Solar powered multi-USB device charger with LiPo backup

Discussion in 'The Projects Forum' started by mikesoniat, Feb 28, 2016.

  1. mikesoniat

    Thread Starter New Member

    Jan 23, 2013
    6
    0
    Hi,

    I'm working on a portable solar project designed to charge multiple (3 or 4) USB devices concurrently. My solar array is producing around 7V @ 3.5A. Using off-the-shelf eBay circuit boards I'm able to charge multiple devices. But as soon as a cloud passes over or something blocks a portion of my solar array, some devices (namely iPhones) stop charging.

    To fix this problem, I would like to include a battery with charging circuit just to keep the power steady during these short periods when the solar power drops below USB levels. I can find lots of battery charging circuits and DC-to-DC boosters, but they all seem to max out at 1A input and only feed the boosted battery power to the USB ports. This seems like a big waste of power since the array is producing 3.5A.

    My question is, how can I use the full solar current when it's available and only supplement with the battery when needed?

    Thank you in advance for any help you can offer.
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,145
    3,055
    The simplest and most versatile solution is to add more PV panel. More power! (Ever see Tim the Tool Man Taylor?)

    Otherwise it sounds like you want a battery-to-USB solution that can sustain 3.5A for ... how long?...maybe 30 minutes?

    Note that off-the-shelf solar charge/load controllers are designed to do what you want, to keep the battery topped up and supply the load directly if possible.
     
  3. mikesoniat

    Thread Starter New Member

    Jan 23, 2013
    6
    0
    Thank you for your quick reply, wayneh, and sorry for my delayed one. My project is intended to be portable, so I have limited ability to add more panels.

    Like I said, I'm currently able to charge multiple devices as long as I have full sun overhead. It's only when some cells are shaded momentarily that I need the extra help from the battery.

    Can you suggest a circuit that could supply direct power to the USB ports when the solar current is sufficient to keep the devices charging, but pull a little extra boost from the battery during these short durations? The circuit will also have to include a charging circuit to keep the LiPo battery topped off.
     
  4. wayneh

    Expert

    Sep 9, 2010
    12,145
    3,055
    I don't have a solar charge controller suggestion on hand. Do some reading and searching. See here, for example, or here. If you want something simple, try searching for "simple solar charge controller circuit" or such.
     
  5. mikesoniat

    Thread Starter New Member

    Jan 23, 2013
    6
    0
    I'll check out those links. Thanks for all your help!
     
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