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Author Topic: Combining 3-wire fans  (Read 1283 times)

Hak Foo

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Combining 3-wire fans
« on: December 26, 2004, 01:49:53 AM »

A question-possible project.

If you have several 3-wire fans, assuming you have a header which can supply the combined amperage, can you combine the RPM sensor readings?

Like if fan A spins at 3000 rpm, and fan B at 6250, the resultant readout's approximately 9250.  Useful for mobos with limited or awkwardly placed fan headers (mine has two-- one used by the CPU fan, one so far away from the rear fan area as to be inaccessible for the purpose.


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Combining 3-wire fans
« Reply #1 on: December 26, 2004, 02:05:28 AM »

i believe those two rpm wires together would confuse the fan RPM computation.  The fan sends out pulses to the mobo, which will be multiplied by a constant value, plus dividers that work a clock signal to get an approximate RPM value.  If you have two fans running at different speeds, each fan sends a differently timed pulse on the same wire.  Whatever the readout would be, i doubt it would be a good one.  Unless maybe both fans are running at ideally the same speed, like both are controlled together, then you could probably just use one RPM wire from one fan.  Also, you could just extend the RPM wire to reach the other mobo fan header.
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