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Motherboard fan header boost circuit

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dangar:
Hallo to all ,

I was wondering if anyone have built a circuit that allows you to add more than one fans on a single fan header , exceeding the permittable motherboard capacity . I can understand that this may be built with transistors or mosfets wired in series with the fan header  , but how exactly?

kam:
As you said, adding more than 1 fan may exceed the mb/s capacity. Moreover, any functionality that this header would have-such as to measure the RPM- will not work. So, why don't you add the fan directly to the PSU 12v? You can add as much as you want there.

dangar:
The idea is to control the fans according to system temps , not  only to power them. I believe using the motherbord header is the only way to do it. As for the tacho signal , I will connect only one fan rpm wire to the header , as the fans will all be the same.

kam:
o i see. one more question: you have 4 wire fans or 3 wire fans?

dangar:
Three wire fans . I have tried in the past with 4wire fans and  managed to control 3 fans with a LM358 based circuit , but never with 3wire.

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