Development: USB-Charging Cable for Drone-Battery

[maxpower]

Hi there,

since my first Mavic Pro i always wanted to have a more flexible way of charging the drone batteries on the go. Unfortunately, only car chargers were available, nothing via USB.

I think DJI missed out on a big feature for the mavic air2 by not implementing USB-PD charging.
Finally i got my act together and developed a power delivery system for that.

It is more or less a small cable where you can plug in your drone battery, on the other end are some ICs, Chips, and so on. But pretty small and very light. There is also a USB-C Connector.

So basically it works like this: you have your typical wall charger (for your smartphone, macbook, etc.) or any other type of charger that has a USB-Port.
From there you plug the cable into my dev-charging-cable and it will output the correct voltage to charge the drone battery.

Of course, this can be done quite easily, with some simple step-up converters but using the old-school method would mean: USB-Charging with 5-Volts and maximum of 2 Amps, so well, it would take forever to charge one battery.

This is where the USB-Power-Delivery (USB-PD) Standard comes into play: within my dev-charging-cable is also a small circuit to negotiate the USB-PD Voltage.
Modern chargers (like Smartphone Chargers) can supply alot more than 5 Volts, going up to 20 Volts and also high Amps, so the charging Watt is very high.

For example, there are some wall chargers from apple supply 87 Watts via USB-C! The official DJI Charger for the Mavic Air2 only outputs around 38 Watts. So that's more than enough power.

My circuit is designed, so it tries to negotiate a very high output power from the carger and converts that into the exact same voltage, the original charger uses. Even the Amps are capped, so i won't apply to much power to the battery.

What's the benefit?

I only need to carry around one simple cable. I can charge my mavic air2 battery wherever i want, as everybody has some usb-charger in the car nowadays or a friend nearby or whatever.
If the charger supports USB-PD (which almost every smartphone charger does), the battery can be charged rather quickly - and in the unfortunate event of a charger, that does not support USB-PD, i can still charge my drone (even at McDonalds there are USB-Ports in the tables ...), but it will take longer.

I am currently redesigning the layout of the PCBs and shrinking everything down a little more, then i will post some pics here.

I mainly did this for myself, but i am wondering if i can make a product out of this?
I did not find anything like this anywhere, so what do you guys think?
Would you need one of those? Would you buy one?

Of couse this method can be used for any drone battery, even the ones from the mavic pro 2 with 4S Lipos.

Thanks in advance for your response!

I think you have a great idea. I would like to charge my drone batteries using USB power banks when off the grid. I have 2 iMuto power banks 27000 and 30000 mAh that deliver 5V/2A. For me charging overnight is perfectly fine, I’m not concerned about speed. Since this would replace the need for the official DJI car charger because I could now use the 12V to USB car adapter, I’d gladly pay you upwards of $60 even $70 USD as long as it robust and reliable.

A suggestion if you are really serious about it, would be to incorporate a quick connector so it could be used for other drones that use the same/similar charging voltage (around 13V???). So it’s USB-to-your circuit-to-quick connector and the you have various adapters, quick connector-to-MA2 battery plug, quick connector-to-M2 battery plug, quick connector-to-MP battery plug, etc.

Put me down for one.

 

[crosswired]

Standard USB C cable can carry 100 watts.

are you sure? considering 5V as a standard, it would need 20Amps draw... it will burn it in seconds

 

[Flydude]

are you sure? considering 5V as a standard, it would need 20Amps draw... it will burn it in seconds

that info is correct. USB-PD works differently. You will never achieve 100 Watts with 5V. With USB-PD the Voltage is raised to 20 Volts and up to a Current of 5 Amps. 20 Volts with 5 Amps is also 100 Watts.

The gauge must only allow up to 5 Amps. Or more specifically: thicker cables (less resistance) are only needed if the electric-current has to be raised. This is not needed with USB-PD as the voltage is increased.

Just look at the official apple 87-watt adapter:

The cable is not (alot) thicker than other usb-c cables.

So, the main takeaway is: less current, thinner cables. You want more power (watts) with the same cable? increase the voltage.

 

[Flydude]

I think you have a great idea. I would like to charge my drone batteries using USB power banks when off the grid. I have 2 iMuto power banks 27000 and 30000 mAh that deliver 5V/2A. For me charging overnight is perfectly fine, I’m not concerned about speed. Since this would replace the need for the official DJI car charger because I could now use the 12V to USB car adapter, I’d gladly pay you upwards of $60 even $70 USD as long as it robust and reliable.

A suggestion if you are really serious about it, would be to incorporate a quick connector so it could be used for other drones that use the same/similar charging voltage (around 13V???). So it’s USB-to-your circuit-to-quick connector and the you have various adapters, quick connector-to-MA2 battery plug, quick connector-to-M2 battery plug, quick connector-to-MP battery plug, etc.

Put me down for one.

thanks alot for your reply!

I will definitely consider changeable output cables to accomodate different drones!

currently i am designing a small 3d-printed case for electric-stuff. will post some pics soon!

 

[crosswired]

that info is correct. USB-PD works differently. You will never achieve 100 Watts with 5V. With USB-PD the Voltage is raised to 20 Volts and up to a Current of 5 Amps. 20 Volts with 5 Amps is also 100 Watts.

The gauge must only allow up to 5 Amps. Or more specifically: thicker cables (less resistance) are only needed if the electric-current has to be raised. This is not needed with USB-PD as the voltage is increased.

Just look at the official apple 87-watt adapter:

The cable is not (alot) thicker than other usb-c cables.

So, the main takeaway is: less current, thinner cables. You want more power (watts) with the same cable? increase the voltage.

not exactly true ...
as first I was talking about standard USB-C cable, not a psu itself
as second, try to apply 15V to 5V device and you'll see what happens

 

[Flydude]

i think we have a confusion here... unless i missed a post from you ;-)

a cable is not a device. you can apply whatever electrical power you want to.
if the current (amperes) are to high, the cable will get hot and eventually burn.

for my setup, a usb-c cable is used for the input of electrical power.
and i am using USB-PD which does not ramp up the current but instead the voltage. which is why i can safely put up to 100 watts through that rather thin usb-c cable. that is all within the specifications. actually i will only draw (at tops!) 40 watts.

not exactly true ...
as first I was talking about standard USB-C cable, not a psu itself
as second, try to apply 15V to 5V device and you'll see what happens

so let's have a real world scenario:
imagine i have an apple charger like the above picture. This adapter will output 5 Volts and 2 Amps (so 10 Watts) in normal mode.
Only if the receiving device (my cable!) talks to the charger and establishes a valid link they can "agree" on higher voltages and/or higher amps.

So my device (aka cable) wants the power-adapter to send 20 volts and 2 amps. The apple adapter complies and outputs 40 watts via the usb-c cable into my cable (more an adapter of sorts).

my adapter is also a step-up and step-down converter with a fixed output voltage. so my adapter sees: hmm 20 volts... that's too high. the battery needs 13.2 volts. i will drop the volts.
also my adapter checks if the amperes are too high and throttles that aswell.

in the case that the power-adapter (like an older powerbank) does not handle usb-pd and only delivers 5 volts my cable handles that too. it checks if the voltage is too low. then it will raise the voltage through an step-up and that will charge the DJI battery, but slower because we just have 5volts x 2amps = 10 Watts.

i hope that clears things up? if not, i am happy to try again ;-)

 

[crosswired]

yeah, missed the idea of psu and device negotiating charging conditions, with constant values e.g 100W=5V*20A on maximal power draw cables diameter will be crucial as thinner will start to heat up and burn

 

[Flydude]

i am glad we could clear everything up! thanks for your input, this might help other people! i always appreciate a good discussion

 

[Kueller]

Excited to see someone working on this, can't believe DJI didn't make a Type-C PD charge cable from the start, would've appreciated one of those about 1000x more than the battery bricking sequential charge dock they did send.

I'm currently waiting on some parts to arrive to try bubba rigging a type-c charger myself: SCS001V1 eval (STUSB4500) sink board and the 4x multicharger from Ali. I'm no EE though, just kind of bored, hope I don't blow anything up!

 

[Flydude]

The STUSB4500 is a great choice. It will work with almost all PD objects you need to have and is highly configurable and programmable.

Best of luck on your implementation!

 

[Cw4bray]

Wait for an aftermarket double the length cable (two meters) then look at the line loss, even at a higher voltage.

 

[Flydude]

That's right. Most "cheap" cables are bad and have high resistance.

I am using my custom built solution with a very short (100cm) cable (original Samsung note 9 charging cable). Works great so far

 

[Flydude]

Current status report:

- reworking alot of the internal ICs, switching parts
- designing the case
- lots of testing

The parts have to be arranged a little better but currently the final (3D-printed) case will look something like this:



Size (in millimeters):
84 mm x 51 mm x 20 mm

For reference: a typical credit card has the base-size of 85.6 mm x 54 mm

So the base is a little bit smaller than a credit card, but the case is still too high (2 cm). I am working on that right now by re-arranging the internals and throwing out some pieces I might not need. Also I am in the process of replacing some parts with industrial grade compontents (means: smaller). I am sourcing them directly from china so it might take a while until I receive the new parts here in germany.

To the left of the case there will be the USB-C Input, to the right will be the Output-Port where the Mavic-Charger will be connected:



As you can see, the plug will be changeable so you can replace it with whatever you need.

Currently, the weight of the complete package is at around 50 gramms. This might also slightly change in the future.

Test-Results:

I tried to charge my batteries at around 15% as i don't deplete them completely. The charge was then again up to 100%. Results may vary a little bit.

Charger	Voltage	Current	Power	Time for full charge (15% -> 100%)
Original Nintendo Switch Charger	15V	2.6A	39.0W (note: Power was capped to 37.0W)	59 minutes
PowerBank with USB-PD	12V	2.0A	24.0W	92 minutes
Nokia Smartphone-Charger	5V	3.6A	18.0W	123 minutes
Smartphone-Charger (USB-PD)	9V	1.7A	15.3W	142 minutes
PowerBank without USB-PD	5V	2A	10W	227 minutes

 

[maxpower]

That is nice and compact, I like it.

 

[otherguy]

I would buy this right now!

 

[upzirons]

That sounds great, I've been searching high and low for a solution like this for some time and none exists. I think to myself someone could make a reasonable profit if they had a cable or adapter that allowed usb battery charging for the mavic airs. I've seen enough people looking for this on forums. I even bought a DC cable for the battery with a DC to USB adapter but couldn't get it to work out of a wall outlet or out of a power bank. Can you please advise me on how to configure a DIY solution to this? You can DM if you'd like. Thanks!

 

[Flydude]

sorry, was a little busy the last weeks, just sent you a PM.

The progress on my end stalled a little bit since not all parts arrived yet from china. So i still just have my working prototype. As soon as the first cheaper and finalized version with all the parts is ready i will post the pictures!

 

[Flydude]

Status update:

Still working on internals. Currently there is only support for USB-PD, but many chargers in the USA use quickcharge [aka QC] (in my opinion far inferior to USB-PD). Quickcharge is mainly for mobile phones and a proprietary standard used by qualcomm and usually only licencensed for phones with a qualcomm chip (aka snapdragon). I am thinking of implementing both standards, but the USB-PD seems the better option as it is almost royalty free and supports much higher watts. on the other hand, many people in the USA (maybe even all of North America) use wall-chargers with QC.

Without support for that, those chargers would be limited to 5V and 2A. So i am still not finalizing the product right now.

Attached you will find some pictures how i charge my mavic air 2 battery (Input and output labels are switched, don't worry about that ...):

Here i am charging with my nintendo switch adapter. Input is 15Volts with around 2.4 Amps, so about 35 Watts.



The output to the battery is around 29 Watts. Don't worry about the Voltage, it is normal, that the voltage drops while using high currents.




Next up is charging with a typical usb-wall charger, which does not support USB-PD, so 5 Volts and 2 Amps.



As you can see, the battery charges just fine, albeit it will take longer without USB-PD

 

[dawgpilot]

Status update:

Still working on internals. Currently there is only support for USB-PD, but many chargers in the USA use quickcharge [aka QC] (in my opinion far inferior to USB-PD). Quickcharge is mainly for mobile phones and a proprietary standard used by qualcomm and usually only licencensed for phones with a qualcomm chip (aka snapdragon). I am thinking of implementing both standards, but the USB-PD seems the better option as it is almost royalty free and supports much higher watts. on the other hand, many people in the USA (maybe even all of North America) use wall-chargers with QC.

Without support for that, those chargers would be limited to 5V and 2A. So i am still not finalizing the product right now.

Attached you will find some pictures how i charge my mavic air 2 battery (Input and output labels are switched, don't worry about that ...):

Here i am charging with my nintendo switch adapter. Input is 15Volts with around 2.4 Amps, so about 35 Watts.

View attachment 111244

The output to the battery is around 29 Watts. Don't worry about the Voltage, it is normal, that the voltage drops while using high currents.

View attachment 111245


Next up is charging with a typical usb-wall charger, which does not support USB-PD, so 5 Volts and 2 Amps.

View attachment 111246

As you can see, the battery charges just fine, albeit it will take longer without USB-PD

View attachment 111247

Very cool. I agree that QuickCharge support would be pretty useful to have here in the USA. Many of my extra Anker battery packs and cellphone chargers support QuickCharge but not USB-PD.

 

[Tomcat16]

Hi there,

since my first Mavic Pro i always wanted to have a more flexible way of charging the drone batteries on the go. Unfortunately, only car chargers were available, nothing via USB.

I think DJI missed out on a big feature for the mavic air2 by not implementing USB-PD charging.
Finally i got my act together and developed a power delivery system for that.

It is more or less a small cable where you can plug in your drone battery, on the other end are some ICs, Chips, and so on. But pretty small and very light. There is also a USB-C Connector.

So basically it works like this: you have your typical wall charger (for your smartphone, macbook, etc.) or any other type of charger that has a USB-Port.
From there you plug the cable into my dev-charging-cable and it will output the correct voltage to charge the drone battery.

Of course, this can be done quite easily, with some simple step-up converters but using the old-school method would mean: USB-Charging with 5-Volts and maximum of 2 Amps, so well, it would take forever to charge one battery.

This is where the USB-Power-Delivery (USB-PD) Standard comes into play: within my dev-charging-cable is also a small circuit to negotiate the USB-PD Voltage.
Modern chargers (like Smartphone Chargers) can supply alot more than 5 Volts, going up to 20 Volts and also high Amps, so the charging Watt is very high.

For example, there are some wall chargers from apple supply 87 Watts via USB-C! The official DJI Charger for the Mavic Air2 only outputs around 38 Watts. So that's more than enough power.

My circuit is designed, so it tries to negotiate a very high output power from the carger and converts that into the exact same voltage, the original charger uses. Even the Amps are capped, so i won't apply to much power to the battery.

What's the benefit?

I only need to carry around one simple cable. I can charge my mavic air2 battery wherever i want, as everybody has some usb-charger in the car nowadays or a friend nearby or whatever.
If the charger supports USB-PD (which almost every smartphone charger does), the battery can be charged rather quickly - and in the unfortunate event of a charger, that does not support USB-PD, i can still charge my drone (even at McDonalds there are USB-Ports in the tables ...), but it will take longer.

I am currently redesigning the layout of the PCBs and shrinking everything down a little more, then i will post some pics here.

I mainly did this for myself, but i am wondering if i can make a product out of this?
I did not find anything like this anywhere, so what do you guys think?
Would you need one of those? Would you buy one?

Of couse this method can be used for any drone battery, even the ones from the mavic pro 2 with 4S Lipos.

Thanks in advance for your response!

That sounds awesome, I would be interested. How quickly could a MA2 battery fully charge?