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I've got a Nexus 5X phone which does not support QuickCharge, but it does support 'fast charging' through a 5V/3A USB Type C charger.

Normally I charge it with a Type C 5V/3A charger, and a USB Type C to Type C cable:

USB Type C 5V/3A Charger + USB C-to-C cable

This works fine. This is the original charger that came with the phone.

Now I'm wondering, what if I get a dual charger like this:
(note that those are two Type A USB ports, not Type C)

USB dual charger

Along with a USB Type A to Type C cable:

USB A-to-C cable

Will this allow me to charge just as fast? And in that case, should I use the QuickCharge 3.0 port, or the 'regular' 5V/3A (non-QC) port? Or can I expect them both to work?

Basically what I'm wondering is:

  1. Can I get my Nexus 5X to fast charge over a Type A to Type C cable as well, provided that the charger does indeed deliver 5V/3A through the Type A output?

  2. The Nexus 5X does not support QuickCharge 3.0. But considering that QC3.0 specifies support for various voltage and amperage ranges including 3.6V-6.5V/3A, could I still expect my Nexus 5X to fast charge through a QC3.0 charger? (which would again be through a Type A to Type C cable)

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  • @Xavierjazz how is this not related to computer hardware? Or what would be a better stackexchange area to post this? I actually posted it here on moderators' suggestion in electronics.
    – RocketNuts
    Aug 28, 2017 at 5:32

2 Answers 2

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For the Nexus 5X and Nexus 6P you need a USB-C to USB-C cable and proper charger to properly fast charge.

No USB-A to USB-C cable that is compoiant should be able to supply 5 V at 3 A. The most you can expect if both the charger and the phone are compliant is to fall back to USB BC 1.2 and pull about 1.5 amps. This is per the USB Specifications. The max "legacy" power USB Type-C to Type-A cables is allowed to support is 1.5 Amps per BC1.2.

enter image description here

If the USB-C to USB-A is non-specification compliant it may "lie" and have the phone try and pull a full 3 A. This XDA Article goes further explains what is going on:

xda article snip

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  • Actually, the 56 kOhm pull-up should force the device (consumer) to limit its consumption to 500 mA if it is USB 2 port, or to 900 mA if in USB 3 port. Not 1 A. Aug 26, 2017 at 20:49
  • Thanks, however one thing I don't understand: to my knowledge there are tons of legacy USB chargers with a Type A connection that provide 2.1A or 2.4A. There are supposed to be used with devices that either have a Micro USB post (so that's a USB Type A to Micro USB cable), or Apple Lightning post (through USB A to Lightning cable). I assume they do support charging at 2.1A or 2.4A? Is that situation fundamentally different to my phone where I use USB A to C ? (assuming I have the right cable)
    – RocketNuts
    Aug 28, 2017 at 5:38
  • @RocketNuts I have expanded on my answer quite a bit. In general, the 2.1A and 2.4A were not actually fully compliant, and were created by the manufacturers to charge everyone's new ipads and phones fast enough while the USB specification caught up.
    – justing
    Aug 29, 2017 at 0:14
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In order to get full charge over Type-A to C cable, the Type-C end of cable must provide 10 kOhm pull-up inside its overmold. Then a Type-C compliant device/phone should be able to take all 3 A. However, this would make this nice short A-C cable illegal, because if someone will use this cable with a regular PC, it might create hazardous overcurrent condition.

Since the Nexus 5X doesn't support QC (no v2.0, nor v3.0), and the QC3.0 port in the QC charger likely doesn't have an alternative BC 1.2 protocol, your phone will rely on CC pin pull-up in the Type-C cable overmold. If the particular QC charger doesn't police the QC protocol and will output the minimum (5 V 3 A), then your phone will take the same current as from any other port.

Therefore, I expect that there will be no difference which Type-A port to use, unless the LG phone/charger uses full-blown Power Delivery protocol. In the latter case your "dual charger" won't work at all, maybe at 500 mA.

To get a practical sense of what difference do you have, I recommend to invest in a USB power meter/tester like this one, with proper voltage range.

enter image description here

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  • Thanks, I'm gonna get one of those. I don't fully understand what you mean with a short cable being illegal, and causing overcurrent in a regular PC? (btw I just posted this cable picture for illustration purposes, to make clear what I'm connecting to what, my cable is actually 1m)
    – RocketNuts
    Aug 28, 2017 at 5:42
  • @RocketNuts, if your actual cable (A-C) has 56k pull up, your phone won't take more than 500 mA from whatever it is plugged in, be it PC or your charger. If your cable allows your phone to get more, it means that the cable has either 22k or 10k pullup, which is illegal for a A-C type of cables. Because if you use this cable with a PC, your phone may overload the PC port. Aug 28, 2017 at 6:03
  • I see, thanks. But how does that work with QuickCharge 3.0, which also operates through A-C cables, in case of a device that (unlike my Nexus 5X) does support QC3.0. That is supposed to support fast charging i.e. more than 1A, right? So far all QC3.0 chargers I've seen, always use Type A connectors. Do they come with these special 22k or 10k pullup cables (don't even know what pullup is, will google that) that are meant explicitly for a QC3.0 charger and not to be used in regular PCs?
    – RocketNuts
    Aug 28, 2017 at 10:06
  • Or all the legacy USB chargers out there with a Type A connector, there are plenty of those with 2.1A or 2.4A output. In what circumstances are they supposed to deliver their full power?
    – RocketNuts
    Aug 28, 2017 at 10:08
  • @RocketNuts, Type-C connectors do allow third-party protocols over D+/D- lines. Most regular "fast" chargers employ Chinese charger signature, where D+ is shorted with D-. It could be either inside the charger port, or in a specially supplied "charger cable". There are many variants, that's why it is a confusing mess. Aug 28, 2017 at 17:30

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