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Connecting two USBs from power bank in series

Discussion in 'General Electronics Discussion' started by vuse10, Aug 15, 2016.

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  1. vuse10


    Aug 14, 2016
    I have portable speakers (Supertooth Disco) that receive about 10v input (on the speakers written 12v but the inner batteries total is 10v).
    I have a power bank of 18650 batteries:

    The power bank has two ports of usb, each is 5v dc.
    If I cut the two USB cables, and connect them in series to the powerbank, I will get 10v dc which is enough for my portable speaker, I suppose.

    My question is- can it damage the power bank? because it is manufactured for 5v dc, and I am not sure, maybe if I create a circuit of 10v dc, the computer for the lcd indication might burn.

    What do you think?
    I believe in this forum there are people with more experience in elctornical circuits than me.

  2. Gryd3


    Jun 25, 2014
    I'm willing to put money on the table that you will break your charger if you do what you are thinking...

    The USB port on a power bank most often is powered by a 'boost' type power supply.
    Additional USB ports are often simply just wired in parallel. Making your 'custom' cable would simply result in shorting the ground of USB port 1, to the power of USB port 2... remember they are connected in parallel?
    That means the power of USB port 1 and 2 are connected together internally... What happens if you connect the power of USB 1 to the ground of USB port 1?

    The *only* way this would work, is if the USB ports were *completely* isolated from each other. If they share a common ground, or common power you are going to have a bad time.
    You *may* be able to use two separate power supplies and daisy chain their usb ports together, but they may not operate as expected... they are not meant to operate like this.

    My suggestion for you is to buy one or more lithium based batteries from a hobby store, then go online and find a 'boost' or 'buck' type converter that will convert the lower, or higher voltage to the 12V you need for your speakers.
    These batteries are relatively cheap, and chargers can be picked up easily from various sources. They are also going to hold more power and weigh less than other types of batteries that you may find yourself working with...
    That said, you can buy a 'sealed lead-acid' and simply run the speakers directly from that without any voltage conversions if you are willing to carry around that heavy battery.
    Last edited: Aug 15, 2016
    Anon_LG likes this.
  3. vuse10


    Aug 14, 2016
    Wow! Thank you for the knowledge.
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