# Hand Crank Flashlight

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## Introduction: Hand Crank Flashlight

This hand crank flashlight charges a supercapacitor to power an LED when you turn the crank. In fact, the hand crank system provides enough power that you can also power the LED directly if the capacitor has run out of charge. This flashlight uses no batteries and converts your own energy into light. It could hypothetically run for decades and is great in an emergency situation.

## Step 2: Generating Electricity

The secret sauce to this project is a stepper motor. A stepper motor is a special type of motor that has two power coils. By powering the coils one after another, and then alternating the polarity and powering them again, the motor is able to move. Don't worry too much if this doesn't make too much sense right now. The key word here is "alternating." If you consider that a motor is actually a transducer and can both be powered by electricity, and generate electricity when manually powered, a stepper motor actually has two coils producing alternating current when you turn the motor shaft. Since stepper motors tend to have large magnets and multiple coils, this makes them highly efficient at generating electricity.

All we need to do is crank to the motor shaft. To test this out, add an LED to each pair of motor coils and observe what happens.

Of course, it is not quite that easy. There is one problem to this approach. We are getting alternating current out of the motor, but we are trying to power a DC circuit. This is where diodes start to come in.

## Step 3: Bridge Rectifier

By arranging diodes into a bridge rectifier we are able to convert AC electricity to DC. In this arrangement, regardless of where the AC waveform is in its cycle, electricity is always flowing between power and ground in a uniform direction, and you end up with a DC waveform output.

The reason for this is that as the alternating current fluctuates between positive and negative, two diodes are always forward biased and two are reversed biased. Through this clever arrangement, there is always a pathway for electricity to flow only between power and ground.

Since our flashlight has two coils that each generate an AC signal, we need two bridge rectifiers. To get them to work together, we simply wire them in parallel: positive to positive, and ground to ground. We're also going to add a small capacitor to help smooth out the voltage and fill in any dips in voltage created as we cycle between the power created by the two coils.

## Step 4: Zener Power Regulation

Once we have a nice clean DC signal coming out of the rectifiers, we will then need to charge a supercapacitor. However, before we do that, we need to make sure that the voltage from the rectifiers will never exceed the voltage of the supercapacitor.

While the voltage coming out of the motor is probably fairly small, to be on the safe side we can use a zener diode to ensure it never exceeds the capacitors 5.6V operating voltage.

By connecting a 5.1V zener diode in series with a 100 ohm resistor in a reverse bias position between power and ground, we can ensure the voltage to the capacitor never exceeds 5.1V.

If the voltage exceeds 5.1V, then the zener effect kicks in limiting the voltage across the diode to 5.1V, and dropping any additional current across the current limiting resistor. For instance, if the motor produces 9V, then 5.1V will flow across the diode and 3.9V will fall across the resistor. Any component connected in parallel to the diode will receive at most 5.1V.

This is not the best means of voltage regulation since it can potentially generate a lot of heat, but since the current we are working with is relatively small, it should be fine.

## Step 5: Storage

After the power is generated and regulated, it is then stored in a supercapacitor like we used in the vibrobot project. The capacitor is simply in parallel with the zener diode.

## Step 6: The LED and Switch

The LED and its current limiting resistor are wired in parallel to the zener diode and supercapacitor.

A switch is then connected in series with the resistor in order to toggle on and off its connection to the supercapacitor power supply.

When the supercapacitor runs out of power, the LED can be powered directly by the hand crank to long as the switch is toggled on. If the switch is toggled off, the capacitor gets charged instead.

## Step 7: Attach the Template

To begin with, cut out and attach the drilling template for the stepper motor. It should be taped to the lid of the enclosure on center about 1" from one of its shorter edges.

## Step 8: Drill the Template

Drill the outer mounting holes with a 1/8" drill bit and the center hole for the shift with a 3/8" drill bit.

## Step 9: Attach the Motor

Fasten the motor to the lid using M3 x 12mm bolts.

## Step 10: Widen the Crank Hole

Widen the hole at the end of the crank arm to be 1/4" wide to receive the bolt for the crank knob.

## Step 11: Attach the Crank Knob

Insert thread-locking fluid into knob's threading to prevent the bolt from later loosening while you crank the flashlight.

Loosely fasten the knob to the crank arm using an M6 x 20mm bolt. It should be attached loosely enough that the knob will be able to spin in place.

## Step 12: Attaching the Coupling

Attach the shaft coupling to the crank arm using four 6-32 bolts.

## Step 13: Attach the Motor Crank

Fasten the crank arm to the motor shaft using the shaft coupling's set screw.

This completes the motor's crank arm assembly.

## Step 14: Trim the Wires

Trim the wires coming out of the stepper motor to be about 4" - 6" long.

This will make it easier to work with later and fit in the case.

## Step 15: Reflector Hole

Drill a hole on center on one of the smallest faces of the enclosure for the flashlight's reflector cone using a 1-1/16" hole saw.

The easiest way to find center of any rectangular surface is to draw an X from corner to corner.

## Step 16: Power Switch Hole

Drill a 1/8" pilot hole in the side of the enclosure near the hole for the reflector, and then widen it to 3/8". This is for mounting the switch.

## Step 17: Wire the Circuit

Now is time to build the circuit on the PCB as pictured in the schematic.

To begin, I wired the two bridge rectifiers in place.

I then connected the zener diode voltage regulator.

After that, I wired in both capacitors.

Lastly, I added the resistor for the LED. The remaining components will be mounted off the board and connected later.

## Step 18: Wire the LED

Connect a red wire to the LED's anode and a black wire to its cathode. Insulate the solder joints with shrink tubing to protect them and prevent potential shorts.

## Step 19: Mount the LED

Apply contact cement to the reflector and the lip around the edge of the LED.

Wait for both to dry until they are tacky to the touch and then firmly press them together to make a firm bond.

## Step 20: Attach the Lens

Attach the lens to the reflector by applying contact cement around the front inner lip of the reflector and the outer edge of the lens.

Again, wait for both to dry until they are tacky to the touch and press them together firmly.

## Step 21: Switch

Pass the switch up through the hole in the enclosure and fasten it in place with its mounting hardware.

## Step 22: Mount the Reflector

Apply contact cement on the enclosure around the outer edge of the reflector mounting hole, and the edge of the reflector.

Press the two firmly together once the contact cement is dry enough.

## Step 23: Attach the Motor

Solder the motor's wires to the appropriate rectifiers on the circuit board. If you have forgotten where this is, reference the schematic.

Also, make sure you get the wire pairs correct. In my case red and blue were attached to one coil, and black and green were attached to the other coil. If you mix it up and take one wire from each coil - let's say, black and red - then not much will happen.

## Step 24: Solder the LED

Solder the LED in series with the resistor on the circuit, and the switch in series with the power supply.

## Step 25: Solder the Switch and LED

Solder the switch and LED together to complete the circuit. Now, when the switch is pressed the LED is either connected or disconnected from the supercapacitor, enabling you to turn it on and off.

## Step 26: Apply Velcro

Cut two small adhesive-back velcro tabs and mount the circuit board neatly on the inside of the enclosure in a spot that will be out of the way of the servo motor.

## Step 27: Case Closed

Put the lid back on the case, and fasten it shut with the enclosure's mounting screws.

## Step 28: Attach the Rubber Cover (optional)

Attach the rubber lens cover gasket with contact cement over the edge of the lens to seal it up.

## Step 29: Crank It Up

Give your flashlight a couple minutes of solid cranking, and enjoy no longer being in the dark.

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## 16 Discussions

I'm in the process of making this, but it doesn't seem very efficient. I didn't have a 15F 5.5V capacitor, so I used a 4F 5.5V capacitor, and it took nearly 30 minutes of non stop cranking, then eventually I switched to using my drill to crank it just to get to a potential difference of 3.0V. After which the light was only a useable brightness for about a minute, then it was quite dim. It stayed on and dim for a long time, but I can't imagine how long it would take for a 15F to charge up. I tried it again with a 1F 5.5V and it took 13 minutes of solid cranking to charge up to 3.10V, and again, was only a useable brightness for about 1 minute, then it dimmed quite a bit. I tried it again with a 0.11F 5.5V capacitor, and it charged up quite quickly, and the useable brightness was about 30s (about half that of the significantly larger capacitors). It stayed dim for quite a while as well. Maybe gears are required? Or a more efficient LED?

Adding this as a project for my electronics class, thanks!

Shottky diodes have a lower voltage drop

Very nice project!
How much lumen does the lamp have?

Like the idea of a emergency flash light that doesn't require batteries but how long does the light work on one instance of cranking?

I have owned at least 3 dynamo powered lights and 2 "Survival Radios". All were complete crap The Solar cell feature worked weakly for a few minutes and the lights same. I tried and tried with dynamo's and they never got me more then 2 minutes of power. All with Ni-Cd batts not the useless button batts in the wind up flashlights.

So how many minutes of pumping does one need to charge the cap for how many minutes of full brilliance light? If you need to recharge every 2 minutes these have little value o/t scientific curiosity. I would love it as a power source for small radio and a jewel thief lamp, emergency light/radio. Years ago I made the Flash Film Camera Circuits - CF lamp units, this would make a nice addition, provided you do not have to crank for 10 minutes to get 5 minutes of light. If it could power a tiny amp it could make a very quiet Xtal Radio louder with a small amp.

I do not wish to be mean to this idea, I love the concept. But in practice I have not found a system that works well enough to say yes yes yes , I want 6 please one for each family member and in the auto too!

Very nice 'ible, clear & great images & diagrams. What S/W did you use for the circuit diagrams?

+1 re this question, "So how many minutes of pumping does one need to charge the cap for how many minutes of full brilliance light?"

TOTALLY. I want to have 6 of these at a decent cost, but not functionally useless. A decent flashlight with no battery just sounds great, but commercial versions I have had have been garbage too!

since a nema 17 stepper motor cost ~12 USD why can't we use a dc motor or a dynamo ? its way cheaper and you don't need the bridge rectifier since you will get a dc voltage from a brushed DC motor

Superb Instructable by the way - nice photos , clear instructions, easy to follow

well done

From my research on DIY wind mills, you want a motor to be low RPM and high voltage, Otherwise you need to turn the motor above it's rated RPM to get the voltage out that it is rated for. Hard to do with out gearing which adds to the complexity of the build. Lets say you had a 12V PM dc motor rated for 1,500 RPM's and you wanted the 5.1V like this project, you may need to turn the motor at around 700-750 RPM's.

ah! now it makes sense , i didin't think about rpm. looks like a stepper motor is a great candidate for low rpm high torque motor thanks for the reply

Add a pistol grip to make it ergonomically convenient. I presume your use of stepper motors instead of a DC can motor is because of the efficiency and power of the former.

How much do all these parts cost approximately?

I'm thinking of making this with my kids and they LOVE flashlights, but if it is more than \$20, I can't justify it.

another project on the way thanks

well done great idea. never thought of using a stepper motor that way. goes in the project bin for up coming projects