Smart Battery Explained... (and why it's so stupid) ... :-\

[DBS]

Just did some hacking into the smart battery and was very surprised by the stupidity I found in there...

I'm about to get into my own extended battery build and need to chop out the "smart board" from this stupid battery...
Did some tracing and figured out how I'm gonna use the board etc... (will post more on that later)

Then as I was sitting there daydreaming how I would go about this ... and at the same time reading the forum ... I noticed something so completely irresponsible i can't even believe I'm putting my $1400 up in the air with this piece of **** :twisted:

Look at it for a second... And I've labelled it so it's glaring at you...

Top board is "smart board"...
Lower board is just a consolidator putting all the cells in parrallel and series...
Marked that lower board with double arrows showing current path...


Do you see it?!?!

THIS IS A SIX CELL BATTERY RUNNING IN THREE PARRALLEL PAIRS WITH THREE BALANCE LEADS...

COMPLETELY UNACCEPTABLE!!!

AND... HERE'S WHY...

You can't accurately balance two cells in parrallel with a single balance lead... look at any of the major branded , reputable battery manufacturers and you won't see it done this way...

When the battery is at rest it's not a huge problem because if the cells differ in value they will balance eachother off... the problem occurs during charge and discharge...

the scenario:
let's look at cell one as two parts ... cell 1a and 1b ... (I'm about to exaggerate numbers to show average and make a point)

cell 1a is running fine... very healthy
cell 1b has a problem... lithium contamination

you launch your bird...

cell 1a is outputting 12.4 volts at startup as normal
cell 1b drops to 10 volts immediately because of the defect and is quickly draining
your smart board is seeng the cell 1 voltage as 11.2... (the average of the good and bad cell both soldered to the same balance lead)

Under these conditions you will notice something is wrong because you will get an early low battery warning and land or whatever...

But let's say the numbers are not so exagerrated and cell 1b wasn't that bad... just "out of balance"

Now your bird will fly too long and undervolt that cell and damage it...

Then you will go back and put it on the charger thinking it's all good... and it will still have a low volt problem... causing cell 1a to high volt and damage during that next charge cycle... (it's trying to hit 12.4 as an average between the good and bad cell)

Now you have this landmine of a battery that has destroyed itself in the span of one flight and one charge and won't fly past 50% of it's rated time on the app... and you're out 2000ft away ... and can't make it home ... and have to go and chop down a goddamned tree to get your phantom back!!! SOUND FAMILIAR ANYBODY?

I'm just ranting I guess... lipos get old and fail and have problems like anything else... but usually the slowly fade away and you see it coming over several flights with decreasing flight times...

But don't sell me something and call it "smart" when it has this kind of stupidity built in... jeeezzzz that gets on my last nerve...

as the other guys thread said...

"No more using DJI batteries for me"

I also had an early low battery warning last week and after reading DirtyBird's post... I'm glad I didn't go out and fly with it again...
I don't own a chainsaw :?

 

[Dirty Bird]

Re: Smart Battery Explained... (and why it's so stupid) ...

Wow DBS that blows me away. Why didn't they just use three higher capacity cells instead of 6 smaller ones? So there are 6 approximately 850 mah cells? That sure would explain a battery dying in the span of one cycle.

 

[DBS]

Re: Smart Battery Explained... (and why it's so stupid) ...

Why didn't they just use three higher capacity cells instead of 6 smaller ones?

I wish I knew... I've seen it before in cheap chinese knockoffs of other brands but with all the talk of "never use a battery other than the DJI branded smart battery" ... I never expected to see this ...

I probly made it sound more terrible than it really is... When everything is perfect maybe there's an advantage...
But when things are a little off balance this really makes things much worse much quicker...
And I'm betting my bird on that crap every time I go out for a run... :evil: ... frickin irritating bro.

 

[ilovecoffee]

Re: Smart Battery Explained... (and why it's so stupid) ...

Well good that there looks to be some qualified opinion here about what's going on with the batteries. Thanks DBS.

I'm not sure if I can lend my expertise but I do know I can get rid of any battery warnings from the app itself, I'm not sure if this is a problem with building your own pack, but I have seen error messages about non authentic battery packs in the app's code, and they seem to be simple to get around.

 

[burlbark]

Re: Smart Battery Explained... (and why it's so stupid) ...

The first thing I did when I purchased mine used was take the battery apart and check individual cell voltage. I may have busted up the plastic a little but I knew I was flying with a good battery. Throw in the failing wifi modules and the gimbal/camera made of glass and we have a real winner. Not to mention the 5.8ghz tx/rx signals.

 

[HunterSK]

Re: Smart Battery Explained... (and why it's so stupid) ...

Thanks for the write up.

Can you please provide any more information to confirm that the balance leads are not connected to each cell. From what is presented we have a photograph and visual inspection may be misleading. I think a simple electrical continuity test on the balance leads going to each cell would be useful information.

Also, has anybody else independently verify this to substantiate?

I'm not so keen to sacrifice my battery. I've got five genuine DJI packs and have done well over 100 flights spread across the five packs and haven't had any issues so far. But I will consider all relevant facts, as understanding my machine will help allow me to make better future decisions.

Thanks.

 

[Panamon Creel]

Re: Smart Battery Explained... (and why it's so stupid) ...

Kind of surprised that you only found out now that the P2 battery is a 3S2P design, that's been already brought up in this and all other P2 forums in the past.

HunterSK, the cells are configured with 3 in series connected parallel pairs of cells and you can't measure the individual cells in the parallel pairs unless you break the parallel connection between them.

 

[HunterSK]

Re: Smart Battery Explained... (and why it's so stupid) ...

Kind of surprised that you only found out now that the P2 battery is a 3S2P design, that's been already brought up in this and all other P2 forums in the past.

HunterSK, the cells are configured with 3 in series connected parallel pairs of cells and you can't measure the individual cells in the parallel pairs unless you break the parallel connection between them.

Thanks.

Wouldn't wiring the cells in parallel automatically balance the cells in the pair?

I did some digging around according to this link on RCGroups:

http://www.rcgroups.com/forums/showthread.php?t=2082830

As a 3S2P pack, the outer cells already provide a balance connection through their main discharge leads. So if that is true, you end up with only four wires for the balance connector along with two wires for the main discharge lead.

So while you won't be able to get a voltage across six cells individually, each pair of cells balance as they are connected in parallel. As the parallel cells are now very close in voltage potential, they can be charged safely.

 

[DBS]

Re: Smart Battery Explained... (and why it's so stupid) ...

Wouldn't wiring the cells in parallel automatically balance the cells in the pair?

As the parallel cells are now very close in voltage potential, they can be charged safely.

I touched on that in my post... and like i was saying... in a perfect world this is correct
the problem starts when one cell starts to have an issue... batteries that are assembled this way destroy themselves quickly because of that same "parrallel balance" assumption...

and like i said in my second comment... i probably made a bigger deal out of this than it might actually be... but i had this assumption this battery was some sort of "smart" device essential for P2 function... especially considering the price we were paying for it earlier this year. turns out it's wired in a less than ideal method for my taste.

 

[HunterSK]

Re: Smart Battery Explained... (and why it's so stupid) ...

I touched on that in my post... and like i was saying... in a perfect world this is correct
the problem starts when one cell starts to have an issue... batteries that are assembled this way destroy themselves quickly because of that same "parrallel balance" assumption...

and like i said in my second comment... i probably made a bigger deal out of this than it might actually be... but i had this assumption this battery was some sort of "smart" device essential for P2 function... especially considering the price we were paying for it earlier this year. turns out it's wired in a less than ideal method for my taste.

Thanks DBS. Yeah I see your concern.

In my mind the DJI Phantom 2 battery is called 'smart' because of these things:

- Nasty product encryption/authentication with the aircraft (similar to some ink jet printer cartridges)
- A fuel gauge function built in
- Charging and balancing circuitry built in

There are other things too, going on the DJI product page like over current protection and so forth.

 

[DBS]

Re: Smart Battery Explained... (and why it's so stupid) ...

Thanks DBS. Yeah I see your concern.

In my mind the DJI Phantom 2 battery is called 'smart' because of these things:

- Nasty product encryption/authentication with the aircraft (similar to some ink jet printer cartridges)
- A fuel gauge function built in
- Charging and balancing circuitry built in

There are other things too, going on the DJI product page like over current protection and so forth.

yeah... aware of all the features etc... that's why I'm in there hacking out the smart board from a battery that's acting goofy after only about 45 cycles... I'm not arguing the smart features ... just the bottom end.

 

[slothead]

Re: Smart Battery Explained... (and why it's so stupid) ...

I'd still like to see a schematic and parts list. There looks to me (from better photos than DBS provided) that there are several ICs on the card(s) that have to be doing something a little more significant than what was described, but I sure can't see enough detail in any photo to trace the circuit (even if that was possible).

What surprises me is that the charger does not seem to interface with the control contacts (just the two big terminals), although I am not sure it would need to as long as the balancing was all controlled on the battery ckt cards.

I've got a bunch of large dumb batteries (and they are pretty cheap) that I may sacrifice one of to see how they compare.

 

[DBS]

Re: Smart Battery Explained... (and why it's so stupid) ...

There looks to me (from better photos than DBS provided) that there are several ICs on the card(s) that have to be doing something a little more significant than what was described.

The top board yes... it's the smart board and it does everything the smart functions are supposed to... don't know what you mean about "more significant than what was described"

The bottom board is just a hub... nothing there but solder connections and traces.

 

[GerdS]

Re: Smart Battery Explained... (and why it's so stupid) ...

There are good reasons for connecting several cells in parallel. With former LiPo battery generations single cells were not able to take the high discharge rates typically occuring in aircrafts, so it was very common to use several cells in parallel to increase the maximul current. Also the built-in resistance goes down this way.

Modern LiPo cells allow very high discharge rates but on cost of lifetime. E.g. I had two first-generation 4s4p battery packs from ThunderPower since 2002 and have used them in my helicopter until 2012. No puffed cells and still about 80% of capacity, but increaed inner resistance when disposing them. In contrast, new cell types can only dream of such a durability as they may be just good for 2-3 years or even less until they are usually puffed and need to be disposed.

I don't know the cells DJI is using, but I would prefer using cells with lower discharge rates and better lifetime, so maybe DJI did exactly this.

Regards, Gerd

 

[slothead]

Re: Smart Battery Explained... (and why it's so stupid) ...

There looks to me (from better photos than DBS provided) that there are several ICs on the card(s) that have to be doing something a little more significant than what was described.

The top board yes... it's the smart board and it does everything the smart functions are supposed to... don't know what you mean about "more significant than what was described"

The bottom board is just a hub... nothing there but solder connections and traces.

Sorry Chuck, I just don't have enough knowledge or experience with LiPos to know what that smart function is supposed to do. From what I saw in other photos, it looks like there is a lot going on there, however it may be a guise for exaggerated value (like the old transistor radios of the 50 and 60s that used transistors as diodes so they could increase the transistor count - Not DJI-related).

 

[DBS]

Re: Smart Battery Explained... (and why it's so stupid) ...

There are good reasons for connecting several cells in parallel. With former LiPo battery generations single cells were not able to take the high discharge rates typically occuring in aircrafts, so it was very common to use several cells in parallel to increase the maximul current. Also the built-in resistance goes down this way.

Modern LiPo cells allow very high discharge rates but on cost of lifetime. E.g. I had two first-generation 4s4p battery packs from ThunderPower since 2002 and have used them in my helicopter until 2012. No puffed cells and still about 80% of capacity, but increaed inner resistance when disposing them. In contrast, new cell types can only dream of such a durability as they may be just good for 2-3 years or even less until they are usually puffed and need to be disposed.

I don't know the cells DJI is using, but I would prefer using cells with lower discharge rates and better lifetime, so maybe DJI did exactly this.

Regards, Gerd

Thanks for the info... I knew there must be a reason :ugeek:

I guess there's a tradeoff for everything right?

 

[N017RW]

Re: Smart Battery Explained... (and why it's so stupid) ...

It seems after reading through this that the 'sky is not falling' as the OP would have suggested and that there are common design and implementation principles at work here.

Besides any electrical differences in the cells chosen, a 2600mAh cell is typically shorter than a 5200 so putting two in parallel to achieve 5200mAh would result in a shorter, but thicker, pack than 3-5200s.

So it seems DJI was more concerned about overall pack length vs. thickness (???) thus [if so] 6-2600mAh cells would be the best choice for this form factor.

Thanks for your efforts but I'm not sure there is anything useful in this 'rant'.

 

[rbhamilton]

Re: Smart Battery Explained... (and why it's so stupid) ...

I was just out yesterday and got a low battery warning with that horrible Klaxon sound at 51% battery. Then it went off again at 48% for a moment. I didn't see any issues with the drone flying but I didn't want to tempt fate so I brought it down. I did the diagnostic but everything looks normal. I think this might be the same battery that was giving me some strange error about not being able to communicate. Does this all look normal? Anything else I can do to test it? Any chance DJI will replace this one?

 

[Old Gazer]

Re: Smart Battery Explained... (and why it's so stupid) ...

I was just out yesterday and got a low battery warning with that horrible Klaxon sound at 51% battery. Then it went off again at 48% for a moment. I didn't see any issues with the drone flying but I didn't want to tempt fate so I brought it down. I did the diagnostic but everything looks normal. I think this might be the same battery that was giving me some strange error about not being able to communicate. Does this all look normal? Anything else I can do to test it? Any chance DJI will replace this one?

I had that problem once many months ago. I started cleaning contact points using Deoxit and haven't had a problem since. I see nothing wrong with the battery in your assistant photo.

 

[ToThePoint]

Re: Smart Battery Explained... (and why it's so stupid) ...

Nice investigation DBS and before it turns into a faulty battery topic i wright some of my idea's on why its a 3s2p battery.

First of all your right DBS, the setup is kinda odd to balance the parallel ones and indeed it spells disaster ( hence the large faulty battery reports ? ).
Anyway as i was looking into why it struck to me that it could be maybe to power/weight ratio.
Seems odd but does a lower rated lipo pack store more power to its weight ?
The non DJI lipo's are all heavier for that 5200mah. Even with the electronics and casing included its still significant lighter.
I follow this topic with much interest as i intended to do the same ones i got a faulty battery.
Sended in the first one ( round data contacts ) @ my expense even when it was replaced for free ( also one with round data contacts ).
Anyway i love your DIY things and investigation.