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Old 09-04-2010, 03:43 PM   #1
vugtitan
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Solar Powered Kindle

Today I went to the pound shop and for £4 I bought four SOLAR POWERED GARDEN LIGHTS which I took home and disassembled easily and had as a result 4 "blue stripe thin solar panels" each of which can generate between 1.9 to 2.4 volts and 10 to 20 milliamps on a fairly sunny day.

By connecting 4 of them in series I will generate up to about 8 to 9 volts and through put through a simple diode in series with the output to (prevent battery discharge through the solar cells when it is dark) and then connect to the internal battery of the kindle.


When the kindle arrives i will then use uhu glue to carefully paste them on to the back of the kindle.

This means I can leave the kindle in the window and never need to charge it again.

The output of the solar panel can be either put through the mini usb or through micro holes drilled in the kindle back or the wires put through various crevices in the kindle and then connected to the Lithium Battery.

It is VERY important the diode is inside the kindle to prevent a fire if the wire to the solar panels get frayed and therefore stopping the Lithium battery short circuiting into the short circuit..

The diode will prevent any current flowing into the short circuit.

LITHIUM BATTERIES CAN CAUSE FIRES.


Don't do this if in any doubt.

I will of course be very careful and use uhu glue to fix everything in position on the inside of the kindle.

A friend suggested i get more solar cells and also paste them on to the front of the kindle on the bezel and the empty area about the keyboard buttons but I thought this as too complicated and ruin the look of the kindle.

However solar cells on the front would mean it charging even when i am reading from the light above, whereas with solar cells on the back this will only happen when the backside is up.

If you are going to do this get the thin stripe plastic encased blueish solar cells as the thick glass ones are thick , heavy and fragile.

We should get Amazon to produce a case with the THIN solar cells already printed on the front and back.

This means even in a zero electricity country or desert island the kindle will always work.

After Word War Three at least you won't be bored.

Last edited by vugtitan; 09-04-2010 at 03:57 PM.
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Old 09-04-2010, 04:06 PM   #2
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That's a bit more hard core than my skill level, but very cool.

I took the lazy way and bought three Scosche solar batteries (2 are the SolBATII, which is much improved from the original SolBAT). At $20 each, they're pretty inexpensive for a 1500 mAh battery that can be charged 3 ways (solar cells, AC, or USB port).
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Old 09-04-2010, 04:31 PM   #3
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I am using my flexible solar panel - usually used for trickle charging a deep cycle marine battery - to top off my Kindle3 as I type this msg and read outside ... I am on koi watch, as one was attacked amd injured by a raccoon.
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Old 09-04-2010, 10:11 PM   #4
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The battery inside the Kindle is a 3.7V Li Poly so wiring in your 8+V solar cells would be an extremely bad idea. Even with the 0.7V diode drop, you're going to be trying to feed it a significantly higher voltage than it is expecting. If you've wired all the solar cells in series then you're just going to end up with around 10mA in total and that is nowhere near enough to charge the Kindle considering it is expecting 500mA+.

The micro USB socket on the bottom also only will take 4.75V to 5.25V.

Charging a lithium battery directly isn't simple either. If you just try to charge it without the correct monitoring circuitry then you're risking a lithium fire.
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Old 09-04-2010, 11:48 PM   #5
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I am using a regulator and a drop-down box with USB ports. Been doin' this type of work since 1993 or 1993.
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Old 09-05-2010, 12:08 AM   #6
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Originally Posted by clintbradford View Post
I am using a regulator and a drop-down box with USB ports. Been doin' this type of work since 1993 or 1993.
Nah. I meant vugtitan since he/she said that they were going to directly wire it to the lithium polymer battery inside or wire it to the micro USB socket. Either connection won't be expecting 8V+.
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Old 09-05-2010, 12:30 AM   #7
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I agree about the voltage...keep it under ~5.2V but better yet, why not jigger up what amounts to an external surface mount panel that uses a USB splitter cable or even a direct connect then sent the current straight through the existing power system. You get proven charge regulation as well as likely can rig it so you don't void any warranty.

Still I love the idea however ya make it work...but remember, if we don't see pics then it never actually happened.
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Old 09-05-2010, 03:12 AM   #8
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Since you need light shining on the Kindle to read it anyway, I wonder how long it would take to generate enough power for a single pageflip, with solar panels on the outline of the front; if you could get enough power, may never need to charge it, or even put it down.
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Old 09-05-2010, 04:07 AM   #9
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Quote:
Originally Posted by Tiersten View Post
The battery inside the Kindle is a 3.7V Li Poly so wiring in your 8+V solar cells would be an extremely bad idea. Even with the 0.7V diode drop, you're going to be trying to feed it a significantly higher voltage than it is expecting. If you've wired all the solar cells in series then you're just going to end up with around 10mA in total and that is nowhere near enough to charge the Kindle considering it is expecting 500mA+.

The micro USB socket on the bottom also only will take 4.75V to 5.25V.

Charging a lithium battery directly isn't simple either. If you just try to charge it without the correct monitoring circuitry then you're risking a lithium fire.
solar cells have high output impedance depending on light falling on the cells.the 8 volts figure is only true if no current is being drawn.as current is being drawn into the 3.7 volts lithium battery the output voltage will fall to just over 3.7 volt.

somebody measured the current consumption and it varied from 1 to 3 milliamps with wi-fi off and 3 to 6 milliamps with it on.

it is not about 500 mA in 3 hours...it is about trickle charging such that daily usage of the initially fully charged kindle would be nearly replenished by the solar panel.

i have aware of lithium fires and the diode and uhu glue takes care of both.

solar cells will not cause over charging due to high output impedance of same.
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Old 09-05-2010, 08:39 AM   #10
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Quote:
Originally Posted by vugtitan View Post
solar cells have high output impedance depending on light falling on the cells.the 8 volts figure is only true if no current is being drawn.as current is being drawn into the 3.7 volts lithium battery the output voltage will fall to just over 3.7 volt.
Even with the output voltage sagging due to load, it isn't going to be 3.7V. The possibility of overcharging the battery still exists though.

If you really want to build a solar charger for the Kindle then create an array with a LDO regulator so you can wire it into the USB socket. Being cheap and using a diode or two to drop the voltage could work as well but regulation will be poor. Whether it is worthwhile making this yourself becomes slightly debatable at this point because there are many cheap USB solar charger gadgets around which may prove to be better value.

Either way, all the best to your project. I'm just concerned about the safety of yourself and the Kindle.

Last edited by Tiersten; 09-05-2010 at 08:41 AM.
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