[Milsurplus] rotary inverter

[Richard Brunner]

Re:
>> I have the 115/230vac, 60HZ to 115vac, 800HZ MG set that went with the 
>> TBW.
>>  Screams like a banshee.  First time I turned it on thought I had big 
>> time
>> bearing problems but when I cut excitation to the generator only heard 
>> normal
>> mechanical whirr.  Appears that the generator frame and magnetic circuit 
>> form
>> an acoustic transponder.  Hear the same kind of thing with a 400HZ MG set 
>> I
>> have but not nearly as loud.

In thinking about this, there is always magnetostriction in an ac unit, and 
probably it couples better to the air at higher frequencies because the unit 
is larger with respect to wavelength.  Also, we don't hear well at 50 or 60 
cycles, but hear very well at 400 and 800 cycles.  If we could hear like 
elephants perhaps we would complain about the 50 and 60 cycle units too.  In 
power stations some transformers are pretty noisy, but the really noisy ones 
are used in the dc-ac converter stations which have lots of harmonics.  They 
are also screamers...

Richard Brunner, AA1P