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Old 17th July, 2008, 10:45 AM
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Wiring in series to drop voltage?

I am using 5v fans on a chipset and want to still use the MB 3pin header. I tested it and I think I'm right. I took 2 fans that i know won't spin on less than 12v (mean ass 60mm Mitsubishi fans out of Sun Spark V PSUs), I wired them in series, and they didn't spin.

So am I right that they are both at 6v wired that way?
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Old 17th July, 2008, 12:47 PM
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Odd things happen when you wire fans like that if they don't both run at the same speed all the time. The resistance of a fan is dependant on the speed it's rotating at. Generally, if you stall a fan, it'll have it's lowest resistance.

Thus, if one fan is turning ok, and the other stalls, then the one that's turning will be subject to a much higher voltage.
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Old 17th July, 2008, 01:24 PM
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So, the fans I was planning to do this with, being dissimilar, would not split the voltage evenly, but rather, stall the slower one and keep the faster at 12v screaming away like a dremel? It would fit with what happened with the two matching fans. Neither could spin with the voltage they had, both stalled. Had i wired two fans that could both operate at 6v, the slower fan would have stopped?
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Old 17th July, 2008, 01:29 PM
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Funny observation when messing with 5v fans: A 40mm 5v fan actually creates enough thrust to hang from it's wires at a 30 degree angle and fly in circles at 12v.
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Old 17th July, 2008, 02:58 PM
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Yeah, careful of your fingers though

Dissimilar fans wouldn't work well in series with each other. The two fans you tried were both 12v devices, so really needed 12v to get them running. If you had two fans that would run at a lower voltage, you might have found the that one that started first got itself spinning to the detriment of the other fan. That very much depends on various parameters for the fan though.

One alternative would be to provide a voltage regulator (like a 7805 device) to drop the voltage to 5v. It might get a little warm though, regulating the power, depending on the fans you have.
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Old 18th July, 2008, 08:25 PM
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Flying fans, must spice up a dull afternoon?
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Old 31st July, 2008, 11:07 AM
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You could use a resistor or two and wire them in parallel?
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Old 31st July, 2008, 01:22 PM
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I just skipped the mobo connector and powered them off a single power connector. the 30mm fan on the 5v, and the 40mm on the 12v. While I was at it I made 8 ram sinks for the video card and 6 mosfet sinks for the mobo. by cutting up a large heatsink. This machine needs to be quiet, so I'm trying to heatsink everything that I can. It's only going to have one intake fan, with passive exhaust through the I/O shield, which is going to be aluminum gutter guard.
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Last edited by Azriel; 31st July, 2008 at 01:30 PM.
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Old 31st July, 2008, 09:05 PM
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Custom cut I/O shield. Genuine mod!
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