3ModeStove Mini - Camping / Emergency Stove

Mode1: Wood Gas (12V Fan Forced TLUD)

As a continuation of my hobby of burning stuff in tins, this project arose from my fascination with wood gas TLUD (Top Lit Updraft) Stoves. I favoured the fan forced option (Mode 1), as it produces a very clean, hot burn with hardly any soot. But what if the fan batteries run out? Modes 2 and 3 use the chimney / potstand for either an alcohol or twig burning backup.

Due to the size / burn time, 3ModeStove Mini is intended as a camping / emergency use stove.

Apologies if this is very UK specific. I hope you can use some of the ideas anyway!

3ModeStove Mini Is Environmentally Friendly Because:

Does not burn fossil fuels which release carbon into the air.
Produces hardly any smoke into the air or soot on the pot.
Generates more heat from less wood by extracting and burning the wood gas.
Avoids cutting any live wood to burn, as it uses small twigs or other waste biomass as fuel.
Sequesters carbon from the atmosphere (albeit a tiny amount), leaving unburnt charcoal (biochar).
Batteries can be charged via domestic green electricity tariff; solar; wind; bike generator etc.
Uses recycled / saved / scavenged materials in its construction.

How Does It Work?

The fuel burns from the top down.

The burn chamber sits inside the stove body with a small air space between the two.
There are air holes in the bottom of the burn chamber (primary combustion).
The air holes you can see at the top of the burn chamber are for secondary combustion.

The burn chamber is filled with small twigs to just below the secondary air holes.
The fuel is lit on top with a small amount of accelerant (alcohol).
After a minute or so, when the flame bed is established, the fan is inserted and switched on.

The fan blows air into the primary holes, feeding the combustion from underneath.
The fuel burns with a restricted supply of oxygen, turning to charcoal and producing
lots of smoke (wood gas). The wood gas drifts up through the fuel.

The secondary air is heated as it is blown upward through the space between the
hot combustion chamber and stove body.
It exits the secondary air holes, mixes with the wood gas and together they burn!

It is a gas stove that extracts its own gas from wood, turning the wood to biochar in the process!

Step 1: Tools and Materials

YOU WILL NEED:

Heinz Baked Beans can, half size
Diameter: 73.5mm

395 grams baked beans can x 2
Diameter: 73.5mm
(tapered, stackable base - see photo)
The lids from these cans
Pet food can cover to fit this size can

300 grams mushy peas can x 1
Diameter: 66mm

425 grams fruit cocktail can x 1
(+ 1 identical, if you want to make Modes 2 and 3 later)
Diameter: 85mm
(tapered, stackable base - see photo)

Drinks can
Duct tape

12V fan (mine is 40mm)
12V battery pack (I used 8 x 1.5V)

Cutting mat with grid, or graph paper
Ruler
Sharpie
Awl or sharp file
Utility knife with plenty of spare blades
Sharp scissors (Leatherman Micra is great)
Drill with 4mm and 4.5mm bits

+ LOTS OF OTHER (OPTIONAL) STUFF AS WE GO ALONG . . .

Step 2: The Cutting Technique

Mark: with the Sharpie
Punch: with the awl or file at the ends of each line.
Score: with the utility knife.
Cut: with the knife (small, controlled cuts) or scissors.

The score lines should guide the knife / scissors.
This method breaks the cutting into smaller tasks
and the knife usually stops when it reaches the next punch-hole.

Please always cut away from your free hand.
The cans will cut your hands if you don't wear gloves!

A Dremel can be used if you prefer, but it is not necessary (I tried both ways).

Place the cans onto the cutting mat grid to divide them up into 4, 8, 16, 32 by eye.
Just use the grid as a guide.
I find this much easier than using a measuring tape and lots of division.

Step 3: Stove Body

I made the stove body from two cans (73.5mm), but you could use one taller can of the same diameter.
I wanted the bottom open, but you could leave the end on this can.
When not in use, I use this space to store a fuel bottle and tinder.
In use, I seal the bottom from air leaks with the pet food can cover,
lining it with the 2 spare can lids to protect the plastic against radiant heat from the burn chamber.

I cut a hole in the bottom of the upper (full size) can, 2 ridges in from the edge.
The hole needs to be at least as big as your fan.
I marked a circle of corresponding size in the top of the lower (half size) can and cut it into 8 segments.
I fixed the two cans together with 2 screws, but high temp. epoxy could be used.
The 8 tabs on the lower can fold up into the upper can to cover the sharp edges.

In a prototype, the fan was mounted in the base section.
You guessed it - it melted from the radiant heat!
So I opted for a removable, ducted fan.

I stuck with the base section, as it blows air up evenly around the burn chamber.
Also, that can stays nice and shiny and does not discolour from heat.

The bracket feet are attached with bolts.
I used an extra bolt as a spacer between bracket and can, to give room for the plastic can cover.

Step 4: Burn Chamber

The burn chamber is made from the 66mm can with a collar
cut from the stackable base of the other 73.5mm can.
The shaped collar is a perfect fit in the top of the stove body and
suspends the burn chamber inside with an even gap all round.

4 x 4mm (primary) holes are drilled in the bottom of the burn chamber.
16 x 4.5mm (secondary) holes are drilled around the top, just below the collar.

Cut off the hard metal ring (side of lid) from the top of the 66mm can.
Mark, punch and cut 16 slits, down to where the ridges start.

To Make the Collar:
Cut out the base of the 73.5mm can with the knife, after scoring around at least 3 times.
A Dremel could be used. I used a round file to even up the hole (or Dremel).
Work a smooth screwdriver or similar around the hole to roll back the edge,
until the 66mm can will just push in.

Then drill your holes.

Step 5: Fan and Duct

I found a small tea tin which fitted my fan, so I made a stronger housing from this tin and screwed the fan into it. I also found a food tub that is the perfect size for a case.

All you really need is a rectangular duct folded from drinks can metal.
I used duct tape to hold mine together.

I cut wedges out of the end of the duct, so that it fits tightly.
You can also draw the duct out of the stove body to leak air slightly and reduce the flame.

I bought the fan, grill, 8 x AA battery box and 9V clip from Maplin
for £3.99, 99p, £1.59 and £1.29 respectively.
Total spend: £7.86. Ouch!

Step 6: Chimney / Potstand

Use the 85mm can (stackable base) to make this piece.

Cut out the triangular sections symmetrically, as in the photos.
Cut a circle out of the base of the can about 60mm dia.

The remaining lip of metal swirls the flames and mixes air and wood gas.

If you don't want to make Modes 2 and 3, you can try your own potstand designs.

Step 7: How to Use

1. Read the Intro. Watch the Mode 1 video on the intro page.
2. Secure the stove on a level surface with 3 tent pegs through the feet.
3. Fill the burn chamber with dry twigs, typically pencil thickness and 1.5 inches long.
4. Sprinkle 2.5ml (half a teaspoon) of meths / denatured alcohol on top of the fuel.
5. Light it immediately!
6. As the alcohol burns off and the wood starts to char, insert and turn on the fan (1 - 1.5 mins).
7. The burn should be clean (smoke and odour free) within 3 minutes.
8. Place the potstand on top and then your pot.

Performance
Using my potstand, the stove should bring 500ml (2 metric cups) of 10 deg. C water
to a rolling boil in 7.5 minutes.
Using 12V power, 100g of fuel should burn for about 20 minutes
(and therefore boil 1 litre of water).
The bottom of the pot should be free of soot.
Apart from the lighting phase and end burn (charcoal), there should be no smoke or smell!

Tips
Use 6 or 9V batteries or partly pull out the fan for a slower burn to simmer.
Remove the potstand at the end of the burn and cap the burn chamber
(e.g. with a can lid or empty pot) to save the charcoal from burning to ash.

Step 8: Modes 2 and 3

These videos demonstrate how the backup modes are used.

Mode 2: Alcohol Burner Priming Potstand

Mode 3: Twig Burner (Top Lit)
I use wood pellets for the demonstration, but Mode 3 is intended to be more like a hobo stove backup,
burning twigs, pine cones etc. (top lit to cut down on smoke).

YOU WILL NEED:

The other 425 grams fruit cocktail can
Diameter: 85mm

Large tea strainer or fine metal mesh
Diameter: to drop inside the potstand, but fit tightly

Bicycle spoke or wire coat hanger

TO MAKE:

Base
The height is up to you, but needs to allow a triangular
hole to be cut, size: 60mm across the bottom and 30mm high.

Alcohol Burner Shelf
Bend the bicycle spoke as shown.
The shelf needs to be 25mm wide to fit tightly
through the small triangles in the potstand.
The length needs to match the diameter of the potstand.

Twig Burner Grate
I just cut the handle off a cheap tea strainer,
but cut other mesh to a slightly smaller diameter than the can.

Step 9: Packing + Case

I stacked the stove, accessories and pot as compactly as possible,
then I built the case around the whole bundle.

The card corrugations run top to bottom.
I creased every 2 corrugations to make the cylinders.
Then I just covered it in duct tape!

I know this is not waterproof, but it is splashproof and keeps everything together!

See me attempt to pack up this mess neatly . . .
Featuring Custom Case Made from Cardboard and Duct Tape.