Hand-crank IPhone Charger




I had always wanted to make something that converted mechanical to electrical power. So when I salvaged a high-torque motor from a broken microwave, I knew exactly what I was going to do with it.

This Instructable details the making of a hand-crank iPhone charger, a charger that operates solely on mechanical energy YOU provide. The build uses a completely original circuit and a design that is sleek and easily portable. In addition, this charger is probably cheaper to build than it would be to purchase a normal wall charger. If you've ever been frustrated about running out of battery while on the go, you've come to the right place! With just a few adjustments, this charger can be used to power not just iPhones but anything that runs on electricity.

Step 1: What You Will Need (and How to Get It)

  • high-torque DC motor:

Motors operate on the principles of electromagnetism to produce rotational energy from electrical current. In this Instructable, we will be reversing the motor's inputs and outputs in order to generate electrical potential from mechanical work. The motor I used was taken from a broken microwave, but any motor will work as long as it uses permanent magnets rather than polyphase coils and is coupled to a gearbox with a high torque output.

  • step-down transformer:

A step-down transformer is needed to lower the voltage of the sinusoid generated by the motor. Transformers can be found in almost every piece of electronics that plugs into a wall. The precise primary to secondary ratio of the transformer will depend on the voltage produced by the motor you use. In my case, I used a 120:12.6 (approx. 10:1) transformer from RadioShack.

  • diodes (x4):

Four diodes (or an equivalent bridge circuit) will be needed to rectify the AC generated by the motor to DC. Diodes are common in electronics, and red colored signal diodes tend to stand out on circuit boards. Since the emf's generated by rotating the motor are unlikely to be huge, signal diodes as well as power diodes are probably acceptable for use. I used power diodes purchased at RadioShack.

  • resistors (assorted):

You will need several resistors for the timing and feedback circuitry. You should have no trouble finding resistors in old electronics. The values I used will be listed on the circuit schematic, but minute deviations from these specific values will not greatly affect performance.

  • capacitors (x2):

You will need two capacitors: a low value ceramic capacitor for timing and a larger electrolytic capacitor for energy storage. The specific values I used will be given on the circuit schematic. Again, capacitors with slightly different values than the ones listed may be used. Electrolytic capacitors can be salvaged from old electronics with ease. RadioShack sells packets of assorted ceramic and electrolytic capacitors, which can be very helpful if you're just getting started in electronics.

  • NPN transistor:

A transistor is used to control charging. Any transistor could work, but for this application a low power NPN bipolar junction transistor is probably best. Such transistors are abundant in electronics. I used a 2N4401.

  • 555 timer IC:

A 555 timer is the central component of this switched mode power supply. The 555 will be configured in astable oscillator mode and will drive the discharge transistor with a pulse width modulation (PWM) signal. You will have to purchase the 555 timer from RadioShack (current price $2.00). I would recommend the low power TLC555 over the NE555.

  • LM741 op-amp IC:

A LM741 op-amp provides linear feedback in order to maintain constant output voltage relative to a reference. You will have to purchase the LM741 from RadioShack (current price $1.50).

  • button cell battery:

A button cell provides the reference voltage used to maintain steady output voltage. Button cells can be found in electronics with timing circuits that must operate even when the device is "off". I used a 3V lithium button cell taken from a radio. If button cells are unavailable, other batteries may be used so long as they do not drain quickly from continuous use.

  • USB receptacle:

If you are planning on charging an iPhone or other device with a USB interface, you will need the proper USB receptacle to connects to the charging cable. You can find USB receptacles everywhere in electronics. I extracted mine from a USB port array found on a broken computer.

  • housing for the complete project:

This can be anything, a cardboard box or tube for example, so long as it protects and encloses the working parts of the charger. You may also need some nuts and bolts to hold everything in place.

Step 2: Circuit Schematic

Now that you have gathered the required parts, its time to put them together.

The above schematic details the charger circuit. The functional diagram compartmentalizes the circuit and describes how various components interact to produce the regulated 5V output. Note that component values may deviate slightly from those given in the schematic with little noticeable effect on performance.

Step 3: Testing the Completed Charger

With your circuit built, you may now begin charging devices with energy you supply!

To demonstrate the working charger, I made several videos.

The first details the operation and construction of the charger. The second shows the output across a 100 ohm resistor, which is expected to exhibit slightly greater impedance than that of an iPhone. The third confirms the charger's functionality with a demonstration of the charger connected to an old iPhone. The fourth shows the charger powering a rail of LED lamps.

Step 4: Notes on Energy, Efficiency, and "green-ness"

The charger is innately a green-machine. As it relies solely on mechanical power (the button cell sources negligible current), the charger does not contribute any waste in the form of used batteries to the environment. The rotational input of the charger can be coupled to a bike to provide more energy on the go or to a stream to derive energy from nature.

The charger was built from several recycled materials, including a high-torque motor salvaged from a broken microwave and a USB receptacle taken from a USB port array.

After some experimentation and rough calculations, I approximated the charger's efficiency to be 53%. I based this result on the equation for the work required to complete one rotation of the motor shaft. I charged a capacitor first from the USB output of the charger and then directly from the rectified output of the motor. The ratio of the two energies produced by one rotation was 53%.

Green Design Contest

Runner Up in the
Green Design Contest



    • Comfort Food Challenge

      Comfort Food Challenge
    • Faux-Real Contest

      Faux-Real Contest
    • Cardboard Challenge

      Cardboard Challenge

    24 Discussions


    Reply 2 years ago

    can i please have your help making mine work, tried to build it but couldnt get it to work


    2 years ago

    Hi there! Are we allowed to use this as a basis for our investigatory project? Hope to hear from you. Thank you and Godbless


    3 years ago on Introduction

    if i were to wrap a copper wire instead of using brushes around a dc motor commutator would i still be able to get electricity if i just spin the magnets around the motor?


    4 years ago on Introduction

    You keep using the term DC to refer to your motor but the motor is AC and you even call the output sinusoidal which is also concurrent with AC.

    AC is alternating current which is the sinusoidal voltage waveform which must be rectified to use with any battery powered electronics.

    DC is direct current wherein voltage stays at a constant level.

    You really should correct the names in your instructable because it gets very confusing talking about "rectified DC" and sinusoidal waveforms from a supposedly DC motor.

    A DC motor (as stated) would be better to use in this application because DC motors generally have permanent magnets whereas some AC motors do not. However, using DC eliminates the need for the rectifier circuit and the step-down transformer. all you would need is a voltage regulator for the USB output. Another potential problem is that some phone batteries do not like pulsed DC for charging and it can damage them. A "ripple" cap in line with the USB output can help smooth the DC output.

    Other than that, the instructable is well written and laid out.

    1 reply

    Thanks for the suggestions!

    I changed the motor section of Step 1 to better explain the requirements regarding permanent magnets. I also changed "rectified DC", which I intended as a shorthand for "rectified to DC", to the more general "output".

    The output is actually quite smooth when connected to an iPhone. There is sometimes a slight ripple, but this only occurs when the rotational power supplied is below a threshold. I think placing a smoothing capacitor across the USB output would cause the total voltage to be split between the "storage" capacitor and the smoothing capacitor.

    Overall, the charger is working really well! My newest (and very approximate) estimates put the power output at roughly 500mW, which is about what I determined the power delivered by a regular charger to be. I hope to have the charger working with a bike soon.


    4 years ago on Step 4

    Handy little gadget that you have here but I did the same but with a motor out of a defunct 8 track car stereo. With a small wheel on the motor and a large wheel on a cranking handle. The radio played beautifully at moderate speed on the crank

    1 reply

    4 years ago on Step 4

    I suspect you may find that you could couple a fishing real swivel handle the input shaft and have mor leverage, this in turn mak it Easyer to rotate and more productive.

    1 reply

    Reply 4 years ago on Introduction

    The electrolytic capacitor, which is what I assume you are referring to, is used to smooth incoming rectified generator voltage and discharge 5V pulses through the USB. The capacitor will charge until the transistor is triggered by a PWM signal. The op-amp and 555 timer are configured so that the capacitor discharge will be triggered around 5V, the voltage required for charging such devices as iPhones.


    Reply 4 years ago on Introduction

    Capacitor banks are used to regulate power supplies by minimizing spikes and dips. It keeps the power supply at a steady level.


    Reply 4 years ago on Introduction

    Sorry about the test, I had trouble posting.

    The circuit has a major fault. The output pulses are directly fed to the USB connector. This could easily destroy whatever you plug in to it with high voltage pulses. PWM might average 5 volts, but it will pulse full maximum voltage as wired. Nice try though, but you need some video production skill.


    Reply 4 years ago on Introduction

    Hmm, well it seems to be working fine.

    A few of your statements are not correct. Perhaps I should try to better explain to you the operation of the circuit. The storage capacitor is charged continuously with the rectified output of the generator. The op-amp will increase the duty cycle of the PWM signal from the 555 when the voltage across the capacitor (divided by 2) is greater than a 3V reference and will decrease the duty cycle when the voltage is lower than the reference. The PWM signal triggers the discharge of the capacitor through the USB. This produces a pulsed 5V output, with an average of 0-5V depending on the PWM duty cycle. If you're still skeptical, feel free to ask me more about the circuit (I have a feeling I know where you're getting confused).

    As for the video, I agree that my filming abilities aren't great, and I plan on putting out a better quality video soon (possibly with some additions). However, I can assure you that the videos are real and that no devices were destroyed in the making. :)


    4 years ago

    Attach this to a exercise bike and u be hitting 2 birds with 1 stone!

    1 reply