[GreenKeys] History - Why voltages and frequencies are chosen(5v & 3.3v logic, 6.3v filaments, 120/220 VAC, 50/60Hz etc)

[Richard Knoppow]

----- Original Message ----- 
From: "Keith Lueck" <kwlueck at swbell.net>
To: <notbago at yahoogroups.com>; 
<i3detroit-public at googlegroups.com>; <acti at provide.net>
Cc: <Greenkeys at mailman.qth.net>
Sent: Wednesday, November 21, 2012 12:57 PM
Subject: Re: [GreenKeys] History - Why voltages and 
frequencies are chosen(5v & 3.3v logic, 6.3v filaments, 
120/220 VAC, 50/60Hz etc)


I think 60 Hz was chosen b/c it's above the human perception 
for flicker - although you'd think that the thermal time 
constants of incandescent filaments (the only light source 
at the time) would've tended to smooth that out anyway. 
Certainly a low frequency was chosen to minimize the 
rotational speed of large generating equipment. IIRC, there 
used to be some industrial systems that used 25 Hz, here in 
the US. Don't know why we ended up w/ 60 Hz and the Brits 
used 50...

Early (mechanical) RF alternators had a nasty habit of 
flying apart - literally sending shrapnel everywhere b/c of 
their high rotational speeds and large numbers of poles.... 
but that's another story.

JM2CW,

Keith

     60 Hz is at a point of steep inflection in the curve of 
perception of flicker vs: frequency. Those used to 60 hz 
systems will notice the flicker in 50 hz lamps despite the 
thermal lag of incandescent lamps.  A lot of people also 
find the old UK TV system at 25 frames (fifty fields) had 
more noticeable flicker than US TV at 30 frames 
(approximately 60 fields but color is very slightly 
different).
     25 hz power was used primarily for heavy motors such as 
the traction motors of electric railways.  I think its 
because the iron losses in motors and transformers are less. 
The Pennsylvania RR used 25 hz AC.  The generators at 
Niagara Falls were 25 hz and lighting on the Canadian side 
was 25 hz. I remember how definite the flicker of these 
lamps was.  I don't think there is much 25hz left in the US.
     Voltages for home mains are a compromise between losses 
and safety. Industrial supplies are often considerably 
higher voltage and sometimes three-phase.  The voltages used 
in radio sets were primarily chosen to make tubes operate 
well and for filaments to be a compromise between efficiency 
and voltages which could be conveniently supplied by 
batteries.  There are other factors too.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com