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  Help me build a multi fan controller block please 
 
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Reason   Jun 13, 2012, 02:49pm EDT Reply - Quote - Report Abuse
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Goal: to have a single switch that will control up to 7 120mm LED fans, Off/Low/High.

I don't need a rheostat, I just want them either off, quiet, or performance, and I don't see the need for individual switches if I can avoid it.

The fans I have coming from Amazon have three pin connectors, so it makes sense to me to build a block that would have a set of those, powered by a 4pin Molex. I would mount this block somewhere convenient and then wire the switch to it.

I can get the TPX3s from Frozen CPU:
http://www.frozencpu.com/products/1841/ele-192/FrozenCPU_3-pin...44c155s641

The switch and wiring should be easily available, and I can find or scavenge a Molex.

Here are my questions:
1. What should I use for the "block?" A PCI slot mount would be relatively convenient, and I won't have an extra 5.25 bay,* although I might have an internal 3.5 I could use. So it would have to fit in one of those areas.
2. How do I calculate the power requirements for the switch? If I'm running the current for 7 or 8 fans through it, I want headroom for safety.
3. I've also seen something about not running components at 7V as it's bad for the PSU. Can anyone elaborate?

*I have two optical drives and intend to use the third bay for a card reader. I think if I get a 3.5" reader with a 5.25" adapter, I could fit the switch into the adapter.


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john albrich Jun 13, 2012, 04:25pm EDT Reply - Quote - Report Abuse
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Edited: Jun 13, 2012, 05:45pm EDT

 
>> Re: Help me build a multi fan controller block please
.
For something like that, I'd use Silicon diodes to create the voltage drop for the fans.
Something like the 1N4001 (1Amp), 1N5400 (3Amp), or 6A05 (6Amp) types.
http://en.wikipedia.org/wiki/1N4001

Power-wise, all you have to do is make sure you select diodes that can handle the total current for the X number of fans. For example, 7 x 0.3amp = 2.1amp, would mean 3A or 4A diodes would work fine. Or you could simply use separate multiple 1A diodes for each fan. Using diodes reduces issues with using bulkier resistors that also create more heat (that would also have to be removed from the case).

For a given fan, each diode provides ~0.7V voltage drop. So if you wanted to power a fan with ~8V you'd use 12V-(Xdiodes*0.7V)=8V, therefore X=6 diodes. Note that different model types of fans run at different RPMs at 8V, so you'd have to experiment to find out what voltage drop you need the diodes to provide for a given fan model. E.G. a given Typhoon "xyz" fan might run at 800RPM at 8V, whereas a Zalman "abc" fan might run at 1200RPM with the same 8V, and likely move a different volume of air.

My post at this link provides details:
http://www.hardwareanalysis.com/content/topic/77363/#589826


edit:
clarified to use Silicon diodes and post link re: typical low power diode info
These diodes might still be found at Radio Shack (probably higher priced than needed), and are available from suppliers like these for less than $0.10 each:
http://www.digikey.com/product-detail/en/1N4001/1N4001FSTR-ND/976982
http://www.mouser.com/Search/Refine.aspx?Keyword=1n4001
(they may require a minimum quantity or $ order, but they sometimes deal with very small orders)

Reason   Jun 13, 2012, 04:28pm EDT Reply - Quote - Report Abuse
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>> Re: Help me build a multi fan controller block please
Awesome, thanks for the pointers, John.

Without researching the information in your older post any further, an idea popped into my head. LEDs are diodes: could I use them as double duty to create light and to drop the voltage? They'd only be on when the fans were running at the lower voltage, but it might be a fun way to kill two birds with one stone.

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john albrich Jun 13, 2012, 05:19pm EDT Reply - Quote - Report Abuse
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>> Re: Help me build a multi fan controller block please
Reason   said:
Awesome, thanks for the pointers, John.

Without researching the information in your older post any further, an idea popped into my head. LEDs are diodes: could I use them as double duty to create light and to drop the voltage? They'd only be on when the fans were running at the lower voltage, but it might be a fun way to kill two birds with one stone.


Short answer is no. The main problem is that LEDs can't handle much current at all...a fraction of the current required by a typical fan.

Also, the voltage drop is different for LEDs, and the voltage drop also varies by what color the LED is. While one could compensate for the varying voltage drops, the current is still the limiting factor. See here for more details.
http://www.oksolar.com/led/led_color_chart.htm

john albrich Jun 13, 2012, 06:58pm EDT Reply - Quote - Report Abuse
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>> Re: Help me build a multi fan controller block please
Reason   said:
3. I've also seen something about not running components at 7V as it's bad for the PSU. Can anyone elaborate?


I ASSUME that they're talking about powering a fan by connecting the (+)red lead to +12VDC and the (-)black lead to +5VDC to use the differential of 7VDC.

I wouldn't say it's "bad" for the PSU itself, but on the more sophisticated PSUs I could see that it could lead to some issues on some PSUs. It depends very much on exactly how they designed their PSU, and I've not looked at the nitty-gritty designs of more recent PSUs.

Personally, I've never read or heard of anyone having an PSU issue doing this with a typical low-power type of 12VDC brushless DC case fan (e.g. a few hundred milli-amps). That's not to say no one has ever had a problem doing this. Important note: in all cases of which I'm aware the +12 and +5 were tapped from a single 4-pin Molex HDD power connector in which both voltages shared a common ground. Tapping the +12 or +5 power from somewhere else might produce entirely different results.

As an added observation, I've had a few fans that would not start spinning at that "7V" level.


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