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25 Jun 2018

DIY air filter/"Fume Extractor"

 Having many dead hard drives laying around I decided to make use of one of the motor. Most hard drive motors today have it's housing is the hard drive chassie itself so unless you are able to mill out the motor portion you can't really use it. Fortunately I had a couple of the older hard drives where the motor was it's own seperate unit and removeable with just three screws. 

What I decided to do was to make an air filter for my little "office", work area. From Amazon I purchased a HEPA air filter pack (https://www.amazon.com/gp/product/B075K5J94D/ref=oh_aui_detailpage_o09_s00?ie=UTF8&psc=1), and from Lowes an air duct reducer (https://www.lowes.com/pd/IMPERIAL-8-in-dia-x-6-in-dia-Duct-Reducer/1000230237). The impeller design and housing was designed from scratch to be 3D printed. It ended up being a very simple design as the original more complex impeller design would've taken 13 hours to print, whereas the final design only took just under 2. To save additional time and material the final design placed the impeller with a little adhesive on a CD to guide the airflow. The original controller from the hard drive is used to power the motor, and that was plugged into a molex power adaptor specifically to power computer devices from the wall that I already had. 

The filter is just slightly smaller than the air duct so some 1/2" foam was added to fill the gap, with that it actually holds itself inside the duct rather well without any additional fastners. A 3D printed, grill if you will, fits perfectly in front of the filter to keep the prefilter in place.

Foam was added to each of the post. After the fan was up and running I noticed an audible noise roughly 300-350Hz. It was clearly comeing off of the posts and what I realized is that the air hitting each post just happen to create that audible noise, by adding the foam it dampened the sound. With 6 blades on the impeller, I calculated that the fan would have to spin at roughly 3000RPM to generate that tone, which is much lower than the hard drive standard RPM. It could be my methedology to calculate the RPM was wrong, or it could be the air resistance the blades produce as well as the heavier weight than the hard drive plates could contribute to the lower RPM. 

The reason I have "Fume Extractor" in quotes is because strictly speaking it doesn't really fit the definition and design for one. However I use it quite effectively as one when I solder things to pull the fumes from it into the filter. The end result is actually pretty good, has really good air flow and maintains enough negative pressure inside to produce significant suction from the filter. It is quite noisy, definitely more noise than the actual fan the filter was designed for, but not a problem for my use. 

I have no idea what the actual air flow is, I have no means of measuring this. Also on list of things to learn is how to simulate and determine how much air the impeller can move within Solidworks Flow Simulation:-)

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Last modified on Monday, 25 June 2018 10:29
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profile.largeGeorge Tsai attended California State University, Long Beach and graduated in 2010 with BS in Electrical Engineering, Audio Engineering, and an Entrepreneurship Minor. He is also a United States Marine with combat deployments to both Iraq and Afghanistan. He concluded his service with an honorable discharge as a Sergeant. Today, he freelances in the film industry with his Red Epic-X camera package and production audio equipment. He is also the founder of FUZE Ti.  Read more...

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