Battery error?

[leecow]

Trying to sus out an odd thing that happened during a flight this afternoon. Was about a 1/4 mile out, plenty of gps and radio signal, and began getting low voltage warnings and immediate landing actions with about 45% battery left. Here are the bits of the log across the "all is well" and "we're landing now" events. Nothing interesting with the voltage that I can see.

NONE 0 ALREADY 0 1 21.24 3.338 3.329 3.292 10.39 0.046000004 220.68361
SERIOUS_LOW_VOLTAGE_LANDING 0 ALREADY 0 1 21.24 3.338 3.329 3.292 10.39 0.046000004 220.68361

Then there's the smart_batt.gohometime which goes from 55 to 0 in a single event at the time of the error and a bit later (after I had coaxed it back toward the house) it went from 0 up to 75.

Anyone had experience with this behavior?

 

[leecow]

Here's the log file (renamed from csv) filtered to a few events before and after the voltage error.

 

[msinger]

Your battery voltage reached 3.2V (it auto shuts off at 3.0V) and your Mavic decided it needed to land right away in order to make it to the ground safely. All looks like it was working as designed to me.

 

[leecow]

Thanks msinger - then there's something else as the battery data at the time of the flight seems to indicate a different situation.

I think the screen shot below shows that, at the time of the low power warning, the battery was at 45% and there was quite a bit of time remaining before the alarms should have been going off. Perhaps I'm misreading?

 

[Motley]

This may not be right but are you sure you were looking at the right battery indicator. I am wondering if that battery indicator is the level of the controller and not the Mavic. I am not familiar with that screenshot you posted so not sure if that is the case or not.

You may also want to make sure your settings are not set to land at 45%, I am pretty sure you can set that.

 

[leecow]

Hey Motley,

Confirmed the indicator shown on the screen shot is aircraft battery and I'm seeing the same reading on the remote and app display. Yes, you can set both the low battery and critical warning levels. Mine are set at 30% and 10% respectively which I think are the defaults.

 

[Kilrah]

Voltage measurement always has priority over the percentage estimation. If voltage becomes critical you want to take the appropriate actions NOW and ignore the percentage that's probably wrong/unreliable.

That's exactly what would happen if a battery is too cold for example. Yes it's got remaining energy, but the cold increases internal resistance so that it's unable to supply it properly, although it doesn't seem to be the case there.

 

[SkyRider]

The flight time line indicates 4:23 of flying time left, even though the battery shows 45%. I would guess that has something to do with it. Mine gives me alerts at that amount of flight time remaining as well.

 

[leecow]

Kilrah, thanks for that. Yes, understand that voltage is king. At this point I'm working to understand the apparent discrepancy between the estimate still being "in the green" and the critical voltage "I'm landing right now" critical warning.

Skyrider, yep, remaining time as reported by the timeline is understood. The question is why did it begin an emergency landing with so much time apparently remaining on the clock.

 

[SkyRider]

It's almost 400 feet high and 1200 feet away if I read that correctly. It takes some time to come down from that height and fly 1200 feet laterally, so the safety settings are likely kicking in to get it safely down with a bit of reserve for landing. Better safe than sorry and all that...

 

[tooFLYforayoungGUY]

Voltage measurement always has priority over the percentage estimation. If voltage becomes critical you want to take the appropriate actions NOW and ignore the percentage that's probably wrong/unreliable.

That's exactly what would happen if a battery is too cold for example. Yes it's got remaining energy, but the cold increases internal resistance so that it's unable to supply it properly, although it doesn't seem to be the case there.

This seems to be an issue I faced yesterday. LED indicators had at least two solid greens and my RC was showing 48% battery life on AC, but about 45 seconds -maybe- a minute, I had the same error and RTH prompt. My MP had been subjected to about 35-37 degree temps before flying. Only went about 50-75 ft in vertical altitude & just about 15 ft horizontally.

Popped in a warm battery and everything was well.



Sent from my iPad using MavicPilots

 

[Kilrah]

Skyrider, yep, remaining time as reported by the timeline is understood. The question is why did it begin an emergency landing with so much time apparently remaining on the clock.

Because as said voltage is king, and a healthy cell going below 3.3V is about to die.

Now why is it already at 3.3V when the indication is 45% left is the question. Could be the cold, or simply a defective battery. Your log is trimmed too close so we don't know what happened before in the flight, but if you did some full power punches then combined with the cold that could have pushed it under the threshold.

The first couple of samples of the log show a high current draw of 21A which I seem to remember is about full power. In these conditions you can see there's quite a bit of voltage difference between the cells, and cell 3 crossed the safety threshold of 3.3V.

So for me it's a combination of a battery that isn't in perfect shape with some cell imbalance, and pullling on it like crazy when it probably was a bit cold.

 

[leecow]

Thanks for the further thoughts tooFLYforayoungGUY and Kilrah. @tooFLYforayoungGUY , this was a critical "I'm landing now" and not RTH. RTH never happened. Craft went from "I'm happy" to "I'm coming down right here, right now". Ambient temp was 40 degrees and batteries had come from a 68 degree house 15 minutes prior.

@Kilrah Interesting that a 100% battery has just over 4.2V in each cell and yet falls out of the sky at 3V. Could you point me at the test data? Think I'll "run a hover until dead" test today and see what numbers pop up.

 

[leecow]

Thanks again @Kilrah - workload theory makes sense. I had popped it into Sport and full throttled it to the point where it "misbehaved".