This project show you how to do a flashlight using a cell phone battery

## Step 1: Part List

For this Project you will need :

Parts

High Brightness LED (1W) 1

Universal Board (5x5cm) 1

Cell phone Battery Push button switch 1

(http://yqyiwei.en.alibaba.com/product/469752056-20...)

Soldering kit.

## Step 2: Circuit

The resistor is determined by ohm's law, this mean that your resistor depend on of the power of your led. e.g ,

for a led of 1W of power with a cell phone battery of 3.7V (Nominal),Your minimum value of resistor will be :

V=I*R then P=(V^2)/R

where P = 1W and V= 3.7V (note: batteries have a maximum voltage of 4.2 volts be careful)

R=(V*V)/P;

v*v=(3.7)(3.7)=13.69

R=((3.7V)^2)/ 1W=13.69 ohm

Then the current will be :

I=V/R , I= 3.7 volts/13.69 ohms =270mA;

In my case I use a 3W Led

R=(3.7^2)/3W =4.56 ohm, I=811mA,

I recommended to use a resistor with some more ohms because the battery usually have 4.2 volts then I use a 6.2 ohm resistor with power dissipation of 2W.

## Step 3: Soldering the Circuit

The push button is toggle push button
Cut the female headers and solder it to the battery

The board is designed to connect directly to the battery

## Step 4: Testing

After a few minutes of working I noticed that the led need a dissipator

note: the battery has to give more of current that the circuit requires, this battery give around 2500mAh, to know more about battery parameters see this video https://www.youtube.com/watch?v=cxkVxi9P0EA

Hi, that battery you are using is dangerous when used incorrectly. The current draw from the 3 Watt led is in excess of the maximum recommended current draw for lipo batteries such as yours. Risk of thermal runaway and fire. Be careful.
<p>Could use more batteries in parallel to reduce current draw?, thanks for warning.</p>
yes most definitely. The larger the battery the better but i generally avoid non-protected lipo and li-ion batteries since any misuse and they easily experience thermal runaway i.e. catch fire. I have largely adopted lithium iron phosphate batteries since they have excellent safety characteristics. You will see two of my instructables highlighting this battery chemistry.<br><br>Also, applying heatsinks to leds is great if you want long lifespan. I sometimes ignore this requirement depending on what i'm building. I recently completed an led floodlamp instructables you can take a look at. Nevertheless, you made a great DIY instructable so I congratulate your effort!
<p>Gracias por las recomendaciones Mjhobby, y lo felicito pues tiene buenos instructables.</p>
<p>Gracias por las recomendaciones Mjhobby, y lo felicito pues tiene buenos instructables.</p>
<p>Gracias por las recomendaciones Mjhobby, y lo felicito pues tiene buenos instructables.</p>
Great idea for old n*kia battery's ...