Battery Cell Deviation: How much is too much?

[Qoncussion]

I was out flying my MP a few weeks back, using Litchi, when the controller showed a BATT ERROR (I don't
remember the exact text). A little red balloon popped up in Litchi at the same time, but wasn't on the screen long enough to read it. I just figured I would check the logs to see what happened. I landed immediately, and am just now getting around to viewing the logs. There are no errors, warnings or messages showing.

So I figure the error will be found in the Cell Deviation column - but I don't know how much of a deviation is too much...? The battery in question was the original battery that came with the MP back in February of 2017. I am guessing that it's reaching the end of its useful life - but need some help deciphering "what went wrong?"

Hoping some of the big brains here like, @sar104, @msinger, @BudWalker, @Thunderdrones or others can assist me.

LOGS:
Phantomhelp
DJI Flight Log Viewer - PhantomHelp.com

AirData

Thanks!

 

[sar104]

I don't see anything there either. You might want to check the mobile device DAT file - it has more detailed information on power.

 

[Cyberpower678]

Ideally cells should never deviate at all. Cells can deviate up to 0.05V and still hold a reasonable balance. Greater than that and the lowest cell will begin to fail faster until the battery can’t hold a balance. Once a the deviation reaches about .2 or .3V it will discharge unevenly hurting the cell with the lowest voltage and that puts the aircraft in danger while it’s in the air as that cell gets hotter and hotter.

 

[Qoncussion]

I don't see anything there either. You might want to check the mobile device DAT file - it has more detailed information on power.

Where would I find the DAT file on the mobile device? I was using Litchi during this flight and don't see any dats in its main program folder.

 

[Qoncussion]

Ideally cells should never deviate at all. Cells can deviate up to 0.05V and still hold a reasonable balance. Greater than that and the lowest cell will begin to fail faster until the battery can’t hold a balance. Once a the deviation reaches about .2 or .3V it will discharge unevenly hurting the cell with the lowest voltage and that puts the aircraft in danger while it’s in the air as that cell gets hotter and hotter.

It looks like my highest deviation on this flight was 0.026V... From what you said, that doesn't sound alarming to me for an older battery (right?)

 

[sar104]

Where would I find the DAT file on the mobile device? I was using Litchi during this flight and don't see any dats in its main program folder.

That's a good question - I don't know the answer. Can you get the DAT from the aircraft? That likely depends on the firmware version.

 

[Clinton1]

It looks like my highest deviation on this flight was 0.026V... From what you said, that doesn't sound alarming to me for an older battery (right?)

No, that doesnt sound like a big deviation to me. I get on one of my batts a deviation of between 0.03 to 0.05. I get no warnings and no overheating. Gets the same flight time as my other batts. Just keep on monitoring the cells, and when you dont feel comfortable with it anymore, then get rid of it. On my 12s heli batts if they started to get at 0.1 deviation, then i stopped using them, if the balancing on the charger couldnt bring it back anymore.

 

[Qoncussion]

That's a good question - I don't know the answer. Can you get the DAT from the aircraft? That likely depends on the firmware version.

I'm uploading the DAT to Dropbox now - our Internet is slow here... Hang tight! ...and thanks for your help (everyone!).

 

[Qoncussion]

That's a good question - I don't know the answer. Can you get the DAT from the aircraft? That likely depends on the firmware version.

There were two DATs on the Mavic for this flight (at least that's how it looks to me). One started at the beginning of the flight, then another right near the end. Using Assistant 2 I grabbed them both - and they were automatically combined into one file. I hope this is right... I also grabbed them independently of one another. Our internet speed stinks here - and Dropbox is taking forever to load the first (combined) file - so let's start there. I'll share the others if you need them separately.

Dropbox - DJI_ASSISTANT_EXPORT_FILE_2018-08-19_15-07-35.DAT

 

[Cyberpower678]

No, that doesnt sound like a big deviation to me. I get on one of my batts a deviation of between 0.03 to 0.05. I get no warnings and no overheating. Gets the same flight time as my other batts. Just keep on monitoring the cells, and when you dont feel comfortable with it anymore, then get rid of it. On my 12s heli batts if they started to get at 0.1 deviation, then i stopped using them, if the balancing on the charger couldnt bring it back anymore.

12s? **** son.

 

[sar104]

There were two DATs on the Mavic for this flight (at least that's how it looks to me). One started at the beginning of the flight, then another right near the end. Using Assistant 2 I grabbed them both - and they were automatically combined into one file. I hope this is right... I also grabbed them independently of one another. Our internet speed stinks here - and Dropbox is taking forever to load the first (combined) file - so let's start there. I'll share the others if you need them separately.

Dropbox - DJI_ASSISTANT_EXPORT_FILE_2018-08-19_15-07-35.DAT

I still don't see any problems. Voltages and current look fine, and track with motor speed. I would not worry unless you see that message again.

 

[Qoncussion]

I still don't see any problems. Voltages and current look fine, and track with motor speed. I would not worry unless you see that message again.

View attachment 43896

Indeed... Thanks a bunch for taking the time to look. I'm going to run that battery down under 20% and give it a full charge, then keep a close eye on it.

 

[Clinton1]

12s? **** son.

In heli speak that is how we refer to connecting 2 x 6s 4000maH packs in parallel to get to 12s. You drain them in 4 - 5 minutes

 

[Cyberpower678]

In heli speak that is how we refer to connecting 2 x 6s 4000maH packs in parallel to get to 12s. You drain them in 4 - 5 minutes

2 x 6S in Parallel is still a 6S. The batteries need to be connected in series to make it a 12S. So as it stands now you are feeding your helicopter 25.2V fully charged and a capacity of 8000 mAh.

In other words you are actually using a 6S2P setup. ;-)

 

[Clinton1]

2 x 6S in Parallel is still a 6S. The batteries need to be connected in series to make it a 12S. So as it stands now you are feeding your helicopter 25.2V fully charged and a capacity of 8000 mAh.

In other words you are actually using a 6S2P setup. ;-)

My mistake, i got confused between parallel and series. You are correct, it is in connected in series

 

[Cyberpower678]

My mistake, i got confused between parallel and series. You are correct, it is in connected in series

Well then, 50.4V. That's quite a bit. Getting shocked from that is going to sting.