Solar Battery Pack

Discussion in 'The Projects Forum' started by efi, Dec 7, 2011.

  1. efi

    Thread Starter New Member

    Dec 7, 2011
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    0
    Hi guys,

    I've decided to build myself a solar powered power pack so that I can charge my iPad when I'm traveling, but I'm missing the knowhow. Obviously that's why I'm here :)

    So this is my inventory so far:

    1. 20W Solar Panel
    Output: 24V/900mA

    2. Car cigarette charger adapter for iPad (CAR-C29):
    Input: 12-24V DC
    Output: 5.1V DC / 2.1A

    3. I need help choosing the right battery pack (LiPo?) and (4.) effective charge controller combination.

    And since this is a portable pack I need to minimize the bulkiness of the whole thing, so I'm ready rip plastic boxes and melt solder if needed!

    Thanks!
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,087
    3,027
    There's an important distinction to resolve: Are you planning to merely charge your battery with the panel, while it's completely separate from the iPad (much safer!), or, are you hoping to connect your solar panel directly to the iPad? This may also be possible but requires more research and care.
     
  3. efi

    Thread Starter New Member

    Dec 7, 2011
    3
    0
    My initial plan is to leave the solar panel and batteries under the sun and recharge the iPad later.

    Although I've considered the option of a direct charge (that's why I got a 20W panel) I still want to keep the things on the safe side.
     
  4. wayneh

    Expert

    Sep 9, 2010
    12,087
    3,027
    That's the crux. NiMH are cheap and readily available. NiCads are a bit easier to charge (less vulnerable to overcharge) but are getting harder to find. Li-ion are great for volumetric charge density but are the most expensive. Sealed lead acid is another option.

    I don't think we can make these choice for you. Pay attention to the total capacity in mAh. There's no point to your project if it doesn't provide a reasonable operating time. I'd aim to have at least the same capacity as the internal battery. You should also estimate how long it will take your panel to charge your battery. If the panel can't keep up with the iPad (even though they're separated), you'll eventually run out.
     
  5. efi

    Thread Starter New Member

    Dec 7, 2011
    3
    0
    I did some environmentally friendliness research on batteries and it looks like the NiMh and LiFePO4 are best choices? Correct me if I'm wrong.

    So I guess I'll need one power pack which under worse circumstances can operate the iPad intensively for 24h.

    The iPad's internal battery: 24.8 watt-hours, 3.75V.
    So let's say 100watt-hours is a target
    So with the 20W panel 5-7 hours of direct sunlight should top the power-pack?

    Is this scenario possible?

    2x 50watt-hours batteries in the pack.

    Case A: Solar Panel charges 1 pack, the other pack is being used to operate the iPad.
    Case B: Solar Panel charges 2 packs.


    I' need help choosing the optimal operational voltage of the system too.
     
    Last edited: Dec 7, 2011
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