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Mavic Air mobile battery charging (LiPo pack solution)

plexus

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Here’s the final result of a mobile charge solution. A 4S LiPo pack supplies nominal 14.8V which is compatible with the DJI car charger. It just a matter of making a case for the battery pack to protect it. This 5AH 4S pack can charge close to 3 MA batts. I have to validate this with a real-life test - one batt consumed about 30WH out of the pack. The pack has a capacity of 80WH. FYI this equates to about 2.5HA into the MA batt.
I wanted a solution that was cheap (the pack was $58US) and that was upgradeable, maintainable and efficient. The problem with the 120V banks or other commerical options I’ve seen is that there will be more loss in the added circuitry. This LiPo solution has no circuitry other than the car charger.
I want to deplete 3 batts and see how charged up I can get them. I am going on a week long backcountry camping trip with no power (or potable water) so whatever I carry in, in terms of power is all I have available. I have 5 batts plus this pack.
The LiPo itself weighs 500g. That works out to about 170g of LiPo per fuly-charged-MA batt. So beware other solutions that weigh less. For example if a charger says it can charge 4 MA batteries, then it whoudl weigh at least 680g plus the case and other electronics. I’ve seen 365g chargers claim they can charge 5 batts - This would be magical if it were real.

RESULTS: The 4S LiPo is brand new and I only used it for testing, no complete charge. Fully charged the 4S and let it rest a day. I depleted 3 MA batts by flying down to failsafe RTH. I was aable to charge up 2 batts fully and the 3rd to about 85% (flashing 4th LED). Not bad!

UPDATE on the LiPo pack: This was the first time I discharged it fully from a full charge. It charged back up to full in 120 mins and pumped 4825mA into the battery with a 2.5A max charge current and another 400mA at 0.5A charge current for a total of 5225mAH.. Not bad. Lets see how well the LiPo does over time!


 
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ChrisW81

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Here’s the final result of a mobile charge solution. A 4S LiPo pack supplies nominal 14.8V which is compatible with the DJI car charger. It just a matter of making a case for the battery pack to protect it. This 5AH 4S pack can charge close to 3 MA batts. I have to validate this with a real-life test - one batt consumed about 30WH out of the pack. The pack has a capacity of 80WH. FYI this equates to about 2.5HA into the MA batt.
I wanted a solution that was cheap (the pack was $58US) and that was upgradeable, maintainable and efficient. The problem with the 120V banks or other commerical options I’ve seen is that there will be more loss in the added circuitry. This LiPo solution has no circuitry other than the car charger.
I want to deplete 3 batts and see how charged up I can get them. I am going on a week long backcountry camping trip with no power (or potable water) so whatever I carry in, in terms of power is all I have available. I have 5 batts plus this pack.
The LiPo itself weighs 500g. That works out to about 170g of LiPo per fuly-charged-MA batt. So beware other solutions that weigh less. For example if a charger says it can charge 4 MA batteries, then it whoudl weigh at least 680g plus the case and other electronics. I’ve seen 365g chargers claim they can charge 5 batts - This would be magical if it were real.

RESULTS: The 4S LiPo is brand new and I only used it for testing, no complete charge. Fully charged the 4S and let it rest a day. I depleted 3 MA batts by flying down to failsafe RTH. I was aable to charge up 2 batts fully and the 3rd to about 85% (flashing 4th LED). Not bad!

UPDATE on the LiPo pack: This was the first time I discharged it fully from a full charge. It charged back up to full in 120 mins and pumped 4825mA into the battery with a 2.5A max charge current and another 400mA at 0.5A charge current for a total of 5225mAH.. Not bad. Lets see how well the LiPo does over time!


Question: I presume you have to use the DJI Mobile Car Charger or equivalent to charge the Mavic Battery correct?
 

plexus

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Well, the battery will stop charging as it normally does but you should monitor it and take it off it the charger because some current will still be flowing into the charger. once the 4S LiPo pack is too low the charger will turn off - this seems to be at a good theshold so as to not harm the LiPo. So far it works pretty good!
 

Downloaders

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Thats actually genius! My guess is 3,3v on each cell when it stops charging, so not to low. Im working on a charger per usb (1,5A qualcom or a 3A 5v)
 

plexus

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Thats actually genius! My guess is 3,3v on each cell when it stops charging, so not to low. Im working on a charger per usb (1,5A qualcom or a 3A 5v)
I experimented with USB but the problem is the spec maxes at 10W. One USB was not enough to power the car charger. I then weighed the effort to create a parallel USB adaptor to get the ~40-50W required and felt it was more work/cost than the LiPo approach. But let us know how your USB experiement/solution works out.
 

Downloaders

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My approach would be to just output 13,3v and connect it to the battery without the car charger. Use 5v 3A and step it up to 13,3 or 12v 1,5A respectively.
 

borislip

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The point of having a power bank to charge a phone is that you don't have to remove the battery from it, so there is no downtime. Or you can't pack more juice in any other way, because battery is non-removable. But, seriously, whats the point of doing this with drone batteries? Why not just have more of them to begin from?

Sometimes the best solution is to just keep things simple.
 

plexus

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The point of having a power bank to charge a phone is that you don't have to remove the battery from it, so there is no downtime. Or you can't pack more juice in any other way, because battery is non-removable. But, seriously, whats the point of doing this with drone batteries? Why not just have more of them to begin from?

Sometimes the best solution is to just keep things simple.
3 MA batteries = $330*. 1 4S LiPo that will charge 3 MA batteries = $75*. "simple" costs over 4x. batteries will eventually die and need to be thrown out, so there is that rationale as well.

*Canadian $
 

plexus

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My approach would be to just output 13,3v and connect it to the battery without the car charger. Use 5v 3A and step it up to 13,3 or 12v 1,5A respectively.
Careful here because the battery also has an IO pin. I would guess that the battery and charger communicate to each other. It may not be a passive charging system. But you can experiment etc and let us know how it goes.
 

borislip

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3 MA batteries = $330*. 1 4S LiPo that will charge 3 MA batteries = $75*. "simple" costs over 4x.

*Canadian $
Agree, it makes sense, price-wise. But if you take the convenience of the end result (having to charge from a power bank with a ready to use, pre-charged, set of batteries), and the effort required (you've probably spent at least a couple of hours gathering the materials and putting it together), i'd say just having more batteries still wins.
 

Downloaders

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You are looking at this from the wrong angle. At least for me, i'm not looking into the most efective way to do it. I'm an electronics enthusiast and for me the pleasure of trying something out is worth more than going to a store and buy something. Of course that to do this, you have to have a slight idea of what you are doing, which normally is the reason why people who dont have any idea and too much spare time come into conversations between people who do and state obvious things that everybody knows and don't add anything to the topic because we can do battery math better than you. :)
 

plexus

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Agree, it makes sense, price-wise. But if you take the convenience of the end result (having to charge from a power bank with a ready to use, pre-charged, set of batteries), and the effort required (you've probably spent at least a couple of hours gathering the materials and putting it together), i'd say just having more batteries still wins.
I can give you my paypal address and you can donate some $ to my MA battery fund. :) :)

Seriously though, I have 5 MA batteries already. From past experience I know these will eventually end up in the garbage. For me 5 are enough, and the LiPo acts as a reserve. I didn't wan to "invest" in 3 more batteries for this purpose so the LiPo what the best middle ground.
 
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borislip

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Something i kinda miss... how the heck do you charge this pack? I don't see any appropriate circuitry, or description of one... so i'd assume an external charger. So add some good CC/CV/balancing charger to the set. And the price ;-)

And honestly... i've been an electronic enthusiast before... and i actually did like coding as well... now i work in this **** :(
 

plexus

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Something i kinda miss... how the heck do you charge this pack? I don't see any appropriate circuitry, or description of one... so i'd assume an external charger. So add some good CC/CV/balancing charger to the set. And the price ;-)

And honestly... i've been an electronic enthusiast before... and i actually did like coding as well... now i work in this **** :(
Good point. I flew RC before the MA and so I have a couple multi-cell balance chargers. the one I typically use is quite small and is powered from 12V DC. In fact, I can power it from a USB pack and it will pump some more juice into the LiPo although USB doesn't have enough power to completely fill the LiPo. So in short, yes you need an appropriate balanced charger to charge up that 4S LiPo. They are pretty cheap on ebay etc for around $20-30 for a single-pack charger, which for me I already had.
 

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