[Gta04-owner] How could GTA04 shine

thomasg thomas at gstaedtner.net
Thu Mar 8 12:37:49 CET 2012

On Thu, Mar 8, 2012 at 11:54, Eikka Laakso <eikka.laakso at gmail.com> wrote:
> 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.
>  -Eikka

I don't think the price is really the matter here. The problem is,
that there are no panels which are so efficient that this small
surface will be good for anything.
Also, the peak performance is really hard to reach, as you say
correctly, it has to be sunny, you have to point the device in the
right direction (and angle!), it can't be too hot (the efficiency at
above 320K temperature will be reduced), so all in all even in good
conditions you're likely not exceed 70% of the peak performance.
Also, in almost any condition the performance will vary, and I'm not
sure this is good for the battery as charging will stop regularly and
the current is very low all the time.

So while it would be nice if it'd work, I think there's no real-world
use-case, and solar panels won't become as good in the near future to
change that.
The only use-case I can think of is, if you are in a civilized area
with network coverage, but far away from the next village or road, and
broke both your legs (can't be in the woods!), then it might be viable
to charge for a day instead of crawling to the next road :P

I think if you don't plan to break both your legs but just go hiking,
better take a solid foldable panel with you :)

> 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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