[CentOS] Off-Topic: Travel Router and Firewall

Wed Nov 23 23:15:58 UTC 2016
Warren Young <warren at etr-usa.com>

On Nov 23, 2016, at 3:40 PM, John R Pierce <pierce at hogranch.com> wrote:
> On 11/23/2016 2:24 PM, Leon Fauster wrote:
>> DIY based onhttp://www.pcengines.ch/  hardware ...
> ...tis not suitable for USB power (5V, up to 2.5 amp)

I think you mean 2.5 *watts* not amps.  USB 2.0 and below are 500 mA @ 5 Vdc max == 2.5W.  There are nonstandard extensions to USB to allow 2+ amps, but you can’t expect to get that from generic USB ports.

USB 3 Type C fixes this, but I don’t think that helps the OP.

> unless you rig up a USB to 12V DC-DC converter.

Increasing the voltage decreases the current.  TANSTAAFL.

With typical conversion losses, you could only expect to get about 170 mA out of USB when boosted to 12V.

Incidentally, the Raspberry Pi is only USB-powered in the sense that the base board will usually run fine from a PC USB port.  Add a couple of wifi radios and an Ethernet adapter, and you may exceed the 500 mA limit.  The Pi is also famously intolerant of power rail sags and such.

It’s best to think of the Pi as a device that just happens to have a micro USB power connector on it, but which is still wall-powered.

> I do wonder how the OP plans on connecting his phone and/or tablet via ethernet to this.

It can be done:


I assume there are equivalent methods on Android.

> the router would need TWO wifi adapters.

Yes, that’s a much simpler option, inherent in a proper travel router, another reason to avoid hacking something up with a Pi.  The problem’s already been solved, and solved well.