The power circuit on the new Raspberry Pi B+ has been completely redesigned. It now has an efficient switching regulator. So I decided to take my trusty emeter, a tool I spent far too much money on a few years ago whilst in the grip of the aero-modelling ‘bug’, and make some measurements.
I measured the current and voltage going into the Raspberry Pi. The emeter has a calibrated shunt (small blue rectange in the photo with ‘battery’ and ‘load’ at each end) that’s good for up to 20 Amps. This is a way of measuring without disturbing the circuit. (It measures the voltage drop across a fairly low-value resistor.)
I did these measurements on both a late rev 2 model B and the new B+. Both were measured with just a wireless keyboard dongle AND with both keyboard dongle and Edimax wifi dongle (which uses an additional 40-50 mA).
The results are in the video, which also shows hot-swapping a wifi dongle without the Pi rebooting…
Here are the numerical results as well as a couple of extras (Watts = Volts x Amps)…
Just Keyboard Dongle
B: 4.98 V, 0.38 A, 1.89 Watts
B+: 5.03 V, 0.24 A, 1.21 Watts
Keyboard Dongle + Edimax Wifi Dongle
B: 4.98 V, 0.43 A, 2.14 Watts
B+: 5.02 V, 0.28 A, 1.41 Watts
Some B+ Only Measurements
With Camera Module Attached
Idling: 5.12 V, 0.21 A = 1.07 Watts (done at different time from above, so slight drift accounts for difference in baseline value)
Shooting video: 5.07 V, 0.27-0.33 A = 1.37 – 1.67 Watts
This was interesting because the camera clearly and repeatably used more power when pointed at a bright light than something darker. I could make it go from 0.27 A to 0.33 A at will. So if you’re using the camera in very bright conditions, you might find it uses a bit more power.
With the USB/LAN Chip Disabled:
5.09 V and 0.15 A = 0.76 W
In a Shutdown State
5.23 V, 0.05 Amps = 0.26 Watts
So we can see that the new Raspberry Pi B+ uses 1.21 Watts with just a keyboard dongle vs 1.89 Watts for the old model B. The difference, 0.68 Watts might not sound like a lot, but it’s 36% less power usage. This great if you’re running on batteries, or have a barely adequate solar panel.