Make a Human Powered Charger for Mobile Phones

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Don’t you wish you had a human powered charger you could rely on when your cell-phone battery was dead? Well here you go:



I remember when I saw my friends portable backup battery I thought to myself: well that’s a stupid idea! What if that battery fails too?

I always though there should be a good way to couple human body with some mechanical contraption to generate energy, while for example you are walking or moving so it would use human power to charge something in the background. There might be some side effect of such system putting pressure on body and joints. But for low power applications that shouldn’t be a problem, and can be a workout too!

In any case, I thought a hand-cranked charger is a good start. So I used my hand cranked flashlight for this purpose.

Inside the flashlight, there is a bridge rectifier like the one in my previous article. The reason is that the output of a generator is either an AC voltage or its polarity can be dependent on the turning direction, depending on the generator. So you need to rectify it to make sure your circuit sees the correct voltage polarity. And that’s what they did in my flash light.

They used the output of the generator to charge a NiMh 3.6V battery as well as powering the LEDs. The battery holds charge and provides power when you are not cranking, because cranking can become tiring. I removed the battery as it would limit the output voltage while I needed 5V as in the USB power lines, which are mainly used to charge cell-phones. But it would be a good idea to also have a higher voltage rechargeable battery there as backup when you don’t want to crank. And then crank to charge both batteries, although it would take more cranking power.

And yeah, I actually broke my cell-phone by not regulating the output of the rectifier! Like I said, I thought drawing so much power from the charger would limit its output voltage, and it did for a second! My cell-phone battery was dead so you couldn’t see the screen lighting up, but it has an orange charging LED that lit up showing it was charging. But as turning the handle is inconsistent and creates uneven output voltage, the cell-phone disabled charging. All of a sudden I felt that the charger was running much lighter, meaning that the phone was not drawing current. Right after, the phone started drawing much more current and I was confused as the charging LED wasn’t on. and so I realized that I killed the phone.

I measured later that with no load, the output of the rectifier could go as high as 20V and I don’t think they designed the phone’s charging circuit to handle such voltages as it should not see over 5V.

So, don’t be lazy and design your prototypes properly! I should have used a regulator from beginning. And I used a switching DC/DC regulator rather than a linear regulator. See, linear regulator is a simpler circuit but inefficient. The input and output currents are the same and so if the input voltage rises, move power is wasted one the circuit. But a switching regulator can be more than 90% efficient, which means the input and output powers are almost equal. So if the input voltage rises, the input current drops. That will greatly help preserve your energy when cranking.



If you convert that to cranking speed and force, at higher turning speed you spend less force to turn the handle. Which means you can find a sweet spot when turning the handle to match your desired speed and force for charging.

I used a buck switching regulator, which steps down the voltage to the desired value efficiently. For a 5V output, the input should be above 5V for the circuit to regulate and if the input voltage is less than 5V the output also drops. A buck regulator circuit generally looks like the circuit below:

Simplified Switching Buck Regulator Circuit

Simplified Switching Buck Regulator Circuit

To simplify the operation of such circuit, there is a controller that opens and closes SW1 switch (generally a MOSFET). When SW1 is closed, current flows through L1 inductor into C1 capacitor and load. At steady state, the current relatively slowly rises through the L1 inductor and so the output voltage. The controller also looks at the output voltage via the feedback line. So when the output voltage rises above a reference voltage, the controller opens SW1 switch. But now that the inductor is charged to some certain level, it discharges by pushing current into the load to the ground. At this point the current has to return to the discharging L1 and so the diode D1 is forward biased and turns on, circulating the current as it slowly drops. C1 capacitor maintains the output voltage during the SW1 off period. Then controller again turns SW1 on and recharges the circuit before the output voltage significantly drops.

Controller provides a PWM (pulse width modulated) signal to SW1 meaning it will tune its pulse width depending on the load. If the load demands more current, the output voltage drops slightly, and the on-time of the SW1 switch becomes longer to allow more current into the circuit and raise the voltage back up

The regulator I used was based on Texas Instrument’s TPS5401 regulator circuit. It is my new favorite so far. If you like reference design and circuits with this regulator, simply find it in TI’s website here.

Having such regulator on the output of my charger would save my phone if I had used it, and it would charge it too. But it wouldn’t work with Apple’s iPhones. Those people try their best to make people’s lives harder to develop something for them. They just want to push people to buy their own products as far as they can. And so simply having a supply wouldn’t charge the phone, and you also need to bias the USB data lines to around 2V.

For that you simply need a voltage divider. which are two resistors in series, between your output 5V and ground of the regulator. You need a pair of these dividers as there are two data lines. The resistor on the 5V side can be 2.7 kOhm and the one on the ground side 2.2 kOhm to create around 2.24V at the connection point between resistors. And that center node connects to data lines.

There are 4 wire lines inside a USB cable which are wrapped in metal foil for shielding. Red and black are power and ground and white and green are USB data lines.

Now this charger can charge anything. I was able to bring my iPhone back to life from dead battery and make a call with it too. So it can become very handy, especially outdoors when no power source is available.



49 thoughts on “Make a Human Powered Charger for Mobile Phones”

  1. I wanted to make mine have a pedal design. But trying to add a capacitor was a pain and I cannot get it to work out. The voltage just keeps getting stuck at 3V and I’m just stumped. Help, plz anyone.

  5. I have a 12 v DC generator and a 12 v solar panel I want to connect both of them to a 12v battery what should I do

    • dude, just hook it up on parrell, just make sure the 12 v dc generator regulates 12 v and 12 v solar panel doesnt go lower than the 12 v battery

  6. Hi how many of each type of resistor do I need because I want to make one of my own and I was just wondering (or do I not need any because I want to use it for my ipad)

  8. Hi Mehdi and others, I have made a circuit diagram of the USB bit, not the hand cranker itself. My circuit diagram is here: http://imgur.com/B2kr23G please tell me if my USB data lines are in the wrong spot, and also I have a feeling I’m going to need a diode, my dynamo is much different then Mehdis, mine just has some wasteful circuit traces and a few switches and an ic chip and a resistor, that’s all. I think I’m going to need to place a diode in the positive line, at the start near the motor, so I might need a 6 volt regulator instead of a 5 volt because of the diodes stupid voltage drop. But anyway please tell me if I mucked up something like the data lines or something similar. Ps I love your videos! Make more! Thanks for reading this in your head, pls tell me if I’m wrong or wright in my diagram and diode prediction.

    • Check TI, and use Webench for a reference design. Also Linear Tech and other carry good chips too.

  11. agradezco todos tus videos, todos aportan algo muy padre y me agradan espero que estes bien

  13. I’m in the middle of making this and I was wondering where I should connect the data lines. Should both be on the 5V side, on ground, or separate?

    • I think that buzzer is made to run on those 12V power lines, if so then this charger can’t put out the voltage required to run the buzzer. But if it can run on USB power, then this charger can do it. Just that I’m not sure if it is meant to run on USB power.

      • Do you think I can try to brute force my way through this, and re-wire/modify the crank’s usb port in order to have it connect directly to the wires?

        Because I’m pretty sure the usb port on the buzzer is only meant for adding mp3 files.

        Or if an alternative hand cranked dynamo that has a wired output we’re available somewhere that would make it work right?

  16. Hi medhi…..

    Can i use a lm7805 instead of TPS5401 regulator circuit?and a full bridge rectifier you shown

    • You can, just that 7805 is much more inefficient. What happens in case of TPS5401 is that if you turn the handle faster, you feel less resistance against turning. But with 7805, it gets harder to turn if you go faster.

      • how do you wire up the 7805? the 7805 is 3 pinned and your texas instrument one has 4 pins. does the middle pin in the 7805 (common) reperesent negative for the input and the output?!?!? please help, btw I luv ur vids 😀

    • The battery voltage doesn’t change drastically or fast. The battery limits the voltage by drawing current.

  18. Hey Mehdi , could you do a detailed video on how to make a home made apple charger? I like to challenge my self and would really love to make one. p.s. I love your videos!

  20. hi mehdi. how many mA does this provide. is it possible for a hand cranked charger to output 5v 2A?

    • You need a higher power regulator for that compared to what I used. But that’s possible. It would require almost 4 times cranking power.

  22. Hi Mehdi, really enjoy your videos, I had a question, why is it that if we connect the generator directly to a multimeter and set it to measure current in A we experience a lot more difficulty and resistance from the motor, and when we set the multimeter to measure current in mA we still experience this resistance but less of it!
    I know we shouldn’t connect it directly but I was just wondering why?

    Thanks@!

    • The reason the generator resist motion is because it is generating power through the meter, and a meter set in current basically shorts the outputs of the generator drawing lots of current. The power wasted in the meter is P = R x I^2. When you set the meter in high current meter setting, its resistance is very small, which means also much higher current goes through, and when you set it to mA setting its resistance is higher and allows less current through. So it also consumes less power and turning the generator is easier in that setting.

  23. So disappointed in you now. Up until now I thought you knew what you were doing and only playing at screwing up but this post shows this isn’t the case. Please be careful with future projects as you may end up hurting yourself or others. Just with the tesla coil the inductor for the dynamo will try to act as an ideal current source and have a voltage spike when the current path is broken. A simple 5v zener and resistor would also have protected the phone from this happening.

    • Ouch! You can’t use a Zener/Resistor to clip a power rail which may draw Amps… The Buck converter is the correct option.

  24. Hey that’s funny… I mean not the circuit design, I could have easily done that myself, (I’m an electronics engineer), I meant the “Hands Free” option… gotta find a way to tether my kids to the crank now…

  25. Dude You Could Make A Good Fortune With This Device!! Seriously!!
    You Have Already Found Some Customers!! Maybe You Could Sell Your Idea?
    The Problem With The Battery Is Global!! You Can Enhance It A Bit, Like Mix IT With The Device You Showed At The First; Or Even A Taser!!(LOL)
    Good Luck!

    • It depends on the device, most phones now use the bias to get told how much current the charger is able to provide and limit the charging rate to that. USB standard is for the host to communicate with the device before the device starts drawing large amounts of current, or for the device to already be limited below the 5mA in the spec.

    • My phone I blew up didn’t need it. Maybe it is a good provision from Apple to try and make sure a proper USB charger is connected! Although I don’t like them limiting designers.

  27. Pingback: DIY Hand-powered Charger

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