EEVblog Electronics Community Forum
General => General Technical Chat => Topic started by: CatalinaWOW on August 06, 2017, 11:59:06 pm
-
I noticed one of my devices wasn't charging, and as I traced the problem found I had just missed having a painful jolt, burn or worse. The culprit was a Motorola branded dual USB charger. First two pictures show the device and its safety markings. I apologize for the photos, my cell phone has trouble focusing up close.
Standard US two prong (no ground) connection. The device has been carefully designed for manufacture, and connection to the pwb is clever. A pair of springs on the cover which holds the power prongs makes contact with the pwb, locking the board in place at the same time. I am sure that the design intent was to ultrasonic weld this cover in place, making it virtually impossible to remove. Whether by accident, or as a cost saving move the cover is only held by the snap detents. The second two pictures show the key parts of this.
This is where the problem cropped up. The USB charger was plugged into a floor mounted outlet. It got kicked sometime and the case and pwb departed the power outlet, leaving the cover with its power prongs in place. If I had happened to step on this I would have had my whole weight ensuring a good contact with the 120V mains. In a wall outlet the problem would have been slightly less dire.
This is the first really strong argument I have seen for the British style recessed sockets, although I still believe they are an overkill solution. Even this case would have been very unlikely to kill anyone. The real message is that the chain of safety has many links, and the real problem comes with the weakest link. In this case an inadequate job of bonding the case together.
-
While its open get some good photos of both sides of the PCB to post here as teardown porn, then glue it back together and call it good.
N.B. the UK BS1363 plug/socket system typically does not have recessed sockets and as the lead exits downwards, parallel to and against the wall, its usually impractical to recess a socket. You must be thinking of the continental EU's SchuKo (CEE 7/3) and compatible (French CEE 7/5 with protruding round ground pin in socket) ones that all take a SchuKo CEE 7/7 plug..
-
RISK OF ELECTRIC SHOCK.
DRY LOCATION USE ONLY.
Made in CNINA ?
Who wrote this, Master Yoda ? ;D
-
The USB charger was plugged into a floor mounted outlet.
This is for sure a very weird aspect of US practices. In the office where I work there are floor mounted sockets, and in every case the plug has been trodden on, bent, warped, and knocked half out of shape. Occasionally someone will kick the plug out halfway through a conference call and the phone will go dead. I do not understand how this could ever be considered an acceptable design.
When you speak of British style recessed sockets, are you thinking of the recessed boxes in the floor that contain power and network outlets in UK offices? These boxes are a few inches deep and have a metal hinged lid with slots for cable egress. You can tread on the cable but you can't tread on the plug.
-
Agreed - I believe it is a fake.
-
Again, I apologise for the photo quality. CHINA is correctly spelled even though it appears wrong in a quick glance at this photo.
It is too late for tear down porn, it is already very firmly glued together.
Now that it is one piece, and now that I am aware of this potential problem I consider it more than safe enough for my use. It did worry when I found the problem because I was not wear shoes at the time and had walked very near the location.
Floor mounted outlets do have issues, but I generally consider them better than wires running across the floor, and far superior to a cable runway with a power strip at the end. The cable runway just adds a tripping hazard to all of the electrical issues.
-
When you speak of British style recessed sockets, are you thinking of the recessed boxes in the floor that contain power and network outlets in UK offices? These boxes are a few inches deep and have a metal hinged lid with slots for cable egress.
That's pretty rare. It would require a double backbox that can take a BS1363 single socket faceplate with its Earth pin oriented towards the end of the recess, and a dual outlet on a single faceplate for the network, comms or AV so there's room for the BS1363 plug lead (opposite the Earth pin) to pass between the data cabling without having to bend too sharply. Also it would need two conduits to feed it as the fixed low voltage and mains wiring must be completely separated by an insulating barrier.
More usual is a single or double socket with a thin flap-up metal cover that's only recessed by the thickness of the cover. The cover typically is spring loaded so cant be flipped back flat and its corners become a hazard when its in use unless protected against being kicked by furniture over it with less than knee height clearance.
You can tread on the cable but you can't tread on the plug.
Most UK residents learn not to tread on BS1363 plugs (especially bare-foot) before they leave primary school. If an elephant tap-danced on a standards compliant one, the plug would be fine but you'd have a big vet's bill for treating the damage to the poor elephant's feet and a man from the RSPCA trying to get your Dangerous Wild Animal Licence suspended due to mistreatment of the elephant.
-
That's pretty rare.
Now you mention it, I think the mains sockets and network sockets were in separate but adjacent boxes. The recessed box was rectangular and had space for two mains sockets.
-
RISK OF ELECTRIC SHOCK.
DRY LOCATION USE ONLY.
Made in CNINA ?
Who wrote this, Master Yoda ? ;D
They saved themselves having to install the H letter on the printer. 25% savings going from 5 characters down to 4. :-//
-
Even the big brands fail, such as Nokia. :palm:
-
That's neither a fail of a big brand nor a fail of an innocent wall wart.
That's a failure to use your common sense and candiate for a darwin award.
-
Agreed - I believe it is a fake.
No, I don't think that's a fake. A fake would just use a couple of bits of wire, tack soldered between the pins and PCB. They wouldn't use engineered contact strips like that.
-
These two prong US connectors always gives me the shivers.
Whole debates about safety and companies spending $$ for proper testing, but apparently these two prong "connectors" are being considered safe?
:-// :palm:
-
Agreed - I believe it is a fake.
si
No, I don't think that's a fake. A fake would just use a couple of bits of wire, tack soldered between the pins and PCB. They wouldn't use engineered contact strips like that.
And in what way would that be inferior to the existing design, which is just asking for intermittent connections?
-
This failure mode is well known. Something very similar affected Apple back in 2008, causing Apple to recall all those chargers and replalce them with a redesigned version where the prongs, and the back plate of the charger, are anchored in an incredibly thick piece of plastic.
Teardown of redesigned charger: http://www.righto.com/2012/05/apple-iphone-charger-teardown-quality.html (http://www.righto.com/2012/05/apple-iphone-charger-teardown-quality.html)
Original design that got recalled: http://www.iphonehacks.com/2008/10/recall-details.html (http://www.iphonehacks.com/2008/10/recall-details.html)
Dave did a teardown of some fakes here, and IIRC mentions this failure mode, based on how easy it was to get inside: https://youtu.be/wi-b9k-0KfE (https://youtu.be/wi-b9k-0KfE)
-
Probably not a fake, just cheap, I have samsung ones that are very similar.
-
Agreed - I believe it is a fake.
si
No, I don't think that's a fake. A fake would just use a couple of bits of wire, tack soldered between the pins and PCB. They wouldn't use engineered contact strips like that.
And in what way would that be inferior to the existing design, which is just asking for intermittent connections?
Well...
1. You've no idea what those thin single insulated wires are going to end up pressing against once they clip the case together, but Sod's law says greater than 50% of the time it will be something on the secondary side.
2. From examples I've seen (I've seen some really crap ones) the soldering is poor at best, with no mechanical restraint - what happens if one of the ends breaks loose as the case is closed or afterwards?
Properly designed spring contacts should make a perfectly predictable contact with the mating pads on the PCB, you'd expect a genuine manufacturer to get that right.
Anyway, all I'm saying is that a fake manufacturer wouldn't have gone to the trouble.
-
Agreed - I believe it is a fake.
si
No, I don't think that's a fake. A fake would just use a couple of bits of wire, tack soldered between the pins and PCB. They wouldn't use engineered contact strips like that.
And in what way would that be inferior to the existing design, which is just asking for intermittent connections?
Well...
1. You've no idea what those thin single insulated wires are going to end up pressing against once they clip the case together, but Sod's law says greater than 50% of the time it will be something on the secondary side.
2. From examples I've seen (I've seen some really crap ones) the soldering is poor at best, with no mechanical restraint - what happens if one of the ends breaks loose as the case is closed or afterwards?
Properly designed spring contacts should make a perfectly predictable contact with the mating pads on the PCB, you'd expect a genuine manufacturer to get that right.
Anyway, all Im saying is that a fake manufacturer wouldn't have gone to the trouble.
The soldered wires need not be thin, & can be properly secured & insulated..
Over many years, I ran into stuff made by genuine manufacturers, where, over time, spring contacts have lost their tension & the contact has become far from predictable".
The fix is usually a "bodge" using soldered wires & good insulation.
Still messy, but reliable!
-
That's neither a fail of a big brand nor a fail of an innocent wall wart.
That's a failure to use your common sense and candiate for a darwin award.
In an attempt to develop some "common sense" perhaps you could explain where common sense failed. Choosing to use electrical power far from a wall? Going barefoot? Assuming that a device was suitable for use? Or something else totally outside the ken of a genetic defect like myself?
Don't worry about the Darwin award, it is already too late. I have already passed the bad genetics on.
-
board slides in from top, slots into contacts molded into plastic.
-
That's neither a fail of a big brand nor a fail of an innocent wall wart.
That's a failure to use your common sense and candiate for a darwin award.
In an attempt to develop some "common sense" perhaps you could explain where common sense failed. Choosing to use electrical power far from a wall? Going barefoot? Assuming that a device was suitable for use? Or something else totally outside the ken of a genetic defect like myself?
Don't worry about the Darwin award, it is already too late. I have already passed the bad genetics on.
My common sense wouldn't plug a wall wart into a floor mounted outlet. A common wall wart isn't as solid as a simple mains plug, I wouldn't expect such a thing to survive beeing kicked. The prongs make up a strong leverage with the housing, simply made to break the housing in case someone applies some force to a plugged-in wall wart.
I don't know the physical layout of your floor mounted power outlet, but I do consider anything (no matter if it is electric or not) that is plugged into the floor as dangerous, as someone could stumble or fall over, or hurt his/her toes. We've got floor mounted outlets sometimes here in a large conference room or a hall, they are recessed into the floor and have a cover, hiding the plugs so one cannot kick them.
So what I wanted to say: Plugging a non-solid object into the floor just asks for accidentally breaking this object, so just avoid doing so and don't blame the object. Sorry for the darwin award, didn't want to insult anyone.
-
The soldered wires need not be thin, & can be properly secured & insulated..
Oh sure, they can be, certainly. It's just not representative of the generic and fake stuff coming out of China.