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Field battery charging ...
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dobmatt
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I'm getting ready for long summer expedition on houseboat with my Inspire 1 Pro and P3P fleet. Having no access to off-shore power outlets, the boat is self sufficient with 1KW solar system available and 12V/225Ah battery bank. That's plenty, no worries here. To charge both Inspire and Phantom batteries I've build a pair of 2-channel chargers, utilizing DC-DC step-up converters. The conversion is set from available 12V (more or less) to Phantom's 17.5V and Inspire's 26.3V accordingly. I'm testing devices right now, trying to determine proper charging current. The chargers works charmingly with 5A starting current for TB-47, filling the batteries 100% from 15% in 67min. 6A charging current packs TB48's from 15% to 100% in 71min. Not bad at all, although I can push it even more. The question is how much more, without sacrificing battery health. With 6A current I'm close to what DJI 180W rapid charger is delivering, but isn't it just enough? After all 5 or 10 minutes less of charging time is not really a big deal, since my charger do 2 batteries at once. And they're smart: too much juice going in causes charging shut-off, I believe around 8A ...

Any suggestions will be appreciated greatly, brothers.   
2016-7-12
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Henry Mo-Yung
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Hi Matthew,

It is always full of expectation for one to start off a long expedition to remote places like you are going to. We are looking forward to seeing your wonderful footages.

Regarding field charging under your circumstances, it appear to me that your setup that limit the current to 6A will be sufficient. The DJI 180W charger will, to a certain extent, push through a 6.9A current through the initial constant current charging state to the batteries, which will heat up a little more than I consider healthy to the batteries, in particular if you will be in hot climate like this moment of the season. May be I am more on the conservative side since DJI intelligent flight batteries are specified to operate up to 70 degree Celsius. But to me, better be safe than sorry, ending up with degraded batteries in a remote area where no replacement batteries can be sought.

Would you have time to share with us at this juncture more details about the pair of 2-channel chargers?

Henry
2016-7-12
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dobmatt
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Henry Mo-Yung Posted at 2016-7-12 19:59
Hi Matthew,

It is always full of expectation for one to start off a long expedition to remote place ...

Henry, thank you for your input, valuable and well articulated as usual. Your opinion about charging current issue sounds exactly like mine: don't push it too much. I'm fine with 6 amps, rendering reasonable charging time without noticeable battery temp rise.

I'm on fire right now, gathering and loading equipment and supplies for my expedition, but I'll try to share more details about my chargers before departure for vacations.

Matthew,
BTW, I really enjoy reading your posts. It's a rare example of good old school of writing with respect to this art. Said that, English is my second language, still in the process of learning ...  
2016-7-12
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Donnie
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dobmatt Posted at 2016-7-12 13:42
Henry, thank you for your input, valuable and well articulated as usual. Your opinion about chargi ...

Henry gives , well thought  answers.  I may have the answer some time but not as well articulated as Henry .  

Well done Henry

donnie
2016-7-12
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RichJ53
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Henry Mo-Yung Posted at 2016-7-12 04:59
Hi Matthew,

It is always full of expectation for one to start off a long expedition to remote place ...

On target Henry!

Nice work

Rich
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dobmatt
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Henry Mo-Yung Posted at 2016-7-12 19:59
Hi Matthew,

It is always full of expectation for one to start off a long expedition to remote place ...

Here we go, this is my field charger ... It's based on an DIY project by Peter Homer, published several months ago on YouTube (), just slightly improved. The charger features two discrete channels with 600W DC-DC Step-up Converters, which can be set up either for 12 or 24V DC power supply and for Phantom or Inspire/Matrice 100 batteries. The converters are available on eBay from China, 12.96 USD each. Thanks to the smartness of DJI batteries no balancing circuitry is required, therefore the concept is very simple: 12V (or 24V) goes in, 17.5 or 26.3V goes out. The charging current is adjustable to a required level, since batteries will not accept anything crazy and perform safety shut-off. Two TB-48 batteries depleted to 15% are charged with 6A starting current in 70 minutes, give or take.
As simple as it is, the conversion process is costly and consumes roughly twice the output amperage. With both channels charging from 12V car battery the supply current can go up to 22 amps! I'm not sure what is the cigarette lighter fuse typical rating, but it may be not up to the task. If I'll have to go into wilderness with my birds I'll carry fully charged 100Ah deep cycle battery in the trunk of 4x4. Not my case, since I have 225Ah battery bank on the boat.

my field charger.jpg
600W DC-DC step-up.jpg
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Henry Mo-Yung
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dobmatt Posted at 2016-7-13 14:26
Here we go, this is my field charger ... It's based on an DIY project by Peter Homer, published sev ...

Thank you Matthew, for sharing this while being on fire packing stuffs for the expedition.

Will search ebay for the DC-DC Step-up Converters. For sure, the 10A fused cigaret lighter connector cannot support dual Converters, but it can be simply connected directly to car batteries - we will have a much faster replenishing speed comparing with the stock DJI car charger.

Thank you again, Matthew.

Henry
2016-7-13
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Rinzler
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Sucks still stuck at 1c rates thou. But thats because of the onboard controller on the baord not being able to take it.
2016-7-13
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dobmatt
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Rinzler Posted at 2016-7-13 23:27
Sucks still stuck at 1c rates thou. But thats because of the onboard controller on the baord not bei ...

Well, one of the duties the DJI battery brain performs is limiting the charging rate in order to protect LiPo cells from being abused by brutal feeding. If I remember correctly mine TB48 batteries shuts down with approx. 8 amps charging current. Another words I'll hardly consider this feature as a weakness or disability of DJI's batteries.

On the other hand the difference while charging with higher (say 6.5-7 A) current is not that dramatic as one can expect, gaining perhaps 8-10 minutes at the expense of battery health.
2016-7-13
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dobmatt
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Henry Mo-Yung Posted at 2016-7-13 20:21
Thank you Matthew, for sharing this while being on fire packing stuffs for the expedition.

Will s ...

Pleasure is mine, Henry. I'll gladly provide you with more tips and hints if you planning to build such device for yourself. Here's one for the beginning: consider 1200W models instead. (http://www.ebay.com/itm/26199040 ... =STRK%3AMEBIDX%3AIT)
Although 600W converters works just fine, bigger model features better designed circuitry with true CV/CC (Constant Voltage/Constant Current). This translates for smoother, more stable output. It also provides 12V auxiliary output for forced cooling, although not really needed with such generous power surplus. I've installed fans on mine charger anyway, just in case.

Feel free if you have any questions or doubts.

Matthew
2016-7-13
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Rinzler
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dobmatt Posted at 2016-7-13 14:48
Well, one of the duties the DJI battery brain performs is limiting the charging rate in order to pr ...

Meh I would expect 2c rates. 2c would not effect the life of the cells. This was probably more of a cheaper solution for DJI and more of a simpler solution for end users. Been flying helis for 10 years now and have never 2c rates degrade a lipo before my thrashing on it in 3D. I've actually got a set of 3s that around 3 years of age now still flying on my 450 . But the 1c vs 2c is an debatable topic
Side note thou. What charge controller are you using for your panels?
2016-7-14
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dobmatt
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Rinzler Posted at 2016-7-14 20:48
Meh I would expect 2c rates. 2c would not effect the life of the cells. This was probably more of a ...


Well, I may try to open the valve a bit more to reach 2C charging rate, since I've got a plenty of headroom in my charger. With 6 amps current the TB48 battery is barely lukewarm at the end of bulk charge (approx. 36 min). After that the current goes down rapidly and the battery is absorbing/balancing for the remaining 30 minutes of charging cycle ...

Controller for my solar panels, you mean? It's a rare find, Italian made by Western Co, model WRM30.
(http://www.western.it/en/regolat ... -impianti-off-grid/)
This charger features 2 discrete MPPT channels summed at output, therefore no matter which side of my boat is exposed to the oven I'm harvesting as much energy as possible.
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Rinzler
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dobmatt Posted at 2016-7-15 01:03
Well, I may try to open the valve a bit more to reach 2C charging rate, since I've got a plenty of ...

Thats not a bad charge controller for those panel load you have. I run a Morningstar Tri-star 30 MPPT. I have two 50v panels hooked in series that are 142 watts each on my camper. I avg around 22 Ah in full sun. Nothing like what you are pulling in lol
2016-7-15
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dobmatt
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Rinzler Posted at 2016-7-15 20:09
Thats not a bad charge controller for those panel load you have. I run a Morningstar Tri-star 30 M ...

For average boat or camper such power plant like mine will be a overkill for sure. My boat, however, is propelled alternatively by 2kW electric motor, and that's the only reason. With this system I can move slowly around for several hours and still have enough energy left for night, running a fridge, laptop, coffee maker etc. Will see how it'll handle additional DJI batteries charging this year, since it is sucking a lot of juice ...
2016-7-15
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RichJ53
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dobmatt Posted at 2016-7-14 22:03
Well, I may try to open the valve a bit more to reach 2C charging rate, since I've got a plenty of ...

Hi dobmatt
I believe the limiting factor will not be your power supply in this case. The Intelligent flight battery circuit will not allow the amps needed for 2C charging and will limit this be shutting off. (flashing LED overcurrent) For what ever the reason is... DJI is limiting the charge rate for these packs. It has been discussed in detail before on the forum.

Maybe this is an indicator of the type and quality of the battery cells used by DJI?  

Anyway, I hope you have a great trip and much success

Rich
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Rinzler
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dobmatt Posted at 2016-7-15 13:12
For average boat or camper such power plant like mine will be a overkill for sure. My boat, howeve ...

Well be ready for some shots once you get them
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Rinzler
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RichJ53 Posted at 2016-7-15 13:42
Hi dobmatt
I believe the limiting factor will not be your power supply in this case. The Intellige ...

The cells are good for it but that controller as you stated the controller is not. For one the gauge used on the balance leads is to thin for full 2c rate. Also it does not seem to have enough FETs to handle the current in real time as it does try to balance while in a bulk state.
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