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Computer Fans

  • Thread starter jimscott
  • Start date

jimscott

Tropical Fish Enthusiast
From time to time someone mentions using computer fans to increase air circulation in their terrariums. Where do you get them? I mean, do you cannibalize a computer or can they be purchased separately? How much does a small / cheap one run?
 
Electronics stores. Try something like Radio Shack.
 
If you want, send me a PM with how many you want and how long you want the cables. I'll wire them up for you and some out to ya.

-Nathan
 
I've always wondered about this too. Can someone list or PM some directions ? Is it as easy as hooking it up to the 12v transformer and plugging it in ? Do you need and inline fuse ? Which fan would work the 5v ? or stick with the 12v ? Can I hook up a series of them or should there be one transformer for each fan ? I will google this too but does anyone have practical experience ?
 
Thanks for the feedback! Lemme ruminate about this.
 
per request of droseraguy....

Directions for hooking up an Old Computer fan. Computer fans are going to be your cheapest fan type available, but you may also find others as surplus.

Computer fans typically run in a few sizes but 80mm or 120mm would be the better sizes for a terrarium. If a fan came from a computer case you'll be working with a DC fan, not an AC one. Depending on the size it will either run 5v or 12v. You'll see a sticker on the fan somewhere that will tell you.

Next thing you'll need in a AC to DC adapter, these are the things you use to charge a shaver with, plug in your cell phone, battery charger, some xmas decoration, etc. You probably have an extra one in a junk drawer that might work. If you look on the sticker of the wall adapater, you'll see an INPUT rating and an OUTPUT rating. You'll want to make sure that the output rating is 5v DC or 12v DC. But there's a fudge factor with this as well, a 4v one or a 8v one might work as well, motors can be forgiving. The important thing to look for though is that it is outputting DC voltage, or AC if you found an AC fan. Not all fan motors are interchangeable from DC to AC. One other rating that is given is amperage you'll probably want around 100mA to 200mA (0.1A or 0.2A) as rating. You'll want to stay away from ones that list something like 1A or 2A. Some cell chargers may be this high and would be too much.

Once you found your parts, you simply cut the end off the fan and the transformer, then strip the ends of the wires. You can use a sharp knife and carefully cut away the insulation if you don't have wire strippers. Next you'll want to find the polarity of each piece. The fan is usually obvious, red positive black negative. However the transformer may be more difficult. The best way is really to just twist the pairs together and plug it in. If it works, you got it, if not switch them around.

*Note: don't let the positive and negative wires of the transformer touch. That creates a short and can burn out the transformer.

Once you get the wires connected correctly, you can just take electrical tape and tape around each pair. Make sure it's nice and secure, you don't want to pull them out by accident.

Then you're done!
 
Good write up mrflytrap.
I use extra computer fans and old cell phone chargers. I just wired them together and they have worked great for 3 years. Didn't cost me anything:)
 
  • #10
One question, although I think the answer can be inferred from your post; when matching voltage and amperage, which needs to go over and which under? I think it's that the amperage of the transformer should be under the amperage for the fan, and the voltage is the opposite (transformer must be equal to or greater than the rating on the fan.) Correct?
~Joe
 
  • #11
excuse me for jumping in but to understand amps and voltage it may be easier to think of a water pump. Voltage in electricity can be thought of as basically a measurement of pressure differential and amperage as a measurement of flow rate.

In an electrical power supply the amperage rating it has is the amount of "flow" it can maintain before it begins to lose voltage (or overheats depending on design)

So if a power supply is rated at 1amp at 12vdc it can supply that much flow if required without a drop in pressure (voltage) or excessive heat.

If you exceed the amperage rating then the powersupply's voltage will start to drop and/or excessive heat will start to build up.

Of course there is usually a decent "safety factor" built into these units.

If you have a 1amp powersupply but the "load" only uses 0.25a then that is all that will flow, the 1amp rating is a max rating.

personally I would recommend to use a power supply with the correct voltage and at least the amperage that the fan/s are rated, 10% over is always a nice buffer for the unexpected.

Interestingly enough, these fans are axial flow dynamic air pumps and their amperage rating is directly proportional to air flow, so if air flow is restricted their draw actually goes down... I know, counterintuitive but true

so to make a long story short, yes there is room to play... to a degree, but its best if the voltage is spot on and the power supply's amperage rating exceeds the load rating.

HTH's
Av
 
  • #12
So... I got it backwards, then? I fail at electrical engineering.
~Joe
 
  • #13
To make matters even more gray the safety factor designed in is also a -+ for bad manufacturing of the supply accuracy. I've seen many 5V supplies run 8v - 12v as well.

If you cut the amperage too low the fan will probably still spin but not at it's true strength (not putting out enough air current). I just warn to stay away from supplies that are willing to give you high amps say 2 as it may start to melt or catch on smoke if you short the wires incorrectly.

Basically if you hook it up, and the fan spins for longer than 10 seconds without smelling like it's burning you did it right!

Nate
 
  • #14
rectifier.jpg
 
  • #15
An AC to DC power supply/converter should have a rectifier built-in. That's how the AC is normally converted to DC.

If you are hooking up more than one fan they should be wired in parallel, not series.

Note: Some fans can have 3 or more wires. Normally the third wire is used to measure the RPMs of the fan but can also be used for multiple speed control. Hooking up power incorrectly to the tachometer wire can burn out the fan. Unless the fan comes with a wiring diagram, avoid fans with more than two wires.
 
  • #16
As not a number stated, there's no need to worry about a rectifier. Pay attention to what I said about looking for a transformer that already outputs DC.

Plus DM, just popping a diagram like that isn't really helpful without any explanation. Also you seem to be mixing diagram conventions, using something not very standard, or just incorrect. It appears you're showing the source power as connected to both grounds. This is the standard labeling of a rectifier. http://www.electronics2000.co.uk/images/data/bridge.gif
 
  • #17
I just picked one of these up at my local computer supply store. It actually came with an ide/sata to usb2 converter. It's a power supply with the power dongle already built in. I'm pretty sure it would work with a standard computer fan, although I haven't actually tried it myself. Maybe someone can confirm if it would work or not. But if you're not comfortable with doing the wiring and are willing to spend a few extra dollars, this might be a good option.

img_0346.jpg
 
  • #18
That PSU looks like it will do the job nicely... You would need a fan with a "4-pin molex" type connector for plug and play... the fans are available in a 3-pin motherboard connector as well, which would not work with that PSU without cutting wires. If you're buying fans, I recommend Scythe s-flex fans. I run them in all of my computers, and they are completely silent and move a good deal of air. Also, they use sony S-FDB fluid bearings, so they'll last forever. They're about $12 each for the 120mm version.
 
  • #19
Ok, here's my thought. Jump in and tell me it's bunk before I burn the house down please. I've been informed that the low voltage lights I put in the front of the house will be replaced this year. They are on a timer that came with the light package so that will be available for my use. My thought is to take the timer/voltage regulator and hook up the computer fans along the wire just like the lights were. So now instead of the 10W lights running the computer fans can be positioned around my grow enclosure where I see fit. With the timer they can go on and off as needed and the whole thing just plugs into the 110 outlet. This should work right ?? Seems to easy.

Anyway if someone needs extra bulbs for their outdoor sidewalk lowvoltage lights (10W) let me know. I'll have about half a dozen new extras sitting around.
 
  • #20
Chris,

Personally, I would need more information before I would tell ya one way or another.

Is the timer/power supply the correct type of voltage (ac or dc)?
Is the voltage correct?
Is the amperage correct?

A 10w low voltage light is still going to be very low current plus it is a purely resistive load. Now you are going to inductive loads with what is prob a higher current rating. Also the lights could very well be low voltage AC instead of DC

errr that make sense?

In other words, what are the specs of the unit in question mate
Butch
 
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