## Step 3: Wiring the Doide...

So what does the diode do?

A basic lithium ion charger is a constant current charger, with an end-of-charge detector, charging ends when the battery reach its full charge at 4.2V (most common) and the charger goes into trickle charge mode.

A solar cell can be modeled as a current source in parallel with a diode. Higher voltage is achieved by stacking these individual cell in series.

http://en.wikipedia.org/wiki/Solar_cell#Equivalent_circuit_of_a_solar_cell

In this case, the charging circuit consist of just a blocking Schottky diode. Advantageous is its low forward biased voltage, which is around 0.3V.

http://en.wikipedia.org/wiki/Schottky_diode

Is it safe to charge the battery in this manner?

The charging current is very small, comparable to a trickle charger, the solar cell act as a weak constant current source. The panel I brought has a open circuit voltage of 5.8V under bright sunlight and a short circuit current of about 80mA, you can measure this with by simply shorting your digital multimeter across the solar panel terminal, this is slightly more than 10% of battery capacity at 700mAh. But remember when charging occurs, it is at a voltage 4.0V and above (3.7V + 0.3V diode drop), the net charging current (minus the current drawn by the phone) is not going to be any more than the measured short circuit current.

In any case, the rule for charging a battery safely is to do it at 0.1C (i.e 70mA) and here, the charging current does not even excess this figure.

A net positive current in excess of the stand-by power will charge the battery. Some experiment I've done shows promising result. It take 3 hours of good sunshine to charge a 'dead' battery with the phone powered off to last 12 hours when the phone is standby without charging.

Again some calculation, working back, given that the phone draws 6mA on standby, 12h x 6mA = 72mAh, each hour of sunshine gets you 24mAh (72mAh/3), on standby the phone consumes 6mAh, thus a net charge of 18mAh will go to the battery. Consider a day with 6 hours of charging (day) and 18 hour without (night), your phone left on standby will run indefinitely.

It is best however, to let solar panel charge the phone ONLY when battery indicator shows one bar below a full charge.

<p>let see what hppen</p>
<p>This is hella awesome! </p><p>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. </p><p>We like to charge our phones at night but solar panels have a little problem at night when there's no light. </p><p>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!) </p>
How would you modify this please?
Hi...what is the wattage of the solar panel?
<p>The answer is sort of hidden in step 3: &quot;5.8V under bright sunlight and a short circuit current of about 80mA&quot;</p><p>5.8v X 0.080A = 0.464Watts nominally.</p><p>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. </p><p>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. </p>
<p>Hi! What exactly is the use of the Schottky diode here???</p>
<p>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. </p>
<p>hello i would like to do this on an iphone 5, any suggestion on parts?? any help will be greatly appreciated... :)</p>
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! <br><br>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.
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, <br /> <br /> What I have suggested about the choice of panel is in the instructables... <br /> <br /> 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. <br /> <br /> 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.<br />
&nbsp;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!
&nbsp;Is your math correct here? [or am i just a fool]<br /> <br /> (700mAh @ 3.7V) = 2,590mWh of battery available.&nbsp;<br /> 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....&nbsp;<br /> <br /> According to the F3 spec... the phone is supposed to have 300 hours of standby time... not 117hrs.&nbsp;<br /> <br /> What am I missing here?&nbsp;<br /> <br /> Thanks!&nbsp;<br />
&nbsp;Also if it jumped up to a Watt durring &quot;talk time&quot; and you spoke for two and a half hours you would have consumed 2.5 Wh ---&gt; &nbsp;2,500mWhrs. The battery is only rated for 2,590mWh and accordint to themotorolla the battery is supposed to get 8.3 hours of &quot;talk time&quot;<br /> <br /> <br /> What am I missing here? :) &nbsp;
Hi, <br /> <br /> 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)? <br />
&nbsp;That is really interesting! I had no idea that the transmission power of the cellphones were switchable. &nbsp;How do you think that their 8.3 hours is calculated?&nbsp;<br /> <br /> <br />
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. <br /> <br /> 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.<br /> <br /> 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. <br /> <br /> Is that alright?<br />
Hi, <br /> <br /> I prefer to use my actual real life run-down test. <br />
&nbsp;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:<br /> <br /> <br /> https://www.instructables.com/id/37v-emergency-charger-Nokia-cellular-with-9v-batt/<br />
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.
This is a good Instructable, I'm going to try this with a few tracphones.
cool
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.
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.
I was thinking of getting a Motofone F3 for a spare phone. Is it nice? Anyway, cool Instructable! Great way to save energy!
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?
Nice! I use this phone already, I will look into getting a solar panel for it. Can you still charge by power cord?
Yes you can, the modification does not in anyway affect normal charging with the wall plug.
thats great news. thanks!
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. <br/><br/>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. <br/><br/>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%. <br/><br/>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. <br/><br/>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.<br/> <br/><a rel="nofollow" href="http://www.linear.com/ltmagazine/LTMag_V18N3_Sep08.pdf">http://www.linear.com/ltmagazine/LTMag_V18N3_Sep08.pdf</a><br/>
where did u install a boost converter? what is the final voltage output ?
Hi,<br/>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 <em><strong>really </strong></em>like to make this and it sounds great, but that 1 small thing is quite ominous as a could be failure. <strong>D =</strong><br/>Reards,<br/>Kryptonite<br/>
could the panel charge the phone with the phone powered down/dead battery? a handy feature for the random occasion someone is marooned without a charger. looks pretty slick to, not a bad way to start an eco-groovy conversation with someone
how long have you got it to last with out a charge from mains power
That's a hard question! Since I live in Edinburgh and since this is Scotland and since winter is a bit hasty this year, I only managed one chance to have the thing bake in sunshine which lasted no more than 4 hours :( But during which I had worked out how much power you would be able get should you have some consistency of sunlight, say in the tropics? I have documented this on one of the steps. In short, 6 hour of sunshine should be is enough to keep the phone on standby indefinitely, which however is an unlikely proposition, for the use a phone is to accept and return calls (or SMS) :D I would think if you're in circumstances where there's not a mains source convenient, this is very helpful in extending usage. For this reason, I decided to document this DIY.
Come to Melbourne in Australia, there is plenty of day light in the summer.
Nearly everywhere in Australia gets a lot of sun<br/><br/><sup> But it gets hot too, Cairns in so darn hot and a bit humid in summer.....</sup><br/>