Help With Configuration Please

Epiales
Epiales Registered Users Posts: 15 ✭
in Solar Beginners Corner #1
Hey all,

Just working on a small project and wanted to see if I was understanding things correctly. Thank you for taking the time to look and check it :blush:

I have 6 battery storage boxes. They each hold 6 X 18650 2400maH. If I connected them together with usb, is it possible to make it 12V? Diagram below. And if so, what would the amps be on it?

I'm thinking that since the usb's would be 5V each (per set of 2), that with 3 of them, that would make it 15V, but not sure at what ampage would be? I'm guessing a 15V 15a battery, but not sure. Also, would be nice to know the wattage. Why I thought I would ask here. As stated, a small project, but I would like to make sure I am thinking it all out straight in my head. Thanks for the help.

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Comments

  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #2
    Re: Help With Configuration Please

    This is very confusingly drawn!

    Are the six cells in each box in parallel or in series?
    and are the two boxes in each pair in series or parallel?
    Just putting in a USB interface gives you a regulated 5V out with a current limit. But if all you are doing is using USB cables with no controller, then just about anything could happen, most of the things not good!

    If you have three ungrounded USB power outputs, then you could in theory wire them to give you 15V, which you could then regulate down to 12V, but it would be quite a kluge.
    Also, the peak current into a short circuit from 6 18650s in parallel could easily be over 40A, which is nothing to play around with.
    Do you have any idea what you are doing?
    SMA SB 3000, old BP panels.
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  • Epiales
    Epiales Registered Users Posts: 15 ✭
    #3
    Re: Help With Configuration Please

    All six boxes are parallel with protected batteries
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: Help With Configuration Please

    The term "USB" is irrelevant here as it is just being used as a form of connector, isn't it? If these are USB packs it gets more complicated.

    Otherwise it is the same application of series & parallel connections anywhere:
    Two in series doubles the Voltage, two in parallel doubles the current.

    The drawing appears to show three "5 Volt" sources connected in parallel, which would still be 5 Volts but at 3X the current capacity.

    If it is meant to be three connected in series then you have 3X the Voltage at the same current as one unit, and also the issue of polarity of connectors and the danger of shared ground.

    On the whole a rather hard way to try and come up with 12 VDC. Two 6 Volt battery packs connected in series gives you 12 Volts. If you have six of these in total, then you make up three such strings and connect the strings in parallel to increase the current.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #5
    Re: Help With Configuration Please
    Cariboocoot wrote: »
    The term "USB" is irrelevant here as it is just being used as a form of connector, isn't it? If these are USB packs it gets more complicated.

    Otherwise it is the same application of series & parallel connections anywhere:
    Two in series doubles the Voltage, two in parallel doubles the current.

    The drawing appears to show three "5 Volt" sources connected in parallel, which would still be 5 Volts but at 3X the current capacity.

    If it is meant to be three connected in series then you have 3X the Voltage at the same current as one unit, and also the issue of polarity of connectors and the danger of shared ground.

    On the whole a rather hard way to try and come up with 12 VDC. Two 6 Volt battery packs connected in series gives you 12 Volts. If you have six of these in total, then you make up three such strings and connect the strings in parallel to increase the current.
    It is not completely clear, but most likely the packs are just six lithium batteries in parallel, giving less than five volts (between about 4 and about 3 volts depending on SOC) but capable of recharging a cell phone battery using the same input as an actual USB charger. But that is just a guess. The six cells may actually be wired in three parallel pairs to give an unregulated 6-8V out.
    SMA SB 3000, old BP panels.
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