# Help powering 2x12v fans

Discussion in 'General Electronics Discussion' started by nopuk, May 24, 2016.

1. ### nopuk

18
0
May 11, 2015
Hello,
Trying to build a simple cooler fan for myself. I have 2 computer fans, one to suck air into cooler box with ice, other to blow it back out. Both fans are 12v - so i need at least 24v.

What would be the best way to power this from a mains voltage, for me that means 240V A/C. At the moment both fans just have bare red/black wire waiting to be connected to 12v DC.

Just looking for something simple and easy and hopefully safe.

Thanks

2. ### davennModerator

13,347
1,774
Sep 5, 2009
if they are in parallel, then you only need 12V

buy a 12V, 1A plugpack

Dave

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3. ### nopuk

18
0
May 11, 2015
Oh cool, never thought of parallel total noob sorry. Would it be possible to ask for help in a circuit diagram. Input is 12v DC - need to power two 12V cooling fans ( not sure what current they need, .1A ? it think )

Ideally I would like a switch to turn it on and a small led to show that there is juice flowing so to speak. Any other useful bells or whistles im missing?

I have very basic soldering skill and plenty LED's and resisters around, and a local electronics store, happy to purchase small parts and slowly learn.

4. ### Gryd3

4,098
875
Jun 25, 2014
I think this is something you should try drawing yourself

You have a 12V supply. (Battery, or wall-wart)
Take the + of the supply and run to a switch.
Take the - of the supply and call it 'ground' (This will go to the black wire of your devices)
Connect the red wire of your devices to the left-over contact on the switch.
Done like dinner
If you want an LED to light up, you can find/buy an illuminated switch from a car parts shop. (They all work on 12V) or you can wire a separate LED to run on 12V and run it in parallel with your fans.

As long as you have a 12V supply that is rated higher than the mA of all the parts you want to use, you should be fine

Edit: Apparently I was addicted to the winking face emoticon for this post...

Last edited: May 25, 2016
Harald Kapp, davenn and (*steve*) like this.
5. ### AnalogKid

2,307
649
Jun 10, 2015
The voltage and average current are on a sticker on the hub of the fan, usually.

ak

6. ### Harald KappModeratorModerator

9,404
1,921
Nov 17, 2011
Don't forget the current limiting resistor.

You'll get a stronger wind if you use both fans to blow the air out of the cooler box to where it is needed. Fresh warm air will be pushed into the cooler box by the ambient air pressure once the pressure within the cooler falls due to the air being blown out of the box. No need to "push" air into the box with a fan.

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7. ### nopuk

18
0
May 11, 2015
Hi OP here again, thanks for all the suggestions. I am going to purchase this power supply
http://www.maplin.ie/p/20w-acdc-multi-voltage-power-supply-l06br

My question, how (or what do i need) to attached simple copper wires for soldering to the output of the power supply. The picture shows nice jacks, but I would need just two points to attached my own wires too - i assume there is some nice connector type thing, I just don’t know the name.

8. ### Harald KappModeratorModerator

9,404
1,921
Nov 17, 2011
I suggest you build a matching receptacle for one of the connectors that come with the power supply into your cooler box. Connect your fans to this receptacle. You can then easily remove the power supply e.g. for transporting the box. Suitable connectors are e.g. here.

Otherwise cut of the connector that's molded to the power supply outlet cord and use any means you like to connect the wires to your box . Don't forget to provide insulation to prevent a short circuit.

9. ### AnalogKid

2,307
649
Jun 10, 2015
Don't think so. Two things:
1. Two identical fans stacked together do not increase the air flow except in situations with very high back pressure. The exit air velocity from tubaxial fans usually is not additive. In high restriction situations, stacking a second fan gets the exhaust velocity closer to the free-air exhaust velocity of a single fan, but never above it. Yes, separating the fans is slightly less efficient because the exhaust air from the first fan slows down a bit before it reaches the 2nd fan and has to be accelerated again, but in a tightly sealed system that decrease in air flow efficiency is more than offset by increased thermal efficiency caused by increased turbulence.

2. Unless you have an array of small protuberances to create turbulence, drawn-in air can have a pretty laminar flow, and much of it can pass through the ice box without touching the ice. An entry fan creates much more air turbulence inside the ice box than simply drawing air in by the negative pressure of an exhaust fan. That turbulence forces a larger percentage of the air molecules to make physical contact with a larger percentage of the total surface area of all of the ice cubes, bits chunks, etc. And, that contact is under higher pressure, increasing heat flow during the brief moments of contact. So the slight decrease in exit velocity caused by separated fans is more than offset by a larger increase in exhaust air temperature reduction.

ak

Last edited: May 25, 2016
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10. ### davennModerator

13,347
1,774
Sep 5, 2009
you misunderstand

two side by side, not in front of each other

11. ### Harald KappModeratorModerator

9,404
1,921
Nov 17, 2011
Yes, this was my idea. I apologize for not making myself clear in my post.

This could be adjusted by creating e.g. a meandering path for the air to go through the box before it exits. Like the tubes where the coolant flows within a fridge, only inside and outside swapped (air to be cooled inside, cold medium outside. Like in a coil jockey box cooler.

12. ### nopuk

18
0
May 11, 2015
Hi OP here again, I prototyped the circuit and it all works!! hurray - stupid simple circuit but very proud of myself

Attached is my circuit and it all works, red LED shows power, Green shows switch pressed to power both fans.

My question now, is how on earth to get this all soldered onto a small need little board. the second image shows my switch and power jack( for 12V DC), find it hard to deal with those legs compared to wires. Tiny bit of solder experience. Any help much appreciated.

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13. ### Gryd3

4,098
875
Jun 25, 2014
I would suggest getting a 'perfboard' or similar. It's copper clad board similar to the breadboard you used, but you dictate where the traces go underneath with solder.
As far as those big posts are concerned... they can be a pain.. if you have an enclosure, mount those larger items to a case, then simply use spade connectors, or solder leads directly from them to the board.