AC20" box fan power usage over a DC replacement

[Dreadstar]

Well i picked up one of the Kill-A-Watt meters and made some interesting conclusions.

20" box fans i have one draws 80watts at medium speed the other is 91watts at medium speed.

So i built a 3 x 3 120mm fan array  to replace it.

I used 9 WFB1212H-BF05 86.5cfm 12 volt dc fans. each leg of 3 uses 10watts

By disconnecting one of the molex connectors that i used i get:

259. 5Cfm for 10 watt draw or
     
2. legs for 519cfm for 20 watt draw
   
   

or lastly 778.5 cfm for 30 watt draw

With all 3 moving it feels almost exactly the same flow as the 20" box fan for 1/3rd the power draw and since it is a direct connection off the battery bank there is no conversion loss just the wire loss for the run but still much more efficient overall.

Total cost for the array was under $30 fans can be purchased surplus for $2-3 each without shipping the costs would be much less.

Maybe not the most cost effective solution but the power usage is much lower so long term they should pay for themselves.

[TLSea]

That's awesome!

Thanks for the info. I get these free at work, I have several at home with a box full at work just waiting to be picked up. I'm just thinking of all the configurations for different window sizes for moving outside air in and out.

Till now I've been trying to harvest energy from them with very little success. My best alternative was strapping them to the front of the Radiator of the care on my 55 mile commute. 50% of them put out .5 to 3 amps for 1 to 10 hours before they fry.

Great out (or In) the box thinking.

[wooferhound]

How loud is that array compaired to a window fan ?

Doese'nt it sound like an airplane taking off when you start it ?

[Dreadstar]

It isn't that bad once your a couple feet away from it and a box fan on high is MUCH louder...I was thinking http://www.fieldlines.com/story/2005/7/4/34446/17324 Ghurd Did a box fan conversion be kinda neat if the conversion of the 20" box fan motor could run 3-6 of the low wattage 120mm fans free airflow that way.

each fan has 36.5dba noise level and 9 of them doesn't seem to be that much louder.

Don't get me wrong it isn't silent but 3 turning isnt' bad at all i would guess under 40dba. there are quieter 120mm fans out there but i liked these for the flow/watts. And for less than $2.50 each shipped (i bought a box of 40) brand new.

The main idea here was to move air for less cost in watts usage. I did exactly that. took out a 1kwh per day ac fan and made a 360wh array that runs off dc solar. that is if all 9 are spinning as i usually only use 2 legs 6 fans that is 240wh so 1/4 of the power draw and all RE power now.

Now all i need to do is make another one and get rid of the other 20" box fan.

60KWH per month for running 2 20" box fans is just a bit much me thinks.

My ratshack noise meter seems to have walked off. So i can't test it.

I was thinking of building a PWM controller for them so i could turn the speed down a bit without alot of watts lost in the process.

[nothing to lose]

You did great work there, I have mentioned the use of fans like this many times myself but never did the actaul power study.

Go to bestbyte.net and look at the fans they have there. Normally 80mm fans can be had for $1 each, they have 120mm ones starting at $3.50. Lots of specs on there site for the fans also. Normally important things like CFM, Bba, Watts used etc... are shown there. Not connected with them, just buy alot of stuff there myself like fans and lights. Shipping used to always be like a flat $5 fee, been awhile since I ordered so not sure now.

MFN: DF128025SL-4 23.12 CFM, 27.07 dBA, sleeve bearing 20K hour MTBF@25°C, 18 inch power leads, 4pin power connector, includes mounting screws

    Unit Price: $0.85

Uses 1.68 watts each.  I normally use 80mm fans because I have them on hand for computers, also they are cheaper each and use less power each. I think the 120mm I looked at was around 5 watts.

 The higher the number for CFM of course is the more air it moves, but that normally also means higher dba numbers and that means more noise.

They have others for $0.99 also

This one,

MFN: DF1212025SM-3/4 76.63 CFM, 38.64 dBA, sleeve bearing 20K hour MTBF@25°C, includes mounting screws, 18in leads with 3pin/4pin combination connector for general compatibility with RPM signal output.

Uses 5.04 watts and costs about $3.50 each.

Myself I normally forget those expensive finger guards and use window screen instead. This make a nice unit that keeps bugs out as well as protecting fingers and is cheaper than the fan gaurds if you have to buy them seperate.

I have built various things like this, camping in a van a nice small unit can fit in the door window, roll it down alittle put fan unit in place and roll window up to hold it

I mentioned a while back too, you can also adjust the fans various ways if you want. Shim a few to point towards the sides, up or down, etc.. so it's not all just a straight line flow like a box fan. Also you could turn the top ones around to blow heat out the window while the bottom ones suck in cooler air. That is a neat trick if you go to the trouble, you could make a small vent tube or shroud to suck hotter air from the ceiling to blow out doors.

Glad to see some-one else doing this now too. I think in general with your 120mm fans you are moving more air for the same power usage than I am with my smaller ones, but I only looked up the cheapest ones there. That's one of the reasons I like bestbyte.net the specs are there to compare the fans for the usage you want them for.

[Dreadstar]

Reason i went with the 120mm fans is. I build computers for a living. And some of them are hardcore gamer systems. These kids take these machines and overclock them. (ie: ramp the speed up on the cpu and video cards) just like adding NO2 to a car makes em run faster and hotter. the 40,60 and 80mm fans most common in computer cases and power supplies cpu heatsink fans generally have to spin at some ungodly rates to move the amount of air that will supposedly keep everything running. 6000 rpm on some of them.

A 120mm fan has more surface area on the blades gee just like a good wind genny. hence it can move alot more air.

I had other 120mm fans available but not 9 of the same type. reason i bought the case of 40.

I have 2 of the delta 120x38mm FFB1212EHE -->190.00<-- CFM @ 4000 RPM, 59.0 dBA, 24.00 watts, 2.00 amps, 12v DC now this one fan moves only 190cfm of air for a wopping 24 watts 36 watt inrush on it. Now this is all well and good if you can only put one fan in a location. but 6 of the ones i used move 519cfm for 20watts of draw.

Oh and the 9 fan array i have in the window is much quieter than the 59dBA delta fan.

and moves 4 times the airflow for 6 watts more power than the single fan.

However i did build a dual amd gamer system that had 1 out the back 1 out the top 2 in the front 4 in the side and 1 each on the cpu heatsinks inside the system a total of 10 of these monsters in that system talk about a jet turbine spinning up. for a grand total of 1140cfm intake and 380cfm exhaust each cpu of course had it's own 190cfm blow job going on. Had to buy an external 12.4vdc powersupply to power the fans. 360 watts of 12vdc is a bit much to ask of even a big computer powersupply plus the fact that fans generate alot of noise on the power buss.

I like efficiency when it comes to my small solar array. i have 4 55watt shell M55 panels that don't do so great when it comes to matching the rated wattage. they should have been rated at 40 watts which they do well at. But of course that is another story and i have 2 posts up about that aswell.

[nothing to lose]

Yea, I don't game myself and don't mess with the hardcore gammers either. Mostly just normal systems with normal Video cards and in airconditioned surroundings. So 80mm is fine and fits the cases, heck most those could probably get by with a chip cooler fan no more than they do with a system anyway.

 Like I said I liked bestbyte.net because you can actually compare the CFM, Dba, power, etc.. between fans. If we have the stats then we can total them up as needed and see what looks best for any given use.

Well still glad to see others using them now too instead of just me

I need to get a decent camera someday, I geuss other than online here I just ain't the camera bug type though.

[Dreadstar]

62dba on my ratshack meter at 1 foot from the array.