[CW] Alexanderson Alternator

Ron W4BIN ka4inm at gmail.com
Sun Jul 11 18:40:34 EDT 2021



On 7/11/21 3:23 PM, Richard Knoppow wrote:
>      There seems to be some interest here in these ancient machines. I 
> have a copy of "Principals of Radio Communication" (1921) J.H.Morecroft. 
> This was a classic in its day.  In it he has a minimal discussion of 
> both the Alexanderson Alternator and the arc converter type transmitters 
> and also mentions the Goldschmidt alternator. The Alexanderson machines 
> would have been very new then. In particular Morecroft talks about the 
> relative efficiency of these machines. He states that there is very 
> little information available about the efficiency and estimates it at a 
> pretty low value, less than 50% for all of these CW sources. I am led to 
> wonder if there was later information about efficiency. In particular, 
> he assumes very high core losses in the Alexanderson machine.
>     I suspect there is much better information in later books but I 
> wonder if anyone on this list has made a study of early CW transmitters 
> and can give a reasonably accurate of the efficiency. Both types of 
> alternators and the arc-converter were built in very large sizes, up to 
> a megawatt for the arc and at least 200KW for the alternators.
>      This is the machine efficiency and doesn't count the antenna 
> losses. One advantage of the Alexanderson machine is the multiple tuned 
> antennas used with them which was considerably more efficient than the 
> various other types used with the arc and Goldschmidt machines.


A 100 kHz Goldschmidt machine with P = 300 poles would require a rotor 
speed of only U = 5000 RPM, one-fourth that of an equivalent 
Alexanderson machine. 80% efficiency could be achieved, but in order to 
keep the leakage flux low enough to achieve this the machine required a 
very narrow clearance of 0.8 mm between the stator and rotor, which 
could weigh 5 tons and be moving at a peripheral speed of 200 meters per 
second.[3][4] Another challenge was that to reduce hysteresis losses in 
the iron rotor at radio frequencies, it had to be made of very thin foil 
laminations, .05 mm (.002 in) thick, separated by paper sheets,[3] so 
the rotor was more than 1/3 paper. No rotor of this construction had 
ever been used in a large machine. The limit of output frequency for 
Goldschmidt alternators, as well as other alternator technologies, was 
about 200 kHz. The mechanical problems ultimately limited the use of 
Goldschmidt machines.

   from:  https://en.wikipedia.org/wiki/Goldschmidt_alternator

-- 
    Ron  W4BIN - Understanding is much better than
                                      knowing how.U


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