Say, there's a laptop with USB-C port, its specs don't mention support for USB Power Delivery, but some pages on the Internet say that a laptop may support USB charging even when it isn't specified. Would it be safe to try it out by inserting USB-C charger taken from another laptop or it may damage the laptop?
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4 Answers
It's perfectly safe to do it since the USB-C Specification does take this into account. This snippet from the spec clearly describes it:
What this essentially means is that unless there is a DFP-UFP attach detected, VBUS will remain at 0V.
Since in this case, the charger and the port on your laptop both pull the CC ( Configuration Channel ) pin to HIGH via a pull-up resistor, there will be no DFP-UFP attach detected and thus no current would pass through VBUS.
Ref: What happens when you attach two USB C host ports together
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I'm not so sure both the charger and the device respect USB-C specs. Also, what if the charger is a USB power-bank? And/or you're attaching the charger via a USB-A -> USB-C cable? These scenarios would seem even less safe.– usretcCommented Mar 7 at 7:22
There are several considerations.
Is the laptop's USB-C port designed as just a host port or for charging the laptop. If it's only a host post, you won't be able to charge the laptop at all through it, because it would lack the circuitry to use the power to charge the battery.
A host-only port is designed to handle the same voltage as a USB charger provides. But the voltage provided internally by the battery won't exactly match the voltage from the charger applied to what is supposed to be the port's output. The voltage difference could create problems if the laptop wasn't designed to expect external voltage applied to the port. So I'm not sure whether there might be actual risks from plugging a charger into it, but I wouldn't bet the laptop on it.
The laptop specs should tell you whether it is designed to be charged through the USB port. If it is, it is safe to plug in the charger. If it doesn't say it can be charged through that port, there is no reason to assume it might work, and no reason to take any risks trying.
If the port is designed to allow charging the laptop, power delivery is a separate consideration. That affects how fast you can charge it. A standard USB connection has limited current available, and charging a laptop could take some time.
The PD spec defines higher available currents and higher available voltages, which would charge the laptop much faster. However, it requires compliant ports at both ends, and handshaking to set the power mode that will be used. If the laptop's port isn't designed for USB-PD, that handshaking can't occur, and only standard USB power would be available from the charger. So if the laptop can charge from the USB port but doesn't support USB-PD, a USB-PD charger would be just like any other USB charger -- it wouldn't provide any special fast charging benefits and wouldn't be any more risky to the laptop.
answered Aug 1, 2019 at 21:28
USB C charging requires the port to be able to accept input current and route it to the charging functions of the computer.
If the computer does not support this function it lacks the hardware to handle this input current, and therefore applying such current will damage the components.
Whether design decisions result in the computer having the necessary equipment to support these features is not something we can answer here.
answered Aug 1, 2019 at 21:15
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1USB-C power supplies will not supply power until they negotiate a power contract, and for that to happen the attached device must indicate this using USB-PD. That is assuming the USB-C power supply follows the spec, I've see some very out of spec uses of USB-C. Buy quality gear from reputable sources and that should remove fears of damaging hardware in normal use. Commented Dec 1, 2021 at 5:50
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USB power delivery is a specific charging standard, but not the only one used by USB-C connectors or devices that can charge over USB-C. It's probably the most common, but it isn't the only. Commented Dec 2, 2021 at 5:07
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1The USB-C spec requires that no power flows until there is an indication that the connected device asked for it. This can be by USB-PD, USB-BC, resistors to indicate a legacy adapter was connected, or some third party protocol. This is not specific to USB-PD but it does apply to USB-C at all times. So, yes, there's more than one way to ask for power. My earlier point is your answer is misleading and unclear. Applying power to USB-C ports not built for it would be bad but that's not going to happen unless someone is using an out of spec USB-C charger. Commented Dec 2, 2021 at 6:01
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The information contained in my answer is not misleading or incorrect. It is not complete either, but it references directly the specific question asked by the person asking. Further, there are a plethora of devices that use the USB-C connector type and do not abide by its standards and rules. My answer is applicable in those cases. OP didn't specify they were using compliant chargers, and the other information in their question indicates they were connecting something that might not be designed to be connected anyway, making my answer even more applicable. Commented Dec 3, 2021 at 22:18
I'd like to chip in 4 years later.
USB-C takes into consideration that the device may not accept power.
Does this mean it is safe?
Probably.
Should you?
Probably not. You can never know if someone went cheap on something like this.
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As it’s currently written, your answer is unclear. Please edit to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers in the help center.– Community BotCommented Jul 10, 2023 at 8:03