Introduction: Hack-A-Lantern: Recycled Computer Power Supply Flashlight

About: Ordinary guy with no special skills, just trying to change the world one backyard invention at a time. See more at: On Twitter - @300MPGBen and at

Do you have lots of spare computer parts? Do you like to be prepared for emergencies? Are you ready for the zombie apocalypse? Do you get what I mean when I say the word "Junk-Punk"?

If so, then you should build yourself a Recycled Computer Power Supply Lantern!
Using salvaged, repurposed, and reused components, we'll build a 12V/11w electric lantern.

This all started recently when I was talking with a friend at the Milwaukee Makerspace. I was working on a simple wiring project and chatting and the friend showed me a couple of 5ah lead acid batteries he salvaged, which were perfectly good, and he was giving to anybody who wanted one. It's a great size rechargeable battery, and the size and shape reminded me of the "old-fashioned" lanterns that use a 9V dry cell. That, plus a discussion of zombie movies made me wonder - Do I have the skills to not only build a portable light from little more than scrap materials, but also build something better than I could buy?

I took it as a challenge, and proceeded to build the Power Supply Lantern. 

Step 1: Tools & Materials

To start, let's review the tools and materials for the project.

Nearly all materials for this project were recycled, salvaged, or reused. The project was based on the materials that I had on hand. If you want to build something similar, you might have to buy something. Better yet, why don't you build a project using just the materials YOU have on hand, and see what you come up with!

Dead computer power supply
12V landscape lighting bulb
12V rechargeable battery - 5AH or other size that fits inside power supply
Foam or other scrap spacing material
1/4" crimp-on spade terminals
Electric tape or heat-shrink
Battery Charger

You might notice that I didn't list either a switch or any wire in the list of materials. That's because we will re-use the switch, wiring, and power port already in the power supply.

Tools are basic, that no respectable DIY'er would be without, but when it comes down to it, most could all be replaced with a Swiss Army Knife or Leatherman.

Phillips Screw Driver
Wire Stripper
Wire Crimper
Side Cutters
Drill and bits
Multimeter (Optional)

Step 2: Open & Remove the Un-Needed

First thing is to open up the power supply.

Remove the four phillips screws that hold the cover on the power supply, and then remove the cover. The cover is actually 3 sides, or half the power supply. Seperate the two parts.

Inside, you will see lots of wire, a circuit board, a fan, and the switch and power port.

Remove the four screws holding in the cooling fan. Unplug the fan from the circuit board, and then set it to the side as material for one of your future projects.

Remove the screws holding down the circuit board. Then locate the wires from the switch and power connector, and follow them to where they connect on the board. Snip the wires close to the board to maximize the length of the cut wire, still attached to the switch and power connector.

Remove the circuit board and set to the side.

You now have a mostly empty box with just a couple of wires on the switch and power supply. We'll reuse those as part of the project. You should have enough wire to reach the battery and the light bulb.

Step 3: Battery

The battery used for the project is a 5 amp-hour sealed lead-acid battery. It fits nicely inside the power supply case.

The terminals on the battery are 1/4" male spade connectors. These are easy to work with, by crimping spade connectors onto wires and then just pushing them onto the battery connector terminals.

The battery is marked with the Positive in Red and the Negative in black, and has a plastic protector around the Positive Terminal to help reduce accidental short-circuits.

Put the battery into one half of the power supply case to ensure that it fits. You may want to use a pencil or marker to outline it so you know where the battery lines up without it being in the case.

Step 4: Lamp

The lamp is a 12-volt, 11-watt light bulb left-over from another project. It would typically be used in outdoor, low-voltage landscape lighting, powered by a 12V AC transformer.

Something as simple as a light bulb doesn't really care if it's powered by AC or DC power, as long as the voltage is right. We are using a 12V battery, so there's no problem repurposing this bulb.

The lamp will take the place of the fan. Hold up the bulb to circular grate where the fan was. Mark how much space the bulb will take up. It's round, and so is the fan, so it should fit OK, but not all the way back into the case. (A different size bulb might fit flush, or even INSIDE the case!)

Using the side-cutters or a tin-snips, snip the tin fan grating to make the bulb fit. You could also use a Dremel or other cutting tool.

Test-fit the bulb, but don't permanently attach it yet. First, we will want to wire up the lantern.

Step 5: Wiring It Up

Wiring on a flashlight is pretty basic. A complete circuit is just Battery Positive to Switch to Bulb and back to Battery Negative.

Since this is a rechargeable battery, it would be nice to also add a way to recharge the lantern without taking it apart to access the battery. To do that, we'll reuse the power cord port as a place to connect the charger to.

First, check to make sure the wires on the switch and power inlet will reach the battery and the bulb.

The "115/230" power switch won't be used, so its red wires can be snipped-off. Save them for reuse. It's good heavy wire, and red is typically used to indicate Positive polarity.

Strip and twist together one wire from each of the power switch and the power inlet. Add a female spade terminal and crimp it on. This connector goes to the Positive terminal of the battery. The other wire of the switch goes to the  bulb. 

The OTHER wire of the power inlet goes to the opposite side of the bulb. That side of the bulb also goes to the battery negative. This bulb has "multi-terminals" on it, so it's easy to connect two wires at once to a terminal - one with a spade connector, and one with a bare wire tightened down under a screw.

Once you are done, power will only go to the bulb when the switch is on, but power will always be connected to two of the pins of the power inlet. (Cut off the third wire.) That way a battery charger can be connected to the two pins to recharge the battery. Mark the two pins with the correct polarity.

(A note on reusing the switch: Switches and other components often have 2 sets of ratings - one for AC and one for DC. The ratings are typically much LOWER for DC. Use a flashlight to look closely on the side of the switch, and you will see its power rating. Because this is only a 1 Amp project, this switch will work fine.)

Step 6: Handle

One classic element of a lantern is a distinct handle, separate from the body of the light.
(Unlike a flashlight, where you simply grasp around the entire shape of the flashlight.)

Usually, I would use some bolts and spacers, and a cross-piece of wood or metal to build a handle. However, I didn't have any material handy that seemed to suit it - other than the wires still connected to the circuit board, set aside earlier.

Those wires were bundled tightly together, and the diameter was about right to be comfortable in the hand. I cut the bundle of wires close to the surface of the board.

I measured the diameter of the wire bundle by feeding it through a drill index. If seemed to fit best in the 1/2" hole. That meant than I could drill 1/2" holes through the sheet metal, and then feed the wires right through. I drilled two holes, centered side-to-side. There were already two stamp marks in the metal about 3/4" from either end, so I used those as a reference for how far in from the ends to drill.

With the holes drilled, I fed the cut end of the wires through from the inside of the case, up and over the top, and back through the other hole. The original computer power board connector is too large to fit through the hole, so it acts as a stop. 

On the other end. I wrapped two zip-ties around the wire to bind them in place. Then I folded back the extra wire, zip-tied it again, and cut off the excess wires.

Step 7: Assembly

With the wiring finished and the handle done, the whole thing just has to be assembled back together.

Now is the time to glue in place the lamp and the battery.

I glued the lamp in place with silicon glue. It works well over a range of temperatures. The lamp will get warm with use, so hot-glue would be a poor choice.

On the other hand, a hot-glue gun worked great to glue the battery into the case. I also glued two bits of scrap foam to act as spacers between the battery and the cover.

Once the glue is cool/dry, reassemble the cover onto the case (minding the foam padding and wire handle) and put the four cover screws back in.

To recharge, I just hook up the small battery charger I already had to the two charging pins, which I noted the polarity of.

Step 8: Test It Out!

Once the lantern is together - go test it out!

It's great for camping, blackouts, Trick-or-Treating - heck, you might even throw the whole thing inside a Jack-0-Lantern.

With the nice square base, it sits very well, so it can be set down and allow both hands free to do what you need to do. You can also sit the lantern on end to point the light straight up and bounce-light an entire room.

I like the way the handle feels. It's surprisingly comfortable, and the lantern hangs just right from it.

It's a 5AH battery, and the bulb is basically 1 amp, so that means it's a 4-hour run time to 80% battery discharge.

The lamp itself is rather bright and has a large area of illumination - it's most comparable to a car headlight in it's pattern, although not as bright as that.

Now you go make one!
Will yours be more steam-punkier? Will you use a different bulb? Let me know how yours turns out!

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