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!

 

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.

 

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.

 

3. I need help choosing the right battery pack...

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.

 

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.