Charging of DJI batterys and various methods

[solentlife]

Part 1 of a series ............

OK ... as this is a non DJI owned board ... I shall explain various test results and observations when charging / investigating the DJI Intelligent battery pack ... specifically the P3 version.

DJI have chosen to provide a sealed battery pack of High Voltage LiPo in a 4S configuration. This gives a nominal of 15.2V and a full charge level of 17.4V. Based on the 4.35V per cell at max charge.
Standard LiPo's have a nominal of 15.2V and a full charge level of 16.8V, based on 4.2V per cell at max charge.

DJI have decided to incorporate a Charge and Telemetry board into the front section of the battery case. This provides Charge Control - cut off at extreme low discharge and at full charge point. It basically takes the Constant Voltage 17.4V of the power brick DJI supply as a charger and it passes to the cells.

The board has connections to the battery and two connections to the 'outside world'.

To the battery :

Via the switch and cutout on the board to the battery, power is passed to charge. This also provides path for power to model when flying. It is as observed when battery dismantled based on a + / - two lead config only.

The balance lead from the battery giving access to each individual cell goes to a connector on the board to allow board to have cell voltages information. This balance lead has no access external for any user control or option.

To outside world :

Two sets of twin contacts are provided >
The main power contacts for charging and power to model. This is +/- two lead only.
Second is the data connection that provides telemetry information from the board to the 2.4Ghz WiFi to pass this to pilot via the Go or Litchi app. This is also only a two lead connection.

What does this mean ?

The battery is reported by DJI to be 'smart' and not only regulate its charge and discharge cycles, but also provide balancing and health info of the battery pack. The requirement for any charger to provide balancing of cells is as DJI state - unnecessary as the board does it within the battery case.
DJI supply a regulated CV power supply. This is no better or different to any other regulated 17.4V supply in fact except it has a DJI plug on the end.

17.4V is supplied to the main power contacts of the battery and the board is said to monitor the cells and set charge to the battery accordingly. The amp rate will change as the charge level changes. As the level increases the resistance to charge climbs but the power supply is regulated to the 17.4V. The voltage of the battery reaches 17.4V - the amp rate basically falls to zero, the board detects this and shuts of disconnecting the power. There is no magic science to this at all.
Balancing of the cells can only happen if the cells are unbalanced and the 17.4V cannot be reached due to any cell being below 4.35V.

Discharge - LiPo's are extremely sensitive to being discharged too low and this damages then seriously. A LiPo should never be discharged to low levels as the damage is not reversible. Therefore the board has an apparent low threshold of 12V based on 3V per cell as minimum before cell damage. As to whether the board actually works on 3v per cell or a total 12V is not 100% determined - but observations so far indicate that 12v total is the means used and NOT individual cell 3V. This then can lead to one or cells going below that threshold of 3V.

OK ... lets move on to methods to charge.

DJI supply an adequate power supply that is regulated to 17,4V. That's fine and it does the job. But its what is termed a 'Dumb Brick' as it gives no information as to what it is doing. It only provides a Constant 17.4V. It relies on the battery packs board to terminate / control charge along with the batterys natural resistance to charge. Standard models are supplied the 57W version giving not much more than 3A rate. Other P3 models such as Pro have the 100W brick giving rate nearer 5A.
The DJI battery is a 4450 mAh capacity and 1C rate is 4.45A ...
There is no facility for User to control charge in any way other than On / Off. There is no balance function that can be used.

Alternative methods and here I will use the Accucel 6 80W LiPo charger as example gives user options to control charge.
The A6 gives options to alter Voltage (1s ... 6S), Amp rate, Timer and mAh cut outs. It also has balance and storage / discharge functions. The charger can be set to basically any of the commonly used battery types including the HV LiPo's DJI use in the packs. The charger has full display of charge going on, voltage. amps, and mAh put in along with time.

DJI brick :

Pros...

Warranty validity
Supplied by 3rd party provider and labeled for DJI
Fixed regulated voltage of 17.4V

Cons ...

No display of charge in progress other than scrolling LED lights on battery face.
Relies on battery board to terminate charge.
Constant voltage which will continue to feed when faults occur and no safety cut-out other than the battery board.
Standard is supplied with low wattage supply below even 1C rate.
Requires 120 / 240V input
DJI pricing of approx. $50 for the 57W and about $80 for the 100W version

Accucel 6 80W charger :

Pros ...

User settable options of amps, volts, mAh maximum, Timer and charge mode.
Charger safety that prevents user setting wrong voltage.
Safety cutouts when any fault detected
Full charge info displayed during charge / discharge.
Storage mode function
Discharge mode function
Battery Meter function
Internal resistance function
This model at 80W means you can only go to max safe charge rate on the DJI battery.
12 - 18V input so car use and on field is fully achievable.
With suitable lead - it can also charge your Controller.
$30 price tag

Cons ...

Invalidates DJI Warranty (this is subject to National Laws though protecting consumers and DJI can be still held to Warranty).
Need to buy separately adaptor lead for about $3
User needs to understand how to use by reading a simple manual.

Here is a photo of my A6 charging a DJI P3 battery ...



You will note that I have information displayed ...

LH4S (that's the battery type used by DJI)
5.0A (that's the charge rate going into the battery)
15.92V (that's the voltage of the pack at that time)
CHG (that's the mode being used ... CHARGE as balance mode cannot be used on DJI batterys)
000:28 (that's the time in mmm:ss charge has been running)
00034 (that's the amount of mAh that have been put back into the battery during this charge)

To be cont'd ....

Nigel

 

[Andy4195]

Nigel this is very informative I for one really appreciate this forum especially having knowledgeable people like yourself around , I have seen a lot of your posts and I have learnt a lot.


Sent from my iPad using PhantomPilots

 

[dronesover Texas]

This is good to know ty I use the same charger for my planes that you have in your photo


Sent from my iPad using PhantomPilots keep her flyin

 

[120CCPM]

Hi Nigel,
thanks for the explanation, although I still don't see any major benefits in using a LiPo charger, vs. potential risks.
Sure, you can pump more amps and reduce the charge time... but you know very well that you can push that up only to a certain point, as the higher the charge rate, the more stress you put on the battery. And while the 57W DJI charger definitely takes its time (charging rate of 0.7C), the 100W charger speeds things up a bit (1.2C). Do I really want to go beyond that, with $100 batteries? Likely not. Is it expensive? Surely yes...
The main concern I have is that in order to use a LiPo charger - correct me if I'm wrong - you must turn the battery on, but instead of discharging it, you're now pumping current into it. What are the implications of that? I don't know...
First thing that comes to mind is balancing: does the intelligent board still balances the cells in that situation? If not, I would see that as a major negative, as a LiPo charger definitely cannot do that (cannot balance w. Does the battery's charging counter goes up, when using an external charger? If that happens, it could be good signal (it could mean that the intelligent circuit understood that the battery was charging).

 

[solentlife]

"120CCPM"

Switching the battery on is exactly the same as you need to do with DJI charger when the battery is at high level of charge. There is no difference.

Second - 5A is the rate that meets all specs including DJI's own. I would not advise using higher. The charger I show would have difficulty giving higher than that anyway - another safeguard.

Third - balancing actually as observed doesn't occur as well as DJI would have you think. In fact not only myself but others cannot find the point when it does occur ! balancing is a function that really can only occur at FULL charge point unless an energy transfer style is utilised - but DJI mention possibility of temperature rise - this indicates a 'bleed of via resistor' format which only occurs at full charge point.

My point in writing this series is to show that you can charge via a LiPo charger, to inform what the battery actually does and help understand what is the DJI battery. As to whether person uses my info or not - is up to that person. But at least the person has a little more knowledge of that item.
DJI would love all to think that ONLY a DJI charger can be used. That plainly is not the case and a standard LiPo charger capable of HV LiPo charging will do the job fully and with added safety factor of its own fault cut-outs.

Plus of course - the charger I illustrate is on your bench for about $30 ... near half the price of the low power DJI item.

Cheers
Nigel

 

[120CCPM]

Nigel, I don't question your intentions, it's all good information. But I'm trying to get the full picture: do you think that the DJI intelligent board balances the cells, when you use a LiPo charger? It does not matter if the balancing method is not ideal, it's definitely better than what the LiPo charger can do (which is absolutely nothing, since it has no access to the balance points of the 4S pack).

As for "DJI would love all to think that only a DJI charger can be used", I think that's a bit unfair. DJI sells drones to the "general public", and with that I mean people who have no RC background whatsoever. My neighbor's son got one, and he (or the father) doesn't recognize a LiPo from a NiMH pack. If you tell them that a LiPo needs balancing, they would probably think at sticking some weight on one end. I'm dead serious. These are the people DJI is dealing with. These are the people that read the "Quick Start" guide, don't calibrate, don't do anything but opening the box of the new toy, sticking a battery in it, sending it up in the air, crashing it, then call DJI because "something is wrong with the drone I just purchased". It's with people like these in mind that DJI designed the Intelligent Battery. Am I happy to pay 3 times than what I pay for other LiPos? Hell no. But I totally understand why they did it.

 

[rocketflyer]

Plus of course - the charger I illustrate is on your bench for about $30 ... near half the price of the low power DJI item.

But you'll still need a power source. Unless you are a rc or electronics hobbyist you're unlikely to have a high current power supply handy. Even a converted atx psu (a decent one not those low power ones you get in cheap computer builds) will easily set you back another $30-$50. So in the end it comes up to about the same.

balancing actually as observed doesn't occur as well as DJI would have you think. In fact not only myself but others cannot find the point when it does occur ! balancing is a function that really can only occur at FULL charge point unless an energy transfer style is utilised -

So are you saying the batteries don't simultaneously charge and balance?

 

[With The Birds]

When you first mentioned this I was sceptical- principally (for the reason I stayed at the time) as I suspected the external charger would not see the internal cells in the DJI pack directly and without knowing the actual state of charge voltage would not work correctly. I waited for you to test it and with confirmation it worked have since found it to be my preferred method of charging in the field. I have LiFeP04 batteries as my remote power source with a sine wave inverter in my vehicle and haven't used the DJI brick since. Works perfectly.

 

[geoffN]

Without doubt you certainly know a lot more about these things than just about everyone here and makes interesting informative reading ......................... keep up the good work. Unfortunately, as 120CCPM suggests.................... most people really don't care as long as the batteries get charged up, charging is fairly quick (well in my opinion anyway!!) and work ok. Can't see that the cost of a charger really comes into it as the DJI one comes "free" with the drone. Very interesting imfo though.

 

[solentlife]

Nigel, I don't question your intentions, it's all good information. But I'm trying to get the full picture: do you think that the DJI intelligent board balances the cells, when you use a LiPo charger? It does not matter if the balancing method is not ideal, it's definitely better than what the LiPo charger can do (which is absolutely nothing, since it has no access to the balance points of the 4S pack).

Hi ... OK ... the DJI charger is NOT a charger but a regulated power supply only ... it does not care about what its connected to. You could get hold of a any other 17.4V regulated brick and it would perform identical.

The LiPo charger is performing same function as the power brick ... plain power supply at suitable voltage for full charge of a 4S HV LiPo.

The DJI charger and the LiPo charger will not balance any DJI pack - that is the function of the board fitted in the battery case.

It has been observed that the BOARD fails to balance the cells in fact - DJI's claim is "optimistic" ... to be kind to them.

As for "DJI would love all to think that only a DJI charger can be used", I think that's a bit unfair. DJI sells drones to the "general public", and with that I mean people who have no RC background whatsoever. My neighbor's son got one, and he (or the father) doesn't recognize a LiPo from a NiMH pack. If you tell them that a LiPo needs balancing, they would probably think at sticking some weight on one end. I'm dead serious. These are the people DJI is dealing with. These are the people that read the "Quick Start" guide, don't calibrate, don't do anything but opening the box of the new toy, sticking a battery in it, sending it up in the air, crashing it, then call DJI because "something is wrong with the drone I just purchased". It's with people like these in mind that DJI designed the Intelligent Battery. Am I happy to pay 3 times than what I pay for other LiPos? Hell no. But I totally understand why they did it.

I do not disagree with this statement - I agree 100% - because the market the Syma and others target are total newbies to RC. DJI hopes to capture also by offering the P3S out ... and so far I believe they cover more than half the market share. BUT note that many other 'beginner' multi-rotors - (I do hate that word Drone ... which USED to be reserved for Military machines) - are sold using CONVENTIONAL LiPo's and chargers.
I believe DJI took the decision to avoid any possible damages to Brand name by stupidity of users.
I would suggest though that DJI sales to existing RC users are increasing as more like the idea of aerial camera. I know in my limited arena - sales were to experienced RC'rs .. with very few new faces seen.

So the question - can a common over counter LiPo charger be used - are there any advantages to use it ? Basically many people buying a Phantom - I reckon would soon move on to conventional RC if not already. So the LiPo charger takes on an advantage that the DJI charger cannot meet.

We all get supplied a DJI charger in the box. But most of us then buy extra batterys. a DJI 57W charger sits about $55 discounted ... but my charger + a 12V 10A power supply comes out at barely over $40 all in ... claims of power supplies needed at $30 or so are exaggerated. But even if someone does pay such for a power supply ... consider what else that charger can do. All battery types can be charged basically commonly used - seems a good investment to me !! Especially when people start recc'ding the 100W charger at over $75 !!

Please - I am just passing on informatoin for people to decide what they wish to do. I am not trying to convince anyone to throw away the supplied charger. I just hope that thought is given if they want a second or wider ranging charge facility.
I am also trying to help understand what really happens inside that DJI battery case ....

Nigel

 

[solentlife]

But you'll still need a power source. Unless you are a rc or electronics hobbyist you're unlikely to have a high current power supply handy. Even a converted atx psu (a decent one not those low power ones you get in cheap computer builds) will easily set you back another $30-$50. So in the end it comes up to about the same.

A 12V 10A supply is well below the figure you quote - even in the high street.

But even if you did pay that figure - think of the wider range of charging jobs you can do ... you can even charge your wifes car battery when she flattens the battery ... charge up your NiCd, NiMh ... LiFe ... Lead Acid etc.

The DJI power brick - because at end of day that is all it is - is overpriced and could in fact be used to power a LiPo charger !! Simple adaptor to plug in ...

So are you saying the batteries don't simultaneously charge and balance?

The type of balancing used or shall we say suggested by DJI comments is of the DEPLETING Resistance type. This means that at near full charge termination - cell inbalance is observed and the HIGH voltage is 'burnt' off via resistors to bring down to similar to the lowest cell. It is a cycled function - discharge - charge - discharge - charge ... until cells are detected to be similar.
BUT unfortunately it has been observed that the Board in the DJI battery terminates charging BEFORE the completion of cycled balancing. And there is no way to force the board to complete balancing properly.

A LiPo charger when it has access to individual cells via balance lead WILL continue the balance phase until it observes cells balanced OR reaches time out. Unfortunately DJI system will terminate same as with its own brick power supply.

Nigel

 

[rocketflyer]

A 12V 10A supply is well below the figure you quote

Maybe in europe - high street prices over here for psu's are extremely high because of certification needed to be sold at retail level. I would personally be wary of a high current psu that sold for $15 tbh.

And in fact I do have an accucel as well (had to complement my 10 yr old lipo charger which doesn't do the newer life's.

BUT unfortunately it has been observed that the Board in the DJI battery terminates charging BEFORE the completion of cycled balancing.

Not so good if that's the case.

 

[120CCPM]

Hi ... OK ... the DJI charger is NOT a charger but a regulated power supply only ... it does not care about what its connected to. You could get hold of a any other 17.4V regulated brick and it would perform identical.

The LiPo charger is performing same function as the power brick ... plain power supply at suitable voltage for full charge of a 4S HV LiPo.

The DJI charger and the LiPo charger will not balance any DJI pack - that is the function of the board fitted in the battery case.

It has been observed that the BOARD fails to balance the cells in fact - DJI's claim is "optimistic" ... to be kind to them.

My question was a bit more subtle. I know that the DJI charger and the LiPo charger, at the end of the day, do the same thing (although DJI is purely CV, whereas LiPo chargers start with CC and then switch to CV). The difference, if any, lies in the battery itself. Let me explain better:
- when you use the DJI charger, you apply a voltage to the battery leads; the intelligent board detects it and starts the charging process. so let's call this operating status "charge mode"
- with a LiPo charger, you need to manually turn the battery on for the leads to become "hot"; this is an operating mode intended for powering the AC, so let's call it "discharge mode"
My question was more like: are "charge mode" and "discharge mode" exactly the same? In particular, does the intelligent board balance the cells (regardless of whatever method it uses) also in "discharge mode"? It's something that could very well happen or not, it really depends on how the intelligent board is designed (and its firmware). But it's not a trivial question, as there could be protections (e.g. over-voltage or over-current) or logic (e.g. charge counter) that is enabled in "charge mode" and disabled in "discharge mode".

From your other posts, you seem to imply that the two modes are effectively one. But unless we can be 100% sure of that, I would not feel completely confident in using a LiPo charger. It's definitely good to know that it's possible, though.

 

[120CCPM]

The DJI power brick - because at end of day that is all it is - is overpriced and could in fact be used to power a LiPo charger !! Simple adaptor to plug in ...

It could, but it won't be any faster... your LiPo charger would still be limited by the 57W...

 

[120CCPM]

Maybe in europe - high street prices over here for psu's are extremely high because of certification needed to be sold at retail level. I would personally be wary of a high current psu that sold for $15 tbh.

Up to 80-100W, you can find laptop power supplies (most modern LiPo chargers accept 11-18V) for less than $20. Beyond that, you're absolutely right and things start to get quite expensive.

 

[solentlife]

OK let's take various items.

The 15v 10a power supply for the Accucel is the recc'd to get full power out of the charger when charging high cell count such as 5S and higher. So I would always advise getting this if possible. But for the DJI battery a 12v 10a is more than enough.

The DJI battery uses resistor depletion for balance and discharge .... when you store your battery DJI advise that it may increase in temp when discharging to storage. It is the reason it is slow and needs no outside connection.
Balancing uses the same method but should alternate with charge.

Charge mode as applied via a lipo charger here would be basic power to max voltage setting user makes, with added protection that charger detects battery voltage and only allows suitable voltage setting. It also cuts off at full / fault - which the DJI power supply will not.

The different charge formats CV / CA doesn't really matter as the charger will supply voltage until cutoff. The board and battery itself will resist charge altering the amps anyway.

The DJI power supply I suggested could be used to power the charger was purely to illustrate what it really is - a CV regulated power brick. It does not care what it connects to. Of course you will have no better rates than without charger.

It seems that some may read my posts as trying to make people throw away the DJI supply and only use LiPo charger - that is not my intent. I use both DJI and my Accucel to charge simultaneously battery's. My LiPo charge of course completing before the slower DJI. But results are identical.
The perception by many is that DJI batterys can only be charged by DJI supply. I wish to show that it is not the case. Any LiPo charger capable of 4s HV LiPo charging can do the job. In fact even a standard B6 Imax can do it once voltage termination is set for 4.35v cells.

The tests and investigation so far shows the DJI battery to be fitted with a charge controller and telemetry data board. The functions claimed for it are sadly not as sophisticated or accurate as DJI would have us believe. The balancing is only partial at best. The individual cell control appears to be aimed more for telemetric data rather than real control. Deep discharge - which I strongly suggest to not do - appears to only work on total voltage and not cell by cell required to prevent cell damage. Full charge is terminated by full total voltage instead of continued balancing.
The limitation being the board fitted to the battery. We cannot change that. But we can consider how to speed up our charging and maybe save a few $ without compromising safety.

Safety - the LiPo charger has built in fault and error protection. If it detects anything - it shuts off telling you why. It also has full charge termination and user settable discharge settings. You can interrogate battery for actual voltage, total internal resistance. The DJI system relies only on the board itself. And it gives you no information other than a few flickering LED's.

? Under $50 for Accucel + PSU + adaptor lead or $50 for a DJI basic PSU to charge your battery's ?

As I said - I use both but when charging only one battery - I use the Accucel - its slightly quicker, I can see charge level and amount of mAH pumped in .... I can also power straight of the car cigarette lighter socket.

I would like to know how many have tried LiPo charger ... I reckon many are staying quiet !

Nigel

 

[dan84uk]

I dont see the point of this thread?

Buying a accucel 6 to charge the batteries is pointless and expensive, as you still need to buy an additional power supply to run the accucel and its still only capable of 80w max.

Better off buying a generic 17.5v power supply capable of 100w its cheaper and faster.

The proper way to use an accucel 6 would be to bypass the onboard charging completely and solder to the balancing wires, which some of us have already done in the battery mod thread.

 

[solentlife]

Just a quick word .... yes a regulated power supply can replace the DJI unit - but please take care if you do.

The DJI PSU is set to 17.4v .... it is likely that the battery control board cannot actually control input voltage - it just terminates when voltage in equals voltage out. This is how many chargers work.
The DJI battery board does 'switch off' but I have no idea if that is due to board deciding voltage is enough or the above in-out method. If it is as I fear in-out method - you risk serious damage by using a PSU of unreliable or different voltage to the DJI unit.
This is one of the reasons I advocate a LiPo charger if you do not use the DJI unit.

Nigel

 

[Quest-So]

Hi Solentlife, 120CCPM and rest,
Your detailed explanations about charging P3 batteries, are coming at the right time for me
I need and advice from you.
I have 2 batteries that run alternatively a P3A and I intend to buy another 2 batts and the DJI hub serial charger.
From what I read, the P3A charger (57W) provides just 0.7C while the P3P charger (100W) provides 1.2C.
I would like to understand, should I buy a non-DJI charger brick that will generate exacly 1.0C or either of the above 2 bricks might satisfy the needs ?
If I'm using the 57W brick will I slowly lose the batt capacity since the unit is not generating enough power to fully charge the battery ? (I've noticed my batts aren't reaching the 100% charge but placing them in the bird it shows from the very beginning just 92-93% @ say avg 40 charges)
By contrary, if I'm using the 100W brick will I jeopardise the battery by forcing a a too speedy charging process ?

What I've noticed these weeks to a 3rd battery that was used up to now to a P3P (means charged with the 100W brick), is that after 2-3 charges with my 57W brick, it has gained over 200mAh in its total capacity. Is it because the 57W is not forcing the battery as the 100W brick ?

 

[120CCPM]

In my opinion, the 100W DJI charger is a valid option, especially if paired with the charging station. Pricey, yes, but you pay for convenience and ease of use.
As for the 100W charger being harsher on batteries than the 57W model... I doubt it, as we're still talking about relatively low charge rates (0.7C vs 1.2C).