This project combines a small craft box, 12v case fan, aquarium carbon filter, dc boost converter and some basic electronic components to create a USB powered fume extractor which treats your lungs to some clean air when soldering.
I wanted the ability to run this unit from a USB port and not require batteries or a wall wort as my bench power supply has an available port. I'll also have the option to plug it into my iphone charger should I want to run it from mains power.
- 12v 80mm PC case fan with grill.
- Carbon filter pad.
- DC Boost converter.
- SPST power switch.
- 5mm orange LED and 220 ohm resistor (Resistor value calculated for a 20ma 3v LED)
- USB cable
- Female USB port
I first saw this style of DIY fume extractor in this excellent Make Magazine article by Marc de Vinck. It's a great design but I wanted one that was USB powered and capable of pushing more air while still being small enough to fit in a desk drawer.
This extractor uses a DC boost converter to increase the USB port's 5v improving the fan speed. I initially set the output to 12v however I ended up dropping it to 11v. This reduced the load from 540ma to 450ma with minimal impact on fan speed. This brings it below the USB 2.0 and USB 3.0 power specifications of 500ma and 900ma respectively. I purchased this one on eBay for a few dollars. It's based on an LM2577. Operation is pretty basic, connect power to the input and turn the knob to adjust the output. Other boost converters may be different so make sure to check the documentation.
I purchased a replacement pack of carbon filter pads from the aquarium section of my local garden center. They're intended to reside in an aquarium pump for chemical filtration of the water but will also suit as cheap air filters. A coarse filter will work the best as they don't inhibit air flow very much.
The fan and filter is located on the left side of the enclosure to leave room for the electronics in the right. I used the fan grill to mark out the four mounting holes and ruled diagonal lines between them to find the center.
To make the fan vent, a circle 80mm in diameter was removed with a hole saw. I just drilled out the center marking then switched to the hole saw for an accurate cut. A jigsaw or dremel would also suffice.
A rectangle slightly smaller than the filter pad is cut out of the lid with a dremel. A spade bit was used to drill the port for the power switch and a 6.5mm standard bit for the indicator LED with socket.
The boost converter needs to be set to increase the USB's 5v. I connected power to the input and my multimeter to the output. The converter I used was unmarked and I had to refer to the documentation to determine the input and output sides. Keep in mind that unlike the pictured 12v, I reduced the output to 11v decreasing the load on the USB port from 540ma to 450ma.
The output was initially 5v but turning the blue potentiometer's tiny knob counter-clockwise steadily increases the output voltage. The fan now operates at high speed and is ready to suck some solder fumes.
I soldered a couple of wires to the positive and ground pins on a female USB b-type connector so power can be routed to the boost converter. This connector was salvaged from an old printer.
After a quick paint job it was all ready for assembly. The components are connected as per the schematic above (higher res).
With the USB port installed and hot glued into place, the positive wire is soldered to the power switch. The resistor and another length of wire attaches to the other side of the switch. The resistor then connects to the positive side of the indicator LED.
The small length of wire is soldered to the positive input of the boost converter. Both negative wires from the USB port and LED connects to the negative input.
The fan direction is usually indicated by an arrow on the side or you can simply power it up and observe. You want the fan to pull air through the filter. Connecting it backwards will blow all the noxious fumes into your face which doesn't make for a very effective extractor. Screw the fan and grill into place and solder it's wiring to the output of the boost converter.
The circuit is complete so plug her in and make sure everything works as intended. I was fortunate enough for the carbon filter to be a firm friction fit in the lid so I didn't need to secure it down with anything, score! This also makes the filters very easy to replace down the track.
I'm pleased with the end result. You can place it next to whatever you're working on and it removes the majority of the fumes while costing less than a cheap commercial extractor.
Keep in mind, you should still solder in a well ventilated area.
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