Building an off-the-grid solar charger for my mavic 2 pro. Please correct me if I'm wrong, I'm fairly uncomfident with electricity.

[zamboni]

Hi.
I've lived on only solar power in my RV for 4.5 years, without hookups or a generator.
I hike, backpack, etc. I'm DIY and I'm cheap. And I have a Mavic Air. I think I can help with this.

I have carried many ridiculous things on backpacking trips. If you have the will, your legs will carry your stuff. Let's not agonize over weight.

Charging a powerbank from solar and then going from that (either a 12V or 5V output) to charge the Mavic is not an attractive option. The charging will be slow and you'll lose a lot of energy to redundant voltage conversions. You already have the batteries, why add one? I think you should go directly from the panel to the battery.

If you do that, you have to be sure the charge will stop when the batteries are full. Because fire. Normally this is the job of the charger, so I would advise buying the 12V mobile charger and using that. However, these batteries do have intelligence built in (such as self-storage mode), so perhaps that circuit is in the battery. But the batts likely take for granted that a DJI charger will be used so may not safely handle anything much higher than 15V input. "12v" Solar panels generally make about 18V. So I still think you should use the 12V charger. You need the connectors anyway; it's worthwhile just for that. Look for a voltage regulator ("buck converter") online with a variable output adjustment. Amazon has these. Make sure it can handle >20V input and is rated for at least 10A. The low-cost ones are generally not capable of handling much power (for small electronics projects) so this may take some hunting to find -- look for large heat sinks on the PCB. This will regulate the power coming from the solar panel (which will be at varying voltages and currents depending on conditions) down to say 14V so the mobile charger can work correctly. This won't be the most efficient arrangement, but is simple and low-cost. Connect a female cigarette-lighter socket to the output of the buck converter, then test that it's outputting correctly (set it to 14.0V output) with a multimeter before connecting the mobile charger. A fuse and on/off switch on the input side is a good idea too, so you're not connecting things together under load (solar panels are always "on" if there's sun). You can use a fuse as a primitive on/off switch by simply pulling it...just don't lose it.

Specs say the Pro2 battery is almost 60Wh capacity. That may sound like 3 hours of charging with a 20W panel, but that's only in perfect conditions (which never happen), and doesn't account for charging inefficiencies. It also doesn't account for the power loss due to voltage regulation. A 20W panel that is outputting 18V but is bucked down to 14V will effectively only deliver 14 / 18 * 20 = 15.5W. If you stop walking at 10am and aim your 20W panel directly at the sun, best case you could maybe charge one battery to full by 2pm (4 hours * 15.5W = 62Wh). If you plan to strap the panels to the top of your pack (do put them on top, not the back!) and charge while you walk, count on taking basically all day for one battery with a 20W panel (clear sky, no haze). It may even take a bit longer than that. Make sure you're not casting a shadow on your panel with your hat!!! (use the drone to take an overhead video of you walking with your loaded pack and panel on top). Even small shadows kill solar output.

So, if you will burn more than one battery per day, you'll need more panel. That's likely too bulky for practical use. AIMS makes a rather efficient 60W foldable panel for about $200, but it's about the size of a movie poster. This seems impractical to me for packing, attaching to pack, and dealing with wind and other trail conditions. If you can find 30W of panels that actually fit on your pack, that's ideal, but I suspect 20W is about as big as practical. One flight per day ain't that bad, just plan it and make it count!

A lot of the 20W folders I see have USB outputs. USB is at 5V and this means the panel has a regulator built in already. If you cut out the regulator, AND if the panel is configured for typical 12V output, you could use it. But it's also possible the panels are configured to output "6V" (to make the regulator cheaper and more efficient). I think this won't work well for you, because at low voltages you'll only get usable current in very, very good light. Since you can't know this until you cut up the panel, I'd definitely look for one that does NOT have a USB output already on it.

Keep in mind this is all just charging the bird. To charge the controller, use a cheap 12V USB converter in the receptacle from the solar panel -- but realize this will take time away from charging the Mavic's battery. Use this in early AM or late PM when panel voltage is too low to meet the cutoff of the charger (panel voltage tapers to 0 as light intensity reduces). It may be worth adding a simple voltage readout to your setup (on the input side of the voltage regulator) so you know when this is happening. Some regulators have them integrated already.

You'll need some kind of plastic case to mount the regulator in, because it will have lots of sharp bits and needs protection from shorting the PCB. Don't seal the heat sinks inside without leaving airflow. It won't be waterproof, but you won't be using it in the rain, anyway : ).

I think this can work, but it will be a bit of a stretch. Leave yourself time to test and experiment at home before setting out!

 

[MAvic_South_Oz]

Good reply @zamboni . . . something might work for this, just a matter of someone having the time and effort to try it, and it being practical.
Solar panels are probably the limiting things here, both size / output . . . and then getting enough 'good light' through the day when walking / weather.
Tech is charging rapidly too, so in the near future there may be consumer gear available that can work (and work well) for self sufficient outdoor adventurers.

For the controller.
At only 2970mAh, a decent little power bank around 9000mAh could handle several near full charges, only needs std phone type output 5w 2a.
Several charges would get you about 12 flights, maybe enough for the 10 days remote trip.

I hope @krikite finds his his charging utopia and gives some feedback.

 

[DanMan32]

Hi.
I've lived on only solar power in my RV for 4.5 years, without hookups or a generator.
I hike, backpack, etc. I'm DIY and I'm cheap. And I have a Mavic Air. I think I can help with this.

I have carried many ridiculous things on backpacking trips. If you have the will, your legs will carry your stuff. Let's not agonize over weight.

Charging a powerbank from solar and then going from that (either a 12V or 5V output) to charge the Mavic is not an attractive option. The charging will be slow and you'll lose a lot of energy to redundant voltage conversions. You already have the batteries, why add one? I think you should go directly from the panel to the battery.

If you do that, you have to be sure the charge will stop when the batteries are full. Because fire. Normally this is the job of the charger, so I would advise buying the 12V mobile charger and using that. However, these batteries do have intelligence built in (such as self-storage mode), so perhaps that circuit is in the battery. But the batts likely take for granted that a DJI charger will be used so may not safely handle anything much higher than 15V input. "12v" Solar panels generally make about 18V. So I still think you should use the 12V charger. You need the connectors anyway; it's worthwhile just for that. Look for a voltage regulator ("buck converter") online with a variable output adjustment. Amazon has these. Make sure it can handle >20V input and is rated for at least 10A. The low-cost ones are generally not capable of handling much power (for small electronics projects) so this may take some hunting to find -- look for large heat sinks on the PCB. This will regulate the power coming from the solar panel (which will be at varying voltages and currents depending on conditions) down to say 14V so the mobile charger can work correctly. This won't be the most efficient arrangement, but is simple and low-cost. Connect a female cigarette-lighter socket to the output of the buck converter, then test that it's outputting correctly (set it to 14.0V output) with a multimeter before connecting the mobile charger. A fuse and on/off switch on the input side is a good idea too, so you're not connecting things together under load (solar panels are always "on" if there's sun). You can use a fuse as a primitive on/off switch by simply pulling it...just don't lose it.

Specs say the Pro2 battery is almost 60Wh capacity. That may sound like 3 hours of charging with a 20W panel, but that's only in perfect conditions (which never happen), and doesn't account for charging inefficiencies. It also doesn't account for the power loss due to voltage regulation. A 20W panel that is outputting 18V but is bucked down to 14V will effectively only deliver 14 / 18 * 20 = 15.5W. If you stop walking at 10am and aim your 20W panel directly at the sun, best case you could maybe charge one battery to full by 2pm (4 hours * 15.5W = 62Wh). If you plan to strap the panels to the top of your pack (do put them on top, not the back!) and charge while you walk, count on taking basically all day for one battery with a 20W panel (clear sky, no haze). It may even take a bit longer than that. Make sure you're not casting a shadow on your panel with your hat!!! (use the drone to take an overhead video of you walking with your loaded pack and panel on top). Even small shadows kill solar output.

So, if you will burn more than one battery per day, you'll need more panel. That's likely too bulky for practical use. AIMS makes a rather efficient 60W foldable panel for about $200, but it's about the size of a movie poster. This seems impractical to me for packing, attaching to pack, and dealing with wind and other trail conditions. If you can find 30W of panels that actually fit on your pack, that's ideal, but I suspect 20W is about as big as practical. One flight per day ain't that bad, just plan it and make it count!

A lot of the 20W folders I see have USB outputs. USB is at 5V and this means the panel has a regulator built in already. If you cut out the regulator, AND if the panel is configured for typical 12V output, you could use it. But it's also possible the panels are configured to output "6V" (to make the regulator cheaper and more efficient). I think this won't work well for you, because at low voltages you'll only get usable current in very, very good light. Since you can't know this until you cut up the panel, I'd definitely look for one that does NOT have a USB output already on it.

Keep in mind this is all just charging the bird. To charge the controller, use a cheap 12V USB converter in the receptacle from the solar panel -- but realize this will take time away from charging the Mavic's battery. Use this in early AM or late PM when panel voltage is too low to meet the cutoff of the charger (panel voltage tapers to 0 as light intensity reduces). It may be worth adding a simple voltage readout to your setup (on the input side of the voltage regulator) so you know when this is happening. Some regulators have them integrated already.

You'll need some kind of plastic case to mount the regulator in, because it will have lots of sharp bits and needs protection from shorting the PCB. Don't seal the heat sinks inside without leaving airflow. It won't be waterproof, but you won't be using it in the rain, anyway : ).

I think this can work, but it will be a bit of a stretch. Leave yourself time to test and experiment at home before setting out!

Charging the AC battery directly from the solar panels will not work. Even if the voltage matches, there is a minimal current draw that the batteries must have to begin charging. Clearly the panels just don't provide it. The batteries need over 3A at 17V, but with only 20W, the best the panel can deliver if it can provide 17V would be less than 1.2A. Although the batteries can adapt to some extent to the capabiliities of the charger, they can't charge with that low of provided current. At best the voltage to the battery will drop to an unusable level with the excess current draw, or the panel damaged to what is seen by it as a short circuit.

It is the electronics of the batteries that controls everything including ending charging when the batteries are full. All the chargers are really are well regulated power supplies.
Powerbanks are generally the same way. Their internal electronics govern when the charging starts and stops.

 

[Donnie Frank]

Lots of comments here that I'm not going to read. But when it comes to solar, I'm going to guess that an intermediate battery is your best friend. Even then, your results are going to be spotty, as even a brand new, fully-charged, full-size car battery will only charge a few drone batteries before running out.

While I applaud your desire to use solar, the harsh reality is the same reality that stops the entire nation from going solar. Solar is just not ready for prime time yet. So I built a car charger that is "off the grid' as you're going to find. Unfortunately, you WILL have to idle your vehicle at some point.



This charger is scalable (will quick charge or slow charge), will charge Mavic, Phantom, M600 or Inspire batteries (as seen in above photo), and works completely off-grid (car battery). I have charged about 50 batteries so far and have been extremely pleased with the performance of this set-up. But to be honest, it's probably not for the "electrically unfriendly."

Here it is charging Phantom batteries in the field:



Good luck.

D

 

[Flycaster]

When does one realize that the "point of diminishing returns" has been reached.
You either are going to be schleeping a small power station, cables, intermediate batteries, or a bunch of Mavic batteries (maybe 1 a day?) already charged and ready to go.
Cost vs. weight/size vs. battery charging current vs. and just the general mental stress of setting up/taking down, connections, etc.

There will be "the magic smoke" that makes all electronics work....
It's basic physics on storing energy..

I would beg/borrow any batteries from friends I could, and then purchase the remaining delta of batteries for the trip, and carry the charger when/if there is a village with power...

 

[israelshirk]

Trigger warning! I’m a rocket surgeon. If this terrifies you, move along ?

I’ve built some pretty similar kits for SAR situations in the backcountry.

So... To charge a Mavic 2 battery you just need any kind of input source (probably a Lithium Ion pack that maxes at your panel’s max voltage), then a few parallel buck/boost switching regs and good-sized caps that will get you to a steady 17.6V, 5A on your output. After voltage is taken care of, a constant-current circuit/SMD/whatever that maxes at 5A. Pass the (cleaned) output to a CFixer Mavic 2 Battery Cable (red is positive, two wires, nice and convenient). When ready and tested, plug in a battery, turn it on, and it’ll hit full at 17.6V/low amp rate.

My personal setup is now just a few 5000mAh LiPo packs, an ISDT Q6 Pro set to LiPo/4.4V/4S/5A, and an XT60 plug soldered right onto cfixer cables.

So, in short... Charge at constant current max 5A (battery circuitry will trigger a reset any higher), 17.6V max.

And if the cfixer cable is difficult to source, you can 3d print one off thingiverse and just stick thin metal strips in. Can’t remember the pinout off the top of my head, but message me if you can’t find it.

Good luck, test well!

 

[DanMan32]

The thing is, with your setup you're providing 88W. OP's panel only provides 20W, which at 17.6v means 1.1A. The battery won't charge with that little amperage. More likely, because the battery (or your constant current regulator) trying to pull more current than the panel can provide, the voltage will drop or panel damaged.

An intervening power storage is needed to provide a reserve wattage/energy.

Are you sure it is the charger that limits the current to the battery? I would think the smart circuit in the charger would dictate the current draw. It makes sense though since the car charger and AC charger seem to deliver different wattage to the battery, with car charger taking less time to charge, thus more current/watts.
On the other hand, LiPos charge up to about 80% with constant current until max voltage is reached, then switches to constant voltage where the battery draws less and less current. When min current threshold is reached, battery is charged.

 

[israelshirk]

The thing is, with your setup you're providing 88W. OP's panel only provides 20W, which at 17.6v means 1.1A. The battery won't charge with that little amperage. More likely, because the battery (or your constant current regulator) trying to pull more current than the panel can provide, the voltage will drop or panel damaged.

An intervening power storage is needed to provide a reserve wattage/energy.

Are you sure it is the charger that limits the current to the battery? I would think the smart circuit in the charger would dictate the current draw. It makes sense though since the car charger and AC charger seem to deliver different wattage to the battery, with car charger taking less time to charge, thus more current/watts.
On the other hand, LiPos charge up to about 80% with constant current until max voltage is reached, then switches to constant voltage where the battery draws less and less current. When min current threshold is reached, battery is charged.

Re-read, plz. TL;DR got you.

 

[israelshirk]

Vid, because 1. Beer; and 2. Flex ?:

Demos most of the stuff you need, in a completely inexplicable way. Going down to 0.1A works, so I’d actually direct charge from solar and save on the power losses you’d get from multiple boost/buck converters, internal resistance of intermediary batteries, etc. I do remember that being an issue with other models though.

 

[DanMan32]

It's usually the powered device (in this case the battery) that dictates current draw so it is strange that 0.1A would work but certainly possible. It would take forever though and it doesn't work with the car charger. Car charger draws 6A from the car when charging actually starts and charger input cutoff voltage is about 11.2V.

It sounds like you have a current limiter (which is wise) and not a constant current regulator. Big difference. Latter would insist on drawing and providing 5A by adjusting voltage no matter what, where the former makes sure that no more than 5A is drawn, which the battery already is supposed to do.

Basic law of electricity: V=IR.

 

[AMann]

Here’s a project Im doing to make an inexpensive solar and vehicle charged 35Ah (400Wh) portable battery to power a refrigerator, charge my drone and camera batteries and other stuff:

Make your own 400Wh portable power battery for less than $100

I made this 12v 35Ah (420Wh) portable power battery with left over parts, but you can do it for $100 to $150 (or more) depending on options you want,...

www.tacomaworld.com

 

[israelshirk]

It's usually the powered device (in this case the battery) that dictates current draw so it is strange that 0.1A would work but certainly possible. It would take forever though and it doesn't work with the car charger. Car charger draws 6A from the car when charging actually starts and charger input cutoff voltage is about 11.2V.

It sounds like you have a current limiter (which is wise) and not a constant current regulator. Big difference. Latter would insist on drawing and providing 5A by adjusting voltage no matter what, where the former makes sure that no more than 5A is drawn, which the battery already is supposed to do.

Basic law of electricity: V=IR.

You TL;DR’d again. Not wasting my time on your metaphysics. Your concerns are clearly addressed in the video I posted.

 

[DanMan32]

Metaphysics is creating or destroying energy or creating watts in same unit time. Can't be done with physics, unless you get into atomic energy, in which you then convert matter to energy.

Now you can store energy at a lower wattage over a longer period of time than you use the energy from the storage over a higher wattage.
In other words charge an intervening battery at 20W rate for 10 hours will store enough energy (200WHrs) to use 100W for 2 hours.

Also W=VI. That's one of the basic rules of electricity. If you increase the voltage for same wattage, amperage goes down. That's why it's preferred to run high wattage devices at 220V rather than 110V. Less current needed at 220V so the wiring doesn't need to be as big and less power loss over the wiring.

 

[israelshirk]

Metaphysics is creating or destroying energy or creating watts in same unit time. Can't be done with physics, unless you get into atomic energy, in which you then convert matter to energy.

Now you can store energy at a lower wattage over a longer period of time than you use the energy from the storage over a higher wattage.
In other words charge an intervening battery at 20W rate for 10 hours will store enough energy (200WHrs) to use 100W for 2 hours.

Also W=VI. That's one of the basic rules of electricity. If you increase the voltage for same wattage, amperage goes down. That's why it's preferred to run high wattage devices at 220V rather than 110V. Less current needed at 220V so the wiring doesn't need to be as big and less power loss over the wiring.

????

 

[AMann]

Metaphysics is creating or destroying energy or creating watts in same unit time. Can't be done with physics, unless you get into atomic energy, in which you then convert matter to energy.

Now you can store energy at a lower wattage over a longer period of time than you use the energy from the storage over a higher wattage.
In other words charge an intervening battery at 20W rate for 10 hours will store enough energy (200WHrs) to use 100W for 2 hours.

Also W=VI. That's one of the basic rules of electricity. If you increase the voltage for same wattage, amperage goes down. That's why it's preferred to run high wattage devices at 220V rather than 110V. Less current needed at 220V so the wiring doesn't need to be as big and less power loss over the wiring.

If you can turn matter into energy, e=mc^2, the equation can also be reversed to e/c^2=m and energy turns into matter, right? At least it has been stated as theoretically right by physicists. But we do this all the time here on Earth whenever we go shopping. I work and then go buy more stuff!

 

[DanMan32]

OK so I watched your video.
The beginning was ridiculous. One could make up any cable/connector combination they want, doesn't mean it will work.

You used a buck/booster so you are cheating a bit. You don't have volt/amp meters on both sides of the buck/booster. I see you allowed 5A to the M2 battery and since the buck/booster is actually a universal charger, you told it the M2 battery needed 17.6V (4S LiHV). However what you didn't show was how much current/watts was being drawn from your source that's providing a lower voltage. I guarantee you that if you measured it, more than 5A was being drawn if it was less than a 4S pack and even as a 4S pack, 88W was being drawn. You mentioned watt-hours. That's a measure of capacity, not power. There's a safe limit on how many amps/watts you can pull from a battery source.

Assuming at the significantly lower current allowed to the M2 that it was actually charging and not just showing it was charging (only way to tell is to see if SoC indication ever goes up) then you may have something there. I didn't think it would allow it to get that low. But 0.1A at 17.6V is a very low wattage and would take FOREVER to fully charge.

We're not told what voltage the 20W panel delivers, probably 12 volts and that's at full sun. Yours based on the connector would suggest 5V but hard to tell. Again no voltmeter was used to show what it was.

Assuming the panel can handle what your "box" demanded from it, the M2 batteries are just under 60WH so in full sun and properly regulated to not pull more than 20W, it would take up to 3 hours to charge an M2, probably more since 20W is max.