Case Fans and an Aquarium

loris32

So, I have an idea that I need advice on. I am building a tank stand for my 20 gallon saltwater fish tank. To cool the Power compact and Metal Halide lights in the enclosed hood, I was thinking of putting in either three 90mm or four 80mm fans.

Here are the questions:

1) For ~ 5 ft^3, would those fans be enough?

2) How would I go about powering them? They would be constantly running and not controlled by a thermometer. Is there a specific "case accessory" mpower supply I could get, or would I use a smaller ( > or = 200w or so) power suplly?


Thanks

GHoosdum

loris32 wrote:

So, I have an idea that I need advice on. I am building a tank stand for my 20 gallon saltwater fish tank. To cool the Power compact and Metal Halide lights in the enclosed hood, I was thinking of putting in either three 90mm or four 80mm fans.

Here are the questions:

1) For ~ 5 ft^3, would those fans be enough?

2) How would I go about powering them? They would be constantly running and not controlled by a thermometer. Is there a specific "case accessory" mpower supply I could get, or would I use a smaller ( < or = 200w or so) power suplly?


Thanks

I don't know if the fans would be enough. Metal halide lights really pump out the heat. Your best bet for power would be a robust 12V DC power brick. The fans would just need to be wired directly to its output. I think that would be less wasteful of power than using a computer PSU.

loris32

Hmm... What fans would you recommend? I originally was going to go with case fans due to the relatively low dB level.

GHoosdum

I'd say go with three relatively quiet 120MM case fans. If they're too loud at 12V, you can lower the voltage for less speed and less noise.

loris32

So, how would I wire the fans? Seperately into the power supply? Or run the fans in series with one power line running to them?

airbornflght

GHoosdum wrote:

I think that would be less wasteful of power than using a computer PSU.

Just a tiny correction, those power bricks arent even 50% efficient. Computer PSU are upwards of 65%, BUT. Those fans might use at the most 3 or 4 watts. depeding. I'm not saying dont use it, actually, I am encouraging you to use it, because those power bricks are very small, and you are useing so little electricity it doesnt matter, it might cost you 2 or 3 cents a day to run it. And if you wanted to get fancy with it, you could wire up a resistor, thermistor, and a relay and a few other componets so that the fans only turn on when the heat reaches a certain temperature.

GHoosdum

I agree, abf - I was referring to the smaller overall power requirement rather than relative efficiency.

muddocktor

You might also consider using some 120v AC fans instead. That way you can get around having a DC power brick and you can also buy a fan controller rated rheostat to control fan speed. 2 good places to look for AC fans are mpja.com and all electronics.com

MPJA AC fans link

All Electronics AC fans link

airbornflght

yeh, but hes wanting some smaller fans, I have never seen a small ac fan. the ones ive seen have all been 120mm. if they have some small one, I could use a few.

Okay, I see an 80 mm ac fan, but im not paying $14 for it.:wow2:

redchief

smaller the fan the higher the speed the louder the noise.

loris32

Well, "size matters not" so to say. The main two fetures I am going for are high CFM's and low dB's. Well, plus relatively inexpensive. If I need to do a dozen (overzealous by all means, but just for arguements sake) 80mm fans, then so be it. As long as it is quite and it pushes a lot of air. Know what I mean?

And how would I wire up a temp regulated switch?

airbornflght

Well, Ive only made on once, and If I were to make one again, I would have to find the instructions on google. but you need a thermistor, and that will put out a linear current curve for the increase in heat (i believe its current and not voltage, am I right?) and then you need a resistor, which limits current. This is how you set what temp the fan kicks on at, you can also use a pot (variable resistor) to have a thermostat type thing, where you can change the kick on temp, but I doubt you need that. then you need a relay, and you need to know how much current it takes to trip the solenoid thing. This is what you base all of you math off of for what size of a resistor you need for a certain temperature. I think that is the gist of it, but I feel as Im leaving something out. I know I didnt go into much detail, but like I said, only made one, and it was quite some time ago. Should be plenty of info on the internet (try google) and if not, try one of the electronics forums. Or someone may even know more than me and be able to do all the math for you.

loris32

So, I was thinking about it last night and thought of getting a controller like this I could build into the hood. That way I could see the temp in the hood AND have a conroller.

http://www.frozencpu.com/bus-77.html

plus, I think I could run it off a 110V - 12V converter. I THINK. Is that right?

airbornflght

Seems like a good deal to me. Although, it is on the expensive side for what it is, you have to set the fan speed (no automatic throtling from what I see) but it should show the temp if thats what you are worried about.

V-P

So what is the point of using these lights that put out immense heat?

airbornflght

I believe they are to heat the water? although, I could think of other ways to heat it. or is it to give the proper wavelength of light that the fist need? Because when I had my lizard, they had to have an infrarad light/basking stone and also a flourescent light to simulate the suns rays.

loris32

First, the point of the lights is not to heat the water. In fact. I'd love to have the lumens and the light temp WITHOUT the side effect of the heat. (there is a difference between the light temp and the physical heat)

Second, I might end up having to get a chiller unit to lower the temperature of the water, but I still think the fans neccessary.

Third, Will that one fan controller turns the fans on and off at a certain temperature? I couldn't tell. As far as throttle control, if the fans went from off to max. revolutions, I'd be okay with that.

Say that the temp setting was 75F. The fans ran all through the time that the lights heated the hood until after the lights shut off and the temp dropped below 75F again. Repeat... That's what I am looking for. If that's what the contriller can provide, I'll take it.

Did any of that clear things up? Ask questions; give suggestions. It helps me all the better.

By the way, that's for all the help sorting this out so far.

airbornflght

No, from the looks of it, that controller will just list the temp, and has manual fan adjustments, that is, you manually adjust the fans speed.

If you find a controller with an auto mode, it will do just that.

loris32

http://www.kingwin.com/pdut_detail.asp?CateID=34&ID=169

I was talking to a comp sci TA that I had worked with in one of my aero eng. labs who is "90% sure" that is brother has one of the above that he'd sell to me.

I think this is has the general features I was looking for.

What do you think?

airbornflght

looks like it should work for you.