DIY wax-powered backpack stove: construction - Frank Groffie's miscellany

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The primary stove unit starts as just a tin can from your pantry or recycle bin. You'll then make a trip to the electronics store for a few small purchases (total $11) for the air blower, and a trip to to hardware store for aluminum sheet metal and other miscellany. That's the easy part. Then you're up against some tricky measurements and assembly operations.

Why anyone would want to make this stove I’m not sure. Consider it a challenge. All things considered, it rates only about equal to your average stove, though it is more powerful than stoves using alcohol or Esbit
® tabs. It does perform well. It's certainly unique and quirky, perhaps cool, even.

General tools and materials

Here’s a partial list of tools and materials you’ll need, some ordinary and some special: handheld sheet-metal shears, sheet aluminum, a drill and ⅛-inch bit, a stepped drill bit for making large holes in sheet metal (Unibit® by Irwin®), soldering iron, solder, hot-glue gun, pop riveter, pop rivets, hammer, file, pliers, and vise.

All pop rivets mentioned are of the ⅛-in.-diam. short variety. Rivets for the windscreen should be steel. Rivets for the supercharger should be aluminum.

A cross section, somewhat schematic and not perfectly scaled, is shown below.

Stove body

The stove body starts as a tin can holding about 8 oz. of water chestnuts or what-not, give or take a fraction of an ounce. Regardless of the contents, these cans are a standard size: 2⅛ inches tall by 3⅜ inches across. The larger can in the adjacent photo is one of these cans with a net weight of 8 oz. Do not remove the top. Use the fuel-chamber can (see below) to mark for a large matching hole in the top of the stove-body can. This hole can be made by drilling several large holes with the Unibit and then gradually, carefully removing the remainder with a small grinding wheel. Check the fit periodically with the fuel-chamber can; it should fit tightly with friction alone. Discard the contents, which will be contaminated with metal shavings. Rinse and dry the inside.

Drill a ¾-inch hole near the bottom for the air tubing. When drilling this hole, measure for, and take care to leave intact, the can’s bottom crimp, which serves a strengthening function.

The four stove+pot supports are made from steel rod (12 gauge) cut from an old oven rack. Braze or weld a small washer, one that just barely goes around the rod, onto a section of rod material. Measure up ¾ inch on the rod, bend at a 90-degree angle for the horizontal pot support, and cut the horizontal segment 1¼ inches long. Do the same with the other three rods.

Mark four points in the top of the stove-body can immediately inward from the crimp. These points need to be evenly spaced around the rim, i.e., be the corners of an imaginary square, and two of the marks need to be located so that the inlet port is midway between two of them. Do the same on the bottom vertically down from the top holes. Drill these eight holes using a conventional bit that exactly matches the rod diameter. Do not damage the crimp around the top or bottom of the can.

Insert a support through both its holes so the washer rests on the top rim of the stove body. Where the rod contacts the bottom crimp, make a 90-degree bend in the same direction as the pot support, and cut this horizontal segment 1¼ inches long. Do the same with the other three rods.

The windscreen is made rom a length of sheet steel taken from another tin can. Bend the ends around the two pot supports nearest the inlet port, and insert a rivet in each end to create a secure attachment.

Fuel chamber

The fuel chamber is made from a tin can formerly holding about 4 oz. of olives or what-not, give or take an ounce. The smaller can in the photo above is one just under 3 inches across holding 4 oz. of fire-roasted chiles. This can needs to be one without a bottom crimp that's wider than the can. The crimp on the top can be wider than the can, but the bottom sides need to be flush. Don't open the can yet.

Drill holes about 3/16 inch in diameter at closely spaced intervals around the top using the Unibit. Don't disturb the crimp around the top of the can. Now remove the top using a can opener. Throw away the contents, which will be contaminated with metal shavings. Rinse and dry the inside. Insert the fuel chamber into the stove body. It should be a tight fit.

The wick can be made from 000 steel wool. Place it in the chamber down to the bottom and extending up to about ¾ in. below the air holes.

Add wax. Melt some wax in another separate clean, dry can. Pour the wax onto the wick so as to saturate it. Do not, however, drown the wick. Fill the can only about 1/3 full of wax. More is not better. The upper ⅜ inch of wick should be saturated with wax but not submerged by it. Too high a wax level leaves too little of the wick exposed, which causes poor stove performance.

The flame diffuser plate is a circular piece cut from sheet steel that has been perforated with numerous tiny holes. I don't recall the discarded item that my material came from, but the perforations came this way from some manufacturer. This plate is merely placed over the fuel chamber after the stove gets going. I believe (although I'm not entirely sure) that (1) the tiny holes diffuse the flame and help it mix more with oxygen, (2) it gets red hot, which aids combustion and efficiency and may reduce soot transfer to the cookware, and (3) it provides heat feedback to the wax fuel supply to get it thoroughly molten and hot.

An inferior main stove unit

Here’s how not to design the main stove unit. This was my first design, which I came up with in 2011. Same supercharger, but the air injection was via internal axial tubing. I used this stove a couple times, but it was difficult to light and, in cold temperatures, would only power up with much coaxing. It was also less stable and heavier. My apologies for publishing this version from around 2015 to 2017.



The supercharger shell consists of a complex bottom piece and a lid. The bottom piece begins as a “net” cut from sheet aluminum. Fold in the rear tabs, and fold up the side faces and rear face. Drill a hole in the rear face for the switch. The lid begins similarly, and its side flanges are folded down. Don't attach the lid yet. Save this step for way later.

A battery holder in the 9-volt size costs about $1 at Fry’s Electronics (a big-box retailer in the western U.S.; elsewhere undoubtedly you'll have an equivalent). Orient the battery holder so its terminals face rearward on the lid. Note the tiny predrilled mounting holes in its backing plate. Select two of these holes at diagonal corners, and enlarge them (if needed) to receive aluminum pop rivets. Install the rivets from the top (outside) of the lid so that their heads are on the outside and the tails protrude through the battery holder. Then,  smash the tails flat using any fat cylindrical steel tool and a hammer.

The fan is a slick little unit fully contained in a black plastic housing. It is rated at 12 volts and is made for cooling electronics. It should be fairly powerful. Mine was rated at 0.195 amps. It measures 40 cm by 40 cm  by 30 cm thick. Such a fan retails for about $8 at Fry’s. Don’t be dismayed by the low cost, plastic construction, and seemingly low air output. It will serve well and not melt during use, thanks to the shielding given by the supercharger housing and the way it will be distanced from the stove heat. And its gentle air output will be plenty, as you’ll observe when you use the stove. Clip away its yellow wire. Plug the fan’s four tiny tubes at its corners with dabs of hot-melt glue, to minimize fan backflow and maximize efficiency.

The switch is a miniature toggle switch that retails for about $2 at Fry’s. It will include a threaded shaft and tiny nuts handy for attaching it to the supercharger.

Wiring is shown schematically in the diagram. Shorten the fan's red and black wires so that the lid can comfortably hinge all the way up but the supercharger isn't crammed with more wire than necessary. Connect and solder the wiring between the three electrical components while they’re still outside the supercharger. Solder the red (positive) wire from the fan to the positive (+) terminal on the battery holder. Solder the black (negative) wire from the fan to the switch and then, with another piece of black wire from the switch, to the negative (-) terminal on the battery holder. Coat all soldered connections with hot-melt glue to lend these connections some strength and to prevent corrosion and shorting.

When both the electrical assembly (plus connected lid) and the supercharger housing are ready, place the electrical assembly inside the supercharger. Attach the switch using its provided nut. The fan should fit snugly inside the supercharger shell, but you should also add a dab of hot melt glue to secure it there. Connect the rear corners of the lid to the supercharger bottom using two rivets. The result is a pivoting lid that allows battery access.

The shroud, now that I think about it, isn't really necessary, but it's made of thin sheet aluminum. My preference is to make it as a one-piece "net" of aluminum, as in the diagram at right (not to scale). First drill a ¾-inch-diam. hole in your uncut metal to eventually accept the air tube. Only then (to prevent tearing up your work during drilling) make your cuts and folds around the hole. The shroud can be attached to the supercharger using aluminum foil tape, aluminum rivets, JB Weld, or a combination thereof (my method).

The air tubing distances the supercharger from the stove flames. It consists merely a rectangle of sheet metal rolled into a tube; overlap and connect the edges using two pop rivets and aluminum-foil tape. Glue it to the supercharger using JB Weld. Dont attach it to the stove body: it merely rests inside the stove's inlet hole loosely during stove operation.


Execute this DIY project and use any resulting product solely at your own risk.

Copyright 2015. All rights reserved.
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