy conservation,

I think really the opposite is more true. Before warts proliferated,
devices were already commonly switched on the secondary side, so either
way the mains tf was left on. The £ advantages of external warts mean
mfrs will at times try hard to ensure anappliance runs on low enough
power to be supplied by a wart, something that was never an issue
before the wart explosion.

Now that warts are commonly no bigger than a standard plug, the
appearance issue, which really is the only genuine problem, is
gradually vanishing. We're left with cheaper smaller lighter goods,
which is good all round.

Also warts today are quite practical to design to eat approx nothing
when not supplying power.


NT

Andy Wade

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Dec 31, 2006, 9:33:44 AM12/31/06
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meow...@care2.com wrote:

> smps produce far worse mains current waveform than small wall warts.
> You've got it backwards there. Lagging load is correctable relatively
> simply, but the kind of current waveform smpses produce isnt, so the
> generators have to supply for it.

But the current drawn by a /small/ SMPS will be too small to mess up the
waveform, especially when off-load. Hence appliances of under 50 W
consumption are exempted from the harmonic current emission limits of EN
61000-3-2. Larger SMPSs require power factor correction these days.

The magnetising current waveforms of typical small mains transformers
isn't particularly sinusoidal either.

--
Andy

Dave Plowman (News)

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Dec 31, 2006, 10:13:47 AM12/31/06
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In article <116756928...@proxy01.news.clara.net>,

CE marking is a form of self approval. Plenty of smallish companies
manage it.

--
*Can atheists get insurance for acts of God? *

Mike Barnes

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Dec 31, 2006, 8:14:18 AM12/31/06
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In uk.d-i-y, Dave Plowman (News) wrote:
>Plenty of things would be unwieldy with the PS
>built in - cordless phones etc.

I agree. Much as I dislike wall warts, the alternative is so much worse.
A wall wart can be hidden away. Otherwise the IEC plug and socket and
the psu would add visible bulk and complexity to the appliance.
Taking a quick look around this room I can see about a dozen appliances
that use wall warts, but the wall warts themselves are out of sight.

And many appliances are so small and light that the weight of a mains
lead would unbalance them.

Of course a universal low voltage DC power supply standard would be so
much better, but that's unlikely to happen soon.

--
Mike Barnes

Harry Bloomfield

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Jan 1, 2007, 11:54:07 AM1/1/07
to
Dave Plowman (News) presented the following explanation :

>> This consideration was sufficiently important for factories with
>> numerous motors to install capacitor rooms where large capacitors were
>> wired across the supply to neutralise the inductive effect and present a
>> resistive load.

> Most factories would use three phase motors.

Which can and do cause power factor problems. Whether the correction is
applied locally at the motor, or as an overall single correction for
the entire factory depends upon the type of use the motors are
subjected to.

If all the motors normally run and the factory has a predictable power
factor, then correction can be done in one go at the mains. If motor
use is irregular and not predictable it needs to be done at each
individual motor.

Ballasted fluorescent lights present the same problem and sometimes
will have a built in PF correction capacitor.

SMPSU's are no more efficient off load than are transformer type PSU's,
but on load they are much more efficient.

Dave Fawthrop

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Jan 1, 2007, 1:04:26 PM1/1/07
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On Mon, 01 Jan 2007 16:54:07 GMT, Harry Bloomfield
<harry.m1...@tiscali.co.uk> wrote:

|Dave Plowman (News) presented the following explanation :
|>> This consideration was sufficiently important for factories with
|>> numerous motors to install capacitor rooms where large capacitors were
|>> wired across the supply to neutralise the inductive effect and present a
|>> resistive load.
|
|> Most factories would use three phase motors.
|
|Which can and do cause power factor problems. Whether the correction is
|applied locally at the motor, or as an overall single correction for
|the entire factory depends upon the type of use the motors are
|subjected to.

Our department had a *huge* three phase synchronous motor which did the
power factor correction for the whole factory.
--
Dave Fawthrop <dave hyphenologist co uk> Google Groups is IME the *worst*
method of accessing usenet. GG subscribers would be well advised get a
newsreader, say Agent, and a newsserver, say news.individual.net. These
will allow them: to see only *new* posts, a killfile, and other goodies.

Andy Wade

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Jan 1, 2007, 6:24:25 PM1/1/07
to
Harry Bloomfield wrote:

> SMPSU's are no more efficient off load than are transformer type PSU's,

Off-load the efficiency is surely always zero (zero power out divided be
finite power in). Thus it's only meaningful to quote a standby power
consumption (power input with no load).

> but on load they are much more efficient.

That's not necessarily the case at all.

--
Andy

The Natural Philosopher

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Jan 1, 2007, 9:15:50 PM1/1/07
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What..not more efficient than zero?
:-)

Agreed SMPS are not used for efficiency, because they will not match a
good transformer, which is up there at the 9-98% sort of areas..they are
used because they are CHEAP.

meow...@care2.com

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Jan 1, 2007, 10:59:51 PM1/1/07
to

Quite. But for wallwarts it is, theyre too small to get decent
efficiency.


NT

Andy Hall

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Jan 2, 2007, 3:39:30 AM1/2/07
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Switched mode?

They don't seem to get particularly warm in most cases.


meow...@care2.com

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Jan 2, 2007, 4:38:59 AM1/2/07
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Andy Hall wrote:
> On 2007-01-02 03:59:51 +0000, meow...@care2.com said:
> > Andy Wade wrote:
> >> Harry Bloomfield wrote:

> >>> SMPSU's are no more efficient off load than are transformer type PSU's,
> >
> >> Off-load the efficiency is surely always zero (zero power out divided be
> >> finite power in). Thus it's only meaningful to quote a standby power
> >> consumption (power input with no load).
> >
> >>> but on load they are much more efficient.

> >> That's not necessarily the case at all.

> > Quite. But for wallwarts it is, theyre too small to get decent
> > efficiency.

> Switched mode?


>
> They don't seem to get particularly warm in most cases.

Yes. I meant mains frequency transformers, in warts theyre just too
small to be efficient. Fairly high copper losses plus magnetising
current with minimal iron isn't really a formula for high efficiency.


NT

Dave Plowman (News)

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Jan 2, 2007, 5:00:43 AM1/2/07
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In article <116770407...@proxy00.news.clara.net>,

The Natural Philosopher <a@b.c> wrote:
> Agreed SMPS are not used for efficiency, because they will not match a
> good transformer, which is up there at the 9-98% sort of areas..they are
> used because they are CHEAP.

Another sweeping statement? SMPS will be smaller and lighter for the same
current output. Have the ability to work properly on a wide range of input
voltages, which a transformer supply can't.

As regards being cheaper, how do you price such things? In all practical
costings they're more expensive.

--
*If we weren't meant to eat animals, why are they made of meat?

Sylvain VAN DER WALDE

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Jan 2, 2007, 5:43:11 AM1/2/07
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"The Natural Philosopher" <a@b.c> wrote in message
news:116770407...@proxy00.news.clara.net...

Isn't that a rather sweeping statement? They are smaller and lighter, and
that's why they are/were used in VCR'S, etc...
Or so I believe.

Sylvain.


Anita Palley

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Jan 2, 2007, 7:19:50 AM1/2/07
to
patrick j wrote:

> My octogenarian mother has become fearful that the small black
> transformers which are supplying electricity to various things around
> her flat might burst into flames.

Transformers are not safe. They are robots in disguise. Better warn
your old mum.

Andy Wade

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Jan 2, 2007, 7:22:40 AM1/2/07
to
meow...@care2.com wrote:

> Yes. I meant mains frequency transformers, in warts theyre just too
> small to be efficient. Fairly high copper losses plus magnetising
> current with minimal iron isn't really a formula for high efficiency.

That is very dependent on the required output power level though. Where
only a few milliwatts DC (or secondary AC) output is required it's
usually possible to keep the standing losses in a 50 Hz transformer to
under half a watt or so. TBH I don't really know how that compares with
SM designs as I don't have so much experience of those as with 50 Hz
trannies.

Magnetising current, /per se/ is not a cause of loss - it's the in-phase
component of the primary current due to hysteresis and eddy current
losses that's relevant. Indeed when designing for higher power output
levels the transformer efficiency on-load will be improved by keeping
the core flux density as high as practicable. This increases the iron
loss but reduces the turns per volt figure for the windings, leading to
lower winding resistances and therefore less copper loss (and better
regulation). IOW there's a design trade-off here where achieving high
efficiency at full load leads to increased standing loss off-load, and
vice-versa. In an ideal world one might be able to optimise a design
for minimum energy consumption, taking the usage duty cycle into
account. In practice this approach might be frustrated because the
lower full-load efficiency leads to some combination of excessive
temperature rise on-load, size or cost.

For very small transformers though (say 3 VA or less) the copper loss in
the primary winding due to the flow of magnetising current can be a
significant contribution to the standing loss. You will often find that
transformers of this size have unequal primary and secondary winding
window areas (primary has >50% of the net window area) in an attempt to
mitigate this effect.

--
Andy

The Natural Philosopher

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Jan 2, 2007, 7:44:09 AM1/2/07
to

Smaller and lighter=cheaper in this context..seen copper prices
recently? Or magnetic materials..

I can assure you that the driving force of MOST electronic design is
cost. Not smaller/lighter..who cares if a VCR is 6 oz heavier?


>
> Sylvain.
>
>

The Natural Philosopher

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Jan 2, 2007, 7:42:32 AM1/2/07
to
Dave Plowman (News) wrote:
> In article <116770407...@proxy00.news.clara.net>,
> The Natural Philosopher <a@b.c> wrote:
>> Agreed SMPS are not used for efficiency, because they will not match a
>> good transformer, which is up there at the 9-98% sort of areas..they are
>> used because they are CHEAP.
>
> Another sweeping statement? SMPS will be smaller and lighter for the same
> current output. Have the ability to work properly on a wide range of input
> voltages, which a transformer supply can't.
>
> As regards being cheaper, how do you price such things? In all practical
> costings they're more expensive.
>
No, they are not.

That's why they are used. At some point - about 20-50W..the iron costs
and the copper costs of a decent 50Hz transformer outweigh the minimal
costs of a couple of chips and some high voltage transistors and a small
ferrite transformer running at 10Khz. The point at which you DON'T see a
wall wart, and you DO see an SMPS.

Apart from maybe HIFI units, you will be pushed to find any equipment
using an iron cored 50/60Hz transformer at over 50W..OTOH you will be
hard pushed to find anything NOT using one under that power level.

The exception being the National Grid of course ;-) Where efficiency
really matters, and lifetime is long enough to render massive
transformers the optimal solution over many years of amortization.


Andy Hall

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Jan 2, 2007, 8:04:24 AM1/2/07
to
On 2007-01-02 12:42:32 +0000, The Natural Philosopher <a@b.c> said:

> Dave Plowman (News) wrote:
>> In article <116770407...@proxy00.news.clara.net>,
>> The Natural Philosopher <a@b.c> wrote:
>>> Agreed SMPS are not used for efficiency, because they will not match a
>>> good transformer, which is up there at the 9-98% sort of areas..they
>>> are used because they are CHEAP.
>>
>> Another sweeping statement? SMPS will be smaller and lighter for the same
>> current output. Have the ability to work properly on a wide range of input
>> voltages, which a transformer supply can't.
>>
>> As regards being cheaper, how do you price such things? In all practical
>> costings they're more expensive.
>>
> No, they are not.
>
> That's why they are used. At some point - about 20-50W..the iron costs
> and the copper costs of a decent 50Hz transformer outweigh the minimal
> costs of a couple of chips and some high voltage transistors and a
> small ferrite transformer running at 10Khz. The point at which you
> DON'T see a wall wart, and you DO see an SMPS.
>
> Apart from maybe HIFI units, you will be pushed to find any equipment
> using an iron cored 50/60Hz transformer at over 50W..OTOH you will be
> hard pushed to find anything NOT using one under that power level.

Mobile phone chargers?


gort

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Jan 2, 2007, 8:24:11 AM1/2/07
to
Anita Palley wrote:

Do you think you could learn to use google groups correctly and reply in
thread ?

Dave

Anita Palley

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Jan 2, 2007, 8:41:05 AM1/2/07
to
gort wrote:

> Do you think you could learn to use google groups correctly and reply in
> thread ?

Hello Gorty, looks alright to me.

Tony Williams

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Jan 2, 2007, 8:41:03 AM1/2/07
to
In article <459a4e93$0$27097$db0f...@news.zen.co.uk>,
Andy Wade <spamb...@maxwell.myzen.co.uk> wrote:
[snip]
> ..... In an ideal world one might be able to optimise a design

> for minimum energy consumption, taking the usage duty cycle into
> account. In practice this approach might be frustrated because
> the lower full-load efficiency leads to some combination of
> excessive temperature rise on-load, size or cost.

It can be the other way round. Some years ago
I bought an RS 1KVA 240:115 isolating transformer.
The surface temperature was very high on no-load
and actually decreased as it was loaded.

--
Tony Williams.

gort

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Jan 2, 2007, 9:45:23 AM1/2/07
to
Anita Palley wrote:

Hmmm I suppose your looking at it in google groups, nuff said.

Dave

Chris Hodges

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Jan 2, 2007, 4:59:24 PM1/2/07
to
Chargers for practically anything in fact and adaptors supplied with a
lot of low power kit - just checked the collection and even below ~20W
SMPS warts are more common than iron.

--
Spamtrap in use
To email replace 127.0.0.1 with btinternet dot com

Chris Hodges

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Jan 2, 2007, 5:01:29 PM1/2/07
to
No probs here in Mozilla over BT.

Andy Wade

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Jan 2, 2007, 8:15:01 PM1/2/07
to
Tony Williams wrote:

> Some years ago I bought an RS 1KVA 240:115 isolating transformer. The
> surface temperature was very high on no-load and actually decreased
> as it was loaded.

Eeek, on a transformer that size that would appear to indicate a core
far too close to saturation at no-load. Choose from poor design, poor
core material or faulty assembly...

--
Andy

meow...@care2.com

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Jan 2, 2007, 9:58:31 PM1/2/07
to
Andy Wade wrote:
> meow...@care2.com wrote:

> > Yes. I meant mains frequency transformers, in warts theyre just too
> > small to be efficient. Fairly high copper losses plus magnetising
> > current with minimal iron isn't really a formula for high efficiency.

> That is very dependent on the required output power level though. Where
> only a few milliwatts DC (or secondary AC) output is required it's
> usually possible to keep the standing losses in a 50 Hz transformer to
> under half a watt or so.

Warts are normally in the 3VA region though, which you go on to
discuss.


NT

meow...@care2.com

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Jan 2, 2007, 10:03:38 PM1/2/07
to
Mike Barnes wrote:

> Of course a universal low voltage DC power supply standard would be so
> much better, but that's unlikely to happen soon.

Nail on head. But with disposable income ever higher it could start to
happen any time. Its not difficult to put LV cable in and power it off
a 12v psu. Or a 12+diode drop psu, and you leave out the diode at the
appliance end for heavier loads.

The plugs/leads used for non 12v appliances will have a Vreg built in,
perhaps an LM317 so you can dial or switch in whatever V you want. It
would all be cheap enough at new build or rewire time.


NT

Dave Plowman (News)

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Jan 3, 2007, 5:08:15 AM1/3/07
to
In article <1167793418.1...@n51g2000cwc.googlegroups.com>,

<meow...@care2.com> wrote:
> Nail on head. But with disposable income ever higher it could start to
> happen any time. Its not difficult to put LV cable in and power it off
> a 12v psu. Or a 12+diode drop psu, and you leave out the diode at the
> appliance end for heavier loads.

> The plugs/leads used for non 12v appliances will have a Vreg built in,
> perhaps an LM317 so you can dial or switch in whatever V you want. It
> would all be cheap enough at new build or rewire time.

Given that cars are beginning to move away from 12 volts DC to something
higher to reduce wiring costs I'm not so sure. A decent power supply
provides a good clean low impedance source of DC. To do this off a common
rail round the house may not save any money at all - as well as doubling
up on the number of socket outlets.

--
*I like cats, too. Let's exchange recipes.

tony sayer

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Jan 3, 2007, 5:19:00 AM1/3/07
to
In article <4e9f57a...@davenoise.co.uk>, Dave Plowman (News)
<da...@davenoise.co.uk> writes

>In article <1167793418.1...@n51g2000cwc.googlegroups.com>,
> <meow...@care2.com> wrote:
>> Nail on head. But with disposable income ever higher it could start to
>> happen any time. Its not difficult to put LV cable in and power it off
>> a 12v psu. Or a 12+diode drop psu, and you leave out the diode at the
>> appliance end for heavier loads.
>
>> The plugs/leads used for non 12v appliances will have a Vreg built in,
>> perhaps an LM317 so you can dial or switch in whatever V you want. It
>> would all be cheap enough at new build or rewire time.
>
>Given that cars are beginning to move away from 12 volts DC to something
>higher to reduce wiring costs I'm not so sure.


Are they?, what makes are doing that then Dave?...

>A decent power supply
>provides a good clean low impedance source of DC. To do this off a common
>rail round the house may not save any money at all - as well as doubling
>up on the number of socket outlets.
>

--
Tony Sayer

Tony Williams

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Jan 3, 2007, 5:23:45 AM1/3/07
to
In article <459b0398$0$31235$da0f...@news.zen.co.uk>,
Andy Wade <spamb...@maxwell.myzen.co.uk> wrote:

I think it is regarded as a 'good' design if the
design object is to produce maximum output power
for minimum materials cost. After all, if a
transformer can dissipate X Watts of losses on
full-load, (mainly copper loss), why not also
allow X Watts of dissipation on no-load, (but
now from iron loss). This leads to a reduction
in the volume of iron needed.

--
Tony Williams.

Tony Williams

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Jan 3, 2007, 5:58:05 AM1/3/07
to
In article <9HtMf4EU...@bancom.co.uk>,
tony sayer <to...@bancom.co.uk> wrote:

> Dave Plowman (News) wrote:
> >Given that cars are beginning to move away from 12 volts DC to
> >something higher to reduce wiring costs I'm not so sure.

> Are they?, what makes are doing that then Dave?...

All makes, particularly luxury vehicles with lots of
electrically powered ancilliaries, in order to reduce
the huge current consumption that some cars now take
via their 12V wiring..... US cars in particular.

There have been proposals and discussions for the last
few years, about increasing the vehicle battery from
12V to a new 42V standard.

Note that a dc arc requires about 22V to self sustain,
so mechanical switches are ok on a 12V system, but will
not generally be ok on a 42V system. So us punters are
going to have to pay the extra costs of electronic
modules to do any load switching.... and probably more
failures, and probably rip-off prices for spares. :(

--
Tony Williams.

The Natural Philosopher

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Jan 3, 2007, 6:05:35 AM1/3/07
to
Or it was a voltage stabilising transformer..they are designed to be
like that.

Dave Plowman (News)

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Jan 3, 2007, 6:26:23 AM1/3/07
to
In article <4e9f5c3...@ledelec.demon.co.uk>,

Tony Williams <to...@ledelec.demon.co.uk> wrote:
> Note that a dc arc requires about 22V to self sustain,
> so mechanical switches are ok on a 12V system, but will
> not generally be ok on a 42V system.

Strange that larger vehicles have been 24 volts for years - so say about
30 volts with the alternator charging.

--
*A bartender is just a pharmacist with a limited inventory *

meow...@care2.com

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Jan 3, 2007, 6:32:53 AM1/3/07
to
Dave Plowman (News) wrote:
> In article <1167793418.1...@n51g2000cwc.googlegroups.com>,
> <meow...@care2.com> wrote:

> > Nail on head. But with disposable income ever higher it could start to
> > happen any time. Its not difficult to put LV cable in and power it off
> > a 12v psu. Or a 12+diode drop psu, and you leave out the diode at the
> > appliance end for heavier loads.
>
> > The plugs/leads used for non 12v appliances will have a Vreg built in,
> > perhaps an LM317 so you can dial or switch in whatever V you want. It
> > would all be cheap enough at new build or rewire time.

> Given that cars are beginning to move away from 12 volts DC to something
> higher to reduce wiring costs I'm not so sure.

I dont see how this would impact on domestic appliances.


> A decent power supply
> provides a good clean low impedance source of DC. To do this off a common
> rail round the house may not save any money at all

no, it costs money. Thats why we dont often see it today.

> - as well as doubling
> up on the number of socket outlets.

Not really. If one installs LV outlets, guess what, less mains outlets
are then needed. And key, the LV outlets can be tiny in comparison to
the mains ones.


NT

Dave Plowman (News)

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Jan 3, 2007, 6:43:50 AM1/3/07
to
In article <1167823973.5...@k21g2000cwa.googlegroups.com>,

<meow...@care2.com> wrote:
> > Given that cars are beginning to move away from 12 volts DC to
> > something higher to reduce wiring costs I'm not so sure.

> I dont see how this would impact on domestic appliances.

Even more so since the cable runs will be longer? And you need a lot of
copper for a low voltage supply.


> > A decent power supply provides a good clean low impedance source of
> > DC. To do this off a common rail round the house may not save any
> > money at all

> no, it costs money. Thats why we dont often see it today.

Indeed. It will likely cost far more than just using individual power
supplies. With absolutely no advantages.

> > - as well as doubling
> > up on the number of socket outlets.

> Not really. If one installs LV outlets, guess what, less mains outlets
> are then needed.

You only have mains outlets where actually needed and in use all the time?
And never alter the layout of a room, etc? Add new appliances?

> And key, the LV outlets can be tiny in comparison to
> the mains ones.

You might have problems making off the thick distribution cable to a very
small outlet. As well as making a neat fixing in a wall, etc. It's for a
good reason things like flush telephone outlets stick with the standard
sizes even although they could be a great deal smaller.

--
*A hangover is the wrath of grapes.

The Natural Philosopher

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Jan 3, 2007, 8:10:03 AM1/3/07
to
There is a case for something like 48V DC..now that in itself doesn't
directly solve the problems of getting 5v and 12v you still need an SMPS
- but it does make those a bit cheaper and more reliable.

It would be a fairly sane voltage for a lot of electric motor stuff too..

And possibly lighting.

But the chief advantage would be to the tons of electronics we find
ourselves with..since the voltage is no longer 'dangerous' as defined by
whatever idiots define these things, and DC..all equipment would have
small SMPS built in..or linear regs..and probably switches on it.

And I can envisage a requirement to have it all controlled by a room
switch as well. So that one switch totally removes power from all
devices. My workbench is wired like that..I don't now forget to
unplug/turn off stuff - just hit the master switch and its guaranteed dead.


manat...@hotmail.com

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Jan 3, 2007, 8:11:23 AM1/3/07
to

On Jan 2, 2:15 am, The Natural Philosopher <a...@b.c> wrote:
> Andy Wade wrote:
> > Harry Bloomfield wrote:
>
> >> SMPSU's are no more efficient off load than are transformer type PSU's,
>
> > Off-load the efficiency is surely always zero (zero power out divided be
> > finite power in). Thus it's only meaningful to quote a standby power
> > consumption (power input with no load).
>
> >> but on load they are much more efficient.
>

> > That's not necessarily the case at all.What..not more efficient than zero?
> :-)
>


> Agreed SMPS are not used for efficiency, because they will not match a
> good transformer, which is up there at the 9-98% sort of areas..they are
> used because they are CHEAP.

Try comparing apples with apples. An SMPS is a power supply, a
transformer is just that.

SMPS are used because they *are* more efficient than a transformer
followed by a linear regulator.

MBQ

Andy Wade

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Jan 3, 2007, 8:11:59 AM1/3/07
to
Tony Williams wrote:
>
> There have been proposals and discussions for the last
> few years, about increasing the vehicle battery from
> 12V to a new 42V standard.

This seems to have been "just around the corner" for at least ten years
now. I guess it will eventually happen, just as the equally
long-heralded death of the CRT now seems to have happened.

--
Andy

The Natural Philosopher

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Jan 3, 2007, 8:27:18 AM1/3/07
to

Yup...love my new LCD screen.

Still got plenty of tellies with loads of life in em tho..

will phase them out as they break..

The Natural Philosopher

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Jan 3, 2007, 8:26:18 AM1/3/07
to

That is NOT what I said..

Sure SMPS are slightly more efficient than a well designed linear
regulator doing its thing of a well designed transformer..but actually
NOT THAT MUCH. And only over a smaller range of operating power levels.

At very low currents, the transformer is PROBABLY better. At very high
the SMPS will be definitely better..


> MBQ
>

Dave Plowman (News)

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Jan 3, 2007, 9:30:05 AM1/3/07
to
In article <116782973...@proxy01.news.clara.net>, The Natural

> And possibly lighting.

Think the official safe voltage is more like 30 these days.

> And I can envisage a requirement to have it all controlled by a room
> switch as well. So that one switch totally removes power from all
> devices. My workbench is wired like that..I don't now forget to
> unplug/turn off stuff - just hit the master switch and its guaranteed
> dead.

A large quantity of the things I have fed off wall warts either need 24/7
hour power, or are chargers etc so not organised enough to be switched off
together. The single switch idea is ideal for workshops, though, although
I also have 24/7 power outlets too.

--
*I see you've set aside this special time to humiliate yourself in public

Dave Plowman (News)

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Jan 3, 2007, 9:31:59 AM1/3/07
to
In article <116783076...@despina.uk.clara.net>,

The Natural Philosopher <a@b.c> wrote:
> > now. I guess it will eventually happen, just as the equally
> > long-heralded death of the CRT now seems to have happened.
> >

> Yup...love my new LCD screen.

Yes - they are very flat and slim. Pity about the pictures, though...

--
*Too many clicks spoil the browse *

meow...@care2.com

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Jan 3, 2007, 1:33:49 PM1/3/07