Subject: Temp controlled fan
By: keith (IP: 222.152.194.*)
Written on: 28-11-2007 01:23

The temperature / fan controller article mentions the higher startup speed due to the fan not starting at low voltage.
A cure for this is to fit a fixed resistor between the source and drain of the FET. The value of the resistance will depend in the fan, but should be just sufficient to make the fan run continuously.

A capacitor across the NTC would help the startup of the fan by temporarily turning on the FET while it charges up at switch on. I have not calculated the capacitance value, but it should not be an electrolytic type.
Having the fan running continuously (but quietly) has the advantage that there is some cooling all the time and the fan will not be starting and stopping which can be annoying.

I must admit, I love the simplicity of Mr Steinbrecher’s circuit, but with only two more components we have the deluxe version.

Best regards,
Keith Browning

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