Question about hooking up a standard house fan to a 4-pin molex

[Liberator21]

Hi all, and thanks for the help. So my wife bought this little $6 personal fan from Wal-mart yesterday. I noticed it pushed ALOT of air for such a tiny thing, and was relatively quiet. It's smaller than a 120mm (probably close to 92mm), and pushes more air than my 120mm fans rated at 68 cfm. I've dismantled it from the shroud and housing, where all that's left is the fan, magneto(?), and cords to the on/off switch and power outlet. So...

1. How do I make it turn on and draw power from a standard 4-pin molex connector connected to the PSU, instead of a wall outlet?

2. I'm assuming that 2 of the 4 pins will be for on/off, and the remaining will be power?

I can make a cheap and easy housing for it to mount in the 5.25 bays, pointing to the CPU cooler, via my Lian Li fan module. I also don't want to manually flip a switch to turn it on, I'm pretty sure it's possible...Thanks I look forward to this and will keep you updated! I think done correctly this might be a viable alternative to those $20 case fans, and quieter too!

 

[mechBgon]

Wall outlets normally (in the US) provide 120 volts of Alternating Current. Your PSU provides 3.3, 5 or 12 volts of Direct Current. So this really is not going to work out, it's like filling your car's gas tank with sunflower seeds

 

[Atheus]

mechBgon is right about the current, but there is one case where this would be possible - is the fan's power plug a heavy box or just a lightweight plug? If it's a heavy box, is there anything written on it? This box *may* be a an AC to DC or transformer/rectifier unit, and that would mean the fan *may* be able to run off a computer power supply, depending on voltage.

 

[bigsnyder]

Some AC fans will run from a DC power supply if the amperage is strong enough.

 

[Liberator21]

Well...thanks mechBgon for raining on my parade Ok, so isn't there some sort of inverter/converter I can use? By the way, It's just a plug.

 

[mechBgon]

Originally posted by: El Liberache
Well...thanks mechBgon for raining on my parade Ok, so isn't there some sort of inverter/converter I can use? By the way, It's just a plug.

1) why not just power it from a wall outlet as designed?

2) having a powerful AC motor in your computer case may have some unexpected side effects :evil:

3) the infamous "big picture, part A" is that you probably don't need 68cfm 120's in the first place, so why put up with their noise level instead of using some low-noise 120's, and "part B" it's undoubtedly a sleeve-bearing fan that will not stay that quiet for the long haul either.


Anyway, be careful with the AC power, don't electrocute yourself

 

[Liberator21]

Hmm, okay. I guess I'll have it just in the computer as a test with it running 24/7- the fan not the computer- and see if there's any lowering in temps. By the way I don't use those powerful 68cfm'ers anymore, I've gone totally Noctua

 

[Rubycon]

Hmmm if this is a shaded pole motor running on mains you definitely are NOT going to get it to work on a motherboard header. As a matter of fact even with 12VDC, the back EMF induced from the motor is of sufficient magnitude to kill the driver(s) on the board rendering ALL fan ports inoperable! :Q

The 12V from the header can be used to operate the coil of a small instrument relay whose contacts are of sufficient rating to handle the LRA (locked rotor amperage) of the fan. Remember even the coils of relays have some back EMF so a 20WVDC cap of 100µF across the coil SHOULD be installed for safety.

IMO, this is a LOT of trouble to go through when there are 120MM and larger fans that will run safely off the motherboard headers.

 

[myocardia]

Here's what you need.

 

[Liberator21]

LOL good one myocardia. You guys and your logic, jeez!