DIY cheap & quiet HEPA air cleaner

I really LOVE the way this project turned out. It's 100% practical and also looks very cool too.

When you buy a commercial HEPA (High Efficiency Particulate Absorbing) air cleaner you are basically buying a box with a fan and a replaceable filter. It doesn't matter how many extra gimmicks they add like ionisers, trace ozone generators (in disguise) or air quality monitoring units with wifi connectivity. When it comes to the crunch it's a box with a fan and a filter, and sometimes the replacement filters cost almost as much as the complete unit.

This project is for making your own air filtering unit that uses whatever filter is the cheapest to source, and either a 3D printed adaptor for a common computer fan, or some other means to attach the fan to the unit if you don't have a 3D printer.

I used this filter from eBay UK
https://www.ebay.co.uk/itm/3737201144...

There are two openscad scripts included at the bottom of this description. Copying and pasting the text into openscad will allow you to create a custom self-scaling adaptor for most donut style filters (or even some HEPA vacuum bags) to attach them to a standard 120mm fan.

The second script is for donut filters that are open at both sides. It prints a simple press fit cap to your chosen dimensions. This can also be used to make caps for other applications.

You can either use the fan with no guard, a standard metal or plastic one, or a custom printed one. The fan should suck air through the filter.

I chose a 12V fan and added two 1A diodes in series to nudge the voltage down slightly. This results in much quieter running and potentially longer fan life. The unit is intended to be run 24/7, so will still circulate a lot of air even with reduced flow. Power consumption will typically be just 1 or 2 watts. Running costs will be virtually zero.

The whole assembly can be mounted on its side if desired. Technically speaking, the back cap could be screwed to a wall to mount the unit horizontally.

The end result is a very stylish and minimalist air cleaner that will only require the filter to be changed once or twice a year depending on air particulate levels. You can extend its life by vacuuming the exterior of the filter to remove large dust particles.

If you enjoy these videos you can help support the channel with a dollar for coffee, cookies and random gadgets for disassembly at:-
http://www.bigclive.com/coffee.htm
This also keeps the channel independent of YouTube's advertising algorithms allowing it to be a bit more dangerous and naughty.

#ElectronicsCreators

Here's the first of the openscad scripts. Openscad is open source 3D design software that is free to download and use. This script creates the fan adaptor for your chosen filter. Measure the hole in the middle and enter it as the variable "filterhole". The other variables can usually be left at their defaults. The script as-is will work with the Silentnight filters sold on eBay in the UK.

Make sure you leave the semicolon (;) intact when you enter a new value.


//120mm fan adaptor HEPA filter
$fn=100;
//You can adjust these four variables
//Primarily the filter hole diameter
screwhole=5; //fan screw hole diameter (5)
filterhole=92; //HEPA filter hole diameter
thickness=1.5; //Thickness of plastic layer (1.5)
insert=10; //Length of insert into filter (10)
//Do not adjust anything below here
cone=(120-filterhole)/1.5;
wall=thickness*2;
difference(){
union(){
//flange
translate([0,0,0])
cube([120,120,thickness]);
//taper to filter insert
translate([60,60,0])
cylinder(h=cone,d1=120,d2=filterhole);
//filter insert
translate([60,60,cone])
cylinder(h=insert,d=filterhole);
}
//taper to filter insert
translate([60,60,0])
cylinder(h=cone,d1=116,d2=filterhole-wall);
//filter insert
translate([60,60,cone])
cylinder(h=insert,d=filterhole-wall);
//fan attachment holes
translate([7.5,7.5,-1])
cylinder(h=thickness+2,d=screwhole);
translate([7.5,112.5,-1])
cylinder(h=thickness+2,d=screwhole);
translate([112.5,7.5,-1])
cylinder(h=thickness+2,d=screwhole);
translate([112.5,112.5,-1])
cylinder(h=thickness+2,d=screwhole);
}


This is the second openscad script which will generate a cap for the other end of the filter if needed. It can also make caps for other applications too.


//HEPA filter blanking cap
$fn=100;
//You can adjust these four variables
//Mainly the filter hole diameter
filterhole=92; //diameter of filter hole
rim=10; //size of rim (10)
insert=10; //Length of insert (10)
thickness=1.5; //Thickness of plastic (1.5)
//Do not adjust anything below here
wall=(2*thickness);
cap=thickness+insert;
difference(){
union(){
//seal plate
cylinder(h=thickness,d=filterhole+(2*rim));
//filter insert
cylinder(h=cap,d=filterhole);
}
//filter insert core
translate([0,0,thickness])
cylinder(h=cap+1,d=filterhole-wall);
}