Wi-Fi with Raspberry Pi -- battery powered

[hhu]

Hi,

I want to use a Raspberry Pi with a Wi-Fi dongle for a relatively reliable, portable use. Getting a battery pack for the Pi is not a problem. I do, however, need to power the Wi-Fi dongle plus a USB GPS receiver with a powered USB hub because plugging the dongle directly into the Pi seems to be flakely for power. Any suggestions for a battery pack that can power both the hub and the Pi? The hub I'm using wants an input of 5V, 3A. Since the USB port in the back of the hub needs to connect to the Pi, I'm left with the DC input in the back for power.

Thanks!

[adafruit_support_mike]

You can probably get away with something less than a full 3A power supply.

The RasPi has a fairly tight onboard power budget. You can get up to about 800mA through polyfuse F3 (just past the MicroUSB jack on the underside of the PCB) before it trips and cuts off power. The CPU uses about 350mA when idle, and the onboard USB hub is limited to 140mA.

Wifi dongles usually want 150mA-200mA because in radio, more power is better. It isn't a sharp cutoff though, so the performance curve is something like:

- 150mA to 175mA: tolerable
- 175mA to 200mA: reasonable
- 200mA to 250mA: great

So you may only be using about 1A overall, but the RasPi's limits are keeping the current from getting where it needs to go.

For starters, try hooking everything up to a good wall-based power supply and an ammeter. See how much power the system is using overall, then look for a power supply in that range.