[purohitanuj]

As I am planning to visit Leh, I had few items in my to-do preparation list. One of the item was to build a usb charger which can be powered from anything between 7 volt to 25 volt.
Thus I planned to build my own USB charger using 9volt battery. Idea was to carry 10 pcs. of 9 volt battery and use in case of emergency.

Parts required:
1. LM7805 - This is a simple voltage regulator which can output 5 volts @ 1.5A (provided that the input is in range of ~6V to 24V)
2. 9 Volt battery holder
3. 9 Volt battery itself
4. 4XAA to 9 Volt holder(*not mandatory)
5. USB extender cable with male-female plug
6. 1uf electrolyte capacitor(not mandatory)
7. Slide switch to turn off the power (not mandatory)
8. Soldering iron & some solder

Parts:
I. LM7805 (Cost: Rs 10)


II. 9 Volt Battery (Cost: Rs 50)


III. 9 Volt Battery connector (Cost: Rs 10)


IV. USB Extender cable (Cost: Rs 25)


V. USB Connector pin diagram


VI. Slide Switch (Cost: Rs 5)


VII. 1 uf Capacitor (50v)


VIII. 4xAA cell to 9V holder




Step 1: Prepare the USB cable.

1. Cut the USB extension cable.
2. Peel of the wires and select the red and black wire.
3. Strip the above two wires.

Refer this diagram to see the +ve and -ve ends.


Step 2: Connection
1. Strip the wires of the 9v connector
2. Join the positive and negative ends to the switch
3. Join the other end of the switch (positive) to the input pin of LM7805
4. Join the other end of the switch (negative) to the common pin of LM7805 (middle pin)
5. Now join the USB female cable's positive end to the point made in step 3
6. Join the USB female cable's negative end to the point made in step 4
7. Join a capacitor on points of step 5 & 6 (using the correct polarity)

Simple illustration:


How the finished product looks like? (note, I have tried to place components as close as possible. This is not mandatory and you may follow your way to do so)


*Carry the 4xAA to 9V adapter in your glove box and buy 4 AA battery from local place to use in case of emergency - The LM7805 needs 7v to regulate correctly. In case input is 6V, you may get enough juice to charge a bit (with phone off) and make few calls!!

Hope this is helpful to others!

[Rehaan]

Interesting little project purohitanuj -- however, why wouldn't you just buy a USB power pack?

There are some extremely affordable ones available, and even if you buy a more expensive one (than the cost of your alternative project), it might work out cheaper in the long run - since they are also rechargeable...

[greenhorn]

why not use something like this
http://www.ebay.in/itm/DC-DC-Adjusta...item210059c62c

http://www.ebay.in/itm/5V-USB-Output...item1a0386b6c7 (if you want to avoid soldering)

A DC to DC convertor is much more efficient (>90% claimed for both items) than a linear regulator which is throwing away around 40% of the energy with a 9V Source

[purohitanuj]

Originally Posted by Rehaan

Interesting little project purohitanuj -- however, why wouldn't you just buy a USB power pack?

There are some extremely affordable ones available, and even if you buy a more expensive one (than the cost of your alternative project), it might work out cheaper in the long run - since they are also rechargeable...

I do have power pack but I needs to keep it charged(I forget to charge it sometime).
This is specifically for cases when no other option is available. One can easily find 9v or 4 AA batteries and use it to power for "that last minute" call.

Originally Posted by greenhorn

why not use something like this
http://www.ebay.in/itm/DC-DC-Adjusta...item210059c62c

http://www.ebay.in/itm/5V-USB-Output...item1a0386b6c7 (if you want to avoid soldering)

A DC to DC convertor is much more efficient (>90% claimed for both items) than a linear regulator which is throwing away around 40% of the energy with a 9V Source

Two reasons:
1. Its very cheap to build own
2. Its DIY! and one can enjoy building it!