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I'm working on a project that requires a 5V, ~4A power supply. This project needs to be portable, so I am looking at power banks. However, I cannot find a portable power bank that will output that much current through a single USB port.

I did find the following, which provides 2 separate 2.4A USB ports: https://www.amazon.com/gp/product/B01EIHCRYC/ref=ox_sc_act_title_1?ie=UTF8&psc=1&smid=APBASW1H82KJH

I am thinking of creating(or buying) a USB Y cable to connect both ports in parallel which would keep the voltage at 5, while adding the current together for a total of 4.8A. My project uses a barrel jack, so I would need a female USB to barrel jack cable connected to the end of the USB Y cable. Is this feasible? Or is there a better way for me to power up my project? Thanks.

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  • I don't think it would work, the old USBs aren't meant to transfer that much power and even if it will work (which I doubt) it will very fast overheat. The One Plus 3's USB Type C charger does claim to have that kind of power amazon.com/Oneplus-Dash-Type-Charge-Cable/dp/B01K43UTWG (using a special technology) but it is not a power-bank.
    – Yisroel Tech
    Commented May 30, 2017 at 2:07
  • @YisroelTech Some Apple products such as iPad Pros take 12W to charge and come with USB power adapters that can provide 2.4A @ 5V. That's more than the USB spec requires a USB power supply to provide, but lots of third parties have adopted Apple's way for the power supply to signal that it's capable of supplying 2.4A. That said, the USB Type-C has optional higher power draw capabilities built into the spec so that's a cleaner way to go over some de facto standard that started out as a vendor-proprietary extension.
    – Spiff
    Commented May 30, 2017 at 7:18
  • Are you sure that the two outlets are "separate"? Also, keep in mind that the typical USB Type-A connector has contact rating of 1.5A, so be aware of possibility of melt and smoke, unless you solder your leads directly.
    – Ale..chenski
    Commented May 30, 2017 at 18:12
  • Thank you for all your replies. My project only requires 4A of current when used at full tilt. I don't plan on using it to the max, so since I am unable to find a single port 4A powerbank, I'm thinking a 2.4A will be sufficient enough. I guess I'd rather not guess and risk burning the power supply - or worse, my project..! Thank you again!
    – Anne Lam
    Commented May 31, 2017 at 3:15

2 Answers 2

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Simply using a Y-shaped cable is likely not to work for two reasons. The first one has already been explained in Overmind's answer. You need to know if the power bank can actually deliver 2.4A simultaneously on both ports. Not all power banks can.

Secondly, USB devices have to communicate to the charger how much current they want to draw. Otherwise they are supposed to fall back to 500mA for USB 2.0 or 900mA for USB 3.0. This communication is done by connecting the data pins with a resistor. The resistor value tells the charger how much current the device would like to draw. The charger should support this kind of communication to actually deliver the requested current.

Then again, many kinds of non-standard implementations exist. I wouldn't risk it for a potentially expensive project. I'd recommend you get some guidance from someone that knows about electronics so that you can build a proper mobile power supply.

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Not recommended to be tried. It's all a matter of how the bank is designed internally. With multiple cells in parallel you certainly are not limited by them, but then you have the problem of how the internal circuits are designed.

  • case 1 - there could be one circuit with 2 ports connected to the same area, which means you only deal with a limitation of current due to connections and/or wire thickness, in which case you can merge together the 2 outputs and you get to double the max current of one output

  • case 2 - there could be separate circuits (charge channels), in which case connecting them together can have unforeseen consequences, including frying the circuits of both channels

A better way to power up your project: maybe so - judging by the case, it has either 5 or 6 cells of 3000/2500 mAh. 5 or 6 cells means at least 5A continuously guaranteed. If your consumer does not need exactly 5V and can function correctly with 3 to 4.2 V, you can connect a solid cable directly to the combined cells terminals and get your high current. If you need 5V you can't bypass the internal circuit of the bank - you'll have to actually see how it is constructed (if it's case 1 or 2).

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