On 17 Mar 2005 06:35:54 -0800, wrote:

... For example the Zalman resistor Mike
linked wasn't a great picture but appears to be striped:
Green, Blue, Black, Gold, which is a 56 Ohm 5% tolerance
resistor.
Generally speaking, the faster the fan is at default (12V),
the lower the value of the resistor to use to reduce it's
speed. This initially seems contrary to reason but is due
to the lower resistance of the fan's windings & circuit. I
expect 68 ohms to not be a large enough value but I do not
have any of that particular model of fan to experiment with.

If I understand this correctly, you are say these:

- We could have gone down to 56 ohm for maximum reduction of fan speed
and (hopefully) noise. But we may run the risk of the fan fails to
start spinning.

No, it varies based on what fan is used. Per the same fan,
the higher resistance would reduce speed more and have
higher chance of failure to spin up. Per a different fan
that starts out (with no resistor) having higher RPM,
current, a lower valued resistor would be used than for the
(unmodified) slower fan.



- In order to reduce the chance of fan failure to start spinning while
still cutting down noise, we may want to choose a 68 ohm resistor
instread of a 56 ohm version.

This makes sense to me. Thanks.

No, the chance of fan failure (to spin up) would be higher
with 68 Ohm, BUT as I mentioned previously, the value
(range) applicable to a particular fan is different than for
a (different) fan. It cannot be assumed that 68 or 56 Ohm
will have same result with one fan as another. For your fan
the threshold might be much higher, like around 160 Ohm. I
cannot predict this as I don't have your fan. Similar (but
only slightly faster) fans I've had can use over 120 Ohm,
but there was not much point beyond 120 Ohm as the fan was
already inaudible.

I presume Zalman chose the 56 Ohm value because the most
typical, common fan has amperage spec around .2A, rather
than your .05A (IIRC you wrote .6W ?). The majority of
people seeking fan noise reduction started out with a much
louder fan that "usually, typically" needs a lower resistor
value than you should, but again I don't have that specific
model of fan so I can only speculate based on experience
with other fans.