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Development: USB-Charging Cable for Drone-Battery

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Flydude

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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!
 
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Haha, nice one :)

But i hope you never had to charge your phone using 1W ... ever ;-)

The (really) old chargers out there, which only do 5V and 2A are almost gone for good. But with them you have 10 Watts not 1 Watt.

If we assume a simple world without upping the voltage and linear charging rates the math is pretty simple:

Using the original DJI charger which outputs ~ 37 Watts it takes to charge one Mavic Air2 Battery (with 40 Wh) around 65 Minutes - as i said, only assuming an ideal world with linear charging and so on. Reality is different.

So, to answer your question: if you are out of luck and really have only a charger with 5V/2A = 10 W it would take around 4 hours for one charge.

If you would use a wall charger from, let's say an old Samsung Galaxy S7, which has a rating of 5V/2A in normal mode, but 9V/1.67A in quick charge (and assuming you can negotiate the higher voltage), the charging time goes down to around 2.5 hours.

Using a charger from a nintendo switch, which has 15V/2.6A = 39 Watts, the charging would be on par with the original DJI charger.

Using an apple usb-c charger like mentioned above with 87 Watts, the charging would be capped, because (as of now) i do not want to use more power than the original charger.
But i might be able to increase the output, if the battery does accept that. But i do not reccommend that, as charging above 1C is not so good for the Lipos.

I really know, that this charging cable is not for everyone, but i built it, because i have use for it. Just think of this use-case: i go on a ride with my bike take my mavic and a powerbank. Most powerbanks nowadays do support USB-PD so i can charge my batteries real fast, in the field.

Best regards!
 
tcope said:
USB-PD can deliver up to 100 watts. USB-PD car charger typically put out about 18 watts. Most standard USB chargers put out 12-14 watts.
Click to expand...

USB charger FAQs | CMD

Looks like the standard is more like 2.5W but it can go up from there. I suspect any public places will support the minimum to be the most compatible.

Help me with the math on 3500mAh...
 
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swooshdave said:
USB charger FAQs | CMD

Looks like the standard is more like 2.5W but it can go up from there. I suspect any public places will support the minimum to be the most compatible.
Click to expand...
That article looks old. Quick search on Amazon:

Amazon Choice:
15 watts

Best Seller:
24 watts

Most chargers have quick charge capability these days so they have higher output.
 
tcope said:
That article looks old. Quick search on Amazon:

Amazon Choice:
15 watts

Best Seller:
24 watts

Most chargers have quick charge capability these days so they have higher output.
Click to expand...

Well there will always be exceptions, but the point still stands that publicity accessible USB charging places will be at the minimum rate. My laptop charger is 87W.

The reality is that if you are near a 120v (in the US) plug you would just use the DJI charger. But the original comment was that you could plug into any USB port like in a car. How many watts is a car USB? 1-2? Or even if you had an inverter?
 
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swooshdave said:
USB charger FAQs | CMD

Looks like the standard is more like 2.5W but it can go up from there. I suspect any public places will support the minimum to be the most compatible.

Help me with the math on 3500mAh...
Click to expand...
I think there is some confusion... also i don't know where you are getting your "standard of 2.5W" because that is not the case (anymore) and also relates to power drawn from an old usb-standard port off a PC. This has nothing to do with wall chargers or USB-PD.

The units and math behind electrical power is rather simple. I don't know if the formulas we use here in germany are the same in the US but the math definitely is :)

So the most basic formula is:

P = U * I

Where:

P == Watt U == Volts I == Amps

So just take a look at your wall charger. For USB the Volts have to be at least 5V
The Amps are typically 2A, but could be lower (10 years old maybe?!) or even higher (3-4A).

So: P = 5V * 2A and we get P = 10W

So a very very basic wall-charger without USB-PD (you really get a PD-Charger with every phone produced in the last 5 years), you get an output of 10 Watts.

Your question about the maths with 3500 mAh: the Amps say nothing without the Volts, when charging is concerned.
Yes, the Air2 Battery is rated at 3,5 Ah, the Voltage is around 11.55 V so we get 11.55 * 3.5 = 40.425 Wh (Watt-Hours), aka the capacity.

So, if you charge with 10 Watts for 1 hour, you have charged 10Wh. To charge 40.425 Wh, you need 4 hours. Pretty simple.

The beauty of USB-PD is, that we don't have to charge with 5 Volts and 2 Amps but can ramp that up alot.
Imagine: The Amps stay at 2A but the Voltage is increased from 5V to 15V. So instead of 10 Watts we get (15V * 2A) 30 Watts. The charging time is now only (40Wh / 30W) 1.33 hours.

and as @tcope already mentioned, USB-PD is rated up to 100 Watts. Far more than the 38 Watts of the official DJI charger.


sberfield said:
I'd buy one depending on price.
Click to expand...
That i cannot say for sure right now. as this is only a prototype, all the materials (excluding my work) are around of 40 Euros. Far too high to make a sellable product. But with alot of tweaking i can get to a far (!) lower production price, let alone the fact of mass producing this at my business partners in china.

It would be interesting to know what your maximum price tag would be.

Thanks to all!
 
swooshdave said:
But the original comment was that you could plug into any USB port like in a car. How many watts is a car USB? 1-2? Or even if you had an inverter?
Click to expand...

my BMW 4 Cabrio outputs 5V/3A via the USB-Port in the console.

On my wifes car we have a hot-chilli 12V adapter to charge our phones. It's a simple adapter that provides 2 USB Ports. The rating is 5V/2.4A.

As you state the rating with 1-2 i think you are confusing Amps and Watts maybe?
 
Flydude said:
I think there is some confusion... also i don't know where you are getting your "standard of 2.5W" because that is not the case (anymore) and also relates to power drawn from an old usb-standard port off a PC. This has nothing to do with wall chargers or USB-PD.

The units and math behind electrical power is rather simple. I don't know if the formulas we use here in germany are the same in the US but the math definitely is :)

So the most basic formula is:

P = U * I

Where:

P == Watt U == Volts I == Amps

So just take a look at your wall charger. For USB the Volts have to be at least 5V
The Amps are typically 2A, but could be lower (10 years old maybe?!) or even higher (3-4A).

So: P = 5V * 2A and we get P = 10W

So a very very basic wall-charger without USB-PD (you really get a PD-Charger with every phone produced in the last 5 years), you get an output of 10 Watts.

Your question about the maths with 3500 mAh: the Amps say nothing without the Volts, when charging is concerned.
Yes, the Air2 Battery is rated at 3,5 Ah, the Voltage is around 11.55 V so we get 11.55 * 3.5 = 40.425 Wh (Watt-Hours), aka the capacity.

So, if you charge with 10 Watts for 1 hour, you have charged 10Wh. To charge 40.425 Wh, you need 4 hours. Pretty simple.

The beauty of USB-PD is, that we don't have to charge with 5 Volts and 2 Amps but can ramp that up alot.
Imagine: The Amps stay at 2A but the Voltage is increased from 5V to 15V. So instead of 10 Watts we get (15V * 2A) 30 Watts. The charging time is now only (40Wh / 30W) 1.33 hours.

and as @tcope already mentioned, USB-PD is rated up to 100 Watts. Far more than the 38 Watts of the official DJI charger.



That i cannot say for sure right now. as this is only a prototype, all the materials (excluding my work) are around of 40 Euros. Far too high to make a sellable product. But with alot of tweaking i can get to a far (!) lower production price, let alone the fact of mass producing this at my business partners in china.

It would be interesting to know what your maximum price tag would be.

Thanks to all!
Click to expand...

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.
Click to expand...

You said about plugging into a car. Given that how fast would your charger be?
 
swooshdave said:
You said about plugging into a car. Given that how fast would your charger be?
Click to expand...
as stated above: with my BMW you can do the math pretty quick: 5V/3A equals to 15 Watts. So roundabout 2.5 hours?
But with a typical powerbank, which supports USB-PD, that time goes down real quick as the output is much higher. It all depends on the device that is sending the power, not the cable/charger i developed.

And that is my use case. i use my bycicle alot, don't have access to a 240 Volt grid anywhere but you always have a powerbank with you in theses cases. Or you visit a friend. everyone has a smartphone and (almost) everyone has a USB-PD charger. no need for the bulky DJI charger anymore.

But i really don't want to convince you. as i initially stated, this charging cable might not be for everyone. i developed it primarily for myself :)
 
Last edited:
swooshdave said:
Well there will always be exceptions, but the point still stands that publicity accessible USB charging places will be at the minimum rate. My laptop charger is 87W.

The reality is that if you are near a 120v (in the US) plug you would just use the DJI charger. But the original comment was that you could plug into any USB port like in a car. How many watts is a car USB? 1-2? Or even if you had an inverter?
Click to expand...
Exceptions? These two listings were from the biggest online seller and the Amazon recommendation and best seller. I'd hardly call them exceptions. Truth is, as I mentioned, most USB chargers are 12-14 watts and USB-PD's go up to 100 watts.

I don't completely get the OP's device either. It plugs into an outlet, the same as the DJI charger so no difference there. Seems the benefit would be that the OP's charger then also plugs into a vehicle power outlet. With DJI''s you'd need a seperate car charger or an inverter. So you'd need another device/cable to do both. Most car chargers put out the same watts as USB as they are both quick chargers and quick chargers are (always?) higher in watts. But they are all low in amps. I'm not smart enough to start talking about watts, amps and volts. But even DJI's car charger is slower.

I think it is an interesting idea but not that big of a market. But the OP mentioned he was making it for himself and just asking if there was any other interest.
 
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The standard USB cable seams awfully small gauge to supply more than 20-30 W, especially if it was two meters long ?
 
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Flydude said:
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!
Click to expand...

Get a utility or design patent on this ASAP. YES! You have a very viable solution and depending on the production cost, it will sell for drones or I would imagine almost any rechargeable device.
 
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Cw4bray said:
The standard USB cable seams awfully small gauge to supply more than 20-30 W, especially if it was two meters long ?
Click to expand...
Will work pretty good. Higher voltages work better with the thin cables
Cw4bray said:
The standard USB cable seams awfully small gauge to supply more than 20-30 W, especially if it was two meters long ?
Click to expand...
it really depends on the resistance (ohm) of such cable.
while a thicker cable typically is better, a thinner cable can provide high watts, if the a higher voltage is applied. With USB-PD the Amperes are rarely pumped up above 2-3A and only for higher Amps, thicker cables are needed (not exclusively). Because we ramp up the voltage, there is not much of a problem here.

Cw4bray said:
If it were linear/wattage or smart and managed temp. I'd buy one.
Click to expand...
Fixed Voltage and capped Amps - same specifications as the original charger.
The rest is handled by the intelligent battery which implement all the other safety protocols and is responsible for balancing the individual cells.
The DJI batteries all have some sort of cell-balancer integrated, and some specific checks to prevent a misuse.
 
Last edited:
DanaMc said:
Get a utility or design patent on this ASAP. YES! You have a very viable solution and depending on the production cost, it will sell for drones or I would imagine almost any rechargeable device.
Click to expand...
haha, will think about it!
thanks for your reply!
 

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