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?

I discovered that when I cut the green wire, the fan is blowing even faster.
This may provide some clue but I'm not sure how to -lower- the speed.

"Fpbear II" wrote in
. net:

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 usual way to slow down a DC fan is to drop the voltage below 12v
until you get the speed you want. But it sounds like you've tried that
and it didn't work. What kind of equipment is it hooked up to?

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
--
Please remove one 'i' from my address when replying by email.

Thanks Franc. I just discovered, I was able to use the resistor method on
the positive wire -after- I cut the green wire. I had to disable the
thermosister before it would accept the resistor.

Fpbear II wrote:
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?




Pick up one of the little speed control boxes made for computers. They
plug in series with the fan and use PWM to control the speed. Any place
that sells parts for high performance PCs will have them.

On Tue, 20 Feb 2007 07:51:17 GMT, James Sweet
put finger to keyboard and composed:

Fpbear II wrote:
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?




Pick up one of the little speed control boxes made for computers. They
plug in series with the fan and use PWM to control the speed. Any place
that sells parts for high performance PCs will have them.

Brushless DC fans use Hall effect sensors for electronic commutation.
If you must chop the supply to these types of motors, then you should
ensure that the PWM frequency is much lower than the fan's rotational
frequency, otherwise the speed control logic will be disturbed.

This old post illustrates the strange things that happen when external
PWM control is applied to a PC CPU fan that has its own internal speed
control:

http://tinyurl.com/2y9eqk

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

On Wed, 21 Feb 2007 07:47:39 +1100, Franc Zabkar wrote:

Brushless DC fans use Hall effect sensors for electronic commutation.
If you must chop the supply to these types of motors, then you should
ensure that the PWM frequency is much lower than the fan's rotational
frequency, otherwise the speed control logic will be disturbed.


Not any of the fans I've ever come across. They usually use a chip to
generate AC out of the DC supply and drive an AC motor.

On Tue, 20 Feb 2007 21:01:49 GMT, AZ Nomad
put finger to keyboard and composed:

On Wed, 21 Feb 2007 07:47:39 +1100, Franc Zabkar wrote:

Brushless DC fans use Hall effect sensors for electronic commutation.
If you must chop the supply to these types of motors, then you should
ensure that the PWM frequency is much lower than the fan's rotational
frequency, otherwise the speed control logic will be disturbed.


Not any of the fans I've ever come across. They usually use a chip to
generate AC out of the DC supply and drive an AC motor.

According to the following article, a BLDC motor is essentially an AC
motor.

http://en.wikipedia.org/wiki/Brushless_DC_motor

"BLDC motors have come to dominate many applications: Consumer devices
such as computer hard drives, CD/DVD players, and PC cooling fans use
BLDC motors almost exclusively."

"A brushless DC motor (BLDC) is an AC synchronous electric motor that
from a modeling perspective looks very similar to a DC motor.
Sometimes the difference is explained as an electronically-controlled
commutation system, instead of a mechanical commutation system,
although this is misleading, as physically the two motors are
completely different."

"Because the controller must direct the rotor rotation, the controller
needs some means of determining the rotor's orientation/position
(relative to the stator coils.) Some designs use Hall effect sensors
or a rotary encoder to directly measure the rotor's position. Others
measure the back EMF in the undriven coils to infer the rotor
position, eliminating the need for separate Hall effect sensors..."

"Although BLDC motors are practically identical to permanent magnet AC
motors, the controller implementation is what makes them DC. While AC
motors feed sinusoidal current simultaneously to each of the legs,
(with an equal phase distribution), DC controllers only approximate
this by feeding full positive and negative power to two of the legs at
a time."

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.