VCC Low and Fluctuating

ArduCopter Copter 3.5
1

Hi all, I’ve been having some issues with VCC to my Pixfalcon ever since upgrading to copter 3.5. I did an auto analysis and got a warning for VCC min/max diff and upon checking noticed that my VCC was both low (close to 4.6 at times) and fluctuating more than I’d like. Checking on old flight logs I see that VCC is 5V and only fluctuates about ±0.1V, often less.

In addition to upgrading to 3.5 I also added an OSD in parallel to my telemetry radio (using one telem port), added ground wires to my ESC leads, and switched ESCs to Oneshot mode. Users on RCGroups suggested powering the OSD from the FC was causing voltage loss so I changed the power to the OSD to an ESC BEC. However this only help a little, and VCC still fluctuates between 4.9V and 4.7V. Interestingly I disconnected both the telemetry radio and the OSD from the telem port and VCC only rose to between 5V and 4.8V. As I mentioned before with a telemetry radio installed I used to have VCC between 5.1 and 4.9V. My Holybro power module reads 5.27V on both VCC outputs.

So I’m curious why I am seeing these VCC problems. Could it be some hardware failure/change or something in the new firmware. I have attached a log file from a flight today which had a telemetry radio (powered by FC) and OSD (powered by ESC BEC, but grounded on FC) installed, and of course GPS. The flight had some hovering, slow circles, and fast forward flight. Curiously VCC also seems to rise over time.

2

I have similar picture with my pixracer as well.
Have tried 3 different power supply sources all with the same result - VCC is noisy within 0.3 volts range.

Then I’ve connected FC via only USB cable and captured a log. And that log has the same fluctuations (well, maybe just a bit smaller).

So I thought that it’s either HW or FW inaccuracy that doesn’t affect on functionality.

3

So today I did a flight involving an auto mission and found the VCC to be between 5.10V and 5.0V. Interestingly my other flight logs with auto missions show similar VCC values, whereas flights where I’m in control have much more fluctuation. I’ll have to try a non-auto flight tomorrow to see if the VCC is different or not.