How to Undervolt a Fan Inside a Small Device?

I would like to know the way to reduce the speed of a fan inside a
small device in order to cut down the noise from the fan. If I
understand this correctly, I am supposed to do this by undervolting the
fan from 12-volt it is now to something like 6-volt using some kind of
"inline resistor" or someting. I can soldering wires together. But I
really don't know much about resistor and such. I am hoping someone can
give me the "exact" information about the way to do this.

The small device is a LinkSys gigabit switch that has a very noisy 40mm
fan in it. I have replaced it with a slightly quieter Papst 60mm fan.
My intention is to oversize the fan and then reduce the fan speed; then
I will be able to maintain the same air flow as the 40mm fan but with
less noise. Now, I have the oversized fan mounted inside the gigabit
switch. And I can feel that its air flow is definitely stronger than
the 40mm fan. This means I can go ahead to reduce its speed without
worrying about the possibility of not getting enough air flow. I need
to figure out how to reduce its speed.

My questions a

- I am under the impression that I should use something
called an "inline resistor". Is it the right product?

- Because the gigabit switch has very limit space
inside, the "inline resistor" must be small enough
to fit inside. Will it be small enough?

- The fan is rated as 12V and 0.6 watt with two wires.
What type of "inline resistor" should I use? I am
under the impression that inline resistor is rated
by "ohms". Can someone give me a RadioShack
product-number or something like that?

- Which wire should I solder the inline resistor to the
fan? Red-wire or the blue-wire of the fan?

- Does this matter which way I orient the inline resistor?

Thanks in advance for any information.

Jay Chan

wrote:

I would like to know the way to reduce the speed of a fan inside a
small device in order to cut down the noise from the fan. If I
understand this correctly, I am supposed to do this by undervolting
the fan from 12-volt it is now to something like 6-volt using some
kind of "inline resistor" or someting. I can soldering wires
together. But I really don't know much about resistor and such. I
am hoping someone can give me the "exact" information about the
way to do this.

.... snip ...

- The fan is rated as 12V and 0.6 watt with two wires.
What type of "inline resistor" should I use? I am
under the impression that inline resistor is rated
by "ohms". Can someone give me a RadioShack
product-number or something like that?

- Which wire should I solder the inline resistor to the
fan? Red-wire or the blue-wire of the fan?

- Does this matter which way I orient the inline resistor?

Well, at least you know you don't know anything about electricity.
If the figures you give are accurate (which they aren't, they are
probably maximums) you want about the same ohmage as what the fan
appears to be. This would be about 12 v. / 0.05 A = 240 ohms. All
that really does is give you a ball park number. You may want
anything from about 100 ohms to that. They should probably be at
least 2 watt rated for safety, but have virtually no tolerance
requirements. Get a set of 2 watt carbon resistors, worth about 5
to 10 cents each (but expect to pay more unless you can raid
someones junk box), say 100, 150, 220, 330 ohms and try them out.
No, it doesn't matter which lead they appear in, nor which
direction they are connected in. Ohms and watts are an adequate
specification, and you don't need anything better than 10 or 20%
tolerance.

To try them out you don't need to solder anything. Clip leads with
alligator clips on the ends will be useful. Feel the resistor
while running with it - it should not be too hot to touch. If so,
it is a sign you need a higher wattage. But I expect 2 watts will
be more than adequate.

--
"If you want to post a followup via groups.google.com, don't use
the broken "Reply" link at the bottom of the article. Click on
"show options" at the top of the article, then click on the
"Reply" at the bottom of the article headers." - Keith Thompson

snip

Well, at least you know you don't know anything about electricity.
If the figures you give are accurate (which they aren't, they are
probably maximums) you want about the same ohmage as what the fan
appears to be. This would be about 12 v. / 0.05 A = 240 ohms. All
that really does is give you a ball park number. You may want
anything from about 100 ohms to that. They should probably be at
least 2 watt rated for safety, but have virtually no tolerance
requirements. Get a set of 2 watt carbon resistors, worth about 5
to 10 cents each (but expect to pay more unless you can raid
someones junk box), say 100, 150, 220, 330 ohms and try them out.
No, it doesn't matter which lead they appear in, nor which
direction they are connected in. Ohms and watts are an adequate
specification, and you don't need anything better than 10 or 20%
tolerance.

Just wondering... When trying to slow a fan in a PC, which is better - using
5v and 12v to get 7v to the fan, or adding a resistor inline?

I've got a Media PC that's very quiet except for one case fan.

Thx

On Wed, 16 Mar 2005 16:15:30 GMT, "Noozer"
wrote:



Just wondering... When trying to slow a fan in a PC, which is better - using
5v and 12v to get 7v to the fan, or adding a resistor inline?

The resistor, assuming a reliable connection is made
(soldered or good crimp, not just twisted bare wires) and
electrically isolated (like heatshrink or similar, as
electrical tape can degrade and unravel especially in hotter
environments).

In practice, either has worked fine for most people trying
(either). The resistor is certainly a higher level of
control, being able to choose some other voltage... 7V is
too slow for some applications and 5V too low for some fans
to even reliably spin-up. With today's larger 92-120mm fans
becoming more common, in some cases running the fan from 5V
(5V rail & ground) could be a good alternative instead.


I've got a Media PC that's very quiet except for one case fan.

Only issue there is being aware of the resultant temp
changes that come from flow reduction.

"kony" wrote in message
...
On Wed, 16 Mar 2005 16:15:30 GMT, "Noozer"
wrote:

Just wondering... When trying to slow a fan in a PC, which is better -
using
5v and 12v to get 7v to the fan, or adding a resistor inline?

The resistor, assuming a reliable connection is made
(soldered or good crimp, not just twisted bare wires) and
electrically isolated (like heatshrink or similar, as
electrical tape can degrade and unravel especially in hotter
environments).

Thanks. I felt that the resistor was better, but I wasn't sure if there was
anything about it that I had overlooked.

I've got a Media PC that's very quiet except for one case fan.

Only issue there is being aware of the resultant temp
changes that come from flow reduction.

Machine runs cool. I'd just disconnect the fan completely, but I think that
would be a bit drastic as the chassis isn't the best design.

Noozer wrote:

snip

Well, at least you know you don't know anything about electricity.
If the figures you give are accurate (which they aren't, they are
probably maximums) you want about the same ohmage as what the fan
appears to be. This would be about 12 v. / 0.05 A = 240 ohms. All
that really does is give you a ball park number. You may want
anything from about 100 ohms to that. They should probably be at
least 2 watt rated for safety, but have virtually no tolerance
requirements. Get a set of 2 watt carbon resistors, worth about
5 to 10 cents each (but expect to pay more unless you can raid
someones junk box), say 100, 150, 220, 330 ohms and try them out.
No, it doesn't matter which lead they appear in, nor which
direction they are connected in. Ohms and watts are an adequate
specification, and you don't need anything better than 10 or 20%
tolerance.

Just wondering... When trying to slow a fan in a PC, which is better
- using 5v and 12v to get 7v to the fan, or adding a resistor inline?

I've got a Media PC that's very quiet except for one case fan.

You can only use the 12-5=7 trick when the 5 V line has enough load
on it to sink the 7 V current. That will usually be so. However,
that also gives you only one possible operation point, while the
resistor allows you to select what you want, at the cost of a watt
or two.

Please try to get in the habit of preserving attributions for
material you quote.

--
"If you want to post a followup via groups.google.com, don't use
the broken "Reply" link at the bottom of the article. Click on
"show options" at the top of the article, then click on the
"Reply" at the bottom of the article headers." - Keith Thompson

Thanks for specifying the range of inline resistors that I can try.
This is especially useful if I need to mail order them. Then, I can
order a range of inline resistors instead of just one type. Otherwise,
the shipping cost will kill me if I need to order various types
multiple times.

Anyway, I will look for them in the local RadioShack first. If not, I
may have to mail order them.

Jay Chan

On 15 Mar 2005 20:18:20 -0800, wrote:

I would like to know the way to reduce the speed of a fan inside a
small device in order to cut down the noise from the fan. If I
understand this correctly, I am supposed to do this by undervolting the
fan from 12-volt .....

The small device is a LinkSys gigabit switch that has a very noisy 40mm
fan in it. I have replaced it with a slightly quieter Papst 60mm fan.
My intention is to oversize the fan and then reduce the fan speed; then
I will be able to maintain the same air flow as the 40mm fan but with
less noise. Now, I have the oversized fan mounted inside the gigabit
switch. And I can feel that its air flow is definitely stronger than
the 40mm fan. This means I can go ahead to reduce its speed without
worrying about the possibility of not getting enough air flow. I need
to figure out how to reduce its speed.

My questions a

- The fan is rated as 12V and 0.6 watt with two wires.

Thanks in advance for any information.

there should be also a +5 V somewhere inside the case available!
Find it & tray that instead of 12V ...
--
˛˛ ˛˛ Regards , SPAJKY ®
\\.//_. mail addr. @ my site @ http://www.spajky.vze.com
\°/ ".. long live & prosper.." - 3rd Anniversary running it:
|| "Tualatin OC-ed / BX-Slot1 / inaudible setup!"

I only see one single two-pins connection on the circuit board of that
small gigabit switch. This means this option is not available.

Moreover, I believe 5-volt may be too low, and the fan "may" have a
problem to start spinning according to what I read in other newsgroup
about undervolting a fan to keep a PC quiet.

Jay Chan

wrote:

I only see one single two-pins connection on the circuit board of
that small gigabit switch. This means this option is not available.

Moreover, I believe 5-volt may be too low, and the fan "may" have a
problem to start spinning according to what I read in other
newsgroup about undervolting a fan to keep a PC quiet.

Without quotes and attributions your messages make no sense. See
my sig below for a means of sane use of google.

--
"If you want to post a followup via groups.google.com, don't use
the broken "Reply" link at the bottom of the article. Click on
"show options" at the top of the article, then click on the
"Reply" at the bottom of the article headers." - Keith Thompson