I ran across the attached article excerpt describing the risk of using a cheap AC adapter. I post it here because I see a lot of posterd state "....they are safe because they are using a retail AC adapter...".
While I think most realize the cheap adapters from China can be of inferior quality I'm not sure they understand the risk these products represent.
In the attached excerpt, the transformer was made with the primary wire (mains) wound right on top of the secondary wire (low voltage). The only insulation that keeps the mains from connecting to the output is the wire enamel which is not designed for such a high voltage.
The result of a wire insulation failure would be your arduino connected directly to the mains! And you would likely not know it until it either fried or you touched a ground of some sort.
I'll admit I am cautious sort, I will only buy adapters that are UL listed or at the very minimum CE compliant. Of course an unscrupulous vendor could lie about the certifications.
According to NEMA and ICEA standards such as ICEA S-95-658 "Standard for Nonshielded Power Cables Rated 2000 V or Less for the Distribution of Electrical Energy"... If the insulation is rated for 600 Volts (in the US) then no further insulating material is required. Enameled wire easily passes this test.
When someone says "safety violations", ask them what safety regulation or standard is being violated.
If you cut open any low-power Wall Wart, this is exactly the type of transformer you will find.
Switching supplies use toroidal power transformers like this one. The specs say "Hi-Pot test of 4,000VAC RMS between primary & secondary". There's no core; no additional insulation. Just a secondary winding wound over the primary winding of enameled wires. Just like the one in the photo.
You quote a power cable spec? Apples and oranges anyone?
Enameled wire easily passes this test.
Common sense and UL 1561, 5085, IEC 61558 and others say otherwise. Cheap transformers that wind the secondary on top of the primary put a couple of wraps of polyester tape, fish paper or other insulation between the layers. High isolation transformers use split bobbins.
Maybe the Wung-hug-low brand transformers don’t insulate but then I guarantee you that’s a fake UL label on the device. Which makes JohnRob’s point.
It’s shocking I tell you, just shocking. Wink wink nudge nudge.
First I must say you do those without experience in electrical components a disservice. These folks are the most likely group to over load and generally electrically abuse power supplies as they learn.
The reason I created this post was I got the sense that many folks simply figured a cheap wall wart would fail sooner than a good one but being so cheap they could just toss them a buy another.
I wanted to show there is more at stake than just premature failure.
Having said that.......
If the insulation is rated for 600 Volts (in the US) then no further insulating material is required. Enameled wire easily passes this test.
This is not a cable application. 600V will not cut it.
Switching supplies use toroidal power transformers like this one. The specs say "Hi-Pot test of 4,000VAC RMS between primary & secondary". There's no core; no additional insulation. Just a secondary winding wound over the primary winding of enameled wires. Just like the one in the photo.
Not so. Toroidal cores are usually used for 50/60Hz power transformers and lower frequency inductors. They are most often powered iron. There is inter winding insulation and in many cases there is added insulation on the core itself. In addition they do not lend themselves to low cost production. Pretty much every high frequency inverters use E-E ferrite cores.
If you cut open any low-power Wall Wart, this is exactly the type of transformer you will find.
Go ahead, I think you will be surprised.
You should also know that power supplies designed for "Medical" applications must have a split bobbin, inter-winding tape will not meet the requirements.
