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  Help me build a multi fan controller block please 
 Date Written 
Reason Jun 13, 2012, 02:49pm EDT Report Abuse
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:

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.

Ultima Ratio Regum
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john albrich Jun 13, 2012, 04:25pm EDT Report Abuse
>> 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.

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:

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:
(they may require a minimum quantity or $ order, but they sometimes deal with very small orders)

Reason Jun 13, 2012, 04:28pm EDT Report Abuse
>> 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.

Ultima Ratio Regum
john albrich Jun 13, 2012, 05:19pm EDT Report Abuse
>> Re: Help me build a multi fan controller block please

john albrich Jun 13, 2012, 06:58pm EDT Report Abuse
>> Re: Help me build a multi fan controller block please



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