What would happen if a charger tried to pull more current than a QC 3.0 source can output?

[fuzzybabybunny]

I've got this charger:

https://store.dji.com/product/mavic-car-charger

It takes 12.7 - 16V input from a car and outputs 13.05V at 6.1A (~80W)

I want to utilize a USB-PD and / or USB-C QC 3.0 charger.

I can get a USB-C trigger:

https://www.ebay.com/itm/UPD005-PD-...C4-polling-HID-/273424369188?oid=273518419377

It connects to a USB-C QC or PD power source and allows me to select the output voltage.

What I want to do is connect:

QC 3.0 Power Supply -> USB trigger set to output 12V -> 12V car charger for DJI battery -> DJI battery

The idea is to use a QC 3.0 power supply to recharge a DJI battery (albeit slowly).

QC 3.0 can only output up to 18W of power, so if I used the USB trigger to select 12V as the output voltage, the QC 3.0 source would only output a max of 1.5A, but the DJI battery charger wants to output 80W of power.

Would this destroy the QC 3.0 source? Or would the QC 3.0 source just happily output a continuous 12V @ 1.5A and the DJI charger would simply charge the batteries at a slower rate (18W?) without damaging anything?

 

[LTC8K6]

I believe your last sentence is correct.

One possibility is that the DJI charger will try to supply 6 amps, and this will pull the QC voltage too low, causing the DJI charger to stop charging due to low voltage.

 

[LTC8K6]

Some folks have had the DJI charger refuse to charge unless the supply voltage was above 13 volts, so you might want to look into that.

Above 13 volts would mean the car is running.

 

[fuzzybabybunny]

I believe your last sentence is correct.

One possibility is that the DJI charger will try to supply 6 amps, and this will pull the QC voltage too low, causing the DJI charger to stop charging due to low voltage.

Is there a way to calculate voltage drop if the charger tried to pull a lot of amps? What if I set the USB port to output something like 16V instead via USB-PD?

 

[LTC8K6]

The DJI charger will try to protect the car battery, so it will give up if the voltage is pulled too low.
I suppose you could just measure it with a USB voltage meter or tester.
I think you need to set it above 12.7 volts anyway. I'd probably start with it at 14 volts, to mimic a running car.
https://www.amazon.com/Klein-Tools-ET920-Capacity-Resistance/dp/B07GXZHPVR

 

[fuzzybabybunny]

The DJI charger will try to protect the car battery, so it will give up if the voltage is pulled too low.
I suppose you could just measure it with a USB voltage meter or tester.
I think you need to set it above 12.7 volts anyway. I'd probably start with it at 14 volts, to mimic a running car.
https://www.amazon.com/Klein-Tools-ET920-Capacity-Resistance/dp/B07GXZHPVR

Hmmm...


Say that I had a USB-PD charger that could only output 45W max.

So I could set it to output 15V but it could only deliver 3A.

When the DJI charger pulls from it the voltage drop might not be pulled that low, maybe 13V. In that case would the DJI charger continue to try to pull 80W (6.15A) and blow up the USB-PD charger? 13V isn't low enough to have reached the stage where the DJI charger is made to shut off to protect the battery.

 

[LTC8K6]

I'm going to guess that the DJI charger is intelligent, since it monitors the port temp and the voltage, and it will monitor the supply voltage and adjust accordingly.

Generally they start off at a low current, and begin to ramp the current up, until they detect a supply voltage drop, which indicates the limit of the supply, then they ramp down the current until the voltage recovers. They look for a "sweet spot" with max current at an acceptable voltage.

I was not able to find the exact specs of the charger though, so I'm just guessing that the DJI charger is chip controlled.

 

[fuzzybabybunny]

I'm going to guess that the DJI charger is intelligent, since it monitors the port temp and the voltage, and it will monitor the supply voltage and adjust accordingly.

Generally they start off at a low current, and begin to ramp the current up, until they detect a supply voltage drop, which indicates the limit of the supply, then they ramp down the current until the voltage recovers. They look for a "sweet spot" with max current at an acceptable voltage.

I was not able to find the exact specs of the charger though, so I'm just guessing that the DJI charger is chip controlled.

Interesting.

One of the pain points of owning a DJI drone is that the batteries don't charge via USB. You've gotta carry with you a separate charging system and an AC-DC power brick just to charge the batteries, which makes it very difficult or inefficient to charge their batteries out in the field in places that only have DC power sources (USB power banks, solar panels, the car).

But their 12V DC car charger option looks like it could be made to work then with a USB-PD source, huh?

If it doesn't work, what are the chances of ruining the DJI battery and the DJI charger? I'd imagine that the greatest chance of ruining something is ruining the USB charger, right?

 

[LTC8K6]

Perhaps this could work?

https://mavicpilots.com/threads/dji-car-charger-setup.21361/post-333501

https://www.ebay.com/itm/DROK-Numer...-Boost-Converter-DC-10-40V-to-6A/272349236646

 

[kfe1026]

You should be fine, and you'll definitely be fine to test it at the very least. USB C is becoming the new standard, specifically because of its ability to be used universally; with the exception of some very early C port devices (which are basically just normal USB connectors with a C port swapped in place of a micro connector, that are merely providing a symmetrical plug).

The variance oscillator contained within USB-C charging rectifiers is what will allow a broader power supply input conversion, and should most likely ONLY effect the rate at which a device charges.