I have posted some teardowns of serveral electronics devices and have some notes on their electrical safety. Examples of ones with questionable safety were this is tiny USB charger and this USB charger. The later USB charger posting has also example of power supply that seems to have properly built safety in it.
But how is really safe power supply built ?A very recent EEVblog #659 – Medical Plugpack Teardown video gives some answers to that. It shows what is inside an IEC60601-1 medical class 5V mains power adapter (German FRIWO 5V FW7555M/05 brand medical grade isolation unit). It also compares the medical power supply construction to a consumer brand power supply. Besides what is in the circuit board the video take a look at the transformer construction.
1 Comment
Tomi Engdahl says:
#105 Unsafe Encapsulated TSP-05/HLK-PM01 PSU? AND other stuff (cheap!)
https://www.youtube.com/watch?v=xodLuR6C8N4
This TSP-05 encapsulated 5-volt PSU looks like an HLK-PM01 (both externally and internally) so it is safe to use?
The answer is not straightforward. Although thousands of the HLK-PM01s have been successfully used over the years it doesn’t mean they are safe; and being made in a country where safety standards are very different to those in Europe and the United States it means that there is always going to be an unknown ‘safety gap’ in the design or application of whatever standards are being used.
I’m tempted to use a TSP-05, however, as it is small (far smaller than a plug-in wall-wart) and cheap, and on closer inspection seems to be as good as the HLK-PM01.
Comments:
yes the HLK-PM01 is only little more money. I would use a tiny mains supply but the box if metal or any switch is metal it must be mains earthed. The best way is to have “Double Insulated” with no exposed metal parts or wires. Send the clone and orignal to “Big Clives channel”. He will do a high voltage isolation test and take the transformer apart as ther are many safey rules just in a wound transformer. For 99.9% a wallblock is best route. I don’t truss the China and buy from Farnell and the like so the marking are real.
You need to put mains filtering on this to use this for sensitive electronics like MCUs or SBCs. Just chuck in a y capacitor, fuse and a common mode choke on the mains input and 10uF capacitor on the output. I wouldn’t use this on any commercial design though.
The AC pins on the Hi-Link looks to have more space between them.
Yes, I used the hi link ones in different output voltages a few times now and had no problems at all until now. I would use them again. Most stuff I place such things in are projects that won’t run for days on their own, so most of the time I will be in the room when they are powered. And of course I won’t touch even the low voltage output just in case…..
The important issue, in the context of Ralph’s video, is that as a maker, a lack of caution in isolating users from mains voltage (be it 110v, 240v or 415v) may result in somebody else (perhaps one of your children) receiving an electric shock. Now many people survive electric shocks but the statistics (or should I say corpses) indicate that electricity can and does kill.
Simple answer Ralph, NO I would not use one of those.
If I really need one like this, I’d get one UL listed from digikey or mouser (I’m in Canada). Most likely “meanwell” brand. Not too expensive and good for any use. I mention “meanwell” because it’s “far east”. “far east” peoples can do any quality you want. If you willing to pay $1, power supply will be with quality of $1.
I had Hi-Link SMPS and someone mounted it on a double-layer perforated prototyping board…
It obviously exploded. The power supply was a-ok, but the circuit board tracks vanished with a bang.
I just removed all the tracks near the mains connection and made some isolation slots so under no condition mains would connect straight to the safe 5V output.
there does seem to be some kind of “rule of thumb” at the very least, according to John Ward, that 3mm between mains conductors and “other parts of the circuit” is desirable, perhaps with an air gap (eg a cut slot on the board). You can “get away with” 2mm and a gap, anything less than that is asking for trouble (the smallest amount of dust and it will arc.
UL60950-1 and I believe the IEC version specifically have a chapter on encapsulated electronics, which basically says you can use whatever clearance/creepage if you know what are you doing. Search UL60950-1 on Google and download a pirate copy, read it before reviewing another power supply.
Best to start with bs60601 for medical equipment. Then work up to bs61010 for lab type equipment and end with 60950 for it equipment. With 60601 your looking at 10 uA to 50uA as leakage limits.