***If you think it's worthy, Vote for it for "Make Energy" Challenge***
Mobile phones / Tablets have become an integral part of our life. One big hustle which every mobile user faces is charging the device. Well if you have a power source like AC wall supply or batteries lying around then it is easy but what if you are stuck in a place where there is no power source, like for few days?
I got this idea when a cyclone struck my area and we had no power in the whole city for like 10 days. The phone towers started working from the 2nd day itself but since our smart phone's charging doesn't last more than a day or two, it was of no use. That's when I realised how dependent we are on electricity provided by power stations.
This project will help your phone stay alive in those kind of situations. Remember, my objective is to make a charger with parts which will easily be available.
Step 1: Designing
What we don't want to use: Batteries, AC household power
What we want to use: Muscle Power (Mechanical Energy)
Solution : DC Motor/Dynamo
I'll be using a DC motor in this tutorial since it is more easily available than a dynamo. Well technically a DC motor is also a DC generator so when you apply mechanical energy to a DC motor (rotate it's shaft), it produces some amount of power.
But we have another problem. Depending on the speed at which we rotate the shaft, the voltage across the terminals vary and we don't want anything above +5 volts for our USB charging. So we need a regulator block which would take in the variable power from the motor and convert it into DC +5V
Option 1: Linear Voltage Regulators (Like 7805)
This itself does the job but linear regulators have a very low efficiency. This is because here if the load draws 'X' amps of current then even the input needs to provide the same 'X' amps of current.
Power wasted = (Input voltage - Output voltage) * Current drawn by load
We would be wasting more than half of the power we generate through the motor and hence not advisable. Well if you are in a hurry and have no other option then go for this.
I realised this after reading the Instructable "Solar Powered Heart Rate Monitor" written by Dangerous Tim. Thanks to him.
If you want to use this option, then head to my first version of this project which I published on EngineersGarage.com (DIY- Emergency Phone Charger using a DC Motor)
Option 2 : Switching Voltage Regulators (LM2576/LM2596 5V version)
Switching regulators are more efficient since they turn on/off the input at high speed (Pulse Width Modulation) to bring down the voltage at output and waste less power in form of heat. They require few external components but totally worth the complexity.
To make things more easier, I'm using a ready-made switching regulator based power supply module which is easily available. But since they are only adjustable versions available, we need to first set the potentiometer present on it such that it gives output close to +5V
-Use an external DC power supply (Battery or adapter) which can give more than +7 Volts to power up the module.
-Connect the multimeter in voltmeter mode to the output of the module and start adjusting the potentiometer using a screw driver until you see a value very close to 5 Volts (5.0 to 5.1)
Step 2: What We Require:
Note: If you want to build the power supply module on your own, refer the schematics in the next step. Or else you can skip the next step :)
Step 3: Schematics
- The motor I used is 100 RPM. I chose it because the ones with lesser RPM than this required more force to turn and the ones with higher RPM although easy to spin, had to be rotated at high speed to generate same power.
Step 4: Fix the motor:
Attach the motor to the clamp/chassis and then attach them to a firm place like on top of a table or something. This is to ensure that the motor doesn't move away when you start rotating it.
Step 5: Put a hole into the wheel away from the center
Heat the screw driver (make sure you don't burn your hand) using a candle or any other fire source and punch a hole into the wheel, away from it's center. The hole should be big enough for the screw driver to slide in and out smoothly but not too big.
Step 6: Fix the wheel to the motor's shaft using the screw given along with it
Step 7: Connect motor to power supply module
Connect one wire from the motor to the negative terminal of the module and other wire to the positive of the module through the diode. The diode is used to protect everything from reverse current. If you spin the motor in wrong direction, it acts as open circuit and doesn't let the reverse current to pass.
Step 8: Soldering the USB connector
Solder the USB female connector onto a small GPCB.
- Apart from the 4 terminals of USB, you will also find two V-shaped leads on the connector. These won't normally fit in the PCB and hence you need to enlarge them using the tip of scissors. Just insert the tip of scissor in the hole and start rotating it, pushing it into the PCB. Do this until the hole widens enough.
- Once the holes are wide enough, attach the USB connector to the PCB and bend the V-shaped leads towards each other. This would let the connector to hold onto the PCB tightly.
- Solder the +5V and GND terminals of connector onto the PCB(You need not solder the data lines but soldering them would make the connector stay firm ) . Then solder a male header near to it and link them.
Step 9: Testing and Adjusting
-Connect two female jumper wires, i.e. for the +5V and ground terminals and attach them to the output terminal of the power supply.
*****Polarity is very important. Make sure you don't mix up the +5V and GND lines.*****
- Hook up the multimeter(in voltmeter mode) to the input of the power supply module.
- Insert the screw driver into the wheel's hole and start spinning the motor at a nominal speed in one direction say clockwise. If the meter's reading starts going up, then this is the correct direction to spin. If there is no change in the reading then the reverse (i.e. anti-clockwise) direction is the correct one.
Also make sure you spin with enough speed such that it at least shows 8V in the multimeter.
- Now hook up the multimeter to the output of the USB connector (Red probe to +5V pin and Black probe to GND pin) and start spinning once again.
- You need to check two things now:
1) Sign: If there is no sign, then it means the polarity is correct and if there is negative sign then reverse the USB connection coming from the power supply.
2) Voltage level: The level should be in between 4.8 to 5V. If it is not in this range then adjust the potentiometer present on the power supply module using a screw driver.
Step 10: Implementation and Improvements Suggestion
Now connect your Phone/ Tablet to the USB port using a cable and let your muscles do the rest of the work!
Since many people asked, I tried looking for the output current. I used this battery monitor widget to check the current and found out that at the system is capable of delivering 550mA current to the phone.
Points to be noted:
1. You can attach the above setup to the bottom part of a manual sewing machine. Then you would be able to rotate the motor shaft for longer time with lesser effort.
(Sewing machine image from google images)
2. You can attach it to a bicycle's wheel. Because it is healthy to ride a cycle, saves fuel and now it will charge your phone for free :D
P.S. I've written few project tutorials before (you can checkout them in my website) but this is my first time on Instructables. So apologies in advance if the Instructable is not organised properly. Please leave your suggestions as comments which would help me improve the quality.
Hope you liked it! :D
Bottom part of a manual sewing machine is called a "Treadle"(Exact word added from comments. Thanks to thatto, diamonddozen)