A computer components & hardware forum. HardwareBanter

If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below.

Go Back   Home » HardwareBanter forum » General Hardware & Peripherals » General
Site Map Home Register Authors List Search Today's Posts Mark Forums Read Web Partners

How to Undervolt a Fan Inside a Small Device?



 
 
Thread Tools Display Modes
  #32  
Old March 19th 05, 09:01 AM
kony
external usenet poster
 
Posts: n/a
Default

On Fri, 18 Mar 2005 21:49:53 -0800, ric
wrote:

wrote:

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).


Why 2-watt? Even at a 5 volt drop, current would have to be 0.4a to
equal 2 watts. At 7v (a 5 volt drop), most 12v fans draw in the 0.05-0.1a
range. I've used 1w carbon resistors (much smaller) and they hardly get
warm.



True, either 1 or 2W could work for this specific
application, but the 2W seems potentially less problematic.
At the time I didn't realize OP would have problems finding
them or go to ebay for these.

Why not 2W? Typically one does not try to match up watt per
watt on power resistors, rather using what the space and
budget allow, overengineering them. It's not a PCB space
issue and cost is maybe a few cents, or maybe even cheaper
per piece since this is spot-pricing on items not often
(percentagewise) sold 1 at a time. Yes, 1W would usually
work, but IMO, 2W is as good or better choice if someone has
nothing (yet).

Also, "barely" warm is a relative term. They can and do get
warm, even 2W, and some components in a PC/router/etc
shouldn't be placed in contact with a "warm" power resistor.
Granted in this one instance it shouldn't get as warm as
others. The installer could isolate it, but then has to
consider that method and typical nylon wire-ties aren't so
great if the resistor did get more than warm. The router
itself will already be warm inside, hence the need for the
fan. Metal, well, sure if challenged we could all think up
some way to do it but ultimately choosing a larger resistor
also results in lower thermal density, it's not going to be
as hot against (whatever it's touching if it were touching
anything).
  #33  
Old March 19th 05, 09:12 PM
ric
external usenet poster
 
Posts: n/a
Default

kony wrote:

True, either 1 or 2W could work for this specific
application, but the 2W seems potentially less problematic.
At the time I didn't realize OP would have problems finding
them or go to ebay for these.

Why not 2W? Typically one does not try to match up watt per
watt on power resistors, rather using what the space and
budget allow, overengineering them. It's not a PCB space
issue and cost is maybe a few cents, or maybe even cheaper
per piece since this is spot-pricing on items not often
(percentagewise) sold 1 at a time. Yes, 1W would usually
work, but IMO, 2W is as good or better choice if someone has
nothing (yet).


Only because I found a good assortment of 1W carbon resistors at
my local Radio Shack. 2W? No such luck. 1W is plenty.
  #34  
Old March 19th 05, 10:13 PM
kony
external usenet poster
 
Posts: n/a
Default

On Sat, 19 Mar 2005 12:12:07 -0800, ric
wrote:

kony wrote:

True, either 1 or 2W could work for this specific
application, but the 2W seems potentially less problematic.
At the time I didn't realize OP would have problems finding
them or go to ebay for these.

Why not 2W? Typically one does not try to match up watt per
watt on power resistors, rather using what the space and
budget allow, overengineering them. It's not a PCB space
issue and cost is maybe a few cents, or maybe even cheaper
per piece since this is spot-pricing on items not often
(percentagewise) sold 1 at a time. Yes, 1W would usually
work, but IMO, 2W is as good or better choice if someone has
nothing (yet).


Only because I found a good assortment of 1W carbon resistors at
my local Radio Shack. 2W? No such luck. 1W is plenty.


Do they have one of those packs with several assorted values
inside or is one forced to buy the individual smaller packs?
I suppose it could depend on the store too, those I've been
to in the past couple years seem to have scaled back their
stock of these types of components. The individual packs
from Radio Shack always seem wildly overpriced to me, though
it could be a good idea for only a few values.
  #35  
Old March 20th 05, 07:20 AM
ric
external usenet poster
 
Posts: n/a
Default

kony wrote:

Only because I found a good assortment of 1W carbon resistors at
my local Radio Shack. 2W? No such luck. 1W is plenty.


Do they have one of those packs with several assorted values
inside or is one forced to buy the individual smaller packs?
I suppose it could depend on the store too, those I've been
to in the past couple years seem to have scaled back their
stock of these types of components. The individual packs
from Radio Shack always seem wildly overpriced to me, though
it could be a good idea for only a few values.


Man, this was years ago. Before I started using potentiometers. As I
remember, each package had about 5 resistors of the same value.
That store isn't even there any more. Progress!
  #36  
Old April 4th 05, 04:20 PM
external usenet poster
 
Posts: n/a
Default

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.


I finally use the following power resistor from eBay to reduce the
speed to the point that the noisy gigabit switch is now very quiet:

100 ohm 2W 5% carbon composite

I have a feeling that I still have more air flow from the new 60mm fan
with reduced speed than what the old noisy 40mm fan can produce in full
speed. This means I could have reduced the speed further. Obviusly, I
am not going to mess with something that is working so well (plus the
fact that this is so difficult to find that type of power resistors).
But just for the purpose of curiosity, which rating of power resistor
would you recommend if someone in my situation wanted to further reduce
the fan speed slightly.

Thanks for your help and any other info that you may provide in the
future.

Jay Chan

  #37  
Old April 4th 05, 04:23 PM
external usenet poster
 
Posts: n/a
Default

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


Seem like what you have suggested previously probably is a better
choice than what I end up buying. Yours is 120 ohm, and what I get is
100 ohm. Your probably can reduce the fan speed slightly better than
what I get can do. Moreover, yours is _much_ cheaper than what I have
paid for ($20). Oh well...

Jay Chan

  #38  
Old April 5th 05, 12:25 AM
kony
external usenet poster
 
Posts: n/a
Default

On 4 Apr 2005 08:20:11 -0700, wrote:

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.


I finally use the following power resistor from eBay to reduce the
speed to the point that the noisy gigabit switch is now very quiet:

100 ohm 2W 5% carbon composite

I have a feeling that I still have more air flow from the new 60mm fan
with reduced speed than what the old noisy 40mm fan can produce in full
speed. This means I could have reduced the speed further. Obviusly, I
am not going to mess with something that is working so well (plus the
fact that this is so difficult to find that type of power resistors).
But just for the purpose of curiosity, which rating of power resistor
would you recommend if someone in my situation wanted to further reduce
the fan speed slightly.

Thanks for your help and any other info that you may provide in the
future.

Jay Chan


I dont' know how much further that particular fan will
tolerate a voltage drop so I can't help much. Past a
certain point a larger resistor will prevent it from
spinning up which obviously should be avoided. I doubt you
could use 220 Ohm but slightly higher than 100 Ohm might be
possible. If would be easiest to use a rheostat (variable
power resistor) to determine the maximum resistance value
then keep the (more expensive and large) rheostat for some
future use (like more fan resistor sizing?) and put in the
appropriate value of resistor in it's place.
  #39  
Old April 6th 05, 07:04 AM
ric
external usenet poster
 
Posts: n/a
Default

kony wrote:

I dont' know how much further that particular fan will
tolerate a voltage drop so I can't help much. Past a
certain point a larger resistor will prevent it from
spinning up which obviously should be avoided.


Placing a cap in parallel with the resistor seems to cure startup
problems.
  #40  
Old April 6th 05, 02:26 PM
kony
external usenet poster
 
Posts: n/a
Default

On Tue, 05 Apr 2005 23:04:54 -0700, ric
wrote:

kony wrote:

I dont' know how much further that particular fan will
tolerate a voltage drop so I can't help much. Past a
certain point a larger resistor will prevent it from
spinning up which obviously should be avoided.


Placing a cap in parallel with the resistor seems to cure startup
problems.


"Cure"?
To what extent?
I mean, does it actually allow a lower working RPM then or
just offset the overly high resistance?

This is an interesting idea, do you have an example of what
gain there will be for any particular fan?
 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Probs MSA1000, "I2C_Read_Chunk: Device = EMU, I2C_SetAddress() failed" Daniel Schwager Storage & Hardrives 1 February 4th 05 06:54 PM
Are mains surge protectors needed in the UK? Bagpuss General 259 July 20th 04 08:19 PM
Radeon 7500 Saphire Windows ME Problem Pamela and Howard Signa Gateway Computers 5 February 17th 04 11:07 PM
A7N8X-Dlx and win98se - No Audio - has me stumped Kyle Brant Asus Motherboards 13 November 26th 03 12:08 PM
a7n8x AGP not working? Soulcatcher Asus Motherboards 6 November 21st 03 03:54 PM


All times are GMT +1. The time now is 11:16 AM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 HardwareBanter.
The comments are property of their posters.