24/7 Unattended Comms Equipment - Preventing Electrical Fires?

[ban-all-sheds]

I think (fairly certain) that for a product to be UL listed is has to undergo testing by an accredited 3rd-party test organisation, whereas CE can be entirely self-certified.

Of course, there's little to stop a manufacturer from having false UL logos, or changing the design or quality of the product after getting approval, but it's got to be better than nothing.

 

[winston1]

You cannot buy plugtops separately. A plugtop is the cover of a plug. ... That website does not seem to know that either. I would not buy from a company that does not know the difference between a cover and a plug.

In that case, I guess you need to take TLC off your suppliers' list - click here !!

Kind REgards, John

I have never used them actually, but after your reply I have emailed their technical section pointing out their error. I await their reply with interest.

 

[JohnW2]

Of course, there's little to stop a manufacturer from having false UL logos, or changing the design or quality of the product after getting approval, but it's got to be better than nothing.

In terms of big picture, it presumably is "better than nothing", since it means that at least some products will have been legitimately certified, and have remained unchanged since that certification. However, in terms of an individual specimen of a product it could be regarded as "worse than nothing", since it seeming provides a reassurance, which may not be justified.

Kind Regards, John

 

[endecotp]

Learning what a CE mark does, and does not, look like is also a help.

Well I can imagine all four combinations of right/wrong graphic and compliant/non-compliant device, e.g. the label designer for a compliant product deciding to save some space by putting the C and E closer together without realising the significance and the faker accurately copying the correctly-spaced version.

 

[JohnW2]

In that case, I guess you need to take TLC off your suppliers' list - click here !!

I have never used them actually, but after your reply I have emailed their technical section pointing out their error. I await their reply with interest.

Whilst you are e-mailing, you might want to add QVS (click here), CEF (click here) and Discount Electrical (click here) to your list ... and that's just for starters!

Kind Regards, John

 

[endecotp]

I'm still hoping that we'll get a photo of the entire innards of this particular PSU, and also confirmation of whether it had a US or UK plug. But I'll post this anyway based on the photos we do have.

I think that the mains input pins were on the bit that has been broken off, so we're looking at the mains input components. There appear to be no EMC filter components of any kind, i.e. the mains goes straight into the rectifier. Normally I'd expect to see a common-mode choke and a capacitor. I think it's very unlikely that this could possibly pass any EMC tests.

There also appears to be no fuse. I would hope to see a PTC thermistor fuse in there, though I know it's possible to get approval without one.

I now think Bernard Green is right that the failed component is a series current-limit resistor. A better design would have (a) rectifier diodes that could cope with inrush current and (b) some series resistance and inductance in the EMC filter components. Or they might use an NTC thermistor or varistor or similar. A series resistor will compromise the efficiency.

Capacitor failure is still a likely root cause; an electrolytic dries up, the control loop fails and the switching transistor goes permanently on. Lots of current flows and in this case the series resistor was the first thing to fail.

 

[JohnW2]

I think that the mains input pins were on the bit that has been broken off, so we're looking at the mains input components. There appear to be no EMC filter components of any kind, i.e. the mains goes straight into the rectifier.

I suppose it's possible that some such components were attached to the bits that have broken off (i.e. directly to the mains input pins). Photos of that broken off bit might therefore also be interesting.

Kind Regards, John

 

[SimonH2]

I suppose it's possible that some such components were attached to the bits that have broken off (i.e. directly to the mains input pins).

Unlikely, it's by far the cheapest to put them on the PCB.

 

[JohnW2]

I suppose it's possible that some such components were attached to the bits that have broken off (i.e. directly to the mains input pins).

Unlikely, it's by far the cheapest to put them on the PCB.

If, as has been suggested, the PCB (and hence presumably also the rest of it) was assembled by hand (maybe 'on a kitchen table'), it probably wouldn't make a lot of difference (to cost), would it?

Kind Regards, John

 

[SimonH2]

Actually I suspect even hand assembling it, it's cheaper to have all the components on the PCB. When putting that together, it's "pick, place, solder" for everything so a couple of extra components would make very very little difference in assembly time. Putting them on the "back of the plug" would introduce a different step to the process which would have a bigger impact on assembly time.

 

[ban-all-sheds]

If, as has been suggested, the PCB (and hence presumably also the rest of it) was assembled by hand (maybe 'on a kitchen table'), it probably wouldn't make a lot of difference (to cost), would it?

If the "manufacturer" is selling them for $0.84 each, even a few cents difference would probably be equivalent to a significant % of his profit.

 

[JohnW2]

If the "manufacturer" is selling them for $0.84 each, even a few cents difference would probably be equivalent to a significant % of his profit.

Indeed, but in terms of what is being assumed, a minute or three longer to install a couple of components in a different way would probably not cost even "a few cents" in extra labour costs, would it?!

Kind Regards, John

 

[SimonH2]

... but in terms of what is being assumed, a minute or three longer to install a couple of components in a different way would probably not cost even "a few cents" in extra labour costs, would it?!

You'd be surprised, labours costs are rocketing in China, and manufacturers are now starting to "offshore" manufacturing to the next cheap supplier (India is mentioned in many of the articles I've read).

 

[bernardgreen]

Whether protection is incorporated into the design is decided more by the business ethics of the manufacturers.

The ethic appears to be that as long as the device works then there is no need to over elaborate the design by including protective components.

There is also in some people a total dis-regard for the safety of the end user's equipment and even for the safety of the end user.

 

[ban-all-sheds]

There is hardly anything in the world that someone cannot make a little worse and sell a little cheaper, and the people who consider price alone are that person's lawful prey.