[Amps] Resistors

[R@contesting.com]

On Apr 26, 2005, at 3:13 AM, Steve Thompson wrote:

> On Tuesday 26 April 2005 10:51, G3rzp at aol.com wrote:
>> ....... The problem
>> turned out to be a  ball race in the three phase fan of a humidifier, 
>> which
>> had seized after  only 3000 or so hours. The situation was was 
>> exacerbated
>> because  Boeing had managed (quite accidentally) to fit a 25 amp 
>> breaker to
>> protect  wiring rated at 4 amps, instead of a 2.5 amp breaker. Now if
>> aircraft quality  bearings can fail that soon, what does it say for 
>> cheap
>> fan bearings?
>
> I'm with you on cheap fans. On the other hand, in 1990 I build 16 
> class A
> amplifiers for a tunnel distribution system - they dissipate 150W
> continuously and needed fan cooling. I chose a Papst 24V ball race 
> 100cfm fan
> for the job. They have been running at 28V 24/7 since late 1990 with no
> failures yet. I recommended replacement every 5 years and designed the 
> units
> to allow that without interrupting operation, but the customer decided 
> it was
> acceptable to wait for failure before replacing.

Panasonic (Matsushita) makes fans that use "surface-wave" oilite 
bearings.  As I recall, the life expectancy of them is c. 4x that of 
ball-bearing fans.
>
> I think it's over 120k hours continuous, and about 2m hours 
> accumulated so
> far. I'm also pleased that none of the amplifiers have failed either.
>
> Steve
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>



Rich Measures, 805.386.3734, AG6K, www.somis.org