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Re: United Airlines CPAP policy

Posted by Bird Watcher on May 24, 2006 at 20:36:44:

In Reply to: Re: United Airlines CPAP policy posted by D.H. on May 24, 2006 at 15:53:02:

The land based electrical standards in the US were set over a century ago, and 60 hz was the choice since it was a convenient way to sync electric clocks in that era. Standards never changed, since there was never any call for it. And, the slower a generator spins, the longer it lasts, which may be a financial consideration to utility companies. But the faster you can spin the rotor of a generator, the smaller and ligher you can make it for the same output, which is a consideration with aircraft. Also of note is that an aircraft generator getting it's power directly off the shaft of the jet engine (the N2 shaft)has to be spun at a constant speed, and always reduced in RPM from the high rotor speed, which flucuates in flight. That in layman's terms, fewer reduction gears are necessary with a faster (400Hz) generators to get the speed down, as compared to a 60 Hz generator. This accounts for further weight savings.

All CPAP units that run off of 110 volts 60/50 Hz have a rectifier type power supply with a reduction transformer, and you can only use 60/50 Hz with those because 400 Hz would overheat the windings.

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