General > General Technical Chat
Charging Cell phone form a 9V battery
madires:
Hack the charger: https://www.zdnet.com/article/badpower-attack-corrupts-fast-chargers-to-melt-or-set-your-device-on-fire/ >:D
tom66:
--- Quote from: NiHaoMike on July 20, 2020, 10:09:32 pm ---
--- Quote from: tom66 on July 20, 2020, 07:11:47 pm ---A friend of mine had one of these cheap switchers fail and test the OVP circuit on his phone. It had 13.8V on the USB output. Thankfully most modern phones have these protection ICs and it simply refused to charge ("Charger Not Compatible With This Device"), but I can imagine some devices could easily be damaged.
--- End quote ---
And now the various fast charge standards intentionally boost the voltage when requested by the device. How long before some cheap charger comes out with a bug that causes it to raise the voltage on something other than the proper command? Might the USB standards get amended to require devices to survive up to 20V to cover that scenario?
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The protocol is alarmingly simple for Qualcomm Quick Charge as well. You just have to pull D+ and D- down separately within a certain time window, and you can get the full 20V. There's no negotiation or communication, and cheap chargers omit the discharge circuitry which can keep the 20V output active for some time, potentially damaging a new device. It is all a bit dodgy in my opinion.
james_s:
I've never been a fan of using USB strictly for power, and these various nonstandard USB implementations to transfer more power are doubly stupid. If they want to use higher voltages they should have used a different connector.
richard.cs:
--- Quote from: NiHaoMike on July 20, 2020, 01:13:24 pm ---Haven't seen one that bad in a very long time, even the really cheap ones use switchers nowadays.
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I have seen poundland ones (think dollar store) with a 78L05 in them - it's generally enough to make the phone indicate it's charging but not to deliver much energy, they normally provide 200 mA before the current limit kicks in, and then the thermal shutdown is triggered in a minute or so. This is more in the "fake charger" category really.
tooki:
--- Quote from: james_s on July 21, 2020, 08:12:05 am ---I've never been a fan of using USB strictly for power, and these various nonstandard USB implementations to transfer more power are doubly stupid. If they want to use higher voltages they should have used a different connector.
--- End quote ---
In fairness, the USB-IF pretty much did, in that USB-PD requires USB 3. Whether with Type-A/B or Type-C, it's a new connector type.
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