On Tuesday 26 April 2005 10:51, G3rzp@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.
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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