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Docs Power & Battery Power Measurement

Power Measurement

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How to measure the beacon's current draw in every mode with a multimeter, and the numbers you should see.

Power Measurement

“You think the beacon draws 50 mA” is not data. Measuring it takes five minutes with a multimeter and answers the questions that actually matter: is the sleep actually sleeping, is the radio efficient, and will the battery last the trip.

Measuring average current

The honest tool for average draw is a USB meter or a bench power supply with current readout. The quick approximation with a multimeter:

  1. Set the meter to mA DC.
  2. Put it in series with the battery positive lead.
  3. Run the beacon in each mode for 30 seconds and record the average.

The problem with peaks

The TX burst pulls 120 mA for a second. A multimeter’s averaging hides this and reads somewhere between sleep and TX. To see the true picture, log with a scope or a data logger, or compute the average from the duty cycle (see Battery Capacity Math).

Expected numbers

StateExpected current
Deep sleep (firmware default)0.02 - 0.15 mA
Idle, radio off20 - 30 mA
GPS acquiring+40 - 60 mA
RX listening+10 - 15 mA
TX burst (+22 dBm)110 - 140 mA

Red flags

ReadingProblem
Sleep current above 1 mABoard LED, regulator, or GPS left powered
TX current below 80 mAPower level setting wrong, or radio in a low-power state
Idle current above 60 mASomething is not sleeping: OLED backlight, GPS, WiFi
Current jumps randomlyBrownout protection cycling

The WiFi trap

A common mistake is leaving the ESP32’s WiFi or Bluetooth stack enabled. WiFi alone adds 80 - 160 mA whenever it is active. The beacon’s firmware keeps WiFi off in normal operation (see WiFi and Security).