Thanks for all your input so far. I'll press this with DJI support and let you know what they say about it.
Just an FYI, they may request the aircraft and/or the aircraft .dat. before doing anything.
I thought they might...but I'll need to tell them about the Assistant 2 issue. It's already been flagged on the DJI forum and apparently their support people are looking into it.
Do you know the specific function of those pins? Just curious if they are load carrying or data transmission.
I would be fairly confident in saying that they are load carrying, but without a schematic.......well you know how that goes....
I had that same problem a couple of days ago when trying to run Assistant 2 on my Windows 10 environment. This Utube video solved the problem and I could install Assistant 2.
Hope this helps.
Chris
I'm not at all familiar with these batteries but I'll assume the terminals are made out of some metal alloy that would have a melting point much higher than 55C. That at a minimum indicates the 55C noted in the data doesn't explain the condition of the terminals, at least not as the direct cause of the discoloration. The heat that produced the charring and discoloration is somewhat localized so my educated guess, if those are load carrying terminations, would be termination oxidation/corrosion over time that increased the resistance of the terminations and under higher than normal load (flight in high winds) produced self-heating to the point of termination separation and an open circuit condition that caused the motor(s) to shutdown.
I'm a field applications engineer (electronic components) with a background in component failure analysis AND I could be totally wrong given I know next to nothing about these particular batteries...but no harm in a little speculation.
O.k., for some reason (maybe another thread I was reading) referenced motors stopping while still flying. But that aside my main point is 55C doesn't cause battery terminals made out of a metal alloy to char, discolor and appear (at least in the photograph) to experience some level of separation. As you mentioned, current, resistance equals heat but heat to cause charring of terminations surfaces to the degree shown in the photograph doesn't happen at 55C.
As I mentioned, there is no determination that the 55C was the cause of the terminal char...that is only an indication in addition to the data supplied that there was an excessive amount of current drawn for a prolonged period of time which is not normal. This is why we need the aircraft file. The transmitted files only give you so much data to work with. Usually it is enough to determine an issue. Other times it requires more data, which usually the aircraft file will provide. That remains to be seen. Each incident is different in one way or another. There is not much more that can be done with what has been provided thus far. That is where I am with that. I do understand completely what you are suggesting, but again there is no definitive "proof" of anything. This is just part of the P4 mystery that goes on still.
We do have definitive proof of something. The charred terminations is "proof" there was very excessive heating of those terminations. There are two things that are going to cause terminations to heat excessively, higher than normal current flow through the terminations or higher than normal termination resistance. What is the normal resistance of the terminations? Assuming the terminations were in a normal condition (low resistance) when the flight began what level of current would be required to produce heating sufficient to cause this type of charring? Is the battery capable of discharging that level of current and if it is under what conditions would it do so (internal failure of some circuit, failure of some component, etc.)?
This isn't an attempt to answer the root cause question definitively just a request for some educated speculation on the possible causes from someone that knows the system as a whole a lot better than I do. This kind of speculation doesn't mean you eliminate any of the possibilities but it can be a help prioritizing how you search for answers.
I work in electronics and have seen bad terminal connections, either tarnished or loose fitting have this result. The tarnish adds resistance right at the connection. The current going through this resistance causes heat. A loose fitting connector can cause arching which also generates a lot of heat. I suspect we should be concerned with the condition of the battery connectors and that they are seated properly.
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@Valentiaman .....As I suspected...(thanks to @msinger for the wind data)....The aircraft was really fighting the wind. During RTH ( and pretty much for the entire flight ) the winds were quite strong around 25-30mph. Being that the aircraft during RTH travels at a much slower speed, that makes sense. It appeared to be really struggling to return and maintain speed. That would account for the increase in current for that portion.
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Until DJI provides faillure models for its drones and batteries, we can only guess. I am pretty sure something like this could be reproduced in a lab with the right conditions and I don't believe it is related to strong winds or something like that. I think it has more to do with a sudden discharge due to a bad battery chemistry, or a combination of several factors like bad chemistry or increased internal resistance and a huge power demand. I am more interested to know the prior history of this battery, number of cycles, last time charged, was the battery full at take off or it was already self discharging when you took it for flying, if you regularly wait for it to cool before charging, etc, because I believe it was already compromised when inserted. Are the internal cells swollen if you look through the side holes ? Anyway with a flight profile like that you are asking for problems.
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If this were the case there would be many more instances of the issue across the board with all models. Thus far, these have only occurred with the P4's. I have never seen this with any other model and the batteries are all "basically" the same in composition, other than the number of cells.
Definitive yes- at least with respect to LioN temp increasing with discharge current. This is normal and expected. The temps logged here seem to be no cause for concern.
As to the current draw 20A should be well within the design spec of the connector.
As has been suggested the most likely issues contributing to the connector failure are improper mating (not fully inserted), poor spring tension (contacts), corrosion and/or connector unsuitable for purpose (inefficient current carrying capacity).
I would agree with that completely, however, with the P4's having much smaller contacts than the P3's, a prolonged high current situation could be an issue.
Also agreed, arching due to "intermittency" of the connection could also cause the degradation of the contacts.
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Because it is always a combination of factors, for instance a battery with lot of cycles and not so optimal maintenance takes off already in self discharge zone for a demanding flight and a sudden power runaway causes the otherwise good connector to melt. As I have said since DJI does not provide failure models for its products, we can only guess. And I believe DJI has issues with batteries from other models as well (Inspire, Matrice). This is why I am more interested in the battery history than in the flight conditions.
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