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

[Mike]

Christian,
I worked for Burroughs / Unisys "back in the day" mostly on proof (check encoding and sorting) machines, and the S3000 & S4000's ran on three phase 208 AC into a constant voltage transformer that split the 208 into multiple 12 and 24 volt feeds. Those voltages fed multiple AC/DC converters and power supply cards to produce 5 volts at fairly high currents, (10-20 amps  in the S4). The constant voltage transformer cold be tapped for other voltages, including 110, 115 and 220, though the lower voltages would require more current. Drat that pesky conservation of energy rule.

Mike O'Day
N9ODM


On Nov 23, 2012, at 10:14, Christian Gauger-Cosgrove <captainkirk359 at gmail.com> wrote:

> The larger DEC minicomputers (the PDP-15 family, the "large" PDP-11
> family members (like the 11/70), the PDP-9 if I remember correctly;
> the PDP-10 doesn't count since it's a verdammt mainframe), and I
> believe most of IBM's earlier midrange systems -- like the System/3 --
> used 208V three phase wye.
> 
> 
> At least in North America. I don't really recall what the manual said
> they ran on in Europe.
> 
> 
> Cheers,
> Christian
> 
> 
> 
> 
> On 22 November 2012 21:37,  <WA5CAB at cs.com> wrote:
>> 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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