Hacker News Reader

Comment by kephra | Hacker News Reader

It will work fine in 95% of the cases, but 5% will ruin their computer USB port, because the PI is not within the specs. The PI not only draws 750mA (old) or 600mA (new) when idle, but much more, if you attach SSD, and USB devices.

The ramshackle micro USB port is a nogo for me.

View on HN

You don't have to power it from the USB port. You can supply juice to the 5V and GND pins on the GPIO header. That's probably a better power inlet interface than either a ramshackle micro USB connection or a janky barrel plug.

reread the usb spec. it will not ruin the USB port.

I'm not aware of any spec requirements for overcurrent protection on the host ports (devices have strict power behavior per spec), though they may be there.

I am aware, however, of countless USB host designs that simply put a 5v regulator rail on the power line and could probably be induced to overheat by a misbehaving device.

It's definitely in the USB 1.1 spec, (with some verbiage that excessive current draw on one port is not allowed to affect other ports) though they may have relaxed it later. I have several old Belkin hubs that will terminate (with prejudice) power to any port that draws over 550 mA, until you physically power-cycle the hub. This is annoying for obvious reasons, especially on 7-port hubs with beefy power supplies, so most hub manufacturers don't do that anymore.

What the pi should do is monitor the voltage level of port it is drawing from, if it draws it down, it should turn on a fault LED or disable onboard services (like ethernet and usb).

Some really old computers have physical fuses on the USB ports that can - and will - blow if you draw too much power from them.

Should probably upgrade, then, before spending more money on Raspberry Pis.

Reply on news.ycombinator.com