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How to Undervolt a Fan Inside a Small Device?



 
 
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  #21  
Old March 17th 05, 05:28 PM
kony
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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.
  #22  
Old March 17th 05, 06:28 PM
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That looks fine. Very good. Now you just need to learn to snip
the useless portions that are not germane to the reply. In this
case it would be all the lines preceded by * above.


OK, I will reply through the Show-Options button from now on.

I am still wondering what happened to my previous reply that doesn't
show up.

Jay Chan

  #23  
Old March 17th 05, 06:36 PM
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Thanks for the correction that you and Noozer have pointed out. I got
it backward. The higher ohm rating should mean higher resistance and
the fan will run slower and supposedly quieter.

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.


Seem like this is one more reason to get a range of resistors instead
of just one. Talking about getting a range of resistors. I cannot find
any suitable resistors from RadioShack. Their selection in term of watt
is very limited (1/2, 1, 5, 10 watts). I will have to order online and
pay shipping. Oh well...

Jay Chan

  #26  
Old March 18th 05, 02:39 PM
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If you're going to order, might as well get a 100 ohm potentiometer,
and
adjust for the noise/cooling of your liking. Let it go full speed

when
you are out of the room, and much slower when you are around it.


Too late for that, I have already ordered an assorted number of
resistors from eBay. And I don't understand potentionmeter enough to
know what to do with it. Thanks anyway. I hope someone else who reads
this message may find this useful in keeping the noise of his PC down.

I was quite surprised that I could only find one place (eBay) that has
more than one type of 2-watt resistors that are in the range that I am
looking for. Many places don't sell 2-watt any resistor. Those place
that sell 2-watt resistors only sell 2-watt resistors in one ohm rating
(but I need resistors in a range of ohm ratings).

Jay Chan

  #27  
Old March 18th 05, 02:43 PM
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I didn't see any on Radio Shack's website, maybe I
overlooked them but I dug up another source, might as well
get a good deal on 'em?


http://www.goldmine-elec-products.co...m=2&mite m=11

Yesterday, I browsed around to look for 2-watt resistors, and I was
surpised that I could only find one vendor (in eBay) that offered
resistors in a range of ohm ratings. Most places don't sell any 2-watt
resistors. Now, I _really_ appreciate the fact that you had spent the
time in digging up a link for 2-watt resistors. That had to be quite
hard.

Jay Chan

  #28  
Old March 18th 05, 04:48 PM
kony
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On 18 Mar 2005 05:39:46 -0800, wrote:

If you're going to order, might as well get a 100 ohm potentiometer,

and
adjust for the noise/cooling of your liking. Let it go full speed

when
you are out of the room, and much slower when you are around it.


Too late for that, I have already ordered an assorted number of
resistors from eBay. And I don't understand potentionmeter enough to
know what to do with it. Thanks anyway. I hope someone else who reads
this message may find this useful in keeping the noise of his PC down.

I was quite surprised that I could only find one place (eBay) that has
more than one type of 2-watt resistors that are in the range that I am
looking for. Many places don't sell 2-watt any resistor. Those place
that sell 2-watt resistors only sell 2-watt resistors in one ohm rating
(but I need resistors in a range of ohm ratings).

Jay Chan


Generally the parts would be found at electronics supply
houses, online at places like Digikey, Mouser, Newark,
Allied Electronics, to name a few. The link I previously
gave for the 200 pieces was just one of myriad hit-or-miss
surplus type companies that don't always have what you need,
but when they do it's often cheaper. Main problem with many
suppliers is minimum order requirements like $25. Digikey
comes to mind as one that doesn't have the minimum order
requirement.

Previously a 100 Ohm POT had been mentioned. POTs generally
do not have sufficient current capability for a fan, or
rather, when they do they're called rheostats rather than
POTs. A POT would be better for fine-tuning something like
a LM317 based fan control, but then probably not 100 Ohm
range. More elaborate fan controllers have their place with
those desiring more frequent changing of speed but higher
cost, time to construct, size, etc, make them less viable
for this kind of simple mod.
  #29  
Old March 18th 05, 04:51 PM
kony
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On 18 Mar 2005 05:43:57 -0800, wrote:

I didn't see any on Radio Shack's website, maybe I
overlooked them but I dug up another source, might as well
get a good deal on 'em?


http://www.goldmine-elec-products.co...m=2&mite m=11

Yesterday, I browsed around to look for 2-watt resistors, and I was
surpised that I could only find one vendor (in eBay) that offered
resistors in a range of ohm ratings. Most places don't sell any 2-watt
resistors. Now, I _really_ appreciate the fact that you had spent the
time in digging up a link for 2-watt resistors. That had to be quite
hard.

Jay Chan



Well I've bought stuff from them before... plus I've heard
of others calling, asking them to send very small items in
an envelope for cheapest shipping/total-cost. In another
post I listed a few more full-featured electronics companies
with online stores... generally such parts would come from
electronics-oriented companies rather than computer focused.
  #30  
Old March 18th 05, 06:15 PM
kony
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On Fri, 18 Mar 2005 15:48:57 GMT, kony
wrote:

snip

Main problem with many
suppliers is minimum order requirements like $25. Digikey
comes to mind as one that doesn't have the minimum order
requirement.


Correction- Digikey does have a $25 small order fee ($5),
I was thinking of Mouser, https://www.mouser.com.
 




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