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Voltage drop during flight

pixhawk2
battery
lowvoltage
quadcopter

(Sohaib Ahmed Jalali) #1

Hi,

I am using a Pixhawk Cube 2.1 on a F450 quad with 2212 920KV motors and 30Amp ESCs. The battery is a 5200mAH 25C 3S Lipo connected via the power module which came with the cube to it. I configured the power module to the ProfiCNC HV power module and it showed a voltage of 12.3V instead of 12.6V shown on my multimeter but was the closest to the actual value. But that is not the major problem. During flight it gave a voltage drop of about 7V, which, according to my experience, is just too much.

Can anyone tell me the cause for such a drop? Kindly look at the log file here as well.
https://drive.google.com/open?id=1Trl9Z3qXsCVktiIVS1hOyvU_hd06AHwL

Thank you,
Regards.


(henrik04) #2

7 Volts drop!?? I would just land immediately!

Something is very, very wrong!

either:

  • Measurement is completely wrong
  • one or more battery cells are dead and under load just become high internal resistance (Should make a very hot battery

My suggestions:

  • With a known good battery:
  • Use a separate telemetry which measure and report to you each voltage cell while you’re flying. (Total voltage is completely meaningless!) Quanum or others…
  • Definitely do not fly with a problem of this kind! (restrain aircraft on ground while troubleshooting)
  • Use hall effect ammeter to measure current consumption under load. (If an ESC becomes shorted under load can consume large number of amps and create voltage sag.)

Happy fault hunting!

Henri


(Sohaib Ahmed Jalali) #3

Hello Henri,

Thank you for the reply. I used a hall effect ammeter (clamp meter) and saw the motors drawing current as follows;

1A at No load (I have a Pixahwk, Raspberry Pi and Lidar V3 as well)
2.29A during Arming
15.5A at 15% Throttle
22.1A at 35%
27A at 50%
40.1A at 100% Throttle

According to the thrust table at full load each motors draw 10.27Amp. So 40Amp for a quad is okay. I used 1045 Slowfly props inverted and rotated them one place on the motors. The thrust was also okay.

I’ll get a new battery and report back.
Thank you for the help. Highly appreciate it.

Regards,
Sohaib AJ


Pixhawk 2.1 Power Brick Mini Accuracy is all over the place
(Sohaib Ahmed Jalali) #4

Hello,

So the problem wasn’t the battery. I tried with a brand new battery but using that, the voltage also dropped significantly. Changed the ProfiCNC power module to the 3DR Power Module and the drop was only 0.6-0.8V during flight, which is totally fine.

So I am quite certain that my power module was faulty.

Regards,
Sohaib AJ