Safety of high power USB with low power devices

[onlyconnect]

I have generally assumed that USB power is always safe even if it is high wattage Thunderbolt or USB-C that can power a laptop, into a low power device like an earbud case.

I have seen some devices come with warnings though and I am wondering if this is no longer the case. Perhaps depends on careful implementation on the device side?

By "safety" I mean more the concern about frying the low power device rather than smoke.

Is it always safe in practice?

 

[gavreid]

USB4 certainly ramps up the power. I don't remember the spec but 100W or thereabouts

 

[Darth Vader]

USB C is just a plug/socket spec as is USB A and B. You can interconnect B and C devices using a cable.

USB spec is for 5 Volts and the amount of current available depends on the circuit design and usually around half an amp max. External USB power will often provide much more current than a PC.

However with USB4 there seems to be different implementations so its best to read the spec for your actual device. My USB4 interface (a tiny desktop PC) will provide 5V at 3A so 15W max power also DP audio and video and an xfer speed of 40Gbps. As mentioned above some implementations can provide more power and may also be used to power the computer from an external power supply such as laptops.

Its the Voltage that is important when considering the possibility of damage so don't use a fast charger on a basic USB device unless its specifically stated that its auto configurable and safe to do so.

I find something like this is useful as not only can you measure the voltage from the USB but also the current draw. Aideepen USB Tester Voltmeter USB Multimeter Voltage Tester Voltage Current Tester USB Power Meter, Color Display Voltmeter Ammeter Voltage Current Meter 0-5.1A 4-30V : Amazon.co.uk: DIY & Tools


DV

 

[davidsrsb]

Hmm, 5A at 48V is the maximum that can be negotiated in USB4.

 

[onlyconnect]

Its the Voltage that is important when considering the possibility of damage so don't use a fast charger on a basic USB device unless its specifically stated that its auto configurable and safe to do so.

That seems to be the key point, thanks.

Tim