Potential Dual Battery Support

[CyberNate]

I finally received my Mavic battery adapter today 3/16/2017 after ordering on 2/22/2017 from:

DJI inspire mods new easy power adaptor phantom 3 pro/adv .

There are no instructions telling which pins to slip them over (sigh). I've emailed them asking specifics.

From MaxxUAV site:


Important: Adapter must be mounted on pin 2,3 and 5,6 from the left. (Connecting to the wrong pin WILL cause damage and your Mavic)

 

[FireFlyer451]

Thanks

 

[ClaudioNC]

 

[ClaudioNC]

About 25-27 minutes flight time with cold weather, at around 10°C, and landing at about 10-15 % batteries power.
18 minutes or less without the two 3S add-on LiPo, here are the Rhino 2250 mAh (bought at HobbyKing), and I have about the same flight time when attach only one unit (rotated at 90°) directly on the DJI battery, with the velcro you can see in the pictures, usually a Turnigy 3000 mAh.
With two smaller Turnigy 1500 mAh, placed laterally as in these pictures, in the same wheather condition can have about 2 or 3 minutes less.
However I think that with the added weight of this yellow batteries, that is 350 g, the Mavic motors begin to be under a little bit too much stress if there is also some wind to counteract, even if at the landing the motors was never warm with these ambient temperatures.
I have taken these pictures some weeks ago, later I have eliminated the extension cable with connectors and soldered the short cable extensions without the added 2 XT60, so to have about 15 g of less weight.

 

[CyberNate]

About 25-27 minutes flight time with cold weather, at around 10°C, and landing at about 10-15 % batteries power.
18 minutes or less without the two 3S add-on LiPo, here are the Rhino 2250 mAh (bought at HobbyKing), and I have about the same flight time when attach only one unit (rotated at 90°) directly on the DJI battery, with the velcro you can see in the pictures, usually a Turnigy 3000 mAh.
With two smaller Turnigy 1500 mAh, placed laterally as in these pictures, in the same wheather condition can have about 2 or 3 minutes less.
However I think that with the added weight of this yellow batteries, that is 350 g, the Mavic motors begin to be under a little bit too much stress if there is also some wind to counteract, even if at the landing the motors was never warm with these ambient temperatures.
I have taken these pictures some weeks ago, later I have eliminated the extension cable with connectors and soldered the short cable extensions without the added 2 XT60, so to have about 15 g of less weight.

The battery clip doesn't work well with larger batteries. There is simply not enough contact patch between the clip and battery connector pins to handle the extra current of the larger batteries. You can verify this after flight by measuring external batteries voltage and comparing to Mavic battery. You'll see that you've only used a portion of the external battery capacity. It gets worse as you use larger capacity batteries. Dual 1500 is about the ideal size for battery clip mod. For larger batteries you'll need to wire directly to main battery leads under Mavic top shell.

 

[geigy]

Another advantage of dual batteries is it would take a double failure to drop the Mavic.

 

[Lelantos]

...There is simply not enough contact patch between the clip and battery connector pins to handle the extra current of the larger batteries....

Assume that the 2250 batteries (4,500 mAh total) are 80% depleted at the end of a 30 minute flight. The current flowing through the connector during the flight will be about 7 Amps. For two 1500 batteries that are 80% depleted after 30 minutes, the current going through the connector will be about 5 Amps.

I think the connector design is poor for either a 5 Amp draw or a 7 Amp draw. Instantaneous current draws will be much higher of course, and that demand will be borne by the main battery.

There is going to be a sweet spot where the extra weight of the batteries and the extra capacity works to make the longest possible flight times. Adding two 2250 size battery packs increases the weight of the Mavic by almost 50%. I think that puts it on the wrong side of the sweet spot. Not because of the connector, but because of the efficiency of the motor/propeller combination - which is designed around a 750g machine, not a 1kg+ machine.

 

[geigy]

Extra batteries does not mean higher maximum current, just a longer more consistent current.

 

[CyberNate]

Assume that the 2250 batteries (4,500 mAh total) are 80% depleted at the end of a 30 minute flight. The current flowing through the connector during the flight will be about 7 Amps. For two 1500 batteries that are 80% depleted after 30 minutes, the current going through the connector will be about 5 Amps.

I think the connector design is poor for either a 5 Amp draw or a 7 Amp draw. Instantaneous current draws will be much higher of course, and that demand will be borne by the main battery.

There is going to be a sweet spot where the extra weight of the batteries and the extra capacity works to make the longest possible flight times. Adding two 2250 size battery packs increases the weight of the Mavic by almost 50%. I think that puts it on the wrong side of the sweet spot. Not because of the connector, but because of the efficiency of the motor/propeller combination - which is designed around a 750g machine, not a 1kg+ machine.

That's true regarding weight sweet spot, however this would not explain a 2.1v or more lag by the external battery pack as compared to the Mavic battery. The external battery had 35% capacity left while mavic battery is less than 15%. This happens with larger batteries. If you run 3000mah or less total external the voltages match pretty closely after flight as they should.

 

[CyberNate]

Extra batteries does not mean higher maximum current, just a longer more consistent current.

External batteries will provide proportionally more of the current as the external capacity is increased. Additionally the extra weight will also increase total current.

 

[Lelantos]

Extra batteries does not mean higher maximum current, just a longer more consistent current.

Yes, mostly. It does mean higher current because the extra weight puts a greater demand on the motors. Also, extra batteries can supply greater current - each battery pack is capable of supplying a certain amount of current, the more packs you have the higher current you can draw from them. Aside from those things a larger battery will not push more current through than a smaller one just because it has greater capacity.

 

[Lelantos]

That's true regarding weight sweet spot, however this would not explain a 2.1v or more lag by the external battery pack as compared to the Mavic battery. The external battery had 35% capacity left while mavic battery is less than 15%. This happens with larger batteries. If you run 3000mah or less total external the voltages match pretty closely after flight as they should.

I think that is because multi rotors put high momentary current demands on the batteries, unlike fixed wings or even helicopters where the current demand is relatively constant. The motors of a multi-rotor are being "throttled" hundreds of times a second. Those peak demands are being supplied by the main battery, the extra batteries serve to supply the main battery. Due to the extra wiring and poor connector they are not capable of supplying high momentary currents. If they were hard wired in so that resistance was minimized, I think there would be a slight improvement in flight time and a more even draw-down of the battery packs. Even so, I think the larger battery packs are on the wrong side of the sweet spot and the inconvenience of hard wiring is not worth it. It would be better to improve the connector.

 

[CyberNate]

...Aside from those things a larger battery will not push more current through than a smaller one just because it has greater capacity.

That part is incorrect. The packs should all maintain the same rate of voltage drop. The amount of current will vary across the pack to achieve that. In the case of the battery mod, there is too much resistance, causing some lag in the external batteries.

 

[Lelantos]

External batteries will provide proportionally more of the current as the external capacity is increased. Additionally the extra weight will also increase total current.

No, they will supply whatever current is demanded of them by the device they are attached to. In flight that means they will provide more current because they are heavier. In other applications it would not matter the size of the battery. It is the device that puts the demand on the battery, the battery does not "decide" how much current to give.

 

[Lelantos]

That part is incorrect. The packs should all maintain the same rate of voltage drop. The amount of current will vary across the pack to achieve that. In the case of the battery mod, there is too much resistance, causing some lag in the external batteries.

To be clear, I mean that swapping out a large battery for a small one, or vice versa, does not change the current being supplied to the device. When you parallel different size batteries together then the larger one supplies a larger portion of the current demand.

This is the problem when paralleling packs of differing capacities. There is no perfect way of handling it. The proportional amount of current provided by each pack will be determined by its level of charge and resistance. In the case of the battery mod the main pack will have the lowest voltage and highest current draw. The (poorly) connected packs will supply less - regardless of their size.

 

[ClaudioNC]

Obviously, it does not increase power consumption by connecting other/s more capable (larger) batteries, but it only increases because the added weight forces the engines to run faster, just to compensate for the flight demands and then rises the current absorption.

Perhaps this Mavic power connection system is not the most efficient and perhaps the position of the batteries on the side is not the best configuration, but it's certainly the quickest and most handy and above all it does not force to open and modify the Mavic body, making a hole.
Maybe in the near future I'll do this mod.
Nevertheless, with these added batteries, for a total of 3000-4500 mAh (declared) I can do what I could not able to do with the intelligent DJI battery.
Slowly, at 30 Km/h, my Mavic fly 4 ... 6 km far and almost always climbs to the maximum restriction limit.
I need to go from one group of mountains to another and then I can allow to stay to fly and hover quietly for a same minutes on the points I have choosen for the pictures I want.

The dull logic of the app, which cannot be adapted to the different configuration and doesn't see the greatest amount of energy available, almost always warns me that the battery is low and the aircraft will do the RTH in 10 seconds, even before I can reach the desired point, but fortunately, having 60% or even 70% of remaining power, the automatic RTH can be cancelled.
Thank you DJI for this ... thanks.

So I do, every time, and the return is at around 30-35%, sometimes even 26-28% if the Mavic is less distant, at only 2 or 3 km.

When I decide to push the RTH button, I move the right stick for increase the speed, so to overcome those modest 30 km/h, and fly at about 50-55km/h.
I prefer to not activate sport mode, here and so.
At the same time, or shortly afterwards, with the left stick I start to descent when is not more necessary to stay high and it go down at 3m/s.

At the end, I often see it arriving, flying like on a virtual aerial ramp, few feet above me, unruffled, and then making its landing with centimeter accuracy, ambient light conditions allowing, at the same take-off point.

4 ... 6 min. to arrive, 3 ... 4 min. to return.
I did in this mode tens of flights, without any particular difficulty and only very few times, maybe 5 or 6, intervening manually to bring it back to home, because the app had decided that my Mavic could not come back, forcing it to land far away, where it was!
... LANDING!
Landing that often would be 1000 or 2000 meters below that point, down in a wild valley ...

No, no ... goodbye LANDING.
Come on, come to me, return at home!

 

[ClaudioNC]

My report of yesterday 07 May 2017.

After two with Inspire 2, I have done one flight with my Mavic Pro, from a valley (no wind at Home Point, 12 °C) towards the mountain walls.
500m up, 2500m far.
During the flight 4 or 5 strong wind alert.
Around my Mavic there are two mountains walls and the peaks are 1100 .. 1200 m higher.
One unit of Turnigy 3S, 30-40C, 3300 mAh, 90° horizontally rotated, attached with velcro above the DJI battery.
In flight for a total of more than 31 minutes.

First flight about 26 minutes from 99% to 23%, second short flight, two minutes later, 200m far, 50 m up, with an additional final, hovering for 2 more minutes, 1 meter above the HP, just to discharge to an overall 7% for the two batteries.

Reading after cable disconnection:
Turnigy Voltage 3,621 V - 3,613 V - 3,562 V
DJI battery 6%.

 

[ClaudioNC]

The battery clip doesn't work well with larger batteries. There is simply not enough contact patch between the clip and battery connector pins to handle the extra current of the larger batteries. You can verify this after flight by measuring external batteries voltage and comparing to Mavic battery. You'll see that you've only used a portion of the external battery capacity. It gets worse as you use larger capacity batteries. Dual 1500 is about the ideal size for battery clip mod. For larger batteries you'll need to wire directly to main battery leads under Mavic top shell.

I am not completely agree with you.

Always, after the flight and later before recharging, I do the necessary check.
On the screen in DJI GO 4, I read the voltage and the theoretical % of the group, the external unit/s and the Mavic battery, both connected with unpowered motors.
Also after the disconnection of the added unit/s, read the two data on the app of the Mavic battery.

Later, at home, before recharging them, almost always I verify again the voltage of both, the DJI and external units, and I have always found comparable energy levels (read V).

Commonly with my missions, they are from low, to a very low levels: 20 ... 10%, or less, about 3.7 - 3.6 V, little less or little more, in total when still are both connected and motors disarmed and so is also when the batteries are separated.
Maybe that my 2 clips are made better, they are handcrafted, and significative variance is possible also for contact capability and Ohm resistence between contacts, there are visible differences in the form of the holes.
I have 2 units of these clips and I'll probably make one by myself, a different version for my needs and preferences.

Can say the same for my Inspire 1 on which I usually add two 6S LiPos 2650, 2700, 3000 mAh, vertical mounted on the left and right sides of the body, between the DJI TB48 battery and the 2 gear arms, connected with a clip (different clip, better for the contact for sure) at the main DJI battery, for a total of 11000 ... 11700 mAh, or if you prefer, more than 11 A.
The added weight to Inspire 1 Pro is 750 ... 820 g for these 2 batteries and few dozen grams for cables, plate and velcro.

Very similar voltages after the flight for each of the 3 units.

Only two or three times I have found that after the disconnection of the external batteries, the main DJI battery was switched off, zero LED, so the Mavic probably was able to fly at the end, thanks to the residual energy of the added packs.

 

[Fredo]

Hello all,
I have an idea.
Why not to put a second Mavic battery on top of the first and connect it with a Dji connector that we can find for few bucks on the net.
The cable must be soldered inside the Mavic to the main battery connector. It can go threw the front arm hole.
Not a hard job for me. Opening a Mavic look easy.
A battery holder must be made and 3D printed to easy clip the second battery on top of the first.
Ok, the extra flight time will not be as better as with the sides lipos mods because of the extra weight.
BUT, it's way cheaper for those like me who already have the "fly more pack".
No other battery do buy, no other charger for lipos, only a cable, and a 3D printed clipper.
What do you think?

 

[ClaudioNC]

Hello all,
I have an idea.
Why not to put a second Mavic battery on top of the first and connect it with a Dji connector that we can find for few bucks on the net.
The cable must be soldered inside the Mavic to the main battery connector. It can go threw the front arm hole.
Not a hard job for me. Opening a Mavic look easy.
A battery holder must be made and 3D printed to easy clip the second battery on top of the first.
Ok, the extra flight time will not be as better as with the sides lipos mods because of the extra weight.
BUT, it's way cheaper for those like me who already have the "fly more pack".
No other battery do buy, no other charger for lipos, only a cable, and a 3D printed clipper.
What do you think?View attachment 12800

It seems a good idea to me, or a possibility for those who have already spent a lot of money for DJI batteries (I have 7 units), but also an alternative solution for those having also other LiPos and LiHVs.

Just after read your message, I thought, the additional weight of a DJI battery on the small Mavic, compared to LiPos would be too penalizing, but I was wrong.
I took scale and batteries to measure the weights and the result is this:

• DJI Mavic Pro battery 3830 mAh: 233 g

LiPo:

• Turnigy 3300 mAh 30-40C: 266 g
• Turnigy 3000 mAh 20-30C: 217 g
• Zippy Compact 3300 mAh 35C: 278 g
• Turnigy 2700 mAh 20-30C: 200 g
• Turnigy 1500 mAh 20-30C (2 units): 246 g
• Tattu 1550 mAh 45C (2 units): 266 g

LiHV:

• Multistar LiHV 3000 mAh 10C: 195 g
• Multistar LiHV 4000 mAh 10C: 272 g
• Bolt Turnigy LiHV 2200 mAh 65-130C 200 g

At this point we should know the added weight for cable and 3D printed holder, with or without an additional velcro, but, at the end, I think we could have a similar, or slightly lower, total added weight, and perhaps a little bit more of efficency, respect the other LiPos.
Maybe in the DJI connector should be connected + - power poles, excluding the others ...?