Fan direction question for a DIY hood..

rsd

rsd

Member
IMO it depends on where the fan is mounted and how loud is too loud for your taste.
I have 1 Radio Shack Fan and it is mounted down in my sump cabinet blowing across my return pump and balast of my sump light. It is freakin loud when I open the door to the sump cabinet. The intake for the fan is a piece of dryer hose from behind the cabinet and the exhaust is a gap that leads behind the tank-stand... doesn't noise pollute the house much.
The other 2 fans are fans from an amp rack. The racks where manufatured by Middle Atlantic (hardware company) but the fans...not sure. Very nice and about 1/8th the volume of the "rat shack" fan.
Hope this helps
 
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billb

Guest
Hmmm..Mum would hate any noise...Maybe I'll slap togather something portable and remove the back part of the tankcover and try it out, for testing only. I'd hate to start drilling and cutting only to find the noise is going to be too much.
thanks..
 
jhueb12

jhueb12

Member
I just finished a DIY canopy(with an open back to encourage more air flow) to mount my MH's in. Two fans on the side draw air in while a slightly larger fan on top suck air out. This has worked great. I know it has been suggested but it has worked for me! My 2 cents. HTH
 
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bluedolphi

Guest
If you want quiet go with a panaflo 80mm L1A, and run it at 7v or even 5v. Let me know if you need to know how to wire them at the lower voltage.
 
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silencer

Guest
If space is available I would use 120mm fans (about 4.75") instead of 80mm fans (about 3.25"). Larger fans put out more air and can be run at a slower rpm which makes them quieter. Thicker fans tend to be more quiet as well. The thinner the fan the higher the rpm it must run to put out the same airflow. Deeper fans can move more air with each turn and thus require less rpm and are quieter.
 
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billb

Guest
Great information here..thanks...
Ok, lets talk a little about wiring...From what I can see, most of these unit are low voltage of varying degrees.
I do have an old 120 AC to 12 Volt converter in the shop (small black unit used to test out car radios/Cb's etc..) is this going to help me? If I pick up say 2 or three fans of varying voltage what can I do to hook them up...
suggestions/comments?
Billb
(seems as though while my tank is cycling and I can't do much else, it's a good time to study DIY aspects and play in the shop...)
 
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bluedolphi

Guest
Using a 12v power supply you do not need to get fans of varying voltage. And in fact if you do purchase a fan that is set at say 5v, you will defeat the purpose, as it will be running at its normal voltage (standard performance specs=same noise level). You can wire a 12v fan to run at 7v or even 5v if you have the right kind of power supply. A computer PS has differing voltage wiring that you can wire into for instance.
It is common to "undervolt" computer case fans to run them quieter. You still want the fans to do their job though so you have to use a fan that has been known to still perform well when running this way.
I tend to agree with Silencer..... I like running 120mm fans. They still move a lot of air even when running "undervolted" (new word?).
 
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billb

Guest
I already have a 12volt power supply so I might just go with the 12 volt fans. I saw a couple at my Radio Shack in the neighborhood. I was thinking about running two 3 or 3 1/2 inch ones. Think they would be to noisy?
 
obtusewit

obtusewit

Member
Blow the air in. Its an aquarium not an amplifier, there are no heat sinks on the water...and it won't pressurize Jack Chit
Fans stay cooler
fan noise is baffled in the hood
AND THE SALT DOESN"T EAT THE FAN MOTOR!!!!!!
Geez no brainer
 
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bluedolphi

Guest
Heatsinks prefer air blown onto them.
All enclosures pressurize. Even if they have openings.
Fans stay cooler?
Fan noise baffled?
Fan will last longer?

Salt eating the fan motor is not likely to increase due to fan direction. And if it were a noticeable difference, it has to be weighed with the resulting performance.
IMO.
 
badkharma

badkharma

Member
I speak with experience, having tried them both ways. Blowing into a canopy is definitely the way to go. The canopy won't pressurize at all, this isn't a laptop or desktop PC. Most canopies have the entire back end open, pressurization is a non-issue in this case. The fans last at least twice as long if you blow the air in, because if you draw it out, you're pulling salty air through it and it craps out sooner - trust me, like I said, I've tried it both ways and with the same type of fans. The fan also DOES stay cooler because you're pushing cool air through it - not hot air. It makes a difference in the life of the fan. I can see if you have a sealed or semi-sealed area (like a light hood with splash cover, not a canopy), then the advantage would be to draw it (the air) out. This is not the case. The water temperature (remember that's the primary goal) stays lower and is consistent when pushing air in. I've also noticed that when the fans are blowing air in, they are quieter than sucking it out.
 
bang guy

bang guy

Moderator
Fans cool aquariums by increasing water evaporation. If the fans are pulling the air out they are mostly just replacing the hot air in the canopy with cool air. This does increase evaporation but not that much. The salt will definately kill the fan prematurely.
Blowing air across the water suface is the best way to increase evaporation and cools the water much much better. The fan will last a lot longer too.
 
rsd

rsd

Member
You know how I love nothing more than throwing gasoline on a fire.... so here I go.
There are a few misconceptions I want to clear up.... and share the results of a little test I have been running.
Misconception: Tha fans are pulling salt water out of the air.
When water evaporates it does not take solid or disolved material with it. It leaves behind what is called "total disolved solids". This term is used anytime you are refering to a large body of water where contaminates, solids, density, etc are measured. If the evaporating water did take salt with it then you would have to use salt water in your top offs and not fresh water.
For instance:
If you added 5 cups of salt water mix to 10 gallons of water... then evaporated 5 gallons of water... you would still have 5 cups of salt mix in the remaining 5 gallons of water... your total disolved solids remains the same unless you remove the water containing the solids.
SO. If it isn't salt water that is ruining the fans, why are the fans that suck air out of the canopy wearing out faster?
Here is what the little experiments I have done have resulted in.
1. The air inside your hood is far more humid than the air outside of your tank. I have to turn the fans off in my hood to take a relative humidity reading. With my fans off for 5 minutes my hood's relative humidity climbed to 90%. Like a good southern summer night! So that means that the fan is pulling very humid air across it's body. And we all know that electronics like a dry climate...not a moist one.
2. Knowing this I set up a water evaporation recovery system in my sump. It was not very efficient and it took 2 weeks to recover the 5 ml necessary to test for PH. The fresh water test kit I had was not very effective below 7.0 (as I expected it to read above 7.0.) What I actually found was the water to be far below 7.0 which makes the humidity acidic. ( I don't know how far...except it was not in the expected color range). Now we know that the humidity being sucked across the fan is of a very low PH... or acidic.
3.1 I also placed a piece of litmus paper (probably spelled incorrectly) infront of the test fan that was pointing out of the hood. Normally all of my fans point in, but in the interest of my curiosity... I reversed one. This piece of paper was like a target for the fan about 1/2" away. At the end of the 2 weeks it was covered in spatter...as if the fan was spitting on it.
Therefore water is being pulled across it from somewhere.
3.2 I placed a piece of L. paper parallel to the water below the fan to act as a splash guard, and replaced another piece of "target" L paper. 2 weeks later it was soaked. The "splash piece of L paper" had gathered alot of splashes and sprays from water movement below... the "target " L paper was only hit about 1/2 as much.
3.3 I attached L paper to the blades of the fans blowing in and the fans sucking out for 12 hours. The fans blowing air into the tank showed 4 spots of water contact... the fans sucking air out showed approximately 38 points of contact...they started blending together.
4. I attached a digital thermometer to the motor of each fan (1 pointing in, and 1 pointing out). I found the average temperature of the fan that blows air into the tank to be 6 degrees lower than that of the fan the sucks air out.
My conclusions (finally)
Here is why I think fans wear out faster when they suck air out of the tank:
1. The fan is drawing high humidy air across an electrical device.
2. The moisture in the air from #1 is of acidic nature... increasing it's damaging effect.
3. When there is any spray or splash generated by fish or water movement near a fan that is sucking air out of the tank it is far more likely to be caught up in the fan. This exposes the fan to direct salt water... which we know to be corrosive.
4. The Fans that suck air out of a hood have an increased running temperature of at least 6 degrees (as this was a reading from the shell...not the actual motor.) Increased temperature = increased wear and tear.
That is my findings... But as I have read before... your tank, your choice.
 
bang guy

bang guy

Moderator
I can find nothing in your post that disagrees with my experiences.
I can only question testing the PH of water that has been sitting for some time and concluding that it was the same PH as it evaporated. No big deal though.
Thank you for going to all the effort to publish your findings!!
Bang
 
rsd

rsd

Member
I agree that it the PH may have "wandered" while in my collection cup....so I tried to see if water varied in ph while sitting.... I took 10 ml of tap water and placed it in with my sump for a couple days. To be honest, I forgot it was in there and I am not sure how long it actually sat down there. I know that the tap water sat there for more than 48 hours and probably no longer than 4 days. It evaporated some but didn't vary a significant amount in PH... not enough for me to believe that the variance could have been due to inconsistancies of the testor, or the test product.
But, I also cannot find a significant reason that the evaporated water would be of a low PH... and to be honest... the meathod I used to gather the water was really ugly and I caught alot of grief from my wife about it. I probably wont be setting it up like that again.
I would be happy to explain what I did if someone else was curious enough to take it on though.
 
suver569

suver569

Member
I say, try it both ways and test it over a few days. Go with what works best for you.
Here is what I did. It's a fan by Middle Atlantic Products. 4 1/2". Model is Qfan. Here's a link. http://www.middleatlantic.com/rackac.../cooling.htm#4
Less than 30 DB, so it's quite. Very quiet. I have a 1" fan on my nano that makes a helluva lot more noise than this fan.
My tank was a steady 80, spiking to 82 when the halide came on. It doesnt break 77 now and stays 99% consistant at 77 degrees with the fan blowing in.
It works for me, and anyone would have a hard time convincing me to change my setup. Do what works for you. There is no "right way."
 
.357

.357

Member
Take it from a Firefighter, the fan points in.
What about power supplies? I have 3 24V fans that would be perfect if I had a power supply. any ideas?
 
rsd

rsd

Member
The easiest way is to go to Radio shack (Rat shack as we call it) and buy a universal power adaptor. Just make sure to use a compatible PSU. It has to be the correct Voltage and Amp rating.
You can always take the fans with you and they will set you up with the correct PSU.
Good luck,
 
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