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DJI FPV - Battery Breakout Mod [1]: First Tests

I'm trying to mod/recreate the DJI FPV battery to use regular 6S lipo batteries. In a first attempt I try to replace the lipo cells.

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The DJI FPV smart batteries are expensive and only allow a flight time of about 8 - 15 minutes. Due to the proprietary design, regular 6S lipo batteries cannot be used and there are no third-party offerings to address these issues.

Strangely, there are hardly any solutions to these problems from the community either. Or maybe I just didn't search well enough...

Inspired by projects from DuaneDegn, theosky, Reversing Entropy and BigBallVlogs I started experimenting with one of my three batteries. Here I will present what I have done so far and what my conclusions are.

YouTube: https://www.youtube.com/@AirCruiserFPV
Discord: https://discord.gg/ktF6D98u
Mail: aircruiserfpv+hackaday@gmail.com

Ref.:
https://hackaday.io/project/178299-dji-fpv-investigations
https://hackaday.io/project/182115-dji-fpv-6s-battery-diy-compatible
https://www.youtube.com/watch?v=1bSUWn0l7Kk
https://www.youtube.com/watch?v=MaxIl53lTQ8

Note: It has been some time since I started the project and it has become much bigger than I initially thought. Therefore, I will split the project into several sub-projects. Logs that disappeared here reappear there ;)


Initial idea...

My initial research showed that DJI FPV smart batteries consist of an "smart" control board and an ordinary LiPo battery. They communicate with the drone via a three-pin plug and provide information about battery voltage, temperature, etc. Without these additional informations, the drone refuses to start the motors.

So my original idea was to separate the brain from the body. The LiPo battery control board from the LiPo Battery cells. My hope was that it would be possible to create some kind of a modular system. Use the original smart battery control board as the base module and add any LiPo battery pack as the second module.

To test this, one of my DJI FPV smart batteries had to be sacrificed...


Disassembly of a DJI FPV smart battery

There are already some pictures and even videos of the inside of the batteries. But I took a few pictures and that shouldn't be wasted.

Opening the battery case without damaging it is not easy (impossible?). It won't open after removing the two obvious screws. In addition to four clips, there is some sort of double-sided tape holding the battery cover in place. It took me a while to open it...

After removing the cover it was still not possible to remove the control board and the LiPo cells. The cells were additionally fixed to the bottom of the housing with double-sided adhesive tape. But the cells and the control board could be pulled out with a little effort and a lot of patience.

Now the time had come to separate the brain from the body. Besides the two main power wires and the six balancing wires, there was a temperature sensor that had to be carefully detached from the LiPo cells. The glue used to attach the sensor to the LiPo cells is very soft and can be carefully removed with a knife or screwdriver.



The prototype of a modular smart battery

After that I thought the hardest part was over. I soldered XT60 connectors to the main power wires and JST-XH connectors to the balance wires. A rapid test showed that the patient survived. In addition to a simple battery test, I tested the modified battery with the drone. Everything worked fine. I was able to turn on the drone and even start the motors. Nice!

In the next step, further battery cells should be tested. The first attempt was to use six Samsung INR18650 35E LiIon batteries as a 6S pack. Weighing around 250 g and with a capacity of 3500 mAh, this battery had almost the same weight (even lighter) as the original battery but with a much higher capacity. So I soldered six of these batteries together to give it a try. Soldering LiIons is not recommended and even dangerous, but I don't have a spot welder... To hold everything together I 3d printed a case for the control board and a seperate case the battery pack. Both could be screwed together to build the battery unit. However, I wasn't sure how changing the technology from LiPo to LiIon would affect the discharge process controlled by the "smart" control board.
(I know that the maximum discharge current of this kind of LiIon batteries is much lower than the maximum discharge current of LiPos. But it was just a test and I even hoped it would be enough for some slow and smooth flights.)



When things started to go wrong

So it was time to assemble the control board and the LiIon 6S package and to turn on the drone. After connecting the pack to the board, two of the status LEDs lit up for a few seconds. After a click on the battery test button, all four LEDs lit up, indicating that the battery was fully charged. Strange because it wasn't. After turning on the drone, everything seemed fine. But then I noticed that the battery status was highlighted with a red rectangle and the drone's status LEDs were flashing...

Read more »

DumlFileTime.txt

12min duml communication between drone and smart battery with timestamps

plain - 1.19 MB - 04/14/2022 at 12:03

Download

DumlFile.txt

12min pure duml communication between drone and smart battery

plain - 909.08 kB - 04/14/2022 at 12:02

Download

  • Battery Breakout Board Rev.1

    AirCruiser09/11/2022 at 15:58 4 comments

    Just a little teaser ... 
    (Don't judge me to hard, it's my first PCB...)

    But before rev1 is fully assembled, rev1.1 is already in the planning stage.

  • Little Frankenstein

    AirCruiser05/04/2022 at 16:53 4 comments

    Just a quick update

    I soldered all the components of my first test onto a perfboard. The display shows the voltage [V] and the current [mA]. Instead of the percentage, the glasses show the voltage (10x). Big and ugly, but it does the job. After some more tests and improvements I will design a PCB.

  • Nailed it!

    AirCruiser04/29/2022 at 00:49 2 comments

    With this modification, any 6s Lipo battery can be used without any modifications/hacks of the drone. Full compatibility with the original batteries is retained. I set the battery percentage to a random number that changes every second just for demonstration purposes.

    Details coming soon...

View all 3 project logs

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Discussions

Dmytro Soldatov wrote 10/07/2022 at 22:00 point

Hi. When you said that you got 7 mins fly with 18650 batts how did you detect the end if fly? Was it return to home/autoland feature from the DJIbsoftware? If it was the case, there is a way to disable it so you can controll yourself how much you want your battery to be discharged.

  Are you sure? yes | no

AirCruiser wrote 10/18/2022 at 21:37 point

I think at this point the problem was that I was charging the 18650 batteries with the smart control board to make it work. But either way, the Samsung 18650 E35s aren't ideal for the job. The max. discharge current is too low. But I can recommend Molicel INR18650 P28A :)

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Adel wrote 08/13/2022 at 23:38 point

what if we provided fake voltages ( generated by a boost converter, source is a 3v coin battery for example ) to the board of the smart battery, and balancing voltages, those fake voltages can be controlled over the time to decrease. yet the power supply to the drone is a 6s battery, basically using the smart battery board just to communicate with the drone as it should, would that work ? im thinking about trying this once i find a cheap defective battery. cheers

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Filip wrote 09/28/2022 at 19:53 point

As far as i know, defective DJI Smart battery will write and "ERROR" code and it wont work anymore. But there is a way how to overcome this, only it is not easy. You need to reprogram BMS with new capacity and other things to work correctly but it is possible to do, only it is not about replacing the cells. 

  Are you sure? yes | no

AirCruiser wrote 09/29/2022 at 14:22 point

I think this would not work for several reasons. The battery board "remembers" how much current was used to charge the battery and measures the current when the battery is in use. If you disconnect the battery from the board, the calibration will be reset and the board will send an error message to the drone. Because of this, the drone refuses to start the engines. And even if you could keep the memory intact (I tested it with a LARGE capacitor), the drone wouldn't see any current when you fight the drone. Maybe that's enough to get an error. If not, you still have the problem that no power is detected and therefore the battery percentage in the goggle OSD does not change. It doesn't matter if you change the voltages with a boost converter. The board "counts the current". So you don't know how much capacity is left. If that's not a problem, you don't have to do any of this. You can change one firmware parameter and use any battery. But then there is no percentage display and you have to guess how long you can fly and when your drone will fall from the sky ;)

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John wrote 06/29/2022 at 19:49 point

Very interesting project. my couple of thoughts about possibility hacking DJI FPV Battery. 

As I see it have another two ways for hacking ,one of them it is modify original BMS with chip bq9006 firmware for any elements like 18650 etc. another one is to root DJI FPV Drone system and modify original battery system file for switch off security identification/check original battery. As I know chip bq9003 already hacked, but bq9006 is on develop status. About root DJI FPV Drone as I know it's already done. 

  Are you sure? yes | no

orthemius wrote 04/27/2022 at 05:33 point

Do you know how https://airdata.com/ works? I mean they somehow know how to download and interpret DJI logs. And it works well with my dji fpv, just plug android to goggles and synchronize.

May be you can combine their logs interpretaion and your communication logs together and find out someth useful.

(unfortunately cannot apply an image https://drive.google.com/file/d/1b8GU5Y_tUYvz46i7CaubmCIgj7JQjqLx/view?usp=sharing)

  Are you sure? yes | no

orthemius wrote 04/27/2022 at 05:08 point

There is no public chat in your project :)

>> But every time you disconnect them, the control board resets and the battery needs a few percent (up to 100 %) of charging to "calibrate" the battery to the new LiPo.

May be it's not enoght. Lipo in contrast to Lion has a vary flat discharge characteristic, so it's almost impossible to say how much power does it left in your battary if you know only its voltage. It's ok, when you fly just till you battary reaches 3,5V per cell (no matter how long it takes, but you have to see th voltage), but not ok if you whant to know how much time have you left during the flight (eq to see battary percantage). It seems that smart battary counts the capacity during the whole charging, and then, calculates left capacity during discharging, plus controls the voltage for emergancy landing. That's why the battary is 'smart'. So, when you change lipo, you need minimum one full charge-discharcge-charge cycle to calibrate battary brains for it. Better 2-4 cycles. Without it, the percantage indicator is not accuracy and shows 'the weather'.

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Poppy Ann wrote 04/08/2022 at 10:20 point

I did something similar for a different drone (which I cannot remember the name of) but all I did was to dismantle a knackered lipo which had its own make connector I just soldered a XT60 connector to the back of the original battery connector then took the end cover of the knackered battery which had a built in clip to hold the battery in place so now I could fit original battery's or any 3s 2500 mA or more battery's  in.

I also did a very similar project to some cordless tools where I took apart one of the original batteries and removed all of the parts I attached an electrical project box which had hinges and clips to close it, I ran some wires from the old battery connectors down through to the inside of the project box and fitted two XT60 connectors wired in parallel so if I wanted I could fit either one or two 3s lipo battery's inside of the box depending on which tool I was using on a couple of tools it was a bit to large and clumsy but on most of them it worked better than any of the supplied battery's that came with the tools whilst not being the most aesthetically looking modification this was a great where it mattered ie at powering the tool.

  Are you sure? yes | no

Duane Degn wrote 04/05/2022 at 15:03 point

Thanks for sharing your work. I was afraid DJI wouldn't make it easy to swap batteries. It seems like you have a semi-workable solution for now. I'll likely try something similar in the future.

  Are you sure? yes | no

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