[Gta04-owner] How could GTA04 shine

Eikka Laakso eikka.laakso at gmail.com
Thu Mar 8 11:54:06 CET 2012

I can see this as a proof of concept project if someone wants to build 
it. However to be usable even as an emergency battery recharge system it 
would require 20 times more powerfull solarpanel. Since it takes 
something like 4 days to charge the battery, assuming we can get 50% of 
the max power for 12 hours per day. Even in this situation someone would 
need to keep the panel aligned with the sun all the time and it has to 
be sunny all day. Unfortunately this means that it's not really feasible 
to integrate this into a phone. Far better solution would be to have a 
bigger solar panel that charges a different battery when you leave it in 
the sun. When it's full you'll swap the batteries.

You might have enough power to make an emergency call after a few hours 
of pointing the phone to the sun, but it's kind of rare situation where 
the call is still relevant after a few hours. There might be a small and 
powerfull solar panel out there, but it's not likely to be cheap enough 
for consumer use.


On 08.03.2012 11:05, Christoph Mair wrote:
> On Thu, Mar 8, 2012 at 9:43 AM, Bob Ham<rah at bash.sh>  wrote:
>> On Thu, 2012-03-01 at 19:27 +0000, Radek Polak wrote:
>>> while we are talking about competing with Android and iPhones, here is my idea
>>> that can make GTA04 attractive:
>>> - solar charging - not many phones have this and it should be quite easy to
>>> place small solar panels on the back of GTA04. And they are quite cheap...
>> I think this is an amazing idea.  Now that we have viable 3D printable
>> case designs, this is a realistic possibility.  It would be easy to
>> design a new, thicker backplate that can house a solar panel.  I can
>> imagine having one unmodified backplate for normal usage and one
>> backplate with a solar panel to take to music festivals, camping, etc.
>> A quick bit of searching turned up this suitably-sized panel
>> http://uk.farnell.com/sanyo/am-5710car-sce/solar-cell-outdoor/dp/1679078
>> which is rated at 134mW.  I presume the electrical output would have to
>> be conditioned somehow before being fed to the battery controller.  Do
>> any of the EE-minded people here have an idea of what that would entail?
> The open circuit voltage is specified with 6V. The AC charge path
> (available at the debug connector) supports 6.5V maximum. Therefore It
> should "just work" to connect it directly to these pins. To get better
> efficiency a MPPT (maximum power point tracker) is recommended. Its a
> chip which regulates its own input voltage to the value where the
> panel delivers the highest output current.
> Just one note: the highest current you can get from this solar panel
> is 15mA. Unfortunately we (still) do consume a lot more power during
> suspend. This solution will only charge the battery (very slowly!)
> when the device is off. But the Idea is great anyways. Maybe there are
> other (foldable?) panels with higher output power..
> Christoph
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