I have a sensitivity to flux fumes which gets pretty annoying after soldering for an hour or two. I could buy a decent fume extractor, but they tend to run in the hundreds of US dollars. Designing a quality fume extractor seems like a great way to spend a few months of weekends and nights!
The goals of the project follow: effective filtering, easily adjustable with a good reach, and easy to set up.
The first decision was to use Loc-Line to provide decent reach and good adjustability. I was inspired by Adam Savage on a one day build Tested filmed. It is very easy to get and not too expensive, but even better is that you can 3d print it incredibly easily! It isn't as nice as the commercial version, but it does the job.
I decided to go with loose activated carbon followed by a HEPA filter. The typical "activated carbon pad" filters found cheaply on ebay/amazon/et al. barely do any actual filtering as studied. This may not be important if you have good ventilation, but I don't! A thick layer of activated carbon is great at catching the bulk of large particles and gases emitted when soldering and the HEPA filter does a great job of filtering any small particles that get through. I anticipate that with the amount of soldering I typically do (maybe an hour or two a month) I will pretty much never need to replace the filter media.
I went searching for a centrifugal blower that would be about 10cm across. A centrifugal is the right choice in this situation as they are better for high static pressure, where you need flow through long or constricted duct. Axial fans are used in high volume, low static pressure situations such as ceiling fans or computer cooling.
Aliexpress turned up a reasonably priced Delta Electronics fan, P/N BFB1012VH, that was about the right size. It is 12V powered and is rated for 2.7A, although in my limited testing draws closer to 0.75A
The next design choice was what HEPA filter to use. I was debating using either a square filter, like a mini furnace filter, or a cylindrical filter. Square filters are easier to find and make if need be, but a cylindrical filter could fit right over the fan intake and simplify my design. After an hour or two of searching I found a well sized cylindrical filter meant for an Electrolux vacuum. If I can't find this filter in 10-15 years I can always design up two 3d printed endcaps and glue in some HEPA filter material from a standard furnace filter.
The last major technical design choice was how to power and control this device. Since I'm already going to be doing a good amount of mechanical integration I might as well make this battery powered and add a microcontroller to adjust the speed of the fan! I have a good supply of 18650 lithium batteries from old laptop batteries and I have a good reference design for charging these from USB, so that's what I'll use. A big reason for wanting this to be battery powered is that I am tired of dealing with wall warts and cables. The way my desk is set up I can't plug things in to wall power easily. On top of this I have a fairly limited space and wires really clutter things up. I figured at a minimum I'd like a few hours of run time at full speed out of this.
My initial fan tests tell me it will draw about 8W. A typical 18650 battery has about 10Wh, so 4 batteries at 40Wh total should get me ~5 hours of run time (assuming my boost converter is 100% efficient). Assuming the worst case of fairly dead batteries (75% max charge) and a mediocre boost converter design (80% efficiency) and we're talking 5hrs0.750.8 = 3 hours of run time. Spot on my goal!
Once I had my technical details roughed in I started sketching out some possible designs. I ended up liking the look of a truncated cone with nicely rounded corners. I also decided to have the loc-line come out of the side at an angle. This design has a few advantages in my eyes. It will be easy to store as the loc-line can just wrap around the base easily. I can stack things on top of it which is good for storing it and when I need to move with it. It also reduces the amount of vertical height which is huge for me, as a good chunk of my desk has my monitors suspending over it. This only gives me about 20cm of clearance.
Some sketches for different shapes and designs
Now that I had an idea of the general shape and all of the items that would need to go in the base I started doing some 3d mockups. I'm using Fusion 360 as it is quite versatile and it is something I've been meaning to learn for quite some time. I'd love to be able to quickly whip up prototypes without fighting the tool and I think Fusion 360 is my best chance at this! My biggest wish for Fusion 360 right now is that it ran on Linux.
Initial 3d mockup of the shell and larger inner components.
I managed to come up with a size and shape that won't be too large, but still gives me plenty of wiggle room when I start doing the real mechanical integration. This will be the first mechanical design I've done that is more than just a few extrudes slapped together. I'll be begging for more room later I'm sure.
Now, some thought needed to go in to the actual filter mechanism. This needs to be relatively easy to assembly and clean looking (a big design goal here is to make something that looks professional, not hacked together). This means the top will need to separate in some way so I can fill the area around the HEPA filter with activated carbon.
With specific design goals set and an initial mockup done I can now start on the true mechanical and electrical design. That will be the subject of the next post!