Join Date: Mar 2017
Location: Chicago, IL
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As they say, a picture is worth a thousand words, so hopefully with the three pictures I have here I'll convince the non-believers that it is possible to draw more than 500 mA from the USB ports in our Mazdas. Please see the attachments (as a new member I'm unfortunately not allowed to include images in the message body yet).
The first picture shows the situation that everybody complains about: a phone connected directly using a regular USB data cable. The current is limited to 500 mA and that's pretty much what the app shows here (it shows 420 mA, but you need to add the regular discharge rate to it, which is slightly over 100 mA on this phone).
The second picture shows nearly the same situation, but here the regular USB data cable was swapped for a "charging only" cable: one where the data wires are not connected on the USB-A side and are shorted on the micro USB side. Lo and behold, the phone now charges at 900 mA! Since in the second case the data wires are not connected, the car infotainment system cannot access the phone so you can't play music stored on it, you can't use Android Auto, etc.
Do not despair though! The third picture shows a more complicated setup, with a powered USB hub. It's not clearly visible in the picture (sorry!) but both car USB ports are connected to the hub: one as the data input, the other as the power source. The infotainment system now sees the phone, yet it still charges at the high rate!
There are two points that I would like to stress:
1. Not all USB hubs are created equal. The hub not only needs to be powered, but it needs to support the USB BC 1.2 specification for fast charging. The particular hub shown (sorry, I can't post links, but just search Amazon for, e.g., "unitek bc 1.2 hub") does, but when I tried the same trick with an Amazon Basics hub, which has an external power supply and ports marked as "Fast charge", it didn't work -- the phone still charged at just 500 mA. This Unitek hub also has the advantage of not using a proprietary charger but a standard micro USB port so it can be powered directly from the second car port without any additional adapters.
2. Not all USB cables are created equal, either. Many cheaper cables use thin power wires (28 AWG) that are unable to handle 900 mA. This is especially the case if, like me, you only have the USB ports under the armrest so are forced to use longer cables, extension cables, etc. I went to the trouble of taking apart the center console to run a USB extension to under the CD drive in the front, only to later find out that I cheaped out and the cable had such losses that I was seeing barely over 500 mA by the time it reached the phone. I then bought extension cables with 21-22 AWG wires and the problem disappeared, but I had to take the center console apart again.