Cheap Effective DIY Fan + Scrubber Combo (WIP/Theory)

I'm in the process of making a small 2x1.5x3 grow box. Like everything I do, i like to plan it all out before bringing out the tools.

I eventually got to the air filtration part, you know some type of fan and a carbon filter. I was recommended a S&P TD-100(x), it's a very good fan that lots of people here use for small boxes like mine. But the cost deterred me almost $160 for the fan and a nice filter. So I begun to look for alternatives and came across these options:

Inline Fan: These are the cream of the crop. They are cost effective in terms of power usage and very reliable but expensive.


Axial Fan(pc) : Not enough static pressure to pull air through a filter and if so very infective. The best of these would be the Scythe Ultra Kraze that is supposed to have good static pressure rating (not published by manufacturer).

Inline (Duct)Fan: Low CFM ratings (look @ free flow not boosted), once again these fans are not for a load (static pressure) and will most likely burn out after a few grows.

So i begin to look at other fans and came across the PC type Squirrel Cage/Blower fan. The cons of blower fans is lower CFM and high noise output.



Now that i have given a brief background on fan types etc. I will compare the Soler & Palau TD-100x to the NMB BG1203-B045-000

Price: The price of the SP is around $70-$80 while the NMB can be for as little as $5 (used/scrap/refurbished) or new for $25.

Sound: The SP is a professional fan so they use a unit of measurement known as the Sone instead of the widely known Decibel (dB). S&P does not state the Sone level of their fan due to it varying with duct installations etc. NMB rates the blower fan @ max rpm 55 decibels. Even if i had the Sone value of the SP you can't really compare it because the way a Sone is measured at a specific frequency (1KHz).

The biggest misconception about decibels is that it is a linear scale. When in fact it is a logarithmic scale. For example a sound that is 60dB (normal conversation) is 2 times as loud as 50dB (Quiet Suburban area/Dishwasher next room).

With that being said you can image how loud this fan is. But remember those dB vales are taken as if you where right beside it (for example the normal conversation of 60dB). With this fan place inside a growbox thats probably inside a closet of some-sort the actual sound will drop quite a bit. (And with the added Carbon Filter Muffler (later on))

CFM: CFM stands for Cubic Feet per minute. It is basically the amount of air the fan can move in 1 minute. It is suggested that cannabis plants have fresh air every 5 minutes. To calculate this for your grow room determine the volume: In my case 2x1.5x3 = 9 cubic feet , Now divide that by 5. 9/5 = ~2 (1.8). That means i need a fan that can move at least 2CFM (after any filters etc). Note that any given CFM ratings are before any obstructions such as filters and air friction.

The SP is rated at 140 CFM
The NMB is rated at 33 CFM

The SP will move about 4 times as much air as the NMB, which is overkill for my box but the SP could possible have cooler temperatures because it will be removing the hot air faster, which is another selling point of high CFM fans.

Static Pressure: This is the most IMPORTANT factor when determining how a fan will perform under a load such as a carbon filter. This rating is the ability of the fan to overcome an obstruction when pulling airflow. Pressure has various units of measurement such as WG,Pa,Psi etc. Most professional fans will give you a WG or h20 rating.

These values vary based on the distance the fan is from the obstruction. For simplicity sake i will compare the fans with their max rating. The SP uses "In WG" which means Inches water gauge(@ 4C). While the NMB is rated in Pascals.

The SP is rated at .44 WG max SP.
The NMB is rated at 260 Pa max SP.

To convert In WG to Pascal the general rule of thumb is that 1 InWG = 250 Pa, since there is not a formula to go from 1 to the other without converting to psi first. But for those who want it i will perform the calculation. To convert InWG to psi you multiply by 0.03613 (.44*.03613)=0.0158972 psi. To convert psi to Pa you multiply by 6,895. (0.0158972*6895)=109.61 PA.

So:
S&P = 109.61 PA
NMB= 260 PA

From those numbers you can determine that the NMB can nearly overcome 2.4 times as much static pressure.

Now that i have proven that this fan is effective to avoid the onslaught of "just get an inline dude" comments. Let's move on to the DIY part.

While my fan has not arrived yet my goal is to end up with something like itsmysubaru's device here: The overall cost should be under $50 and provide excellent performance for us closest growers out there. Once my fan arrives i will post a DIY guide using one of the filters here http://forum.grasscity.com/do-yourself/569506-diy-carbon-filter-compendium.html#post7034882

 

They're on ebay for under $20
NMB BG0903-B047-VTL 97x33 mm High Speed Blower Fan - eBay (item 250794235026 end time May-24-11 08:16:29 PDT)

 

Black - Ground
Red - 12v+ (This is usually yellow on some 4 pin molex connectors)
Any other color - Tach

I couldn't get mine to turn on.. i even hardwired red and black to a 400W powersupply's 12 volt rail and got nothing the PS refused to turn on. Other fans work well with it. So unless i find a 12v 2.1A AC-DC powersupply i have a $17 doorstop.

 

Yeah i was pissed that i couldn't get them to work after all that research! I'm running a 120mm box fan right now. I'm going to attach one of those carbon filter pads to the back end of it so it can filter the air as it sucks it out. I know its not efficient but hopefully enough to hold me over this grow until i get a tent.

 

Here's how to rewire them it's pretty simple
How to: Re-wire Dell OEM Fans for 3 Pin Connection !56K Warning! - Overclock.net - Overclocking.net

If you find a 12v 2.1A DC adapter lemme know! i found them but they're for cars!

 

Looks good man that one has the normal molex connections not the dell one. What's the CFM and Static Pressure on it?

 

The output of the power supply i was using is +3.3V@18A,+5V@25A,+12V1@14A,
+12V2@16A,-12V@0.3A,+5VSB@2.5A. But apparently it was tripping the over current protection on my PSU so it auto turned off... 12V 2.1A should work! I won't be able to figure it out until i check it with a DMM and see what the cranking amps for the motor is.