DIY Hood Fan Heat Extraction Project

[flanque]

Hi all,

I thought I'd share this with you. It's 99% done.. all I need to do is find a suitable junction box or similar to cover the cables and we're set.

The fans are 240v at 80 RPM. They're plugged into the same timer as my lights so as they come on so do the fans.

I've over exposed some of these pictures so you can see more detail in the darker areas of the pictures.

All feedback good or bad would be appreciated... bad in particular so I can fix up any problems. I'm particularly interested in safety concerns. The airflow is both pulling inwards to the canopy from both sides.


Cheers.

 

[tropicalfish]

looks cool!,.. too bad it couldn't be mounted on the inside...
The fans both look like they are pushing in air, is there any place for the heated air to come out?
Also, dunno if this is a great trouble for you, but after the lamps turn off, they are still very hot. If you have a second timer or something, you could have the fans running for 10, 15, 30 more minutes after the lights turn off.

 

[Sicklid]

I believe the fan direction is controlled by the polarity of the wires, not sure though... I would have liked to see (or not see) the mechanical stuff inside the canopy, but hey, that's just me. If it works, and cools things down, then great!

What wires do you need a junction box for? The ones on the outside? I would just cover them in the same wood as your canopy.

 

[tropicalfish]

no, DC fans have a set polarity. Plug it in one way, it doesn't work. Plug it in the other way, it works. The air flow is determined by the position of the fan, usually the motor holder thingy is the air output. Intake is where the blades are exposed, unless by design it is the opposite way.

 

[flanque]

They're AC fans. These particular ones have a specific airflow direction and I certainly haven't taken any special steps to ensure the polarity of the wiring either.

As for the internal mechanics, it's really just as in the picture with the description, "Underside shot with protective waterproof insulation tubing installed" - that's all you see.

If you look at the same picture you'll see that there's a gap at the back of the hood and that's where the heat comes out.

The only reason I wanted a junction box was to cover up those terminators (which are covered with electrical tape) for the sake of presentation of the hood and to help elminate any potential issues with water in the event of splash (very unlikely) or other unexpected accidents.

 

[Sicklid]

No, I meant that I would have mounted the fans and wires inside the canopy, now that I read it back it seems like I was saying something else. Sorry.

You could rig up a couple of exterior gray PVC junction boxes and maybe spray them black with krylon fusion or something. You could screw them in from the inside, and that would give you a finished look.

Out of curiosity, why did you need two fans? If the back of your canopy is completely open, you could've gotten away with one, mounted in back, no?

 

[flanque]

You're probably right about the number of fans, but since they were very cheap and of high capacity (and incidently very close to silent, certainly my skimmer is louder and drowns the noice out entirely), then why not install both of them? That and I wanted to make sure I had an even dilution of heat from the canopy and increased airflow as well on both sides.

These fans turn on when the lights come on so they are definately focused on the heat fromt he lights as my water does peak at 30C in the worst of summer days.

 

[greenmaji]

Are both the fans blowing air in? I think thats what I would have tryed first (since the back of the canopy is open)

and yea mounting them internaly would have been cleaner, but it wouldn't show off your DIY skillz J/K

 

[flanque]

Yeah both fans are sucking air inwards so that there's quite a strong channel of air being blown directly over the tube connectors on both sides, rather than sucking out which I think would have pulled air from other areas not just directly from over the lighting.

I would have liked the fans inside but there just isn't any space. I have about a 1/2 inch gap on each side between the lighting fixture extremities and the hood (which is the fan blades).

I'm not sure if I should add some filter or gause over the insides of the canopy to catch anything such as flies, etc that may be stupid enough to fly into the fans. I once had a cockroach climb my aquarium, fall in and drown. It was floating there for at least eight hours without any problems to water quality levels.

 

[tropicalfish]

how many mm are the fans? you could go to the computer store and get the fan filters for them if the filters are designed for that size..

 

[flanque]

They're 80mm fans.

 

[Sicklid]

Those fans are probably spinning fast enough that any bug unlucky enough to venture through would be met with nothing but pain, devastation, and heartache...

But I guess you mean for when they ain't a'blowin...

How about a louver type of cover like they have for the outside of a dryer vent on your house? They only open when its blowing, and you may be able to fab something up that is only 1/2" to fit inside the canopy, like this:

 

[flanque]

Hmm... not a bad idea. Thx.

 

[tropicalfish]

well, those are usually more of the exhaust type. That can only be placed on the inside of the canopy because you said they were blowing inwards. or, you could cover up the back of the thing, and leave a small square for the louver thingy, that might work... but junk could still go in through the fans.

 

[Sicklid]

I was only suggesting that to keep things out when the fans are not being used. They would have to be mounted inside because they only work when they are being "blown"... Thats why I I said they should be half inch slats/fins so they fit inside the canopy. You would still need a filter of some kind to filter the dust. How about cutting blocks off a cut to size air conditioning return filter? They would be damn near held in place by the suction of the fan itself.

 

[flanque]

Sounds a bit dodgy.. I'd prefer to actually mount it than rely on physics to hold it there!!

 

[tropicalfish]

If you relied on physics to hold it there, maybe the next day, the filter will be stuck on the fan, the blades stopped, and a bunch of torn up filter remains inside the canopy. If you want to use a filter for the intake, get a grille of some sort first.

 

[Sicklid]

You guys are funny, taking things awfully literally ... I was implying that the filter material is so light, that you would not need much fabrication to hold it in place... just a "lip" of some sort... It's obvious that when the fans shut off the material would fall off if not held in place mechanically.

Flanque, I have to ask is that your dog in the avatar?

 

[flanque]

Indeed. Had to put him down a year ago.

 

[Sicklid]

SO sorry... He is a handsome little guy! Did he have a personality to match that face?

Back on the thread, what did you figure out for a box to cover the wires?