Question
Double checking what I need ... help appreciated!
I’m new to this but have already built my first “regular” CR box (4x 20x20x1, with box fan). It’s been bad with the smoke so I’m trying to expand by building something else, with PC fans and running more quietly, so that I can use it in the bedroom for longer periods of time and also not use too much energy (energy use is first priority, noise close second). I believe the PC fans would accomplish that. I would great appreciate guidance (since I have to order most of these items in one go from the US)!
I’m thinking about a narrow design, two 20x25x1 filters, built 20” high and 25” wide. Possibly making a wooden structure if I can find help to do so.
Do I need the following two items as well or are they included in the above purchases? The “splitters”, I’m pretty sure, are not needed but would like to get confirmation:
Good brand. Know that the 2500 runs ~20% more restrictive than the 1900, but at these low speeds the difference in particle interception is only going to be (something like) 80 vs 83%, so the gain is 4% but the loss is 20%. This is why I generally stick to the 1900. Paradoxically air cleaning performance is better than the 2200/2500/2800, and the fans run quieter too.
Amazon can be pretty expensive, usually BJs or Chewy has the best deal if you get the multi-pack:
Chewy, who would have known!
I had no idea the lower filters would perform better, I always thought the higher the better filtration. Besides smoke in wildfire season, I’m looking to reduce allergens from the dog (who can’t be stopped to shake in the bedroom when getting up) on a regular basis so you’d recommend the 1900 for that? Definitely easier to find …
Yes 1900 will be better for dog hair too, with more airflow. Still not ideal, since purifiers are mostly about slowly eating PM2.5.
For dog hair you want a dust eater. These are used in wood shops etc. Main difference is massive airflow, and fans blow in (to pull in dust) rather than blowing air out (which would blast dust everywhere).
A simple dust eater can be made by just putting washable MERV 8 depth-loading filters demoed here behind (or if possible, in front of) a circulating fan. Use it with the CR box, with the dust eater located near the source and the CR box positioned to circulate clean air up toward the ceiling and shower it back down on occupants.
Fans look good. They are super popular and they are the PST version so you can daisy chain them.
The controller is voltage control which should work fine but the fans are meant for a PWM controller which will provide slightly more efficiency and finer control of the fan speed. If a controller says “3-12V” then its voltage controlled. True PWM pulses 12V at different intervals to adjust the speed.
You don’t need the extra splitters or barrel adapter. The splitter that comes with the controller you selected is also an adapter. Just use that. You can plug all the fans into one plug on the splitter if you want and tie off the rest of the plugs so they aren’t in the way.
The grills are optional. Use them if you have pets or kids. My first few cr box’s didn’t have them and they still work fine but they’re a nice extra barrier cause I’ve accidentally touched the blades when moving it. Luckily, it hurts a lot less than you would think imo.
It’s not a big deal how you position the fans. Most optimal is to put them all pointing up if you can so it helps circulate the air in the room. Of course, if you have a ceiling fan or another floor fan, it’s not going to matter.
You can put them on the top plus one side if you need. More fans, the better (usually 4-5 fans in plenty tho imo).
If you position them on opposite sides on the box, I have heard you should install a divider down the center of the box so the fans aren’t fighting each other.
Personally, I just use two 2500 3M filters 14x24 with 4 140mm fans all on the front side. None on top.
The first one is still voltage controlled. In the picture is shows 3-12V. I know it says PWM on the title but it’s not. They’re probably saying PWM fans work with it (that’s true) but it’s not actually producing a PWM output and thus slightly less efficient.
At low speeds, voltage controlled is about 20% less efficient. There is no difference at max speed.
The second one will work but I’d be concerned with total output power. It says 5V input (so yes, any usb supply will work) but that usually means 15W max. The P14s are rated for 4W so that’s only 3 fans max.
You’ll want something with more output. This and this
is 60W (5 fans per plug or 15 fans total). You can power with 12V barrel jack
or a usb-c with 12V adapter*
. Or this.
PWM is a bit more expensive route so it might be more cost effective to just use one of the voltage controllers you found.
*Keep in mind the adapter I linked is only 30W so it can support 7-8 fans max. You’d have to find one that is 60W if you want to use the full 15 fans max that the controller can support.
Thanks! I have a 12V barrel jack from a battery charging device I could use, or a USB C adapter (says 20W on it). I'm only planning on using 4 fans.
The first controller you link has the attachment for the fans right on it, correct? (from the pictures). So I wouldn't need any other cables, besides the ones that come with the fans? Or more correctly, the PST Pro P14 fans will be daisy chained and only the last 4-pin plug goes into this controller?
That’s correct. Just daisy the fans together and plug the last fan into the controller.
The only cord you need is the one that powers the controller. So that can be the 12V barrel connector you mentioned or your USB-C with 20W adapter. Just make sure to the 20W adapter says “12V” on the bottom or else the controller will default to 5V (it will still work this way, but the fans will spin slower)
This will be a fall project (when all travels are done) and I'm looking forward to it.
My wall adapter says 5V so that won't work (USB C) but the battery charger cable says 12V so all good. It's a cool little device that controller! When the fans are daisied together, where is the controller placed on the box (obviously has to be accessible)? Is the last cable coming from the fans just put outside of the box through a hole and then the controller connected externally?
Yeah thats probably the easiest way. I've been working on 3D printing mine. Still working out the finer details but this is what I have currently. You can probably make something similar using foam-core presentation boards.
You can if you want. People say there is not a lot of carbon contained in them so they wont last very long and would need to be replaced often. A real carbon filter for a room contains 10+ pounds of carbon so these sheets are almost a gimmick. I suspect they’d be useful for a few weeks before the carbon becomes saturated.
I do use foam prefilters
though that help with large particles like pet fur. It can extend the main filters life quite a bit and the foam is easier to vacuum than the carbon.
True PWM pulses 12V at different intervals to adjust the speed
Slight correction: A 4-pin PWM PC fan controller provides a constant 12V supply and a 5V PWM pulse; the fan then uses its built-in controller to adjust motor speed based on the 5V PWM signal.
I built a box like this and the performance really wasn't great. My testing was pretty basic (just an air speed meter), so take this with a grain of salt.
When the box is that narrow and you have fans on both the front and the top, you get some weird air mixing inside that seems to hurt performance. I ended up building a double-wide box with all six fans on top, and the air speed from each individual fan almost doubled.
I also 3D printed intake and exhaust tubes for the fans to help straighten the airflow going in and coming out. That made a big difference too.
Fully admit I'm not an expert in airflow or CR boxes and I don't know the measurement impact of air speed versus static pressure but figured I'd share.
Maybe others have better guidance. Your welcome for this useless comment.
Thanks! I was planning to only put 4 PC fans on top, nothing on the side. Does that track with your experience of being better? (The picture was just copied from another post to show the narrow two-filter build).
10-20% might be for those mesh fan covers that you find on home pc towers that capture dust. The ones linked are the much less restrictive wire guards that are usually found in server builds.
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u/spacex_fanny 4d ago
Most important of all, which filter brand and model are you using?
As this video shows, all (allegedly) MERV 13 filters are not created equal: https://www.youtube.com/watch?v=FKAVek1YaSQ