Picture of Build your own DIY solar powered mobile phone
This Instructables describes in detail how to build your own solar powered mobile phone.

Linear Technology article discussing solar charging, using maximum power tracking - see extracts

The idea dates back to 2002 when I was working on my dissertation on methods of energy scavenging that could be integrated on silicon. On a footnote, I added simple calculations demonstrating that if the surface area of a 'candy bar' mobile phone is covered with solar cell of 5% efficiency (which is pretty rudimentary), including a DC/DC converter, the overall output power is sufficient to augment the battery, providing power for stand-by indefinitely.

And here it is! Or rather a simplified version that is equally effective if not better!

Specifically what you need:

The Motorola F3 - a very cheap (I suspect the cheapest mobile phone there is) phone that is widely available both in US and UK. It is this affordability and basic ruggedness that I had chosen this model. More on this later...

A solar panel - the one I had acquired is available online (more on this later) but any other suitable make can be used provided it is rated 4.5V and above, having the dimension not larger than 100mm x 40mm.

A Schottky diode, 1N5817 or equivalent - a basic component which is not hard to find, you can even use the SMT version as long as you can solder some wires on both ends.

Some wires, I use enameled wire, more on this later...

Some basic soldering + a sharp pen knife + aluminium tape + epoxy + a hand drill + super glue

That's it! Surprised it is so easy? Why not get your hands dirty and build one!

The finish product is shown below.
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snotty4 months ago

This is hella awesome!

I think I've found a better work around though. In practice it seems like on-phone solar panels don't go well with being indoors and in pockets.

We like to charge our phones at night but solar panels have a little problem at night when there's no light.

So: Make a solar battery charger and charge your phone off that battery. The ingredients are pretty similar. I like to use solar panels off dead solar garden lights. I also like to use dead car batteries; they won't start a car but they sure will charge a phone (with a 5v regulator!)

profort snotty2 months ago
How would you modify this please?
sindhu750636 months ago
Hi...what is the wattage of the solar panel?

The answer is sort of hidden in step 3: "5.8V under bright sunlight and a short circuit current of about 80mA"

5.8v X 0.080A = 0.464Watts nominally.

BUT I'm pretty sure the operational voltage in this case is dictated by the battery. The battery voltage will vary between 3.6v at empty and 4.3v at full. So the actual wattage may change depending on the battery charge state.

Also solar panels' current (AKA amperage) is very sensitive to the strength of incoming light. So indoors out of direct light you get a lot less electricity.

sindhu750636 months ago

Hi! What exactly is the use of the Schottky diode here???

The diode prevents electricity from back-leaking though the solar panel. When the panel is shaded it stops producing electricity and can start to drain the battery instead of charging the battery. Fancier systems are more complex and efficient but the method in this 'ible is probably the easiest, cheapest and most elegant; I use it all the time.

Macgeekal1 year ago

hello i would like to do this on an iphone 5, any suggestion on parts?? any help will be greatly appreciated... :)

On The 3dge3 years ago
You probably know more about this than me, i found a couple of spare diodes and i was wondering if they would work for this, the only thing i know about them is that the markings on the side read; FR153s - then underneath that it reads - 724
Heh, funny profile pic have you!

If you have a digital multimeter, the diode measurement mode will tell you the forward bias voltage (when conducting), if not so simply set up a circuit, battery and a torch bulb, alternate the terminal of the thing you suspect is a diode, it should block one way.
aitchehtee5 years ago
I want to try this with the F3 but I don't know anything about this type of electronics. would you be able to use a solar panel with a built in diode? Also, would getting a more powerful panel be better and increase charging time, or would it ruin the phone? Also, what is the smallest, or least powerful solar panel you could use for this to still charge at a decent rate? Lastly, now that its been a while what would you do differently in this mod?

What I have suggested about the choice of panel is in the instructables...

However your last question pique my interest, frankly I had abandon the phone for another, reason, it is very basic, the screen does not do text proper.

But since I did this, there are quite a number of phones with the new feature of augmented solar charging on the back of the phone, google, you will probably get a few hits.
sddhhanover5 years ago
 assuming my phone has a 3.7V, 950 mAh battery, what range of voltage and current should i use for my solar cell? (i am asking for a range, not a specific amp/volt level). thanks!
 Is your math correct here? [or am i just a fool]

(700mAh @ 3.7V) = 2,590mWh of battery available. 
If the phone consumes 22mW continuously in one hour it will have consumed the equivilent of a 22mWh battery and in 117 hours it will have consumed the whole 2,590mWh battery.... 

According to the F3 spec... the phone is supposed to have 300 hours of standby time... not 117hrs. 

What am I missing here? 

 Also if it jumped up to a Watt durring "talk time" and you spoke for two and a half hours you would have consumed 2.5 Wh --->  2,500mWhrs. The battery is only rated for 2,590mWh and accordint to themotorolla the battery is supposed to get 8.3 hours of "talk time"

What am I missing here? :)  

I do think you are missing something... Mobile phone transmmission power can vary depending on its distance from the base station, I am suggesting it could go up to a watt, as a typical maximum, assuming worst case, why would I want to rely on Motorola happy-clappy specification of 8.3 hr (if what u say is even true)?
 That is really interesting! I had no idea that the transmission power of the cellphones were switchable.  How do you think that their 8.3 hours is calculated? 

Yes the transmission power of mobile phone can vary, which I believe is why there are some limitation in your understanding of what works in practise and what is just a specification.

I don't really need to know how their ideal figure is obtain, I know for sure it is not true or exact in real life.

I have a suggestion, why not you get one of these phone and test it out, IF you don't get that figure, please sue them for false advertisment, and then ask me to correct my instructables.

Is that alright?

I prefer to use my actual real life run-down test.
 what is the real life rundown test? Did you run it while on a meter?
How can I power my old cell phone with some double A (AA or AAA) batteries? it is a 3.7v & 750mAh battery.
no need to look anymore as i have found the answer:

GreenD6 years ago
Sorry for the noob question, but your idea is great so I'm doing it myself - Does the positive wire have the shotky diode? I just can't see it correctly in the picture.
Fr0ZenWolf6 years ago
This is a good Instructable, I'm going to try this with a few tracphones.
DIY Dave6 years ago
mspark4006 years ago
Great 'ible! for my prototype i am using an ok solar cell but was unable to find the correct diode @radioshack. How critical is it to have that exact diode,and i have a IN4001 50v 1A diode. would this possibly work? If anyone can tell me ASAP that would be great, Thanks in advance! Cheers, mspark400
The significance of the diode specified is that it is a Schottky diode, a special type with a particularly low forward voltage (the amount of voltage required before the diode begins to pass current). Other types of diodes, such as the standard 1N4001 and its brethren, should work, albeit at slightly reduced efficiency.
flio191 themike6 years ago
Thanks guys for the question and answer, I was going to ask about my 1N4004 but now I totally know that won't be possible, err. really that efficient.
BrianKT6 years ago
I was thinking of getting a Motofone F3 for a spare phone. Is it nice? Anyway, cool Instructable! Great way to save energy!
crait BrianKT6 years ago
This is a late reply but it's an amazing phone!
so u mean that combination of a 4.5v solar panel and a diode charges the 3.7 v battery? IF yes than why are the wall unit chargers rated to 5 volts?
Whether the wall charger is rated 5V bears no relation to how this modification work.
can u post the schematic of your dc booster
If you follow through with the steps, you will know that there's no DC-boost circuit, that's the point, keep it simple, it doesn't always have to be more complicated then it should. The joule-thief is a neat circuit, I had build one myself to the size of a AAA battery, but the way that particular boost circuit works, it rely on the light source being a LED (it could be blue green red, IR, basically a diode with forward biased voltage higher than the depleted battery). The simplest lithium-ion battery charger would be a 'linear charger', there are many jelly bean part to choose from (Try OnSemi, TI, Linear Tech, Maxim etc...). Typically these ICs, has an internal reference and a simple time out maybe a LED pin out for indicator. An application circuit would usually be supplied with the data-sheet of the ICs.
where do you get one in the us?
find itt on eeebaayyyyyyy ;)
i think t-mobile
can a cell phone be charged by using a joule thief?
flio1916 years ago
Nice! I use this phone already, I will look into getting a solar panel for it. Can you still charge by power cord?
Corrugator Supercilii (author)  flio1916 years ago
Yes you can, the modification does not in anyway affect normal charging with the wall plug.
thats great news. thanks!
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