Air Purifier

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Introduction: Air Purifier

This is a powerfull air purifier which use G4 and F7 filter. The HEPA F7 filter is sufficient to stop pollens. This air purifier is intended to clean the air of a big room during allergic periods.

Step 1: Hardware

The fan as been chosen from the requisites of the filters. The filters are rated for a amount of air flow and oppose some resistance. When they get dirty, the resistance increase as well. The fan is powerfull enough to deliver air pressure up to the max rated by the filters.

I made a mistake when buying the fan. It is no dimable. It's either full power (and noisy) or off.

The fan is inside a crate, creating a depression behind the filters and the exhaust is located one one side.

Step 2: Building the Crate

The fan is fixed inside a crate. It's made with laser cut 5mm plywood. Because the fan is quite heavy, and a rest for the filters is needed, the bottom of the crate is reinforced with wood pieces. Carrefully cuted with the same length, it wasn't correctly pushed to the maximum. I used wood paste to fill the gape and avoid any air leaking possibility.

Step 3: Exhaust

Since I used some foam to try to reduce vibrations and noise, it wasn't very easy to cut the exhaust a the rigth place with the laser cutting machine. I did it with a drill. Not very clean but it won't be visible.

Step 4: Fixing the Fan

Every contact surface of the fan is using foam in a desperate attempt to lower the noise. Because the fan is quite heavy, it was necessary to have two points of contact. A laser cutted piece of wood is used for the exhaust. The bolds are pointing outside, I kept them like this because I will build a silencer for the exhaust and th bolds are very usefull to fix this extension later.

Step 5: Sealing the Crate

To ensure that the low pressure chamber gets air through the filter, I used some putty. The electric cord is also a weak point. I drilled a hole smaller than the diameter of the cord and slightly enlarge it with a file. It fits perfectly.

Step 6: Electric Box

The electric box is glued on the back of the crate. Since the fan is not dimable, I used a simple on/off switch. Some velcro band are used ton fix the electric cord. I drilled some holes in case of heating issues but I did it on the sides of the box which is not the best choice .

Step 7: Inserting the Filter

The H7 filter is seated on a wooden square which is seated on the wooden pieces that also give more strength to the crate. Some ruber band sold to seal windows or doors is used to seal the sides of the H7 filter.

The last filter is just pushed inside the crate. The size is the same. Friction easily keep the filter in place.

To close the crate a more or less pretty grid has been laser cutted. It offers too much air resistance and needs a real fixing system.

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    37 Discussions

    Nice idea and beautiful design, thank you for sharing!

    You can't dim it? Have you tried using a controlling system with a TRIAC together with a DIAC?

    3 replies

    I answered than on a another topic : I don't know electronics and very few about electricity.

    The principle is as I show in the uploaded image. I hope it helps with future projects.
    And try to search a bit of it, since it can benefit your project.

    07 - esq 5_2.png

    Thank you. I realy need to study electronics...

    Luk. you can use a simple light dimmer for speed control on the fan. i am assuming that the fan uses AC power and not DC power.

    1 reply

    hello, I already tried. It didn't worked and made strange noise and bad smell...

    If I read correctly, PM2.5 are particles that are smaller than 2.5µm. H7 filters are stopping 98% of 3µm ir bigger particles. It's not very efficient for smaller particles (only 25% of 0.1µm particles are stopped).

    A thiner filter would be necessary, E12 or better I guess. I'm not an expert.

    It's very loud. The fan constructor is announcing 70db. I strongly recommend to chose a variable fan. I clearly made a mistake on this.

    I've tried a lot with air purifier ides, but the noise from the fan is always the issue at hand. in order to create proper suction n blower effect with the addition of filters, it becomes major issue.. thats me so far

    Most home fans or air filters have fans which are powered from the AC wall socket power, and may have 1, 2, or 3 speeds selected with a switch. But, you can get DC powered fans (recycled from computer power supplies, for example) which have Tachometer and PWM speed control wires. Such fans have red, black, yellow and blue wires.

    An Arduino (or other embedded controller) can use a PWM output to control the speed. This could be as simple as using an ATtiny85 to read an analog input from a potentiometer between 5v and ground, and map that reading to the PWM output pin, and you'd have a simple speed control.

    The solution above, with a DC fan, combined with these construction ideas, might be a good fit. Maybe adding a barometric sensor inside the box could tell you when the filter is getting clogged (and the fan is working harder to pull the air), or use the tachometer reading at various PWM settings (compare no filter, new filter to get readings) and then set comparisons in the code to light an LED to change the filter. That may be a fun weekend project!

    1 reply

    Yes, I have no doubts it is possible to find a dimable fan. Mine is an extractor, it's probably not intended to work slowly. A bad choice I did.

    Very nice!

    What is the cost of total build and parts?

    1 reply

    around 250€, a bit more maybe. a little more than 100€ for the fan, 60€ for the filter, around 20€ of wood, around 20€ for the electric gears, 20 to 30 for different other things.

    I had other ideas, too complex so I spent more than that but the model itself should not be more than 250€, probably less.

    Please note, "cutted" is NOT a word. The past participle of 'cut' is 'cut'.

    1 reply

    I have very limited knoledge in electricity and none in electronics (I've just searched PWM).

    I guess the fan has an induction motor. It was featured with a control device (the black thing in the electrical box).

    Maybe it is controllable by PWM but it's far from my skills for now.

    Thank you for your concern.

    I understand it is being fed from the mains grid. Thus cannot be fed bij PWM.

    Tou could use a TRIAC to control it by phasecutting. That will most likely work, though TRIACs are not specifically suited to regulate inductive loads