Fried Pixhawk BEC

[Jordan]

Hi all,

Have been using the BlueRov2s successfully for ~5 months now, but have encountered an issue today that I felt the need to post on the forum!

BlueRov2 Specs
2 x 3600mAh Batteries
4 x lights
Rest of the ROV is standard

Was doing a high current test in my testing tank (gain at 75% and thrusting full forward - roughly ~44A), when current suddenly got stuck reading 56A and voltage 0.0V. After doing a reflash of the pixhawk (thinking it was a software issue), and this value not changing, I opening up the main chamber and discovered the fried Pixhawk BEC cable you can see in the images below. Is worth noting that the pixhawk/ROV was still running fine (I guess due to both the USB power and 5V voltage regulator connected to the servo line).

As this current is well within the operating range of the ROV, would love any ideas from you guys on what happened!

Cheers,
Jordan

LINK TO MORE IMAGES

[kevink]

Hi @Jordan,

Well, that’s not something you see everyday! Seems like the power module might be faulty. I’d probably replace it with one from mRobotics, or one off Amazon.

[Jordan]

Hey Kevin, thanks for the reply mate!

Taking on your advice, I replaced the Pixhawk power module with a new one and went about the same test.
…unfortunately this resulted in the same situation

Reading this post here about max current and thrusters, I am maybe starting to think that by expanding my battery capacity to 3600mAh, the thrusters now have far more current than in a standard BlueRov setup to draw from - in turn allowing for more than the 30-60A recommend continuous current draw that the Pixhawk power module is rated for. Was thinking about using a High current meter like this one here to do the same job.

Would love to know your thoughts on this!

Cheers,
Jordan

[kevink]

@Jordan Well shoot, sorry about that one.

Exactly what batteries are you using? The mAh value of the batteries shouldn’t matter, the one we usually use is 18,000mAh. However, if you have a higher “S” value, that may have something do do with it. The BlueROV2 is only recommended to be used with 4S batteries. If you have a 5S or a 6S, those will have a higher current capacity than the electronics can handle.

With that being said, it seems as though the Pixhawk itself is pulling more power than the small 6-wire cable can handle. @adam any ideas here?

[Jordan]

@kevink all good! …You never know until you try haha

We are using 2 x 4S 18000 mAh batteries in parallel (Sorry I mis-typed before!), the larger version that is available from the Blue Robotics website.

As per the assembly instructions, in addition to the pixhawk power module, I 'm using a 3A 5V BEC to power the pixhawk through the servo rails (and i guess there may be a bit of current drawn of that USB connection).
Have been trying to debug this issue all day and have come to the conclusion that there may be a ground loop happening due to the use of multiple power supplies.I’m thinking this because on both occasions, the two ground wires on that six wire pixhawk ribbon cable were the first to fry. The only issue with this theory is that I’ve never seen this before during all normal operation, and, no one on this forum has encountered the same issue!!

Thanks for all the help so far

[Jordan]

Just for everyone’s reference, because the power port on the Pixhawk was damaged I went through and replaced the Pixhawk with a new one and upgraded the Voltage/Current to this Attopilot 180A Voltage/Current Sensor. Will do some tests to see if the Pixhawk is actually damaged or not, but it seemed prudent to change it!

Still not sure what happened, but did a bunch of tests and the ROV was all good thrusting at 50% gain for ~10mins and 100% gain for ~1min today.

Would still love to hear if anyone had a theory

Cheers,
Jordan

[Mikxie]

Please let us know how it works, fried mine as well…

[Jordan]

Hey Mikxie,

Yea changing to the larger current rated attopilot has given me consistent results, and hasn’t broken again since then

It should be noted though that since the attopilot is rated up to a higher current rating, the current readouts at low current levels in QGround control are way less accurate than with the smaller current/volt meter that comes standard with the BlueRov.