Quick question on USB power

BUDFORCE · 3 Dec 2021 at 15:07

I wasnt 100% sure where to post this, this seems the most appropriate.

Do PC usb ports have appropriate surge protection?

Basically, the reason I ask is I want to make a DIY made device, basically something that spins a motor, powered by 5v DC USB output of a PC. If for some reason, the motor fails, or shorts etc, is there any chance a VERY cheap electric motor could damage a pretty expensive PC?

Or even more basic, if you take the DC output on of a PC USB port, and short it, what happens?

Armageus · 3 Dec 2021 at 15:24

Afaik they are protected via resettable polyfuses

Some examples of poly fuses on recent(ish) motherboards are pictured in the following link:
https://electronics.stackexchange.c...uses-protect-usb-ports-in-a-typical-modern-pc

Syore · 3 Dec 2021 at 15:30

If you short it, your PC will either shutdown or hang then shutdown. If your plugging in DC motors makes sure it has a soft start on it as the high inrush current could trip the fuse built-in the motherboard or the sensor in the PSU.

Mr Evil · 3 Dec 2021 at 18:55

Polyfuses will prevent damage, but they don't reset reliably; if you subject a USB port to repeated overloads, you may find that it ends up in a permanent high-impedance state.

BUDFORCE · 4 Dec 2021 at 09:02

Ok thanks guys.

Donnie Fisher · 5 Dec 2021 at 10:32

It is possible to fry a PC via the usb port. It was demonstrated on LTT a while back. Basically the USB stick sent a massive pulse back into the PC and fried it, killing the board instantly.

If you're worried, then spend a few pounds on a cheap powered USB hub that can a) supply lots of power down a port, b) take the hit if the motor does fail