N900 Hardware Power Consumption

This page contains information on the amount of energy used by each subsystem of the N900, and where applicable ways it can be reduced.

Much of any reduction will require additional software, some may be possible by altering user behaviour in ways that don't impact the users overall experience..

Measuring power usage is hard. For example - power consumption of the speakers/speaker-amp has to be disentangled from power consumption of reading a file from SD/emmc, decoding it, pulseaudios power use, and the DAC power use.

Below currents are from l3/l4 manual - assumed to be from a supply at 5V.

  • FMTX 19mA - l3/4
  • WLAN on - no powersave - 200mA
  • WLAN transmit 802.11b - 150mA

Battery parameters can be monitored thru fuel gauge asic TI BQ27200 [1]


Some preliminary numbers using bq27200.

These numbers are biased, and represent best cases. Some have had outliers which may be normal and unavoidable current spikes removed. This is under the assumption that the minimal power represents the minimum power achievable, and it should long-term be possible to - possibly with software patches - achieve these. +x indicates the measurement is for that element only. A raw measurement has no +, and is a total. Unless otherwise mentioned, numbers are for the idle locked case, with screen off.

  • Idle, no SIM, wlan off 7mA@4.1V
  • Wifi on with maximum powersaving. +~2mA
  • MMC card in. Under 1mA
  • Xchat running, sporadic traffic. +8mA
  • Screen on, no backlight. +80mA
  • Backlight on max +150mA
  • Media player playing mp3, one step above mute. 110mA
  • md5sum /dev/zero 250mA
  • md5sum /dev/mmcblk1p1 - 1G SD card. 240mA
  • md5sum /dev/mmcblk0 - internal MMC 240mA (these indicate the CPU is somewhat idle, waiting on IO, and this counteracts any increased power use by the memory)
  • camera active, showing preview. (backlight off) 210ma
  • GPS - location test gui - in continuous GPS recieve mode - +50-80mA
  • 3G connected, good signal, no data or other activity +8mA.
  • 2G connected, good signal, no data or other activity +5mA

2G data, short pings

  • 1s ping 130ma
  • 10s ping 70ma
  • 30s ping 45

3.5G data, short pings

  • 1s 186ma
  • 10s 120ma approx
  • 30s 136ma

3.5g data, long pings (8000 bytes)

  • 1s 240
  • 10s 205
  • 30s 120

2G data, long pings (8000 bytes) (with specified seconds between pings)

  • 1s 160
  • 10s 105
  • 30s 50ma

3G sending file at 150k/s 375ma 3G recieving at 200k/s 275mA