[GreenKeys] History - Why voltages and frequencies are chosen(5v & 3.3v l...

[WA5CAB at cs.com]

I don't recall ever checking on why 5V or 3.3 V were used for logic but 
always assumed it was at least in part because of inherent voltage ratings of 
the components and/or was enough lower than 6.3 VDC to allow a regulator to 
operate properly.

And the 50/60 cps subject has been beaten enough today so I won't add any 
comment.

6.3V (and 12.6 V and 25.2V) for tube filaments is a result of the 
characteristics of the lead-acid cell and the fact that early automotive systems were 
nominally 6 VDC (then 12, then 24) (with engine off of course).  The fully 
charged voltage of a lead-acid cell (after removal of the surface charge by 
a slight discharge) is 2.1 VDC.  Three cells in series yields 6.3 VDC and 
the heavy use in automotive applications made the batteries readily available 
for battery operated radios (farm sets, and the like).  As the AC operated 
sets had no particular technical reason (consumer stuff, anyway) to prefer a 
different voltage, 6.3 volt filaments became common.  

On the 120/220 VAC question, there never has been a system with those 
nominal voltages, whether single or 3-phase.  The standards over the years have 
been 110/220, 115/230, 117/234 and 120/240 for single phase.  Because the 
standard single phase pole pig has a center-tapped secondary and you can't get 
220 volts line to line if the line to CT is 120.  The most common (probably) 
low voltage 3-phase system is currently 120/208 wye.

In a message dated 11/22/2012 18:18:10 PM Central Standard Time, 
1oldlens1 at ix.netcom.com writes: 
> 
> ----- 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)
> 

Robert Downs - Houston
wa5cab dot com (Web Store)
MVPA 9480
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