Crank Flash Light




Introduction: Crank Flash Light

About: Happily married, self employed, full wood shop, some metal work as well as electronics, antique collector.

I wanted a reliable hand crank light that would not wear your arm out in times of need
A retro look was desired too

Step 1: Find a Good Stepper Motor

I found several stepper motors but they were either too big, or did not produce enough voltage at a slow speed
This one is from a scanner off a copier.
What makes it suitable are three factors, one it has gear reduction (increase from our perspective) this saves a ton of time, second it has two armatures stacked, these can be connected in series to double voltage(almost)
Third it's small and makes a solid 6 volts AC
At a slow crank speed

Step 2: Where Is the Current

A very easy way to find the highest voltage is to measure the various wires through a swing meter, I have both digital and analog but watching the needle swing is much easier to see what coil is putting out
In this case the red line was about half so I clipped it off

Step 3: What Kind of Current

What your getting from this little motor is a alternating current I have seen people here using un-rectified current it works but you are working twice as hard using only half the signal
If you don't want to make a bridge just use an old style filament bulb (that's if you were going to be using LEDs )

Step 4: Full Wave Rectifier

This is a very common full wave rectifier made from scrounged diodes
If this does not make sense just google there are thousands of pages about them

Step 5: Add a Crank

I wanted a sturdy crank I thought this is where it would break so I took my time
The red washer is to smooth operation
A step bit is almost mandatory

Step 6: Stick It All Together

This flash light was from the 1960's there is lots of room I plan to add a super capacitor when I place my next electronics order
The bulb is an led upgrade from Walmart
It keeps the retro look the crank is from an old mechanical adding machine
All I can say is when you are testing your motor if you can't get your LEDs to light with a flip of the rotor you are not going to be happy with how hard you have to crank



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    19 Discussions

    How much did this setup cost you? Minus the light.

    And would I need any sautering tools to do this?

    It is an old flash light 6v everything is original except the crank it is off an old mechanical calculator

    While the "Retro" look is cool, from a practical point using an old 6V flashlight would give you a ready made case.

    With a capacitor this would make a good disaster kit light.

    Great idea!
    Steppers are an awesome way to do energy harvesting.
    I used to work for a printer company, eg.
    i have a lot of experience with these.

    Your steppers have is 2 set of coils 90 degrees apart electrically, hence
    the imperfect sum when theyre in series.
    So, its not recommended to just connect them in series.
    Ordinarily, this would be a liability, but
    using diodes can rectify the situation (pun intended)

    Your coils have 3 wires each. Its a uni polar stepper.
    Essentially, each winding is center tapped.
    As a motor, the tap would go to supply and
    trannies would alternately ground the ends
    to get the field reversal.

    So, you could connect the 2 taps to ground and
    use 2 diodes each winding (4 total)
    to get a full wave center tapped power supply.
    The 90 degree aspect of the separate coil voltages
    causes the double humped output of each rectified winding to interleave,
    filling in the gaps, thus smoothing the DC.

    This arrangement would get you half the voltage and double the current.

    If you were to use 2 full bridges across the ends of each winding,
    you would get double the voltage and half the current.
    The phase filling would be the same.

    You would choose the appropriate method to match the bulb.

    Ive even used some 24 volt steppers at high speed with
    stacked voltage doublers and got 600VDC
    to make some interesting fire works.

    Much fun with these!

    1 reply

    So since they're essentially two generators 90° out of phase but wired in series, this setup is losing about 1/4 - 1/3 of the possible power, right? Compared to your proposed 2 taps to ground arrangements? The double current version would make the LED brighter, right?

    Is that box an old ammo can or maybe a ventillated lunch box? Maybe some kind of old radio enclousure? Is the handle hacked off of a old batter mixer? Or was it some kind of tool|appliance. I can't tell.

    It looks like no resistor is used to protect the LED. Do you find you even need one? Can you even exceed the the power rating of the LED if you wanted to by cranking as fast as you can? Maybe this would change if you added a capacitor you could charge with a switch that keeps the light off, but when you flick the switch, all the stored charge rushes into the LED at once. . . .
    And hey, if you can add a capacitor, maybe the next thing is a solar cell too!

    Cool! I'll make this! I'll add sum USB ports to charge things. Maybe a A/C to D/C converter to charge D/C batteries... There are so many possibilities for this project... I got the juices started now! Thanx! Great job! I would like to give a suggestion tho. Utilizing correct grammar, like punctuation and and Cap letters at the first of every sentence. Just tryin' to help... Peace

    a full wave rectifier would work with just 2 diodes but you could try adding some memory capacitors they are low voltage give time a little time.
    I have a small Russian made light that fits in the hand, operates by squeezing a trigger to spin the motor
    I like the look of yours
    uncle frogy

    xarlock667 sir I have torches of this vintage and torches with one power led and some with a stack of leds The single led torch gives a more natural light temperature and those with 8 or more leds make me wonder if it really is worth the effort of making a bar of leds. The single use less current than the clusters and the single is a drrect replacement for the bulb

    Up the voltage to 24 or so, and use a LED bank instead of a single bulb and you will have a MUCH stronger light for the same amount of cranking effort.

    1 reply

    I was using a cluster of 5mm LEDs for testing but just could not get myself to damage that almost vintage reflector plus I detest 5 mm LEDs my Cree 800 lumen was occupied in another creation, this was really just a proof of concept that I have not fulfilled that being the usefulness of a super capacitor in a short charging situation

    What a blast from the past I first encountered a stepper in the Minolta 450Z copier I think it was the first real zoom copier.
    Thanks for the review I figured there must be a center tab from my ohm readings (the red wire) I have many steppers the largest I think is from the Kycera Mita 4000 series
    You have me wondering about the out put wave form though I made a calculated guess it was an AC form based on the fact that both n and s poles were passing the coils now I'll have to get out the scope and have a look


    Next add a battery and some USB ports, and you can charge your phone etc!

    Hi longwinters
    Great idea and pretty well done

    I weíll keep my eyes open to such stepper motors;-))))))

    Yours Aeon Junophor

    Good luck, throw away printer / copiers are a great source of stepper motors and diodes if you don't have a meter just use an LED for finding the ideal motor

    Awesome! I have been wanting to turn an old hawkeye brownie camera into a flashlight - this is super helpful.