Transformers - are they safe?

[Chris Hodges]

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.

[Chris Hodges]

No probs here in Mozilla over BT.

[Andy Wade]

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...

[meow2222]

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

NT

[meow2222]

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)]

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.

[tony sayer]

In article , Dave Plowman (News) writes

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

[Tony Williams]

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]

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. :(

[The Natural Philosopher]

Or it was a voltage stabilising transformer..they are designed to be like that.

[Dave Plowman (News)]

Strange that larger vehicles have been 24 volts for years - so say about

30 volts with the alternator charging.

[meow2222]

I dont see how this would impact on domestic appliances.

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

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)]

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

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

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?

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.

[The Natural Philosopher]

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.

[manatbandq]

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]

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.

[The Natural Philosopher]

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..

[The Natural Philosopher]

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..

[Dave Plowman (News)]

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

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.

[Dave Plowman (News)]

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