[Amps] Resistors

[Steve Thompson]

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.

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