Author Topic: DANGEROUS chinese stuff  (Read 9466 times)
High Intensity
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Re: DANGEROUS chinese stuff « Reply #45 on: July 03, 2020, 07:10:31 PM » Author: High Intensity
My sister just got a new pair of wireless earbuds and the 12" micro USB cable it came with was internally shorted. There's no visible damage to the cable, so it's likely a factory defect.

When she plugged it into her laptop, her laptop immediately shut off.
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Binarix128
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Re: DANGEROUS chinese stuff « Reply #46 on: July 03, 2020, 07:29:12 PM » Author: Binarix128
Do the laptops have an internal protection against short circuits? Seems like China wants our computers sleeping forever.  :P
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Re: DANGEROUS chinese stuff « Reply #47 on: July 03, 2020, 08:51:44 PM » Author: High Intensity
Do the laptops have an internal protection against short circuits? Seems like China wants our computers sleeping forever.  :P
I'm guessing the current draw of the short circuit caused either the 5V buck converter or the batteries OCP (Over Current Protection) to trip and shut the PC off.
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takemorepills
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Re: DANGEROUS chinese stuff « Reply #48 on: July 03, 2020, 09:09:33 PM » Author: takemorepills
In many laptops, the USB system is not just for external devices, but for internal devices also.
For Windows PCs, look in the "hardware manager" and expand the USB tree, there will be many internal devices listed as connected via USB.
If you hard short the USB data or power, the PC can definitely shut down or crash immediately.
Some higher end PCs may have isolated USB, but many won't. The +5V on the USB line may also power other mobo devices, depending on PSU config.
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Ash
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Re: DANGEROUS chinese stuff « Reply #49 on: July 04, 2020, 12:12:29 AM » Author: Ash
In some PCs the USB +5V is protected by a Polyswitch and would "trip" in case of a short to Ground. Not all of them, in some the manufacturers saved on the part and either soldered in 0R resistors (that might or might not blow), or hardwired it to +5VS (capable of delivering 3A+) or even +5V (capable of delivering 20A+). Sometimes through a mosfet for switching the power off when the PC is in sleep, but this mosfet probably won't do anything except burning out into a shorted state if it gets an overload

In laptops and some desktops with "12V only" power supplies the USB is powered from a buck converter on the board. Most such converters do have _some_ internal protection in the control chip (probably one with integrated mosfet), but it might be way above any safe limits for other components

In both cases, a thin cable with a short in the far end from the computer, is in risk of becoming a continuously running heating element

USB chipsets are by design not meant to withstand a sort between +5V and D+ or D-. It is stated in the official specs. Shorting 5V to any of them can burn the chipset (so the mainboard)
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High Intensity
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Re: DANGEROUS chinese stuff « Reply #50 on: July 13, 2020, 08:08:54 AM » Author: High Intensity
I just picked up a pair of wireless earbuds for myself when i'm working on projects (it's more enjoyable to work on stuff with music in the background) and the USB charging cable it came with is identical to the one my sister got (despite getting different brands), though unlike hers, mine says it has built-in 'short circuit protection', it also says not to use other micro USB cables as they could 'overheat and damage the product'. But i think i'll replace the cable anyway as i don't want to risk damaging anything with this cable.
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Re: DANGEROUS chinese stuff « Reply #51 on: July 13, 2020, 08:25:39 AM » Author: Medved
I just picked up a pair of wireless earbuds for myself when i'm working on projects (it's more enjoyable to work on stuff with music in the background) and the USB charging cable it came with is identical to the one my sister got (despite getting different brands), though unlike hers, mine says it has built-in 'short circuit protection', it also says not to use other micro USB cables as they could 'overheat and damage the product'. But i think i'll replace the cable anyway as i don't want to risk damaging anything with this cable.


The earbud internal charger design may count on the cable resistance (the "short circuit protection" is very likely just the conductors being resistive an in that way limit the current; a feature you may get virtually for free when using metalized nylon strands or steel wires instead of copper conductors; these materials are often used on telephone handset cords, there because if their inherent fatigue robustness and low cost), so once you replace the cable for something else, the charger IC within the earbuds may overheat and fail, destroying the battery with it.
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Re: DANGEROUS chinese stuff « Reply #52 on: July 13, 2020, 09:00:09 AM » Author: High Intensity

The earbud internal charger design may count on the cable resistance (the "short circuit protection" is very likely just the conductors being resistive an in that way limit the current; a feature you may get virtually for free when using metalized nylon strands or steel wires instead of copper conductors; these materials are often used on telephone handset cords, there because if their inherent fatigue robustness and low cost), so once you replace the cable for something else, the charger IC within the earbuds may overheat and fail, destroying the battery with it.


I doubt that, for starters, the short cable length (12in or 24in from the to the device and back) seems too short for any meaningful amount of resistance to be added (unless the cable is the cheapest stuff possible), on top of that, no charging ic's i'm aware of need some sort of resistor in series with the input. I think the warning are more of a CYA thing so that they are not responsible for if the 3rd party cable damages anything (i've seen this kind of warning a few times, but very rarely does it hold any merit).
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Re: DANGEROUS chinese stuff « Reply #53 on: July 13, 2020, 09:52:28 AM » Author: Rommie
I don't like those in-ear things, (a) I find it hard to get them to stay in and (b) the wireless type I can see falling out and getting trodden on or lost altogether. I prefer my Beyer Dynamic DT100 cans, if they're good enough for radio studios, they're good enough for me ;D

Not only that, they're cheaper than the Apple earbud things  ::)
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Re: DANGEROUS chinese stuff « Reply #54 on: July 13, 2020, 01:01:37 PM » Author: Medved
I doubt that, for starters, the short cable length (12in or 24in from the to the device and back) seems too short for any meaningful amount of resistance to be added (unless the cable is the cheapest stuff possible),

All that is about 5..10 Ohm. And yes, the 30cm cable could well be designed to have that resistance. And yes, it starts as an intention to make the cable as cheap as possible, yet as robust as possible. Those phone cords use to have 10..50 Ohm/m (with 50cm length and a 50 or 100ohm speaker and microphone such resistance is no problem), but I've never seen any broken yet (speaking about cord from 30+ years old heavily used office phones). It is made as nylon wires coated with some metal (nickel alloy?). It is lightweight, resistant against cracking from all the pulling and tangling, yet cheap to make.


on top of that, no charging ic's i'm aware of need some sort of resistor in series with the input. I think the warning are more of a CYA thing so that they are not responsible for if the 3rd party cable damages anything (i've seen this kind of warning a few times, but very rarely does it hold any merit).

Practically all the sot23-5 ones. The point is, when the adapter voltage is 5.3V, battery voltage 3.5V, the small sot23 can dissipate barely 100mW, so leading to barely 55mA of charging current (average) when there is nothing else to drop the voltage (the current is limited by the charger ic chip reaching its maximum temperature). It is not problem for the chip itself (it is explicitely designed to work that way), but it makes the small PCB of the earbud electronic hot, now because of the space constraints the batterygets exposed to that heat and that becomes the problem.

If you add an extra resistor in series with the input, the IC just turns its regulating transistor completely ON (because the circuit current does not reach the value programmed to the chip by its external components), having very small voltage drop, so dissipating very little heat. All the voltage drop, so power dissipation, is then pushed away to the extra resistor in series with the input. This way the charging current may become way higher, so allowing faster charging, while stressing all the miniature assembly by way less heat. And because having the cable resistive means having a cheap, mechanically robust cable plus a resistor for free, allowing to make the electronic smaller and tighter crammed with the battery so cheaper earbuds alone, I would be very surprized the earbud electronic designers wouldn't choose that concept.
By the way this trick with the external resistance (even mentioning explicitely the cable resistance) is described in all datasheets (better to say the application note section) of such linear regulated charger IC's I've seen... if you calculate it, with charging current starting at 200mA (at 2.7V on the battery) and 5.5V adapter voltage, you need barely 12 Ohm to keep the IC power dissipation at 80mW, not that difficult to have that within the cable. The nearly 0.5W is tyen easy to dissipate over the cable length...
« Last Edit: July 13, 2020, 01:12:02 PM by Medved » Logged

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Re: DANGEROUS chinese stuff « Reply #55 on: July 13, 2020, 03:31:32 PM » Author: Ash
What happens if you place a dead short across the end of such cable ?

5W over 12 inch of 3mm outer diameter PVC cable that would be quite hot. If the resistance is also non uniform (microcracks in the metallization in the places where the cable had been bent the most times) you are up to some fire, without ever pushing the "1A" USB adapter to go to current limiting mode...
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Re: DANGEROUS chinese stuff « Reply #56 on: July 13, 2020, 05:29:32 PM » Author: Medved
What happens if you place a dead short across the end of such cable ?

5W over 12 inch of 3mm outer diameter PVC cable that would be quite hot. If the resistance is also non uniform (microcracks in the metallization in the places where the cable had been bent the most times) you are up to some fire, without ever pushing the "1A" USB adapter to go to current limiting mode...

The metalized nylon just melts the nylon core, without its support the conductive layer breaks so interrupts the current. But that would need quite a long time overheat. But I doubt it would ever go that far, except as a really last resort, e.g. when the cable cooling is compromised (burried in pillows,...) or when the cause was internal short in the cable (so the cable was dead anyway). So at such ELV quite fail safe by itself.

Normal "USB chargers" start to shut down (start to cycle with very low duty ratio; or plain drop the current to few 10's of mA) when the output voltage drops below 3V. So below few ohms, it would be the power supply unit, which will limit the load.
With higher resistance the power supply wont shut down, but the power dissipation will be limited by the cable resistance. But dont forget, the outer thickness matches the rated current, so the resistance. Dissipating 3W on a 50cm long and more than 5mm diameter cable would mean it will get warm, but not dangerously hot. The thinner cables usually have lower current ratings, so higher resistance.

Plus a hard short within a powered device is very unusual, mostly such short is within the damaged cable (its connector,...), so if that causes overheat and consequent conductor interruption, no big deal anymore, as the cable was already bad in the first place.


Generally way greater risk I would see the battery regularly exposed to the high temperature, e.g. from the charger ic, eventually "going wild"...
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Re: DANGEROUS chinese stuff « Reply #57 on: July 13, 2020, 08:14:18 PM » Author: High Intensity
I did a resistance test on the cable to know for sure and:
Positive wire: <0.2Ω
Negative wire: ~1.5Ω
Total Resistance: ~1.6Ω to 1.7Ω

Now the higher resistance could be inaccurate for a few reasons, as it could have been contact resistance from the cheap plugs. Or it could also be something like a fusible resistor in the plug.

I also did a test on a normal 3ft micro USB cable and it came out as <.2Ω per wire.
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takemorepills
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Re: DANGEROUS chinese stuff « Reply #58 on: July 13, 2020, 08:51:18 PM » Author: takemorepills
I don't like those in-ear things, (a) I find it hard to get them to stay in and (b) the wireless type I can see falling out and getting trodden on or lost altogether. I prefer my Beyer Dynamic DT100 cans, if they're good enough for radio studios, they're good enough for me ;D

Not only that, they're cheaper than the Apple earbud things  ::)
Generally, I use Sennheiser or Audio Technica headphones.
However, I bought the Samsung Buds+ recently, for very good reasons:
-I'm old and now need glasses, headphones and glasses are uncomfortable
-When I'm at work I need to wear a head sock to protect my white boy skin from the sun, but I want tunes at the same time (I work on traffic signals)
-The Samsungs have an ambient aware function that allows outside sounds to be heard when the buds are in, it is adjustable on my smartphone, I can have total noise cancelling or 3 levels of ambient sound. Helps me to hear someone who may want to attack me or a car sneaking up on me.
-I considered Apple, but they are only in white and I hate Apple products.

Best of all, NOT MADE IN CHINA!
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Binarix128
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Re: DANGEROUS chinese stuff « Reply #59 on: July 13, 2020, 09:20:44 PM » Author: Binarix128
A bit out off-topic, but the resistance of the chinese xmas light cords is about 20 to 50 ohms, that's HUGE. If the cord shorts out internally all will melt in fire and set your house in fire before the breaker pops.
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