On Mon, 19 Feb 2007 04:25:43 GMT, "Fpbear II" put
finger to keyboard and composed:

I have a 12V 0.8A Nidec TA450DC fan in some equipment and I need to slow the
fan down to about 75% of its speed. It has four leads: red, black, yellow,
and green. I guess that yellow is the RPM sensor and green is the high/low
voltage sensor.

I tried using a 5-ohm resistor as well as a zener diode on the red lead.
This did not work because the equipment senses something is wrong, and the
fan won't spin. To try another strategy, is there something I can place on
the green or yellow lead to trick the system into reducing the fan speed?

The datasheet (http://www.nidec.com/fanpdfs/c2003_4041.pdf) refers to
Alarm/Tachometer/Thermal Speed Control/PWM Speed Control options.

You may be lucky and have the PWM speed control option, in which case
you could control the speed with a 555 timer running at a 75% or
greater duty cycle. I don't know what the "alarm" is, but you could
find out by monitoring the voltage on the wire(s) while heating the
fan, stalling it, or varying its supply voltage. This assumes that the
relevant signal is not OC, in which case you would need a pullup
resistor.

- Franc Zabkar
--
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