Help with Powering 21 CPU fans

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  #1  
Old 03-28-15, 05:39 AM
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Help with Powering 21 CPU fans

Hi all,

I知 completely new to any kind of electrical work and would be grateful if you guys could confirm my setup to be correct.

I値l try to be as clear as I can:

I have 220V coming from my Wall Socket, so I assume I have 220V to use.

What I壇 like to do is, use the power coming from the wall socket to power 21 Computer fans that are all rated at 12 Volts each (total 252 Volts).

But I want to under power them so they run slower, therefore 220 Volts would be enough since all the fans in total can take up to 252 Volts (it leaves me with 32 Volts of head room)

I値l be soldering everything in a Parallel Circuit and will add a 12 Volt Current Limiting Resistor in Series before each fan, onto each Parallel Line (so in total I値l also have 21 resistors in the circuit). I have 12 Volt Fans, so I assumed a 12 Volt Resistor is the correct resistor for each parallel line.

Finally, between the Wall Socket and the 21 Resistors & 21 Fans, I知 going to add a Light Dimmer Switch so that I can manually control how fast & slow the fans will be running on the fly.

For Setup, I plan to attach a Plug onto one end of a 2.5mm Twin Earth Cable and then strip the other end of the cable all the way so that the wires are fully exposed into Positive & Negative, then proceed to make all the soldering connections in Parallel with the Resistors in series, followed by covering up the exposed wires with Electrical Tape when I知 finished.

Do I need to buy a specific Light Dimming Switch?
Is this setup correct?

Thanks all!
 
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  #2  
Old 03-28-15, 05:52 AM
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The volts from the fans are not additive. The amps are additive. The voltage is a constant.
 
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Old 03-28-15, 06:20 AM
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You would most likely need a regulated power supply that would supply a constant 12 volts at the additive amperage required by your fans. You didn't say what that value was. Any connections you make will need to be inside covered junction boxes, possibly mounted on a jig board. The regulated power supply will take the place of the voluminous number of resistors you are planning.
 
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Old 03-28-15, 06:29 AM
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You were probably under the impression that you could put the fans in series. With those types of fans that won't work. As was mentioned you'll need to get a 12v power supply. If you look around you can find 12v supplies that are adjustable if you wanted to slow the fans down.

If you need a direction to look... let us know.
 
  #5  
Old 03-28-15, 06:36 AM
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I think you would be better off using an off-the-shelf 12v power supply. You can build your own, but it's typically cheaper to just buy one.

Something like this:
http://www.amazon.com/12-Volt-Power-.../dp/B00B8TRF0A
(just an example, most electrical places will sell similar ones)

It provides 10A at 12v, which is 120w. Using 5w fans, it should be able to handle 21 of them, though if they are going to be used full-time, you may want to oversize the power supply a bit as it will run a bit hot.

They would be simply wired in parallel.
 
  #6  
Old 03-28-15, 09:27 AM
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Thanks for the replies guys,

The amps on each Fan is: 0.30 A
So all 21 amps together would be a total of 6.3A, so a 10 amp Power Supply would be enough?

Could I buy the 12 Volt 10amp adapter as you suggested and then place a light dimming switch before the parallel connections? Would any Light Dimming Switch do? I could use the Light Dimming switch to control the fan speed. Is this correct? So it would be:

12V/10amp Adapter > Light Dimming Switch > Parallel Connections to all 21 Fans


Thank you.
 
  #7  
Old 03-28-15, 09:30 AM
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could I buy this 12 Volt 10amp adapter
I don't see any link.

No... you can't reduce the AC into the power supply as it will no longer be able to regulate itself.

You might want to consider.....
parts-express/12v-dc-29a-regulated-switching-power-supply
 
  #8  
Old 03-28-15, 09:33 AM
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Hi, sorry, I've updated my reply. I meant the amazon link.
 
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Old 03-28-15, 09:38 AM
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Oh OK, I undestand, so no Light Dimming Switch after the Adapter, what about placing the Light Dimming switch before the adapter? Would this work?
 
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Old 03-28-15, 09:49 AM
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If you were to use that power supply at amazon..... you'd use it with this.....
amazon/DROK-Controller-Regulator-Switching-Modulator/

Basically a 12vdc 10amp in and 0-12vdc 10amp out. A DC dimmer.
 
  #11  
Old 03-28-15, 09:50 AM
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Just got another question:

I took the end of the 12v 10A DC Power Adapter and put it into a 30Amp Connector Block, then curled the 21 fans wires together and placed it on the other end of the Connector Block, would this count as a Parallel Connection?

I'd use 1 connector block for the Positive Cable and another connector block for the Negative Cable.
 
  #12  
Old 03-28-15, 09:54 AM
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OK, I got it, I just need to place the DC Dimmer in between the Power Supply & the 21 Fans.

- - - - - - - - - -

Thanks for that link, would I need to use just 1 of the DROKョ DC after the Power Supply? or would there need to be a separate DROKョ DC for each parallel line?
 

Last edited by Electronic1982; 03-28-15 at 10:14 AM.
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