Slowing down a fan

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Hi
I have posted previously about a modified PC case that my nephew is
currently building. It incorporates a 12V car radiator fan into the base.

We have got it running off an old PC power supply, but as was previously
mentioned, it is quite loud and a bit too powerful.
Now we need to be able to slow it down a bit. The specs on the fan say it
runs on 12V and max current is around 11A (11.2A I think?)

How is the best way to do this? I thought about a resistor, but would it
have to be a huge one to take the 11A current? What size resisters would I
need? What would be the best way to do this? I tried doing the 7v trick by
running it between the 12v & 5v lines but the power supply just shuts
down.The fan itself won't be running all the time. It will just be switched
on when extra cooling is required.

Any help would be much appreciated.
Grenge



Re: Slowing down a fan


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Have you tried running it from 5V only, or is that not sufficient?


Re: Slowing down a fan


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If you are determined to continue with this overkill, find out what current
the fan draws at say 9v and provide a suitable supply. There are many other
fans available that will move the air for much less current and less noise.

--

Cheers ......... Rheilly P

Where theres a will, I want to be in it.



Re: Slowing down a fan



Grenge wrote:
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There's a DC motor speed controller kit that was done by Silicon Chip
magazine that will do the job for you. I think DSE and Jaycar sell it,
so all you need to do is build it and put it between your fan and the
12v power supply.


Re: Slowing down a fan


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   PWM DC speed controller.
  
   maybe something like this.

          in914 x2                                 +12
                                                    |                      
  +-------->|--+----------------------+      1n4001 |                      
  |            |                      |             |              
  +--[10K]-|<--+   +--------+---------|---+---+-|<--+------.
       ^           |        |         |   |   |            |
       |           | . . . .|. . . .  |   |   |+           |
       |           | .   VCC(8)    .  |   |  === 220uF     |
       |           | .             .  |   |   |            +-----.
       |           +--RES(4) OUT(3)---+  ===  | 100nF      |     |
       |             .    555      .  |   |   |           FAN    |
       +---------+----TH(6)   DIS(7)- |   +---+            |     |
                 |   .             .  |   |                +-->|-'
                 +----TR(2)   CV(5)-- |   |                |  
                 |   .             .  |   |            ||--+.                  
            10nF===  .   GND(1)    .  |   |            ||<-.^ IRF540N
                 |   . . . .|. . . .  `---|------------'|--+'              
                 |          |             |                |
                 |          |             |                |            
                 `----------+-------------+----------------'  

Bye.
   Jasen

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What sort of fly trail is that???



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A shcematic one

Re: Slowing down a fan




two bob wrote:
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A shcematic one


****Looks like a fly flew through your flue,it certainly is NOT a SCHEMATIC.

Brian Goldsmith.


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near enough to be readable as one though ... in the trade I am in a
mudmap...

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near enough to be readable as one though ... in the trade I am in a
mudmap...


**** And obviously thick enough not to see the reference to your
"shcematic".



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Or not caring

  as a personal foible I often refer to mud maps as such
  now just to remind you when all else fails a spelling comment proves
you as an ass and certainly won't win any discussion.. on the net at least.

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For the people too stupid to spend 10 seconds cutting and pastings into
a text editor with a fixed font size I've done the hard work for you:

http://satin.sensation.net.au/rowan/fanschematic.gif


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I have no problems reading it :)

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Somewhere back in history in tech, that schematic would be a "FAIL" mark. I
had a boss who used to "create" things like that, and wondered why no one
could get their job done.

Pablo Piccaso, watch out!




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If it's not looking a bit like a schematic try setting your news reader to
use a fixed pitch font (like courier) or pasting the above into notepad.
You'll have to guess where the earth connection goes as I left that bit off.

--

Bye.
   Jasen

Re: Slowing down a fan



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Get a smaller Fan....

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It would not be drawing 11Amp by the time you had a resistor in series....

11A at 12V gives 1.1 Ohm - so a 2 Ohm resistor in series would dissipate
around :

12/3.2 = 3.75A

3.75^2 x 2 = 30W - you would get away with 2 x 1 Ohm 10 Watt resistors in
series and place them in the airflow from the Fan which should keep them
cool enough (You may even get away with a single 10Watt 2.2 Ohm resistor if
it is fan cooled).

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Go down to your nearest Jaycar and buy a number of different value 10 Watt
Resistors and see what speed/Noise you get from the fan with different
Resistors in series - be daring Experiment a little - a 10 Watt Resistor
will actually handle 20-30 Watts for a few Hours - or if fan cooled
indefinately.

Bear in mind though that a Radiator Fan may not be the quietest Fan
available.

Regards
Richard Freeman




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