This is a guide on how to build a simple 12 volt fume extractor that runs off 220V AC mains.

By running off mains, the fume extractor can run 2X fans at full power.
And all of the parts are easily available, maybe even stuff you have lying around.
The shell of it is an empty ATX power supply.

I'm keeping it short and simple, because I'm presuming that whoever wants to try this has basic knowledge of electricity.

If you don't know what you are doing, then this project is a bad idea - 220V AC CAN KILL YOU. If you wire it up wrong, you could short circuit to the metal shell and....

Hope you enjoy!

Step 1: Parts

Apart from the box, you'll need:
1x DPDT switch, rated for mains voltage.
1x 220-12V transformer.
2x 3300microF polarised caps, rated for 25Volts or more.
2x 12V fans
1x bridge rectifier, or 4x power diodes.
1x three-prong socket like the one that computers use.

Lots of wire.
Soldering iron.
Screws, bolts, nuts.
Drill with metal bit.
Aviation snippers.
Gluegun.
Clear pieces of plastic for gluing over the openings of the box.
Electrical tape.
Heat shrink.

And for the extractor tube:
Tin cans
Brown paper
Electrical tape

Step 2: The Box

Mark on the shell where you need to drill and cut.

You need:
1 hole for the second fan, plus holes for the screws
2 holes to bolt down the transformer. Place it so that it sits on the bottom of the extractor.
1 hole for the switch.

Step 3: Sealing Up

ATX power supplies aren't really that watertight. But a fume extractor wouldn't work very well with a hundred leaks.

You'll use clear plastic to seal up as many of the holes as you can.
I used one of those clear fake CD protectors cut into shards.

This will increase the efficiency of the extrator by quite a bit.

Step 4: The Circuit

Here's how the circuit works:

The live and neutral lines are switched at the DPDT, while the earth is screwed onto the chass to provide protection against short circuits.

The Live and Neutral are stepped down to around 12v at the transformer, then rectified with the bridge. The caps filter it and boost the voltage slightly.

The 2 fans are connected in parallel.

And my drawing is very beautiful, if don't say so myself...

Step 5: Assembly

I hope the pictures give a vague idea about how the extractor is put together. A few points to keep in mind:

keep wires out of the way of the fan blades.
use heashrink to reduce the risk of short circuiting.
put the transformer on the base to keep it steady, as it's quite heavy.

use the gluegun to seal up the corners of the fans and any other small holes.

Step 6: Tubing

To make the tubing:
You'll need to remove the other end of your tin can.
Safety can openers work very well and leave it very smooth.

Originally I tried making three holes on each corner and then chaining the tins into lengths, but that didn't work so well.

The best way to do this is to take a length of brown paper, make a tube, tape the one end to the one can, tape the other end to the other can, etc...

To couple it to the fan, take a can, cut wings into it, punch holes in each wing, and use the screws the fan uses to hold it down. I then used electrical tape to seal it on.

Step 7: Fin.

And here it is brothers and sisters!

I added a safety cap...for no reason. I just had one and was itching to find something to use it on.

The only parts I bought were the DPST switch and its safety cap. Everything else - the box, the rectifier, caps, wire, screws, washers, transformer,... all were scavenged.

If you have any questions about this project or any ideas on how to improve it, feel free to tell me.

Have fun!