Question Modifying USB port to support fast charging

operationc4

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So I haven't had much luck researching this since my searches get diluted with non-technical sources. I have a USB port in my car that connects to the stereo so that my phone can connect via Android Auto. The problem is that the charging speed from that port is quite lacking to the point where the phone discharges faster than it can recharge.

What I was planning to do was to run a line from the cigarette lighter to a super-fast charging compatible charger, and then replacing the VCC pin inside the stereo USB so that the phone can draw from that. And yes, I am aware that I will have to use wires capable of at least 45w.

The only problem is that I am not quite sure how fast charging works exactly. The current is limited by the phone, but does it need to communicate with the charger via data pin? If so, would doing so mess up communication between the phone and the stereo? I am also assuming that the voltage stays at 5v the whole time. Also, if there is a better way to do this, please let me know.
 

ex_bubblehead

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Very bad idea. Better have the local fire department on speed dial. Especially if "The only problem is that I am not quite sure how fast charging works exactly" You don't just "add" fast charge to a port as there is much feedback between that being charged and that doing the charging. If you want fast charge then purchase a device with that function built in.
 
Refer to https://electronics.stackexchange.com/questions/265832/how-does-usb-power-delivery-work-with-voltages-above-5v-without-damaging-5v-peri

But the sticking points:
  • USB-PD only goes up to 3A for power profiles under 100W. Which means that to deliver additional power, the voltage is raised ( the other voltages are 9V, 15V, and 20V)
  • While the spec allowed for negotiating additional USB-PD power profiles over the VBus line, almost no device uses it and a later revision of the spec deprecated its use. So it's safe to assume the only way to use additional USB-PD profiles is with a Type-C connector as it uses the CC pin for negotiating.
  • Note that USB-C hosts use the CC pin as a device detection. So no, you can't splice the VBus and CC lines from the stereo (if your stereo has USB-C) and connect it the charger, because the stereo will no longer be able to tell if a device is connected or not.
Basically, you're SOL here.
 
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operationc4

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Refer to https://electronics.stackexchange.com/questions/265832/how-does-usb-power-delivery-work-with-voltages-above-5v-without-damaging-5v-peri

But the sticking points:
  • USB-PD only goes up to 3A for power profiles under 100W. Which means that to deliver additional power, the voltage is raised ( the other voltages are 9V, 15V, and 20V)
  • While the spec allowed for negotiating additional USB-PD power profiles over the VBus line, almost no device uses it and a later revision of the spec deprecated its use. So it's safe to assume the only way to use additional USB-PD profiles is with a Type-C connector as it uses the CC pin for negotiating.
  • Note that USB-C hosts use the CC pin as a device detection. So no, you can't splice the VBus and CC lines from the stereo (if your stereo has USB-C) and connect it the charger, because the stereo will no longer be able to tell if a device is connected or not.
Basically, you're SOL here.
Well, the stereo uses USB-A. Couldn't I just break out to a USB-C and only connect the data pins and gnd from the stereo and the Vbus, CC, VCC pins from the charger to the new USB-C output?
 
Well, the stereo uses USB-A. Couldn't I just break out to a USB-C and only connect the data pins and gnd from the stereo and the Vbus, CC, VCC pins from the charger to the new USB-C output?
Instead of mucking with the stereo's connections, this is what you can do after a cursory glance on the internet:
  • Get a USB-C to USB-C cable capable of fast charging
  • Get any USB cable with USB-A on it
  • Open up the USB-C to USB-C cable, find the four USB 2.0 data lines and cut them. You may want to cut the USB 3.0 data lines as well
  • Connect the USB 2.0 data lines and a ground line to the USB-A cable. Do not connect the 5V line.
As a disclaimer I'm not a professional hardware engineer and this could potentially damage your stereo or device still.

And at the end of the day, you shouldn't really need USB-PD fast charging when running Android Auto anyway. My Galaxy S22 runs off my head unit's non fast charging USB port without losing battery life.
 
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What about something like this ?

https://latestelite.com/products/automatic-charging-car-phone-holder?currency=USD&variant=32395675500626&utm_medium=cpc&utm_source=google&utm_campaign=Google Shopping&gclid=CjwKCAjwlcaRBhBYEiwAK341jZg1LcDyseGXab0_PGJON6nNm-O4rEB2NWwFmKo-5EDWdfBs-6nJOhoCG34QAvD_BwE

Then no cutting no splicing no fire hazards
It would charge as your hooked as normal.

As A Professional Driver I can't stress enough Pay Attention to the Driving
Not the Phone.
This could work on the caveat that a data-only USB cable be used to connect to the stereo. Otherwise the phone will use wired charging. And no, you can't do wireless and wired charging at the same time.

On that note, I'm also curious if OP's stereo doesn't support wireless Android Auto. And if it doesn't, well there's a device that adds it: https://9to5google.com/2022/01/21/aawireless-review-android-auto-dongle/
 

hang-the-9

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So I haven't had much luck researching this since my searches get diluted with non-technical sources. I have a USB port in my car that connects to the stereo so that my phone can connect via Android Auto. The problem is that the charging speed from that port is quite lacking to the point where the phone discharges faster than it can recharge.

What I was planning to do was to run a line from the cigarette lighter to a super-fast charging compatible charger, and then replacing the VCC pin inside the stereo USB so that the phone can draw from that. And yes, I am aware that I will have to use wires capable of at least 45w.

The only problem is that I am not quite sure how fast charging works exactly. The current is limited by the phone, but does it need to communicate with the charger via data pin? If so, would doing so mess up communication between the phone and the stereo? I am also assuming that the voltage stays at 5v the whole time. Also, if there is a better way to do this, please let me know.
Some cars have an upgrade the dealer can do, or maybe a kit sold online, that changes the USB ports. My Mazda has that, to use Android Audio they have a kit that swaps the USB with ones that provide more power. Natively without hacking things apart.
 

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