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What is special about a wall wart transformer

Started by Unknown April 16, 2017
What is special about a wall wart transformer,
as compared to a standard iron-core transformer ?
daku...@gmail.com wrote:
> > > What is special about a wall wart transformer, > as compared to a standard iron-core transformer ? > >
** The big one is user safety. Wall wart transformers have no safety ground so must be designed and built to class 2 ( double insulation) standards. The isolation between primary and secondary winding must survive any possible overload and other known events that might damage the insulation and render the secondary live at AC supply voltages. These days, the use of extra fire resistant insulation and suitable, internal thermal fuses connected in the primary circuit is sufficient - along with more than usual clearance and creepage distances across and through insulation. Compared to some diabolical SMPS designs on sale, they are extremely safe. .... Phil
On Sat, 15 Apr 2017 23:26:39 -0700, Phil Allison wrote:

> daku...@gmail.com wrote: >> >> >> What is special about a wall wart transformer, as compared to a >> standard iron-core transformer ? >> >> >> > ** The big one is user safety. > > Wall wart transformers have no safety ground so must be designed and > built to class 2 ( double insulation) standards. > > The isolation between primary and secondary winding must survive any > possible overload and other known events that might damage the > insulation and render the secondary live at AC supply voltages. > > These days, the use of extra fire resistant insulation and suitable, > internal thermal fuses connected in the primary circuit is sufficient - > along with more than usual clearance and creepage distances across and > through insulation.
I suspect that at least some are also intentionally built with some leakage inductance or high-resistance secondaries, to allow for safe short-circuit operation.
> Compared to some diabolical SMPS designs on sale, they are extremely > safe.
Oh, I'm sure that if the world still wanted big clunky wall-warts then the Chinese would figure out how to carve out 1/20 of a penny of the cost by making them unsafe. -- Tim Wescott Control systems, embedded software and circuit design I'm looking for work! See my website if you're interested http://www.wescottdesign.com
On 4/16/2017 10:29 AM, Tim Wescott wrote:
> On Sat, 15 Apr 2017 23:26:39 -0700, Phil Allison wrote: > >> daku...@gmail.com wrote: >>> >>> >>> What is special about a wall wart transformer, as compared to a >>> standard iron-core transformer ? >>> >>> >>> >> ** The big one is user safety. >> >> Wall wart transformers have no safety ground so must be designed and >> built to class 2 ( double insulation) standards. >> >> The isolation between primary and secondary winding must survive any >> possible overload and other known events that might damage the >> insulation and render the secondary live at AC supply voltages. >> >> These days, the use of extra fire resistant insulation and suitable, >> internal thermal fuses connected in the primary circuit is sufficient - >> along with more than usual clearance and creepage distances across and >> through insulation. > > I suspect that at least some are also intentionally built with some > leakage inductance or high-resistance secondaries, to allow for safe > short-circuit operation. > >> Compared to some diabolical SMPS designs on sale, they are extremely >> safe. > > Oh, I'm sure that if the world still wanted big clunky wall-warts then > the Chinese would figure out how to carve out 1/20 of a penny of the cost > by making them unsafe.
You make it sound like it's a plot to destroy democracy. It's not like crappy, unsafe goods were never made here. -- Rick C
On 04/16/2017 10:40 AM, rickman wrote:

>> Oh, I'm sure that if the world still wanted big clunky wall-warts then >> the Chinese would figure out how to carve out 1/20 of a penny of the cost >> by making them unsafe. > > You make it sound like it's a plot to destroy democracy. It's not like > crappy, unsafe goods were never made here. >
Like every "All American Five" radio sold, the old timers called them "suicide boxes"
On Sun, 16 Apr 2017 09:29:12 -0500, the renowned Tim Wescott
<tim@seemywebsite.com> wrote:

> >Oh, I'm sure that if the world still wanted big clunky wall-warts then >the Chinese would figure out how to carve out 1/20 of a penny of the cost >by making them unsafe.
The approved ones from good makers in China are extremely good- I have bought thousands of 9V/200mA UL/CSA linear adapters. Every material and component is specified and approved. Facilities are inspected by UL and you can get third party inspections for shipments. Of course if you buy something unapproved from Ali or eBay you get what you get and it just might kill you. --sp -- Best regards, Spehro Pefhany
<dakupoto@gmail.com> wrote in message 
news:e06d2b35-cae1-4b92-b525-22b36b3a46a1@googlegroups.com...
> What is special about a wall wart transformer, > as compared to a standard iron-core transformer ?
Some wall warts are iron core transformers - but they're going out of fashion fast. Most are a very compact SMPSU with much better regulation than an iron core. Either way - very few have a safety earth, and must have a "double insulated" rating. --- This email has been checked for viruses by AVG. http://www.avg.com
Tim Wescott wrote:
> Phil Allison wrote: > > > daku...@gmail.com wrote: > >> > >> > >> What is special about a wall wart transformer, as compared to a > >> standard iron-core transformer ? > >> > >> > >> > > ** The big one is user safety. > > > > Wall wart transformers have no safety ground so must be designed and > > built to class 2 ( double insulation) standards. > > > > The isolation between primary and secondary winding must survive any > > possible overload and other known events that might damage the > > insulation and render the secondary live at AC supply voltages. > > > > These days, the use of extra fire resistant insulation and suitable, > > internal thermal fuses connected in the primary circuit is sufficient - > > along with more than usual clearance and creepage distances across and > > through insulation. > > I suspect that at least some are also intentionally built with some > leakage inductance or high-resistance secondaries, to allow for safe > short-circuit operation. >
** Inherently short circuit proof transformers exist, but are not seen in common wall wart supplies. They have poor regulation and cost more to make.
> > Compared to some diabolical SMPS designs on sale, they are extremely > > safe. > > Oh, I'm sure that if the world still wanted big clunky wall-warts then > the Chinese would figure out how to carve out 1/20 of a penny of the cost > by making them unsafe. >
** Garbage, the Chinese have made hundreds of millions of transformer wall warts that are all very safe. The same cannot be said of SMPS types. Regulators in Europe and most places have effectively banned DC output, transformer wall warts on a false pretext. You need to get out more ..... ...... Phil
On Sunday, April 16, 2017 at 1:16:10 AM UTC-5, daku...gmail.com wrote:
> What is special about a wall wart transformer, > as compared to a standard iron-core transformer ?
Design wise, if you are making a big TV set or 200 WPC audio amp, you simply must design your own power supply. Wall warts simply cannot handle it usually. This entails that when designing the layout you must consider what happens if the thing gets run over by a bus, flooded with seawater and all sorts of things. That is for the UL in the US, which is not mandatory, but if your house burns down and they find that a non-approved piece of equipment did it there will be hell to pay. I Europe it is the CE and it might be mandatory, I don't know. You have to think if your SMPS board breaks this way or that way, at all costs do not let the hot touch the cold. This comes down to where you place the components on the board, and even where you can put the mounting screws. But when all you need is 2 volts at 1 amp, it is much cheaper and easier to use a wall wart. You have no worries with the UL or CE, just design your circuit. You don't have to worry about ground faults or any of that. And if you need a split supply, like +/-5 or whatever, there is circuitry for that and voltage conversion is getting cheap.
On Sunday, April 16, 2017 at 8:40:44 PM UTC-5, jurb...@gmail.com wrote:
> On Sunday, April 16, 2017 at 1:16:10 AM UTC-5, daku...gmail.com wrote: > > What is special about a wall wart transformer, > > as compared to a standard iron-core transformer ? > > Design wise, if you are making a big TV set or 200 WPC audio amp, you simply must design your own power supply. Wall warts simply cannot handle it usually. > > This entails that when designing the layout you must consider what happens if the thing gets run over by a bus, flooded with seawater and all sorts of things. That is for the UL in the US, which is not mandatory, but if your house burns down and they find that a non-approved piece of equipment did it there will be hell to pay. I Europe it is the CE and it might be mandatory, I don't know. > > You have to think if your SMPS board breaks this way or that way, at all costs do not let the hot touch the cold. This comes down to where you place the components on the board, and even where you can put the mounting screws. > > But when all you need is 2 volts at 1 amp, it is much cheaper and easier to use a wall wart. You have no worries with the UL or CE, just design your circuit. You don't have to worry about ground faults or any of that. And if you need a split supply, like +/-5 or whatever, there is circuitry for that and voltage conversion is getting cheap.
12 volts