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Bad USB-C cable destroys laptop

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Re: Bad USB-C cable destroys laptop

#71

Post by klodolph »

andrey-g wrote: post #20
krapht wrote: post #17

Earlier quoted context omitted.

Why would you design in reverse polarity protection? It adds cost, and the mechanical connector already makes it impossible for VDD to short to GND in USB type C because of its rotational symmetry.

I constantly have Vdd shorts due to ground loops when measuring stuff. But a more frequent case is worn out cables (every lightning cable I've owned has eventually broke). Its not rare enough of a failure mode to ignore.

Shorts and polarity reversal aren't the same thing, and the protection circuitry is different.

Re: Bad USB-C cable destroys laptop

#72

Post by klodolph »

mindslight wrote: post #19
guan wrote: post #11

Reverse polarity protection is often not done with diodes for the reasons explained. It is more common to use a p-channel MOSFET (or ideal diode controllers when there are multiple power sources) when more than a trivial amount of power is used by the design. They are not cheap when properly sized, but are not ruinously expensive either and are not too large for most designs.

There should be a crowbar diode between the rails. If the design is too cheap for an input fuse, the source will limit/disable the short current.

Crowbar isn't a diode, and it doesn't protect against reversed polarity, and it's a bad idea on the input because you're relying on the other device to limit current properly, when it's the other device which got the voltage wrong in the first place.

Re: Bad USB-C cable destroys laptop

#73

Post by mindslight »

klodolph wrote: post #72
mindslight wrote: post #19

Earlier quoted context omitted.

There should be a crowbar diode between the rails. If the design is too cheap for an input fuse, the source will limit/disable the short current.

Crowbar isn't a diode, and it doesn't protect against reversed polarity, and it's a bad idea on the input because you're relying on the other device to limit current properly, when it's the other device which got the voltage wrong in the first place.

It acts like a literal crowbar, so why not call it a crowbar?

There are likely already plenty of diodes across the rails (the body diodes of the chips), so without a fuse the power is already limited by just the source. IMHO you might as well try and protect the circuit from foreseeable power-limited situations like frayed cables and the OP.

Re: Bad USB-C cable destroys laptop

#74

Post by gpvos »

Seems to be a kind of bait-and-switch operation, see this G+ comment by Lance Nanek: >>It's pretty common on amazon for some good items to be shipped to get some good ratings, then for the seller to replace them with cheap, almost non-functional, shoddy replacements. It's happened to me before with bicycle equipment (pushing the button on a rear light pushed right through the casing, etc.). So it's entirely possible you got a good one from their initial offering, then they started selling something else.

Re: Bad USB-C cable destroys laptop

#75

Post by coleca »

cocoflunchy wrote: post #58

Interesting that most of the reviews for Anker and Aukey products on Amazon have a variation of the same "I was provided with a free sample of this product in exchange for my unbiased professional review."

That seems to be the trend lately. Most of the reviews are polluted with this SPAM now. Amazon Vine is an AMZN sponsored program to enable this.

I had a similar issue with a lightning cable purchased on Amazon that claimed to be a licensed Apple cable, but wasn't. I plugged it into a real Apple charger, went to plug the other end into my iPhone and sparks flew out of it as soon as it got close to the phone.

Re: Bad USB-C cable destroys laptop

#76

Post by wmf »

qb45 wrote: post #69
scld wrote: post #61

I guess he learned that step 1 should be using the ohmmeter and step 2 should be plugging it into hundreds of dollars of equipment.

Do you really test each USB cable you buy like that?

We're talking about a guy whose job is to test USB cables.

Re: Bad USB-C cable destroys laptop

#77

Post by sedachv »

randyrand wrote: post #42
symmetricsaurus wrote: post #37

Killed a laptop when plugging in my phone (with the old 30 pin connector). Turns out a bit of foil from a wrapper had become stuck in the slot on the phone. Since this was in the bad old day the laptop was fixable for under $200 so it wasn't too bad. Still, makes sense to keep an eye on what you plug into your computer.

I recently fried my laptop (still worth $500 on ebay and was $1800 new...), from a cheap chinese pcie adapter. I would love to know where or how I could repair it for and how much.

You can find motherboards and other components on eBay. http://www.laptopinventory.com/ has a very good catalog and excellent how-to videos. I have done parts replacement on a few of my laptops (screens, keyboards, touchpads) and if you have ever added RAM to a laptop the process for the other components is not really any different.

Re: Bad USB-C cable destroys laptop

#78

Post by knughit »

teraflop wrote: post #46
digi_owl wrote: post #29

Earlier quoted context omitted.

Frankly the C plug spec seems overly convoluted. Each cable needs one of 3 resistors depending on them being a A/B-to-C cable, 1.5A C-to-C cable, or 3A C-to-C cable. Note that the A-to-C cable may well be able to carry 3A, but it shall never use the 3A C-to-C resistor (what many of the cables he find as faulty does). Note that all this resistor shenanigans are all independent of the Battery charging spec that has bee…

> Each cable needs one of 3 resistors depending on them being a A/B-to-C cable, 1.5A C-to-C cable, or 3A C-to-C cable. No, for C-to-C connections, the resistance is provided by the host ("downstream-facing") port, not the cable. The resistor in an A-to-C cable is basically emulating the signal that would otherwise be provided by the host. There's no such thing as a "1.5A C-to-C cable"; all type-C cables are required…

A world with smart cables is a dumb world. I want smart devices/adaptors and cheap dumb cables.

Re: Bad USB-C cable destroys laptop

#79

Post by dh997 »

krapht wrote: post #47
mikeash wrote: post #31

Earlier quoted context omitted.

If you stop the current from flowing, you don't have to shunt any power anywhere. You'd have to open the circuit in the face of 5V of potential hooked up backwards, not really a tall order.

I don't want to be a broken record, but you're right, not a tall order, but no it's unreasonable on account of cost. It's impossible for USB C to be hooked up backwards by its mechanical design, so why guard against it? The high-side transistor to prevent reverse polarity faults could be 3 to 4 cents in manufacturing cost! It's also not trivial to make sure that transistor trips fast enough to prevent all your low-vo…

Most likely cheap consumer devices wouldn't get it, but prosumer, enterprise and industrial gear should think twice about cutting corners on peripherial protection circuits and make sure to test vcc ground reversal and application to data pins... because commercial engineering boils down to risk management.

Re: Bad USB-C cable destroys laptop

#80

Post by knughit »

teraflop wrote: post #60
mikeash wrote: post #53

Earlier quoted context omitted.

Sure, but the magnitude of that cost matters a lot. You were saying a dollar or two in raw materials to protect against 100W, now you're saying three or four cents. A few cents to protect hundreds of dollars in equipment from electrical faults seems worthwhile to me.

That makes sense from the consumer's point of view. But imagine you're a manufacturer, producing USB device controller chips by the million. Would you really be willing to spend tens of thousands of dollars to protect against a failure mode that can only happen due to some other company's extreme negligence?

Tens of thousands of dollars total is far less than it costs a company just to moot the question.
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