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Old 06-26-2012, 11:31 AM   #1
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Solar powered Kindle Touch

Hello Everyone!

I have been thinking about this for a while, now I finally made it: My solar powered Kindle Touch!

Here is what I did:

The main component is a Maxim 1551 LiPo charge controller (http://datasheets.maxim-ic.com/en/ds...51-MAX1555.pdf)

You can get a free engineerings sample directly from Maxim.
The other component is a PowerFilm® MPT6-75 flexible Solar cell (http://www.ebay.de/itm/PowerFilm-MPT...item3f00057552)

The Maxim 1551 doesn't need much more, three 1uF Capacitors (I took two 0.47 uF in parallel as they are slightly thinner) and that's it.

For testing I added a control led, that indicates that there is power from the solar panel.

The solar panel is attached to the DC in, as it accepts higher voltages than the usb in.

With this Setup I was able to get a charge rate of 50 mA in direct sunlight, which should charge the battery completely in about 30 hrs in the sun.

I don't have long time experience with it so far, but that should be enough so I never will have to charge my kindle again with a wall adapter, but I will let you know...

So for about $20 you have a solar powered kindle!

AS ALWAYS: BE CAREFULL IF YOU TRY TO COPY THIS, I AM NOT RESPONSIBLE FOR ANY DAMAGE TO YOUR KINDLE OR ANYTHING ELSE!
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Old 06-26-2012, 11:51 AM   #2
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What about temperature rise?
Plenty of bright sun down here in mid-Texas, USA -
Enough to melt a Kindle if left in the sun for 30 hours.

Well, we don't get quite 30 hours of sunshine per day, but live through any day in August and you will think that we do.

For our European members - how far south is central Texas? Think: Casablanca.

A neat idea anyway.

Last edited by knc1; 06-26-2012 at 12:13 PM.
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Old 06-26-2012, 04:33 PM   #3
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Old 06-27-2012, 12:56 AM   #4
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Well, I'm not that far south (Munich region), so I didn't have problems with the temperature rise so far.
If you have enough sunshine (as in Central Texas) it should be fine if you put your solar kindle close to a window inside your house and it still should produce enough energy to load the battery.

Is there a way to check the battery status more detailed? The bar indicator in the menu is quite coarse grained.
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Old 06-27-2012, 04:34 AM   #5
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Quote:
Originally Posted by nick-tech View Post
Well, I'm not that far south (Munich region), so I didn't have problems with the temperature rise so far.
If you have enough sunshine (as in Central Texas) it should be fine if you put your solar kindle close to a window inside your house and it still should produce enough energy to load the battery.

Is there a way to check the battery status more detailed? The bar indicator in the menu is quite coarse grained.
The "diags" mode should have a more detailed battery management report.

Munich? Do they even have "Sun" there?
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Old 06-27-2012, 05:46 AM   #6
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Well, not as much as in in Texas ;-)

So there is no way to get battery information via ssh?
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Old 06-27-2012, 06:24 AM   #7
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Quote:
Originally Posted by nick-tech View Post
Well, not as much as in in Texas ;-)

So there is no way to get battery information via ssh?
The voltage and charge/discharge current is available in the /proc interface, except in the K5 it is deeply buried in /sys, I think...
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Old 06-27-2012, 09:29 AM   #8
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Great job nick-tech!

On K5 the easiest way to get battery info is:
Code:
[root@kindle root]# gasgauge-info 
usage:
gasgauge-info [-chklms] [-i <seconds>] <registers...>
-h      help
--help  help

-i s    interval (seconds)

-c      output state of charge in percent
-s      same as -c
-v      output battery voltage value
-l      output battery charge current (load)
-k      output battery temperature
-m      output battery available capacity (mAh)
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Old 06-27-2012, 02:05 PM   #9
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Quote:
Originally Posted by baf View Post
Great job nick-tech!

On K5 the easiest way to get battery info is:
Code:
[root@kindle root]# gasgauge-info 
usage:
gasgauge-info [-chklms] [-i <seconds>] <registers...>
-h      help
--help  help

-i s    interval (seconds)

-c      output state of charge in percent
-s      same as -c
-v      output battery voltage value
-l      output battery charge current (load)
-k      output battery temperature
-m      output battery available capacity (mAh)
Nice find. A lot of the /proc interfaces have a shell wrapper like this for them, but the proc output is often easier to parse in a script, while the wrapper is easier for human use.
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Old 06-27-2012, 02:18 PM   #10
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Looking at the diags tests, or the test scripts in /test (depending on the Kindle model) may help 'discovering' tools like these .
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Old 06-27-2012, 06:20 PM   #11
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Thank you! exactly what I was looking for. I will keep you informed ;-)
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Old 06-28-2012, 06:01 AM   #12
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Code:
[root@kindle root]# gasgauge-info -l
-23 mA
This is what I get when wireless is on and my kindle is in partly cloudy sunlight (well, Munich ;-), so it still charges with 23 mA with some load present.

The maximum I could get so far were 40 mA (Wireless on). But I also have to say that the battery is 90% full now, so maybe the charge controller already starts limiting the current.
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Old 06-28-2012, 06:44 AM   #13
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That 2600 karma did not last long. Somebody gave a bigger karma bump than I can give.
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Old 06-29-2012, 11:14 AM   #14
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I think I was mistaken. It seems like negative values are discharging the battery. Today I monitored power consumption while downloading a 4 MB pdf and it rose to ~-140 mA which is beyond the physical capacity of the solar cell I use.

So now my correct maximum charge rate (still with system an wireless on) is about 13 mA in direct sunlight.

Has anyone the ability to monitor the power consumption of his kindle in "standby mode" (just displaying a page, wireless of).

Does anyone know how exactly these values are being measured?
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Old 06-29-2012, 11:23 AM   #15
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Quote:
Originally Posted by nick-tech View Post
Has anyone the ability to monitor the power consumption of his kindle in "standby mode" (just displaying a page, wireless of).
The K3 has a hardware diagnostic mode that reports that information.
Ans: 0.893ma for my K3 but I think the diagnostic puts it to sleep for that measurement period.

Quote:
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Does anyone know how exactly these values are being measured?
They are being retrieved from the battery management chip.
You should find them also somewhere in either /sys or /proc
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