PM02 current reading seems too low – only ~4.4A with four motors running

ArduCopter Copter 4.6
1

Hi,

I am using a Pixhawk 6C with ArduCopter 4.6.3, and I am trying to verify the battery current measurement from my PM02 power module.

My setup is:

  • Pixhawk 6C
  • ArduCopter 4.6.3
  • PM02 analog power module
  • 4S LiPo battery
  • Four 2814 motors
  • Four individual ESCs
  • Motors connected to outputs 9–12
  • Battery → PM02 → power distribution/ESCs
  • PM02 connected to the POWER port of the Pixhawk

According to the specifications of my PM02:

  • Voltage Divider: 18.182
  • Amperes per Volt: 36.364
  • Maximum current sensing: 120 A
  • Continuous current rating: 60 A

In Mission Planner I currently have approximately:

  • Voltage Divider: 18.18
  • Amperes per Volt: 36.36

The voltage measurement appears reasonable. For example, the DataFlash log shows the 4S battery at approximately 16.5 V, with voltage dropping under motor load.

However, the current measurement seems unusually low.

During a test with all four motors running with propellers installed, the DataFlash log shows BAT.Curr increasing with motor output, but the maximum recorded current is only approximately 4.4 A.

The current response itself seems to work. For example, different motor-output levels produce clear changes in BAT.Curr, and battery voltage also drops when the motors are running. However, the absolute current value seems much lower than I expected for four 2814 motors with propellers.

I initially thought this might be an issue with my own MAVLink/Python logger, but I checked the Pixhawk’s onboard DataFlash log and found the same low current values. Therefore, the low reading is already present in BAT.Curr on the flight controller.

I have attached the .BIN DataFlash log. The relevant fields are:

  • BAT.Curr
  • BAT.Volt
  • RCOU.C9
  • RCOU.C10
  • RCOU.C11
  • RCOU.C12

Could someone please help me check whether the PM02/battery monitor configuration looks correct?

In particular, I would like to know:

  1. Is 36.364 A/V the correct current calibration value for this PM02?
  2. Is there any other battery-monitor parameter that could cause the current reading to be scaled too low?
  3. Does the DataFlash log suggest a current-sensor/calibration problem?
  4. Is there anything else I should check before assuming the PM02 current measurement is inaccurate?

Thank you!

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2

During the test, the quadcopter was secured on the ground and was not allowed to lift off. All four 2814 motors were running simultaneously with propellers installed. The motors were controlled using the RC transmitter rather than Mission Planner Motor Test.

The Pixhawk DataFlash log shows clear output on all four motor channels (RCOU.C9–RCOU.C12). However, even during the higher-output portions of the test, BAT.Curr only reached approximately 4.4 A.

3

The propellers are12*3.8

4

The .bin log file would be handy, it doesnt appear to be attached.
Check the power monitor settings under BATT and check the voltage and current pins. Maybe show all the BATT settings, and refer to this:

5

Fully charge your battery. Fly for 5 minutes. Check the log for the total amount of amps “consumed”. Charge the battery again and note the amps the charger returned to the battery. Then apply the formula:

If there’s a big difference between the old and new, you might want to repeat the process just to dial it in a bit better.

6

.bin file is needed