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What happens when you draw too much current from a usb port?
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chrisb741:
Hi,

What happens when you draw too much current from a usb port
I've heard reports from people having issues with their development boards when they connect high powered things like relay, servo or a motor up to their board when its powered by a PC/laptop usb port.
I tried to replicate this with a bench power supply set to 5V and 500mA. Unless I connect up significantly more devices I dont seem to have a problem.

What exactly is happening?

It seems that the usb supply from the computer is significantly more sensitive to oversupply or current and will momentarily cut all power much faster when too much current is supplied. Is this what happens? 
Andy Chee:
Current limiting is part of the USB specification.

I don't know the specific document, but I'm sure someone here does!

https://www.usb.org/documents
jpanhalt:
According to this, they are supposed to be "protected from shorts."  That doesn't mean the port you are dealing with meets that specification.

https://electronics.stackexchange.com/questions/541851/can-a-short-circuit-kill-the-usb-port-of-a-pc
amyk:
You can look at some typical mobo schematics and see for yourself:

https://www.eevblog.com/forum/projects/simplest-way-to-get-500ma-out-of-usb/msg4970242/#msg4970242
nctnico:
There are several options for implementers. Gradually lowering the voltage is one of the methods
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