USB quirkiness

[EmptieHand]

I can't figure it out.

I have a Droid Razr (android OS), and I have been using the normal provided micro USB cable to charge my phone with the car USB port for awhile.

Recently I bought a micro USB charger cable that shorts the data connection so that the phone will draw AC charge instead of USB charge from the car. Amazon.com: Naztech Micro USB Charging Cable - BlackBerry, Cal-Comp, HTC, LG, Samsung, Nokia, and Sony Ericsson: Cell Phones & Accessories

Half the time, it works fine and I can drive my entire trip with full AC charging power going to the phone. The other half of the time, the car throws an error and doesn't let me charge my phone using this cable. If I switch to the normal micro USB cable, it works fine (without restarting the car).

Anyone know why this happens?

[EmptieHand]

Thought I'd just update other people on this problem. Seems if the phone is less than 60-70% charge, then the USB won't work. If the phone is greater than 60-70% charge, then the charging cable works fine.

I can't make sense why this would be, but the problem is definitely reproducible with phone charge state.

When taking trips, I just have to be conscious on where my battery level is so that when I get back in the car, I can still charge my phone.

[EmptieHand]

Another update on my monologue here...

Apparently if my Droid Razr is <60% charge and I disable my data connection (I.e., turn off 3g/4g), before plugging in my phone, then it will charge fine. As soon as I turn on my data connection while being charged, the radio throws a "bad USB device" warning and the phone stops charging. If I get the charge state over 70% while charging then turn on my data, the phone will continue to charge without issues.

Weird.

[cyeung]

Does your normal cable allow charging when your phone has less than 60-70% charge?

As for your car not charging the phone below 60% to 70%, perhaps what is happening is that the charge controller on your phone is trying to pull power from the USB port, and the power supply is unable to provide the current (i.e. the oomph). Unfortunately, the USB port was not advertised to be a charging port.

I am not an expert on USB, but the voltage going to your phone is always 5V DC. The minimum current sourcing capacity is 500 mA. Nowadays, it can go up to 2.1 Amps.

[EmptieHand]

My normal cable allows charging when my "special" cable doesn't. I only recall one time, when my normal cable gave me a "bad USB device", but that was about a year ago and hasn't occurred again. I don't recall if my phone had a low charge state at the time.

I use the special cable because it give me faster recharge times. If I'm using GPS navigation and Bluetooth with the normal cable, I lose about 10% charge an hour. With the special cable, I'm able to gain about 10% charge an hour despite "heavy" use.

I guess I could try a cigarette lighter adapter to plug my USB into instead of the USB port.

Now I'm wondering if there is a way to "upgrade" the usb port so that it can provide higher power output.

[cyeung]

Whoever has a service manual can verify this, but my gut says that the USB port is wired to the head unit. Boosting the power output on that would be theoretically possible, but impractical.