[Test-Equipment] Test-Equipment Digest, Vol 105, Issue 4

Fri Jan 4 14:16:45 EST 2013

A bit off topic?

I have a large collection of "boatanchor" tube type radios. I found long ago that small muffin fans can make a big difference.
Here's an example....
One radio (a Drake, made in the USA!!) is fairly small. It has it's power supply externally. However, the radios has 19 vacum tubes. I had the radio on for several hours one day and laid my arm on top of it to reach for something. While not exactly a burn, it was like putting your arm out a black car's window, that had sat in the sun all day!

I asked the local PC shop to save the computer power supplies they replace by the ton (literally). Some of these PS have 2 muffin fans (12 VDC). I added a small muffin fan to the Drake (yes, the covers and chassis have a LOT of cooling holes). Now, after being on all day, the radio covers and chassis are only slightly above room ambient. 
I have also added these free fans to a lot of my solid state radios. I sometimes add a minature pot (1K ohm) to the side of the fan. I can adjust the speed down until it can't be heard, yet still moves a bunch of air.

Just a thought!

ron
N4UE

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Sent: Fri, Jan 4, 2013 12:00 pm
Subject: Test-Equipment Digest, Vol 105, Issue 4

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Today's Topics:

   1. Choosing a quiet replacement fan (Dave C)
   2. Re: Choosing a quiet replacement fan (Eric Lemmon)

----------------------------------------------------------------------

Message: 1
Date: Thu, 3 Jan 2013 09:03:13 -0800
From: Dave C <davec2468 at yahoo.com>
To: Test equipment list <test-equipment at mailman.qth.net>,
	hp_agilent_equipment at yahoogroups.com
Subject: [Test-Equipment] Choosing a quiet replacement fan
Message-ID: <CB3300A9-F7AF-48FB-88A2-975FD9867A4F at yahoo.com>
Content-Type: text/plain; charset=us-ascii

I read occasionally that owners of T&M equipment tire of the noise a cooling fan 
makes and asks for help to determine if/how a quieter replacement can be found. 
There are many factors at play in such a decision, none as simple as "it's 
quieter". 

This web site addresses choosing a fan for PC enclosures, and many of the 
criteria are the same (heat being the most important one for us):

<http://www.silentpcreview.com/Fan_Test_System_2010>

A quote:

"Over the years, we have observed one clear phenomenon about fans and cooling: 
The relationship between airflow and temperature invariably becomes exponential 
at some point. Increase airflow from nothing to something, and the drop in 
temperature can be dramatic. Keep increasing airflow, and the cooling 
improvement becomes less and less significant, until at some point, the 
temperature hardly drops at all. The trick, for the PC builder who seeks both 
good cooling and low noise, is to find the point where any decrease in airflow 
(or fan speed) effects a significant increase in temperature, while only a very 
large airflow increase effects a significant temperature drop. In other words, 
once you have enough airflow, additional airflow has very little cooling effect, 
so all you're doing is increasing noise. "Enough airflow" is not a constant, of 
course, it varies for each system of components."

FYI,
Dave

------------------------------

Message: 2
Date: Thu, 03 Jan 2013 18:58:32 -0800
From: "Eric Lemmon" <wb6fly at verizon.net>
To: "'Discussion of Electronic Test Equipment'"
	<test-equipment at mailman.qth.net>
Subject: Re: [Test-Equipment] Choosing a quiet replacement fan
Message-ID: <F60D73ECAE8247F3B95912D3AB7732B4 at self6a5awnhg2m>
Content-Type: text/plain; charset=US-ASCII

I know that it should be obvious, but it is a fact that a fan cannot cool
anything.  A fan simply allows air to transfer heat from one object or area
to another, provided that there is a difference in temperature.  If a heat
sink was at 100 degrees F, and the ambient air was also at 100 degrees F,
adding one or more fans will make no difference!  Indeed, the fans
themselves add heat of their own, so- ironically- adding a fan will increase
the heat sink temperature.  I found that statement hard to swallow, until I
saw it proved in a thermodynamics class.

I have had several pieces of Hewlett-Packard test equipment that had fans
that were real screamers, and the noise really irritated me.  I ran some
tests on these fans, and was able to select replacements that ran much
slower but produced nearly the same air flow.  Keep in mind that certain
modes of equipment operation produce more heat than others, so if your
planned use does not include those modes, you can use less air flow.  Also
keep in mind that the OEM fan might be overkill, being selected to provide
sufficient airflow despite a nearly-clogged filter.

73, Eric Lemmon WB6FLY

-----Original Message-----
From: test-equipment-bounces at mailman.qth.net
[mailto:test-equipment-bounces at mailman.qth.net] On Behalf Of Dave C
Sent: Thursday, January 03, 2013 9:03 AM
To: Test equipment list; hp_agilent_equipment at yahoogroups.com
Subject: [Test-Equipment] Choosing a quiet replacement fan

I read occasionally that owners of T&M equipment tire of the noise a cooling
fan makes and asks for help to determine if/how a quieter replacement can be
found. There are many factors at play in such a decision, none as simple as
"it's quieter". 

This web site addresses choosing a fan for PC enclosures, and many of the
criteria are the same (heat being the most important one for us):

<http://www.silentpcreview.com/Fan_Test_System_2010>

A quote:

"Over the years, we have observed one clear phenomenon about fans and
cooling: The relationship between airflow and temperature invariably becomes
exponential at some point. Increase airflow from nothing to something, and
the drop in temperature can be dramatic. Keep increasing airflow, and the
cooling improvement becomes less and less significant, until at some point,
the temperature hardly drops at all. The trick, for the PC builder who seeks
both good cooling and low noise, is to find the point where any decrease in
airflow (or fan speed) effects a significant increase in temperature, while
only a very large airflow increase effects a significant temperature drop.
In other words, once you have enough airflow, additional airflow has very
little cooling effect, so all you're doing is increasing noise. "Enough
airflow" is not a constant, of course, it varies for each system of
components."

FYI,
Dave
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End of Test-Equipment Digest, Vol 105, Issue 4
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