DIY carbon filter. Now very little exhaust. Problem?

Hey-

I just installed a DIY carbon filter, which consists of a coffee can stuffed with aquarium carbon inside of a lady's stocking. I stuck it on the end of a 170 cfm 4" exhaust fan, and now the wind speed at the end is markedly reduced; probably a fifth of what it was before.

Is this harmful to the fan? Does it have to work harder to push the air through? Is it moving less air? I don't understand how it could move the same amount of air out, if so little seems to come out through the filter.

Thanks
GA

GoldenAss,
Lol... nice name. DIY carbon scrubbers seem to be the topic the last few days. As a Mechanical Engineer I feel responsible to help people out. Dont ask me a question that pertains to "hey I have a nut problem"... cause I cant help you - I SEEK help for those things. As for building and designing.... thats my ball field. Check out my response to another members diy carbon scrubber https://www.rollitup.org/grow-room-design-setup/254067-activated-carbon-qestions.html from a few days ago. Another member listed a GREAT spot to get carbon from...... and I just purchased some myself from there.

As for your questions.. A coffee can probably will block the air and make it harder for it to suck air through. NOTICE.. I said SUCK air not push air. If you are trying to push the air through the scrubber it does not work as well - if at all. Place your scrubber BEFORE the fan and have it suck through it. A coffee can is fairly small... read through the link I posted above and try something like that. What size carbon are you using? Pellets, grains, dust.... etc. How big is the hole(s) that you are sucking the air through? for example... if you have a 6", 200cfm fan trying to suck air through a 1 inch hole... you are going to loose 87% of air volume MINIMUM. ( and yes.... that is mathmatically correct) After adding a "nylon" of carbon in it.... you are just adding to the loss of air movement.

What size grow room and how many plants are you planning to scrub? a 170cfm fan is REALLY small. I know the smallest I will EVER think about doing is 250 - and that has to be if hell freezes over. I normally go with 500 or higher. Again, this all depends on your grow room and how many plants you have. The more air you can move and scrub the better. Scrubbing is one thing that you CAN NOT!!!!!!!! skimp on. It litterally could mean the differance between smoking good shit... and sitting in jail for 3 years - LITTERALLY!!!! The wrong person smells it... your screwed!!!!

Check out that link I posted and hit me back either on here or personal message. Ill be glad to help you any way possible. My motto is.... do it stealth... do it right.... and do it cheap.

All that college education has to be put to good use. If you need help on where to get parts or aero systems... let me know.
Cheers!

Thanks for the informed response. I'm attaching an artistic rendition of my set-up. I hope to scrub about 5 plants (haven't sexed them yet). Smell doesn't need to be eliminated, just considerably reduced.

My fear with putting the can on the intake is that many tiny particles will get sucked through. Just when I was pushing around the carbon when it was in the nylon sock enough came out to turn my hands a little black.

I never reduce the size of the ducting, it's always 4 inches (as is the can). But I'd be surprised if 30 comes out the end. I didn't think ~1.5 inches of loose carbon would be too much.


Thanks
-GA

Golden... eliminate the problem of sucking the carbon up into the fan by putting a nylon over the otherside of the can also. This way it "in theory" wont suck the carbon out.

Still would go with a slightly larger fan... but if you dont or cant... thats ok. I would definetly put the carbon BEFORE the fan though.

Ever try and suck a mcdoanlds milkshake through a straw.... its thick but it comes.... now with that same milkshake every try blowing a bubble into it?
It might be 5 or more seconds before you hear the bubble in the milkshake rise to the surface (if at all) and pop.
Same principle.
The force of the air movement needs to be greater than the solid stored energy (carbon, nylons etc) for it to move air.

Your lungs can suck air in slower with greater force than what they can expell it. Same principal as a lung test.

Try that and let me know how you make out. If you really want to get technical, depending on the fan you are using, you can bend the blades (if they are metal) and create a larger vacum for the air. Only problem with this is, it can eventually burn out the moter of you angle the blades to far.
-Wyatte
ps... fyi was at lowes today and actually they have 5 gallon buckes cheapier than the 2 gallon ones. You can use them also which isnt bad. (reffer to my link "carbon scrubber questions" for the homemade carbon scrubber) If you use a 5 gallon, you always then have room to upgrade to abigger grow.