intelligent power supply

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I’ve got a PC which had a communicating power supply, telling the BIOS fan speed and temperature, allowing for temperature alerts and so on.

I’ll get a new fan. The fan looks perfectly ordinary to me, just a negative and positive connector.

How does the BIOS know what the fan speed is, do I need a special fan?

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I think it counts pulses in the electrical power that is drawn from the connector, but I’m not really sure – it seems to work correctly with any standard PC fan anyway.

StuartR

Edited to add
Are you sure about “just a positive and negative connector”? Most PC fans have a little 3 pin socket that goes to three pins on the motherboard.

StuartR

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I was looking at the wrong cable, you’re right, 3 is it,

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Claude,

It’s a little “techie” but the paragraph below describes the way fan speeds are calculated in a modern motherboardBIOS.
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How is the fan speed measured? A 3-wire fan has a tach output, which usually outputs 1, 2, or 4 tach pulses per revolution, depending on the fan model. This digital tach signal is then directly applied to the tach input on the systems-monitoring device. The tach pulses are not counted, because a fan runs relatively slowly, and it would take an appreciable amount of time to accumulate a large number of tach pulses for a reliable fan speed measurement. Instead, the tach pulses are used to gate an on-chip oscillator running at 22.5 kHz through to a counter. In effect, the tach period is being measured to determine fan speed. A high count in the tach value register indicates a fan running at low speed (and vice versa). A limit register is used to detect sticking or stalled fans.
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Taken right from the basic engineering handbook.

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Thanks Bob, much appreciated.

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