Mavic - Battery life improvement & Internal Electronics

[Crypto]

Hi guys !

I'll be a Mavic owner soon, and I'm already looking for battery improvement.
Depending on how much risks (about having a dead battery) we're willing to put on, I think there is a way to replace LiPo cells by Li-Ion cells, still using the same battery circuit board. Picture of the board there.

After some calculations (mostly based on internet researches), there is a way to improve mAh capacity by 50% by adding ~50g (battery weight estimated of 280-290g).
It's about swapping the 3S1P (which means 3 batteries in series) original LiPo, by a 3S2P (which means 2 parallel circuits of 3 batteries in serie) which is 6 cells of NCR18650PF Li-Ion.
The increase would be going from the original 3830mAh 340g, to a 5500mAh ~380-390g (depending of the circtuitry's weight).

One of the advantages is that we would be able to charge the battery using the tradidionnal charger, and no risks of surtension by branching the battery externally like some other mods are offering.
The negative side is that we'll need to get rid of the hard case, the batterry will be a little bit bulkier.

There is some data research needed to be sure that the calculations are correct and the improvement possible.
Still not having yet in possession the Mavic, do some owners are willing to share some .DAT log files of a full lenght flight to make some checks about tension, current, min/max draw... ?
And other test would be to study data log for a full flight with an added weight of ~100g on top to compare current draw and flying time evolution.

Looking forward to see if some of you are interested to try going on this way, have a nice fly !

PS: I'm not under FAA/US regulation and always flying LoS or FPV, just want to improve flight duration as safely as possible and having fun proving that we can improve consummer goods.
Be responsible and remember that local regulations apply ;-)

 

[Kingkong]

I.m in for updates

 

[flyNfrank]

I'd like to say welcome to clearly the #1 Mavic Pro website.

 

[armoredsaint]

wait till you need a warranty claim, DJI is going to love you tenderly.

 

[Crypto]

wait till you need a warranty claim, DJI is going to love you tenderly.

They'll be no way to send it back, the battery case/housing will be destroyed/modified.
It is not so different than owner who add mods for spare batteries on the sides.

 

[DarXidE]

I assembled these 6s 18650 packs for my large hex, run 6s4p and get 30 mins flight although it pushes the draw of the pack. Been considering exactly what you have said for the mavic, any idea or max amp draw on the mavic as these cells are rated for 2c although less is always better

 

[Crypto]

Yes, my first though was also to use Panasonic NCR18650B, but as you said there are rated for a max between 1.5 and 2C (which means between 10 and 15Amps).
It's why I proposed different NCR18650PF which are supporting much more current draw, up to 4C (which means 20A for a 3S2P), but with a little bit less for gravimetric energy density at 207Wh/kg instead of 240Wh/kg for 18650B.

I've made some other calculations, for cell type comparison, for a 3S2P:
18650B : 295gr + circuit board, for 6600mAh (@15A peak)
18650PF : 288gr + circuit board, for 5650mAh (@30A peak)

Analysing logs of Mavic with weight addition will make us know how much current draw and peak it's using, and will let us choose between NCR18650B and NCR18650PF.

It is very interesting that you used 18650B at 2C, did you tried to go further than 2C ?
What was the result and conclusion of using a battery bloc at a 2C average for 30min ?

 

[DarXidE]

Batteries are definitely warm/hot after flight, i think roughy 2c average with spikes up to 4c id say. Have to be light on throttle i did push it to hard for to long once and she fell from the sky

 

[Crypto]

Ok, so it's possible to go beyond 2C and still fly, I wasn't sure about that.
Maybe the cut you had (when it fell) was because of a direct voltage drop due by an overdraw of current.

Did you have some capacity drops by using these batteries over limitation constantly ?
And how did the capacity evolves after few cycles of discharge at 2C ? (Any noticeable drop ?)
Did you used protected or unprotected cells ?

At normal weight, the Mavic have a hover current draw around 7.5 to 8.5 Amps which is 1.3C for 3S2P NCR18650B.
Is it possible to implement a % throttle limiter with DJI GO or Litchi app ? (Without using tripod mode)

 

[FredzMaxxUAV]

I have tested Li-Ion from Awesome custom Li-ion packs for long FPV flights - RC Groups on both Phantom and Inspire. And unfortunately, it's not working well, as there is no way to reprogram the ESCs. Li-Ion batteries go much lower than 3.50/3.20V or so, but the DJI bird doesn't see this. It just sees that it is at 3.50-3.20V and needs to land. I have tried with li-ions (18650) on both Phantom and Inspire, with very bad results. You can try, but you will probably be disappointed.

Technical explanation: Lipo or LivHV are both empty at 3.20v. So normal lipo 4.2v to 3.2.
The lithium ion are different. They start from 4.2 and go all the way to 2.5v. So not really the discharge curve is the matter (it is different, but that is not the issue here), but rather that when your quad thinks the battery is drained (all it uses to detect this is voltage) it is in-fact not drained.
Many of these quad and even plane ESC where designed with lipo in mind purely. Having li-ion with usable discharge rate for rc is a new thing, so what used do is disable the cutoff and just monitor manually. This is impossible on a DJI or not self-built bird.
Your quad thinks that is has lipo inside and only watches the voltage. That is why it will report 10% when in fact the li-ion is still left at least 40%.

So the draw and current do not really matter, it's the voltage left that will stop you from flying.

 

[DarXidE]

Still get same mahs into the pack that got over amped and yes i believe voltage drop was reason for crash. Not protected cells wouldnt use for rc since cut off is worse case for a flying rc. Li ion cells will cycle 2 to 3 times more then lipos from what i have read. And yes fredz is right a good part of there capacity is lower voltage then a lipo pack although i never drain mine past 3v under load

 

[armoredsaint]

They'll be no way to send it back, the battery case/housing will be destroyed/modified.
It is not so different than owner who add mods for spare batteries on the sides.

I meant if the battery somehow malfunctions and shorts out the electrical/ board on the Mavic. That would really suck.

 

[Bunny Too]

Cool thread guys, this is why I come to the forum.
Regards,
-d.

 

[Crypto]

Thank you FredzMaxxUAV, I forgot about the cut-off / voltage drop between LiPo and Li-Ion, I don't know if it is something we can work on, with software/parameters modifications.

Your quad thinks that is has lipo inside and only watches the voltage. That is why it will report 10% when in fact the li-ion is still left at least 40%.

What happen after reaching 10%, auto-landing ? Can you override ?
Is there a voltage indication on the remote or phone (instead of % or bars) ?

The Battery circuit board is quite big, I wonder if the cell voltage info is sent from it or from the main board.http://mavicpilots.com/members/fredzmaxxuav.185/

 

[Crypto]

Still get same mahs into the pack that got over amped and yes i believe voltage drop was reason for crash. Not protected cells wouldnt use for rc since cut off is worse case for a flying rc. Li ion cells will cycle 2 to 3 times more then lipos from what i have read. And yes fredz is right a good part of there capacity is lower voltage then a lipo pack although i never drain mine past 3v under load

After looking at NCR18650B charts, at 2C and with 15% remaining battery (2800mAh ot of an average of 3300mAh), we are around 2.9v.



About cell cycles, they tested them with a 400mAh drop after 500cycles at 1C, I think it can be worse by constantly using them at 2C.
So it's around 1mAh/charge (or 0.03%).

 

[ElGuapo]

What happen after reaching 10%, auto-landing ? Can you override ?
Is there a voltage indication on the remote or phone (instead of % or bars) ?

The Battery circuit board is quite big, I wonder if the cell voltage info is sent from it or from the main board.

After reaching 10% auto-landing kicks in. The aircraft goes into auto-land mode, you can temporarily override to maneuver for a safe landing.

 

[flyNfrank]

I have tested Li-Ion from Awesome custom Li-ion packs for long FPV flights - RC Groups on both Phantom and Inspire. And unfortunately, it's not working well, as there is no way to reprogram the ESCs. Li-Ion batteries go much lower than 3.50/3.20V or so, but the DJI bird doesn't see this. It just sees that it is at 3.50-3.20V and needs to land. I have tried with li-ions (18650) on both Phantom and Inspire, with very bad results. You can try, but you will probably be disappointed.

Technical explanation: Lipo or LivHV are both empty at 3.20v. So normal lipo 4.2v to 3.2.
The lithium ion are different. They start from 4.2 and go all the way to 2.5v. So not really the discharge curve is the matter (it is different, but that is not the issue here), but rather that when your quad thinks the battery is drained (all it uses to detect this is voltage) it is in-fact not drained.
Many of these quad and even plane ESC where designed with lipo in mind purely. Having li-ion with usable discharge rate for rc is a new thing, so what used do is disable the cutoff and just monitor manually. This is impossible on a DJI or not self-built bird.
Your quad thinks that is has lipo inside and only watches the voltage. That is why it will report 10% when in fact the li-ion is still left at least 40%.

So the draw and current do not really matter, it's the voltage left that will stop you from flying.

The new Takyon's are real nice and can be used with our aircraft. They open the door for several options. DJI Imaging Solutions

 

[CyberNate]

Hi guys !

I'll be a Mavic owner soon, and I'm already looking for battery improvement.
Depending on how much risks (about having a dead battery) we're willing to put on, I think there is a way to replace LiPo cells by Li-Ion cells, still using the same battery circuit board. Picture of the board there.

After some calculations (mostly based on internet researches), there is a way to improve mAh capacity by 50% by adding ~50g (battery weight estimated of 280-290g).
It's about swapping the 3S1P (which means 3 batteries in series) original LiPo, by a 3S2P (which means 2 parallel circuits of 3 batteries in serie) which is 6 cells of NCR18650PF Li-Ion.
The increase would be going from the original 3830mAh 340g, to a 5500mAh ~380-390g (depending of the circtuitry's weight).

One of the advantages is that we would be able to charge the battery using the tradidionnal charger, and no risks of surtension by branching the battery externally like some other mods are offering.
The negative side is that we'll need to get rid of the hard case, the batterry will be a little bit bulkier.

There is some data research needed to be sure that the calculations are correct and the improvement possible.
Still not having yet in possession the Mavic, do some owners are willing to share some .DAT log files of a full lenght flight to make some checks about tension, current, min/max draw... ?
And other test would be to study data log for a full flight with an added weight of ~100g on top to compare current draw and flying time evolution.

Looking forward to see if some of you are interested to try going on this way, have a nice fly !

PS: I'm not under FAA/US regulation and always flying LoS or FPV, just want to improve flight duration as safely as possible and having fun proving that we can improve consummer goods.
Be responsible and remember that local regulations apply ;-)

I like the way you think; however I don't think it will be a practical option here. There are too many hoops to jump through to make this work. DJI has a tight monitoring on the lipo batteries. The monitor system would need to modified to work with the lithium ion battery characteristics. Good luck hacking the firmware for that. There a much larger range in voltage in lithium ion to get all the usable power out of them. I agree that it would be awesome to take advantage of the high capacity cells such as the 18650GA cells and newer ones coming out with highest energy densities. Unfortunately with the current battery monitoring, you'd only use up 50 to 60% of the energy of lithium ion cells, which would be LESS energy density than LIPO. Best bet is the option of adding lipo packs in parallel. I see that MaxxUAV have successfully tested with dual 1800mah batteries for 14 miles round trip range. That's pretty good. I have dual 1500mah batteries and waiting for my mod plug with dual xt60 plugs.

 

[FredzMaxxUAV]

@flyNfrank AFAIK the Takyons cannot be used with any DJI consumer drones, including Mavic, Inspire and Phantom.

 

[FredzMaxxUAV]

I like the way you think; however I don't think it will be a practical option here. There are too many hoops to jump through to make this work. DJI has a tight monitoring on the lipo batteries. The monitor system would need to modified to work with the lithium ion battery characteristics. Good luck hacking the firmware for that. There a much larger range in voltage in lithium ion to get all the usable power out of them. I agree that it would be awesome to take advantage of the high capacity cells such as the 18650GA cells and newer ones coming out with highest energy densities. Unfortunately with the current battery monitoring, you'd only use up 50 to 60% of the energy of lithium ion cells, which would be LESS energy density than LIPO. Best bet is the option of adding lipo packs in parallel. I see that MaxxUAV have successfully tested with dual 1800mah batteries for 14 miles round trip range. That's pretty good. I have dual 1500mah batteries and waiting for my mod plug with dual xt60 plugs.

The best ones at the moment are 3000 or 4000 LiHV Multistar ones (Hobbyking), used as a single battery.