[SOLVED] How to power 2 PC case fans via 120v wall plug?

I use wood to heat my home and need to move the hot air from the top of one room down through a wall cavity between studs to a vent near the floor in an adjacent room. Here's a commercial version of what I'm trying to accomplish via DIY:


I would like to connect the case fans to a standard 120v wall plug but I'm not sure of exactly how that would look. Power specs for the case fans are:
Voltage:12V
Current:0.45A
Power Consumption:5.40W

Case fan image:

Any assistance is much appreciated, thanks!

first tell me is it operated on DC?

if yes then you have to get a 12V power supply to convert 120V AC to 12V DC. after that you have to connect the fans to the supply in parallel.

Yes, fans are DC.

As for the power supply, do I need to find one whose output exactly matches the input of one fan? What specs should the power supply have?

Yes you must connect 12V supply to fans because their input voltage rating is 12V DC.

A simple 12v DC Power Supply will easily run your both fans. the power rating of power supply Should be at least 20W and its current rating must be greater than 1.5A.

After that what to do is you have to connect Positive terminal of both fans to Positive terminal of Supply and Negative terminal of both fans together to the Negative terminal of Supply. Means you have to connect both fans in parallel to the Power supply. these DC Supplies are easily available in Market.

Hope this will help you.

Regards

U can just use an simple SMPS (Switched mode power supplies) which u can find inside an CPU or replace an new one which will hardly cost u around 5-6$... and just connect the 12V TB to the fans connected in parallel


With Regards
Santosh Kumar

Thanks very much Santosh and Qaisar! I'll see about finding the parts laying around the house here and post a pic of the functional device.

Thanks again!

Good Luck Scott

scott45 said:

Yes, fans are DC.

As for the power supply, do I need to find one whose output exactly matches the input of one fan? What specs should the power supply have?

Click to expand...

Think about a car battery. They are 12V and can supply upwards of 600-1000 amps when you start the engine. However, when you turn on your stereo or headlights (all run off that same 12 volt battery), they don't blow up because they are being force-fed 600 amps; devices will only draw as much current as needed, at some specified voltage. A lightbulb in your house is the same; the electrical grid can supply hundreds of amps to your house, but a 60 watt lightbulb only draws around 0.5 amps.

Take away: Once you have the proper voltage for a device, the load (a light, fan, etc) will only pull as much current as it needs.

So, the trick with power supplies is to remember that you first need to determine the operating voltage, then have your supply be able to produce enough (or more) current for the expected load.

If you have one fan, it will take 12V and 0.45 amps to run. If you connect two fans in parallel, they will each need 12V across the power wires, and each will draw 0.45 amps, so 0.45+0.45 = 0.9 Amps. If you need 3 fans, all three will need 12V across them, and each pulls 0.45 amps, so total current needed will be 3*0.45A = 1.35 amps.

Once you know the voltage and current, you can find a power transformer that will take 110 VAC from the outlet and output 12 VDC, and at least the amount of current you calculated. In the case of two fans (2*0.45 = 0.9 A), you could use a 12V supply that can supply 0.9A, 1.0A, 5.0A, 10A, 10000A.... anything, just as long as it's current capability is greater-than-or-equal-to the amount you calculated.

For 2 fans... 12V @ 0.9A, you can find something like these at most electronics stores (Wal-Mart, maybe... Radio Shack, definitely).
Google - 12V 1A power supply

Hope that helps you understand how voltage and current ratings work.

Finally got the thing together with hot glue and zip ties just so I could test the concept. It's not pretty but it powers up when plugged in and moves air in the right direction which is all it needs to do. Now all I need to do is cut a couple holes in my wall and see what happens!

Since the fans are just a couple of 120mm computer case fans all I did was connect their plugs together and then to those I connected a plug I had laying around. This is probably pretty close to as simple as a circuit can get but does anyone see anything wrong with it? The fans are 12vdc, .36A each and I'm using a 12vdc, 2A power supply.

I think these fans unable to build convection between to parts at your home. could you use greater and stronger fans. it seems very weak to be able to operate properly.
Second you should close and clog all of side around fans so that is improve their efficiency.

scott45 said:

Finally got the thing together with hot glue and zip ties just so I could test the concept. It's not pretty but it powers up when plugged in and moves air in the right direction which is all it needs to do. Now all I need to do is cut a couple holes in my wall and see what happens!

Since the fans are just a couple of 120mm computer case fans all I did was connect their plugs together and then to those I connected a plug I had laying around. This is probably pretty close to as simple as a circuit can get but does anyone see anything wrong with it? The fans are 12vdc, .36A each and I'm using a 12vdc, 2A power supply.

Click to expand...

This is good for a prototype build. I think you will be fine regarding the electrical connections. However, for safety, I'd add a fuse, in case the fans or wiring fail and cause a large current draw (could result in a fire). The fuse (installed near the power supply) could be something as simple as a blade or tube fuse found in the automotive world. You can pick them up for pretty cheap at your local hardware store or FLAPS (Friendly Local Auto Parts Store). Since you have a 0.72A load (0.36x2) and a 2A supply, I'd put in a 1 to 2 amp fuse.

As for air movement, I agree with dv_sa559. Block out the area around the fans so you can build static pressure. That way air won't just sneak back in through the gaps and form a loop (out the fan, back in through the gaps in the grate, back through the fan again). If the fans are very noisy, or run at high RPMs (like putting your hand over them, so air can't move through), then you need a fan with a lower flow and higher static pressure. Typically centrifugal/radial (a.k.a. squirrel-cage/blower) fans are best suited for those applications. You can find axial fans (what you've got now) with very low blade pitches that improve their static pressure capability, at the expense of flow rate. Since (I imagine) this is going to be on for long periods of time, a slow-but-steady method of air transfer may not be a bad idea.

Like all DIY projects, try something... if it doesn't work, fix it. If it doesn't work well enough, modify it. Repeat, repeat, repeat. :smile: Nice start, keep us posted as you learn more.

enjunear - Good idea about the fuse - I hadn't thought of that. The fans are very quiet so no worries about noise, but they may not move the air enough air even if left on all day as I plan to. I'm just going to install it and see what happens.

dv_sa559 - Regarding the strength of the fans, you're probably right in that they may not move enough air. The plan is to cut a hole in the wall just large enough for the two fans to fit into which will allow the metal grate to fit up against the wall. Most of the air leaks should then be taken care of but I can't get them all plugged unless I move to a different design which involves some sort of foam insulation or padding to fill the gaps.

You do know that muffin fans come in a variety of voltages, including
120VAC, right? And a variety of CFM and noise levels too. That said,
a squirrel cage blower will be quieter, more durable and throw much
more air, which is why they are used in home and window A/C units.
Ducting can let you locate the unfortunate bulk, elsewhere.

Now for the application at hand, you might prefer to stay with 12V
and have a handy ability to run off a car battery backup when the
power goes out. I've found squirrel cage marine ventilators in 12V
too, but of course that's well worse than PC surplus pricing.

Muffin fans tend to not be super fussy about supply and a simple
trickle charger with the backup battery might fit the bill. Cheap,
those.

Hello all, just wanted to put an end on this thread by reporting that the fans work as intended. They don't get the room up to 80 degrees like the room where the fireplace is but they DO get that back room warm enough so that my wife doesn't start shivering when she walks back there or jumps in bed at night.

The design has a lot of room for improvement but since I've got a happy wife and maybe $15 in the whole thing I'm going to leave well enough alone.

Thanks again for all of your helpful advice!

Scott