Raspi Unstable Connection / Shuts Down after few minutes of use


I have been trying to build a custom ROV using the electrical setup found in the ArduSub website, with an outside power supply (480W). In addition to this I have been using the new BlueOS software with a Raspi4.

The software initially seemed to work really well. I could move the motors and read data of the pixhawk sensors. However, after 10 minutes or so the raspberry connection became unstable. The BlueOS interface would oscillate between disconnected/connected every 10 seconds or so. This continued for a minute and after that QGC started saying lost manual control and then disconnected. After that the connection didn’t recover.

My initial thought was that RasPi overheated and so it shut down itself as a failsafe. However when I measured the core with a temperature probe, it was 55 degrees Celsius. I thought this was in the normal operating range so I reckoned that couldn’t be the problem. I then tried unplugging the power source, waited a bit for everything to cool down and replugged the power source.

The green LED of the raspi flashed for a minute or so and then became constant. There was no incoming connection. I checked the voltage that was fed to the raspberry and it was 5.02 V. The voltage regulator I am using supports 5V up to 5A so I knew the Raspi was receiving enough power. In addition when I checked the power supply I saw that the whole setup was drawing 0.7A.

Does anyone know what is going on? What could have caused raspi to freeze like this?

Hi @ufocet -
Can you share a bit more info on the “outside” power supply you’re using? The 0.7A sounds low for base power consumption… from your description, I would suspect a very noisy 5V power supply may have damaged the Raspberry Pi?
Please be careful if doing a DIY power system over a tether- this can be very dangerous in water without appropriate safety measures!

Thanks for your reply,

I realize the dangers, so I will not throw this set-up underwater without making sure everything works flawlessly above water.

The main power supply I am using is an old server PSU that I found from a second-hand sale. You can check it out in this link. Also the 5V regulator I am using is this.

Also I wanted to share the output of the 5V regulator I recorded when I was able to move the motors. The spike occured when I stopped the motors.

Hi @ufocet,

This thread is likely worth a read.

One of the noteworthy points is that the back-EMF induced from braking in the air is generally more significant than in the water, so it’s possible your bench test setup is running into issues that would be less of a problem for an actual vehicle in the water. That said, computing devices tend to strongly dislike large power fluctuations, and the 1.52 V range shown on your oscilloscope does suggest you likely want either a more stable voltage regulator, or some kind of filtering circuitry added to your current one.