Transformers - are they safe?

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?

Reply to
patrick j
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In article , patrick j writes

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

Reply to
tony sayer

patrick j was thinking very hard :

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.

Reply to
Harry Bloomfield

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.

Reply to
Sylvain VAN DER WALDE

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.

Reply to
Dave Plowman (News)

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

NT

Reply to
meow2222

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

Reply to
Andrew

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

Reply to
Dave Plowman (News)

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

Reply to
Roger R

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.

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

Most factories would use three phase motors.

Reply to
Dave Plowman (News)

no

no

no

no

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

NT

Reply to
meow2222

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

Reply to
Roger R

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

Reply to
meow2222

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

Reply to
Jonathan Schneider

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.

Reply to
kimble

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..

Reply to
The Natural Philosopher

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.

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

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.

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

Reply to
Dave Plowman (News)

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.

Reply to
The Natural Philosopher

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

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.

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 =A3 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

Reply to
meow2222

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.

Reply to
Mike Barnes

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