Instructables
Picture of Build your own DIY solar powered mobile phone
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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
http://cds.linear.com/docs/LT%20Journal/LTMag-V19N4-04-LT3652-JimDrew.pdf


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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Macgeekal5 months ago

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

On The 3dge2 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.
eirlandes3 years ago
(removed by author or community request)
Mobile phone signal jammer is illegal in the US and UK. I am not really sure how you managed to sell it.
aitchehtee4 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?
Hi,

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.
sddhhanover4 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? 

Thanks! 
 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? :)  
Hi,

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?
Hi,

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:


http://www.instructables.com/id/37v-emergency-charger-Nokia-cellular-with-9v-batt/
GreenD5 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.
Fr0ZenWolf5 years ago
This is a good Instructable, I'm going to try this with a few tracphones.
DIY Dave5 years ago
cool
mspark4005 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 themike5 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 BrianKT5 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?
flio1915 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)  flio1915 years ago
Yes you can, the modification does not in anyway affect normal charging with the wall plug.
thats great news. thanks!
Antpopper6 years ago
Lithium cells can not be trickle charged, it will destroy them after they reach full capacity, so if your solution is to only charge it when it is less than full, that works, but placing a 4.2v zener in parrellel with the battery should guarantee the battery will not over charge.
I don't think that is necessarily true... I'll explain in two parts.

First, over-charging, above the cell maximun floating voltage, typically at 4.2V, might shorten the battery life, destroying the battery in this case? No. I think you need a massive wallop of energy which the solar panel can't ever provide to edge it pass thermal runaway. But note that the Li-ion cell can also self-discharge, and the phone does consume minute standby power, obvious to the fact that it maintains the time and date after you had switch it off.

Second, if you're thinking of using a zener with a breakdown voltage of 4.2V, it is not necessary a good idea, 1)Zener diode reference isn't accurate enough (+/-5%?) 2)Exact value to what you have in mind may not be readily available, or even if there one, I would advise, something nominally derated minus 5%.

I had advise against this (overcharging). I reiterate, in circumstances as such that your mobile phone battery is fully charged, you turn it off, leave it under the sun charging. Do not such thing with this simple circuit.

To find out more about Li-ion battery, I recommend an excellent article from Linear Technology quarterly magazine on the charging and discharging method that extends Li-ion battery life.

http://www.linear.com/ltmagazine/LTMag_V18N3_Sep08.pdf
where did u install a boost converter? what is the final voltage output ?
Kryptonite6 years ago
Hi,
I followed the link to the Wikipedia Web page for this phone, and it said that this is CDMA, didn't they get rid of that in like May? Or is this only in Australia? I got a phone that I found at some garage sale for 10c with charger and instructions so I bought it, to find that I couldn't ring out, send or recieve text because it was CDMA. Now I would really like to make this and it sounds great, but that 1 small thing is quite ominous as a could be failure. D =
Reards,
Kryptonite
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