Ultracapacitor 3d Printed Flashlight




About: I am an author and a maker. My current project is Santa's Shop. I'm working on a science fiction type book--more later. @EngineerRigsby

Using available parts and a 3d printer, I went from idea stage (sketch above) to a working device in one day. 

Printing and designing in 3d allows a designer to build a case and mechanical parts around whatever is available.  For example, I used an ultracapacitor from a Coleman Ultracap Screwdriver.  It was simple to design and print a hollow cylinder to accept the capacitor--this would have been a major challenge a year ago.


Step 1:

First I printed a cylinder, scavenged the capacitor and found an LED.

I used Autodesk 123d (free) to design the 3d parts. Files are available here:


Step 2:

Next, I came up with a plan.  The LED is pretty directional, so I skipped building a reflector.  The light will run for hours and hours on a charge (and I charge it with a solar panel), so I omitted the on/off switch. Note the diode--that prevents the capacitor voltage from going backwards out onto the leads; you can clip the alligator leads together if you want after charging.

If you want to see how I regulate the incoming voltage, look at this instructable:


Step 3:

Check to see that the capacitor fits into the cylinder.

Step 4:

Drill a 1/8 inch diameter hole in the upper part of the cylinder (yes, I should have designed that in software, but I'm far from perfect).

Step 5:

Slide the capacitor (minus any wires) into the cylinder.

Step 6:

Add a 100 ohm resistor to the long lead of the LED (I soldered it).

Step 7:

Add a red wire wrap wire to the other end of the resistor.

Step 8:

Clip the surplus wire from the resistor and put a piece of heat shrinkable tubing over the exposed metal.

Step 9:

Heat the tubing until it shrinks (I use the soldering iron to shrink the tube).

Step 10:

Add blue wire wrap wire to the short leg of the LED.

Step 11:

Clip the excess LED leg, add heat shrink and shrink the tubing.

Step 12:

Push the wire end of the alligator clips through the hole in the cylinder.

Step 13:

Push the LED leads through the cap (it's not really a reflector).

Step 14:

Connect the red LED lead to the red alligator clip.

Step 15:

Connect the diode (end without the band) and blue LED lead to the negative post on the capacitor (there's a big "-" next to the post on this particular unit).

Step 16:

Connect the black alligator clip wire to the band end of the diode.

Step 17:

Connect the red LED/alligator wire to the positive side of the ultracapacitor.

Step 18:

Test the flashlight--it's easier to correct problems now--before it's closed up.

Step 19:

Use aluminum duct tape to fasten the top cap to the cylinder--this is easy to remove if you ever want to go inside.  You can use acetone or superglue to "weld" the parts together, but I prefer easy access in case I want to go inside.

Step 20:

I'm looking at it now, 5 hours after assembly--and it's still shining brightly with no indication of decreased light.

3rd Annual Make It Stick Contest

Second Prize in the
3rd Annual Make It Stick Contest



    • Fandom Contest

      Fandom Contest
    • IoT Challenge

      IoT Challenge
    • Colors of the Rainbow Contest

      Colors of the Rainbow Contest

    33 Discussions


    3 years ago

    Where exactly can you salvage ultra-capacitors from?

    1 reply

    Reply 3 years ago

    They are rather uncommon--the Coleman screwdriver is the only commercial product (other than specialty flashlights) that I have seen using these.


    3 years ago on Introduction

    Nice. I remember my one boss said your resistors you can use to control the discharge rate of capacitor also.Electronic is great! And great instructable!!

    Two minutes of charge will give 12 hours of good light--that's the simple answer.

    Now, the more complicated answer--it depends. From zero volts, with a one amp source; something like 15 minutes to charge. Five amps (circuit needs a higher current capacity diode for this) would do a total charge in three minutes. Because the led takes less current as the voltage declines, it will stay illuminated for days--so it can take a long time to totally discharge.

    In practice, I charge it for two minutes (at a one amp rate) one time per day. It remains illuminated for 24 hours.

    Awesome. I think these are the future (part of it anyways). Thanks for responding, I know that you might have said it somewhere, I was just too lazy to look. Now, though, I want to make one.

    Great job.

    Thank you!

    I want to build one of these with a voltage regulator, switch, reflector and high speed charger (a real flashlight). You've fired me up enough to put it on my "list of projects to do" list.

    Thanks for the encouragement :)


    6 years ago on Step 20

    This is just a suggestion --

    One could easily hold the body of the ultra capacitor, making the container somewhat superfluous. Seems that a PVC container would work just as well.

    However, those alligator clips are remarkably obtuse; just hanging there.
    I would put the power of the 3d printer to IMHO better use by creating a charging station for the flashlight.

    Maybe two concentric rings on the bottom, so that you could set the flashlight into it in any orientation. That way, the contacts could be flat to the surface of the flashlight.

    By the way, kudos on the short protection blocking diode, a great idea for this application!

    3 replies

    Thanks--good suggestions!

    I'm planning on building a flashlight (in the future) using the capacitor, a voltage regulator, reflector etc. (more like a real flashlight). I would use a purchasable capacitor instead of one from my junk bin--to make it more repeatable. I like your concentric rings idea for the charging base. I'm still playing with the idea of fast charge (5 amps or so)--any thoughts on how to make a good simple connection that can handle that without overheating?


    I wouldn't worry about the charge current too much.
    Voltage is low; resistance is very very low; so the power the charge contacts has to dissipate is very small.

    If you want to be crazy about this:

    The table there suggests that ~18 AWG should suffice.
    I personally think this is overkill, but it gives you a ballpark.

    Keep in mind that what really causes a wire to heat up is power dissipated, not amperage, so that P = V * I, where I is the amperage (5A in your example), and importantly, V is the drop *across the wire* which is dependent upon the resistance of the wire and the current. The resistance of the wire is dependent on the length and gauge of the wire. Your length is (very) short for those contact points.

    I think that copper tape would work beautifully, to create contacts on the bottom of the flashlight.

    Then the copper tape could make connection with your charging base merely by the weight of the flashlight holding the concentric tape circles against spring like contacts (which could just be 18 AWG solid wire that is "too long" forced up through holes in the base)

    | | (base of flashlight shown in profile)
    ___ / \ ____ (visible bottom of charging station)
    ------/ \-------- (wire poking through bottom of charging station)


    Digikey.com has some--for example there is a 350 farad (at 2.7 volts) for $11.23 in quantities of one:


    Or, tecategroup.com has some really big ultracaps like a 3000 farad at 2.7 volts for about $76.00 in quantities of one:


    Tecategroup.com often has minimum ordering quantities . . . .

    You could also rewire your LEDs in parallel. 12 volt LEDs are actually a resistor and a couple of LEDs in series. Put a voltmeter across one LED when you're putting 12V into the string, and you'll see what they actually take. Better yet, find out what their current rating is, and design something that supplies that current or less, so they last a long time.

    You could put five 2.7 volt caps in series--but that gets costly.

    I've never built a "joule thief," (try "joule thief" in instructables search box) but that might enable you to use one or two caps and power your 12 volt leds.


    Reply 6 years ago on Introduction

    There's really no accounting for what catches on--I've done a couple of rather involved and (to me) somewhat nifty things and received around 300 views.



    I know you've done some really cool things--just know that you can win a grand prize with less than 1000 views (I have). Popularity and quality both count . . . I just submit anything that may be helpful to others (or that I just like) and let the chips fall where they may :)