I have a quick question: I have a USB battery pack, and I want to use that battery pack to power a little side project that I have.

Currently, this side project takes an input of 5V 4.8A, and I have seen USB Battery Packs that output 5V 2.4A on one port, and 5V 2.4A on another port for a total of 5V 4.8A.

enter image description here

I was wondering, if I ran two USB cables with their heads plugged into a 5V 2.4A (per port, 2 ports) USB battery pack, exposed the proper wires, would I be able to combine the red wire of one USB cable with the red wire of another USB cable and black wire of one USB cable and the black wire from the other USB cable to create an output of 5V 4.8A? sort of like what is happening below in which many wires are soldered together, and then connected into a single red enter image description here

Otherwise, could I split the ends of the wire that extends from the side project (the item I am trying to power) into two, so: split the end of the red wire in half and the end of the black wire in half. Then, attach a red/black wire to each half respectively and in the end have two red wires flow into the 1 red input wire needed to charge? enter image description here

Thanks, A community member.


1 Answer 1


The specifics depend on the battery pack in question, but many usb power banks and usb supplies with multiple ports have their USB VCC output electronically tied together. The 2.4 limit is not a hard limit enforced by the power bank, rather it is a soft limit. The port is wired with the right resistor voltage divider on the usb data pairs, which tell the phone plugged into it that it's okay to draw up to that amount. This is generally the Apple standard. The phone then limits it's own draw.

That means you don't really need to use two usb ports. Drawing from the two ports help distribute the power through more copper which is nice though.

Note this applies to dumber power banks. Newer packs with Quick Charge or other features have more complicated circuitry and the same may not apply. See Ali's comment below.

  • \$\begingroup\$ Hey! Thanks for the input, I am a real beginner, but from what I understand is that I can combine the outputs like I stated above/in the pictures because the outputs are electronically tied together in the beginning anyways? So I can combine the two USB Cables red wires and black wires together and connect it to a single red/black wire input and thus have 4.8A input? \$\endgroup\$ Dec 15, 2017 at 0:39
  • \$\begingroup\$ From my experience, yes. Of course if the power bank is lying about being able to support 4.8 amps at the same time, then no. \$\endgroup\$
    – Passerby
    Dec 15, 2017 at 0:56
  • 1
    \$\begingroup\$ This is a Qualcomm QuickCharge 3.0 device, with two ports. Because of QC, they must have two independent power sources. Combining their outputs might or might not lead to desirable result. And contacts have their limits too. \$\endgroup\$ Dec 15, 2017 at 1:40
  • \$\begingroup\$ @AliChen So perhaps, I can not combine the outputs. It may cause instability? This is not something that I want to risk. So, no go? \$\endgroup\$ Dec 15, 2017 at 1:50
  • \$\begingroup\$ @OmarSumadi, as Passerby said, "The specifics depend on the battery pack". There are considerations that it might work. Or might not. As suggested here, electronics.stackexchange.com/a/344188/117785 , do a controlled experiment, with monitoring current in both branches. Use dummy load of ~1 Ohm if you are afraid of damaging your "side project". \$\endgroup\$ Dec 15, 2017 at 2:38

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